Weather Research

North American storm clusters could produce 80 percent more rain

BOULDER, Colo. — Major clusters of summertime thunderstorms in North America will grow larger, more intense, and more frequent later this century in a changing climate, unleashing far more rain and posing a greater threat of flooding across wide areas, new research concludes.The study, by scientists at the National Center for Atmospheric Research (NCAR), builds on previous work showing that storms are becoming more intense as the atmosphere is warming. In addition to higher rainfall rates, the new research finds that the volume of rainfall from damaging storms known as mesoscale convective systems (MCSs) will increase by as much as 80 percent across the continent by the end of this century, deluging entire metropolitan areas or sizable portions of states."The combination of more intense rainfall and the spreading of heavy rainfall over larger areas means that we will face a higher flood risk than previously predicted," said NCAR scientist Andreas Prein, the study's lead author. "If a whole catchment area gets hammered by high rain rates, that creates a much more serious situation than a thunderstorm dropping intense rain over parts of the catchment.""This implies that the flood guidelines which are used in planning and building infrastructure are probably too conservative," he added.The research team drew on extensive computer modeling that realistically simulates MCSs and thunderstorms across North America to examine what will happen if emissions of greenhouse gases continue unabated.The study will be published Nov. 20 in the journal Nature Climate Change. It was funded by the National Science Foundation, which is NCAR's sponsor, and by the U.S. Army Corps of Engineers. Hourly rain rate averages for the 40 most extreme summertime mesoscale convective systems (MCSs) in the current (left) and future climate of the mid-Atlantic region. New research shows that MSCs will generate substantially higher maximum rain rates over larger areas by the end of the century if society continues a "business as usual" approach of emitting greenhouse gases . (©UCAR, Image by Andreas Prein, NCAR. This image is freely available for media & nonprofit use.)A warning signalThunderstorms and other heavy rainfall events are estimated to cause more than $20 billion of economic losses annually in the United States, the study notes. Particularly damaging, and often deadly, are MSCs: clusters of thunderstorms that can extend for many dozens of miles and last for hours, producing flash floods, debris flows, landslides, high winds, and/or hail. The persistent storms over Houston in the wake of Hurricane Harvey were an example of an unusually powerful and long-lived MCS.Storms have become more intense in recent decades, and a number of scientific studies have shown that this trend is likely to continue as temperatures continue to warm. The reason, in large part, is that the atmosphere can hold more water as it gets warmer, thereby generating heavier rain.A study by Prein and co-authors last year used high-resolution computer simulations of current and future weather, finding that the number of summertime storms that produce extreme downpours could increase by five times across parts of the United States by the end of the century. In the new study, Prein and his co-authors focused on MCSs, which are responsible for much of the major summertime flooding east of the Continental Divide. They investigated not only how their rainfall intensity will change in future climates, but also how their size, movement, and rainfall volume may evolve.Analyzing the same dataset of computer simulations and applying a special storm-tracking algorithm, they found that the number of severe MCSs in North America more than tripled by the end of the century. Moreover, maximum rainfall rates became 15 to 40 percent heavier, and intense rainfall reached farther from the storm's center. As a result, severe MCSs increased throughout North America, particularly in the northeastern and mid-Atlantic states, as well as parts of Canada, where they are currently uncommon.The research team also looked at the potential effect of particularly powerful MCSs on the densely populated Eastern Seaboard. They found, for example, that at the end of the century, intense MCSs over an area the size of New York City could drop 60 percent more rain than a severe present-day system. That amount is equivalent to adding six times the annual discharge of the Hudson River on top of a current extreme MCS in that area."This is a warning signal that says the floods of the future are likely to be much greater than what our current infrastructure is designed for," Prein said. "If you have a slow-moving storm system that aligns over a densely populated area, the result can be devastating, as could be seen in the impact of Hurricane Harvey on Houston."This satellite image loop shows an MCS developing over West Virginia on June 23, 2016. The resulting floods caused widespread flooding, killing more than 20 people.  MCSs are responsible for much of the major flooding east of the Continental Divide during warm weather months. (Image by NOAA National Weather Service, Aviation Weather Center.) Intensive modelingAdvances in computer modeling and more powerful supercomputing facilities are enabling climate scientists to begin examining the potential influence of a changing climate on convective storms such as thunderstorms, building on previous studies that looked more generally at regional precipitation trends.For the new study, Prein and his co-authors turned to a dataset created by running the NCAR-based Weather and Research Forecasting (WRF) model over North America at a resolution of 4 kilometers (about 2.5 miles). That is sufficiently fine-scale resolution to simulate MCSs. The intensive modeling, by NCAR scientists and study co-authors Roy Rasmussen, Changhai Liu, and Kyoko Ikeda, required a year to run on the Yellowstone system at the NCAR-Wyoming Supercomputing Center.The team used an algorithm developed at NCAR to identify and track simulated MCSs. They compared simulations of the storms at the beginning of the century, from 2000 to 2013, with observations of actual MCSs during the same period and showed that the modeled storms are statistically identical to real MCSs.The scientists then used the dataset and algorithm to examine how MCSs may change by the end of the century in a climate that is approximately 5 degrees Celsius (9 degrees Fahrenheit) warmer than in the pre-industrial era — the temperature increase expected if greenhouse gas emissions continue unabated.About the paperTitle: Increased rainfall volume from future convective storms in the USAuthors: Andreas F Prein, Changhai Liu, Kyoko Ikeda, Stanley B Trier, Roy M Rasmussen, Greg J Holland, Martyn P ClarkJournal: Nature Climate Change  

UCAR Congressional Briefing: Moving research to industry

WASHINGTON — Federally funded scientific advances are enabling the multibillion-dollar weather industry to deliver increasingly targeted forecasts to consumers and businesses, strengthening the economy and providing the nation with greater resilience to natural disasters, experts said today at a congressional briefing.The panel of experts, representing universities, federally funded labs, and the private sector, said continued government investment in advanced computer modeling, observing tools, and other basic research provides the foundation for improved forecasts.The nonprofit University Corporation for Atmospheric Research (UCAR) sponsored the briefing."Thanks to a quiet revolution in modern weather prediction, we can all use forecasts to make decisions in ways that wouldn't have been possible just 10 years ago," said Rebecca Morss, a senior scientist with the National Center for Atmospheric Research (NCAR) and deputy director of the center's Mesoscale and Microscale Meteorology Lab. "Now we are looking to the next revolution, which includes giving people longer lead times and communicating risk as effectively as possible."Fuqing Zhang, a professor of meteorology and statistics at Pennsylvania State University, highlighted the ways that scientists are advancing their understanding of hurricanes and other storms with increasingly detailed observations and computer modeling. Researchers at Penn State, for example, fed data from the new National Oceanic and Atmospheric Administration GOES-R satellite into NOAA's powerful FV3 model to generate an experimental forecast of Hurricane Harvey that simulated its track and intensity."The future of weather forecasting is very promising," said Zhang, who is also the director of the Penn State Center for Advanced Data Assimilation and Predictability Techniques.  "With strategic investments in observations, modeling, data assimilation, and supercomputing, we will see some remarkable achievements."Mary Glackin, director of science and forecast operations for The Weather Company, an IBM business, said the goal of the weather industry is to help consumers and businesses make better decisions, both by providing its own forecasts and by forwarding alerts from the National Weather Service. The Weather Company currently is adapting a powerful research weather model based at NCAR, the Model for Prediction Across Scales (MPAS), for use in worldwide, real-time forecasts.The NCAR-based Model for Prediction Across Scales simulates the entire globe while enabling scientists to zoom in on areas of interest. It is one of the key tools for improving forecasts in the future. (©UCAR. This image is freely available for media & nonprofit use.) "We have a weather and climate enterprise that we can be extremely proud of as a nation, but it's not where it should be," Glackin said. "Weather affects every consumer and business, and the public-private partnership can play a pivotal role in providing better weather information that is critically needed."Antonio Busalacchi, president of UCAR, emphasized the benefits of partnerships across the academic, public, and private sectors. He said that research investments by the National Science Foundation, NOAA, and other federal agencies are critical for improving forecasts that will better protect vulnerable communities and strengthen the economy."These essential collaborations between government agencies, universities, and private companies are driving landmark advances in weather forecasting," Busalacchi said. "The investments that taxpayers are making in basic research are paying off many times over by keeping our nation safer and more prosperous."The briefing was the latest in a series of UCAR Congressional Briefings that draw on expertise from UCAR's university consortium and public-private partnerships to provide insights into critical topics in the Earth system sciences. Past briefings have focused on wildfires, predicting space weather, aviation weather safety, the state of the Arctic, hurricane prediction, potential impacts of El Niño, and new advances in water forecasting.

New climate forecasts for watersheds - and the water sector

Nov. 10, 2017 | Water managers and streamflow forecasters can now access bi-weekly, monthly, and seasonal precipitation and temperature forecasts that are broken down by individual watersheds, thanks to a research partnership between the National Center for Atmospheric Research (NCAR) and the University of Colorado Boulder (CU Boulder). The project is sponsored by the National Oceanic and Atmospheric Administration (NOAA) through the Modeling, Applications, Predictions, and Projections program.Operational climate forecasts for subseasonal to seasonal time scales are currently provided by the NOAA Climate Prediction Center and other sources. The forecasts usually take the form of national contour maps (example) and gridded datasets at a relatively coarse geographic resolution. Some forecast products are broken down further, based on state boundaries or on climate divisions, which average two per state; others are summarized for major cities. But river forecasters and water managers grapple with climate variability and trends in the particular watersheds within their service areas, which do not align directly with the boundaries of existing forecast areas. A forecast that directly describes predicted conditions inside an individual watershed would be extremely valuable to these users for making decisions in their management areas, such as how much water to release or store in critical reservoirs and when.To bridge this gap, the NCAR–CU Boulder research team has developed a new prototype prediction system that maps climate forecasts to watershed boundaries over the contiguous United States in real time. The system is currently running at NCAR, with real-time forecasts and analyses available on a demonstration website."We are trying to improve the accessibility and relevance of climate predictions for streamflow forecasting groups and water managers," said NCAR scientist Andy Wood, who co-leads the project. "We can’t solve all the scientific challenges of climate prediction, but we can make it easier for a person thinking about climate and water in a river basin — such as the Gunnison, or the Yakima, or the Potomac — to find and download operational climate information that has been tailored to that basin’s observed variability."The project is funded by NOAA, and the scientists plan to hand off successful components of the system for experimental operational evaluation within the NOAA National Weather Service.  Collaborators include scientists from the NOAA Climate Prediction Center and partners from the major federal water agencies: the U.S. Army Corps of Engineers and the Bureau of Reclamation.This screenshot of the S2S Climate Outlooks for Watersheds website shows forecasted temperature anomalies for watersheds across the contiguous United States. As users scroll across different watersheds, they get more precise information. In this screenshot from early November 2017, the forecast is showing that, over the next one to two weeks, the Colorado Headwaters watershed is expected to be 1.2 degrees warmer than normal. Visit the website to learn more. (©UCAR. This image is freely available for media & nonprofit use.)  Beyond the standard weather forecastPrecipitation and temperature forecasts that extend beyond the typical 7- to 10-day window can be useful to water managers making a number of important decisions about how to best regulate supplies. For instance, during a wet water year, when snowpack is high and reservoirs are more full than usual, the relative warmth or coolness of the coming spring can affect how quickly the snow melts. Good spring season forecasts allow water managers to plan in advance for how to best manage the resulting runoff.For water systems in drought, such as California's during 2012–2015, early outlooks on whether the winter rainy season will help alleviate the drought or exacerbate it can help water utilities strategize ways of meeting the year’s water demands. Historically, making these kinds of longer-term predictions accurately has been highly challenging. But in recent years, scientists have improved their skill at subseasonal and seasonal climate prediction. NOAA’s National Centers for Environmental Prediction plays a key role, both running an in-house modeling system — the Climate Forecast System, version 2 (CFSv2) — and leading an effort called the North American Multi-Model Ensemble (NMME). These model-based forecasts help inform the NOAA official climate forecasts, which also include other tools and expert judgment. NMME combines forecasts from seven different climate models based in the U.S. and Canada to form a super-ensemble of climate predictions that extend up to 10 months into the future. The combination of the different forecasts is often more accurate than the forecast from any single model. Temperature forecasts, in particular, from the combined system are notably more accurate than they were 10 years ago, Wood said, partly due to their representation of observed warming trends. Even with these new tools, however, predicting seasonal precipitation beyond the first month continues to be a major challenge. The NCAR–CU Boulder project makes use of both the CFSv2 and NMME forecasts. It generates predictions for bi-weekly periods (weeks 1-2, 2-3, and 3-4) from CFSv2 that are updated daily and longer-term forecasts derived from the NMME (months 1, 2, 3, and season 1) that are updated monthly. The scientists currently map these forecasts to 202 major watersheds in the contiguous U.S.Analyzing forecast skillThe resulting watershed-specific forecasts are available in real-time on the project's interactive website, which also provides information about their accuracy and reliability."It's important for users to be able to check on the quality of the forecasts," said Sarah Baker, a doctoral student in the Civil, Environmental, and Architectural Engineering Department at CU Boulder. "We're able to use hindcasts, which are long records of past forecasts, to analyze and describe the skill of the current forecasts. Baker, who also works for the Bureau of Reclamation, has been building the prototype system under the supervision of Wood and her academic adviser, CU Professor Balaji Rajagopalan. The researchers are also using analyses of forecast accuracy and reliability to begin correcting for systematic biases — such as consistently over-predicting springtime rains in one watershed or under-predicting summertime heat in another — in the forecasts.The project team has presented the project at a number of water-oriented meetings in the western U.S. Water managers, operators, and researchers from agencies such as the Bureau of Reclamation and utilities such as the Southern Nevada Water Authority, which manages water for Las Vegas, have expressed interest in the new forecast products."This project has great potential to provide climate outlook information that is more relevant for hydrologists and the water sector. It will be critical to connect with stakeholders or possible users of the forecasts so that their needs can continue to help shape this type of information product," said NOAA’s Andrea Ray. Ray leads an effort funded by NIDIS, the National Integrated Drought Information System, to identify tools and information such as this for a NOAA online Water Resources Monitor and Outlook that would also help connect stakeholders to climate and water information.In the coming year, the research team will implement statistical post-processing methods to improve the accuracy of the forecasts. They will also investigate the prediction of extreme climate events at the watershed scale. ContactAndy Wood, NCAR Research Applications LaboratoryWebsitehttp://hydro.rap.ucar.edu/s2sCollaboratorsCU BoulderNCARNOAAU.S. Army Corps of EngineersBureau of Reclamation FunderNOAA's Modeling, Applications, Predictions and Projections Climate Testbed program

NCAR|UCAR hurricane experts available to explain storm behavior, potential impacts

BOULDER, Colo. — As Hurricane Harvey takes aim at Texas, scientists at the National Center for Atmospheric Research (NCAR) and its managing organization, the University Corporation for Atmospheric Research (UCAR), are closely watching the storm and testing high-resolution computer models.Hurricane experts are available to explain issues such as:How we can better predict the possible impacts of hurricanes, including wind damage, flooding, and subsequent spread of disease-bearing mosquitoes;How people respond to hurricane forecast and warning messages and how risk communication can be improvedWhether climate change is affecting hurricanes and what we can expect in the future;The importance of improving weather models to safeguard life and property.Antonio Busalacchi, UCAR president (please contact David Hosansky for interview requests)An expert on ocean-atmosphere interactions, Busalacchi has testified before Congress on the importance of improving the nation's weather forecasting capabilities to better protect life and property, bolster the economy, and strengthen national security. He has firsthand experience with storms along the Gulf Coast as a part-time New Orleans resident, and he is a member of the Gulf Research Program Advisory Board of the National Academy of Sciences.Christopher Davis, director, NCAR Mesoscale and Microscale Meteorology Laboratory, cdavis@ucar.edu, 303-497-8990Davis studies the weather systems that lead to hurricanes and other heavy rainfall events. His expertise includes hurricane prediction and how computer models can be improved to better forecast storms. His NCAR weather lab is running experimental computer simulations of Hurricane Harvey.James Done, NCAR scientist, done@ucar.edu, 303-497-8209Done led development of the innovative Cyclone Damage Potential (CDP) index, which quantifies a hurricane's ability to cause destruction, using a scale of 1 to 10. It can also be used to examine the damage potential for cyclones in the future as the climate warms.David Gochis, NCAR scientist, gochis@ucar.edu, 303-497-2809An expert in hydrometeorology, Gochis studies the causes of floods and how to better predict them. He helped develop pioneering software that is at the core of the National Water Model. The National Oceanic and Atmospheric Administration Office of Water Prediction uses this model to provide a continuous picture of all the waterways in the contiguous United States and alert officials to potentially dangerous floods.Matthew Kelsch, UCAR hydrometeorologist, kelsch@ucar.edu, 303-497-8309Kelsch has studied some of the biggest U.S. flood events connected to hurricanes and tropical storms. He trains scientists and forecasters from around the world on emerging hydrology and weather topics.Rebecca Morse, NCAR scientist, morss@ucar.edu, 303-497-8172Morss studies the predictability of hurricane-related hazards, including storm surge and inland flooding, and hurricane and flood risk communication and evauation decision making.Kevin Trenberth, NCAR senior scientist, trenbert@ucar.edu, 303-497-1318Trenberth is an expert on the global climate system. He has been in the forefront of scientists examining the potential influence of climate change on the intensity of tropical storms and hurricanes and the increased widespread flooding that they cause.Jeff Weber, UCAR meteorologist, jweber@ucar.edu, 303-497-8676As an expert on hurricanes and severe weather in general, Weber closely monitors the behavior of individual storms and the larger atmospheric and oceanic conditions that influence them.

UCAR collaboration with The Weather Company to improve weather forecasts worldwide

BOULDER, Colo. — The University Corporation for Atmospheric Research (UCAR) today announced a new collaboration with The Weather Company, an IBM business, to improve global weather forecasting. The partnership brings together cutting-edge computer modeling developed at the National Center for Atmospheric Research (NCAR) with The Weather Company's meteorological science and IBM's advanced compute equipment."This is a major public-private partnership that will advance weather prediction and generate significant benefits for businesses making critical decisions based on weather forecasts," said UCAR President Antonio J. Busalacchi. "We are gratified that taxpayer investments in the development of weather models are now helping U.S. industries compete in the global marketplace."UCAR, a nonprofit consortium of 110 universities focused on research and training in the atmospheric and related Earth system sciences, manages NCAR on behalf of the National Science Foundation.With the new agreement, The Weather Company will develop a global forecast model based on the Model for Prediction Across Scales (MPAS), an innovative software platform developed by NCAR and the Los Alamos National Laboratory.The Model for Prediction Across Scales (MPAS) enables forecasters to combine a global view of the atmosphere with a higher-resolution view of a particular region, such as North America. (@UCAR. This image is freely available for media & nonprofit use.)MPAS offers a unique way of simulating the global atmosphere while providing users with more flexibility when focusing on specific regions of interest. Unlike traditional three-dimensional models that calculate atmospheric conditions at multiple points within a block-shaped grid, it uses a hexagonal mesh resembling a honeycomb that can be stretched wide in some regions and compressed for higher resolution in others. This enables forecasters to simultaneously capture far-flung atmospheric conditions that can influence local weather, as well as small-scale features such as vertical wind shear that can affect thunderstorms and other severe weather.Drawing on the computational power of GPUs — graphics processing units — such as those being used in a powerful new generation of IBM supercomputers, and on the expertise of NCAR and The Weather Company, the new collaboration is designed to push the capabilities of MPAS to yield more accurate forecasts with longer lead times. The results of NCAR's work will be freely available to the meteorological community. Businesses, from airlines to retailers, as well as the general public, stand to benefit.Mary Glackin, head of weather science and operations for The Weather Company, said, "As strong advocates for science, we embrace strong public-private collaborations that understand the value science brings to society, such as our continued efforts with UCAR to advance atmospheric and computational sciences.""Thanks to research funded by the National Science Foundation and other federal agencies, society is on the cusp of a new era in weather prediction, with more precise short-range forecasts as well as longer-term forecasts of seasonal weather patterns," Busalacchi said. "These forecasts are important for public health and safety, as well as enabling companies to leverage economic opportunities in ways that were never possible before."About The Weather CompanyThe Weather Company, an IBM Business, helps people make informed decisions and take action in the face of weather. The company offers weather data and insights to millions of consumers, as well as thousands of marketers and businesses via Weather’s API, its business solutions division, and its own digital products from The Weather Channel (weather.com) and Weather Underground (wunderground.com).This webpage was last updated on July 5, 2017.

Offshore wind turbines vulnerable to Category 5 hurricane gusts

NCAR scientist George Bryan is a co-author of a new study appearing in the journal Geophysical Research Letters. The following is an excerpt from a news release by the University of Colorado Boulder. Offshore wind turbines built according to current standards may not be able to withstand the powerful gusts of a Category 5 hurricane, creating potential risk for any such turbines built in hurricane-prone areas, new University of Colorado Boulder-led research shows.The study, which was conducted in collaboration with the National Center for Atmospheric Research in Boulder, Colorado, and the U.S. Department of Energy’s National Renewable Energy Laboratory in Golden, Colorado, highlights the limitations of current turbine design and could provide guidance for manufacturers and engineers looking to build more hurricane-resilient turbines in the future.Offshore wind-energy development in the U.S. has ramped up in recent years, with projects either under consideration or already underway in most Atlantic coastal states from Maine to the Carolinas, as well as the West Coast and Great Lakes. The country’s first utility-scale offshore wind farm, consisting of five turbines, began commercial operation in December 2016 off the coast of Rhode Island.Turbine design standards are governed by the International Electrotechnical Commission (IEC). For offshore turbines, no specific guidelines for hurricane-force winds exist. Offshore turbines can be built larger than land-based turbines, however, owing to a manufacturer’s ability to transport larger molded components such as blades via freighter rather than over land by rail or truck.Read the full news release.

Warmer temperatures cause decline in key runoff measure

BOULDER, Colo. — Since the mid-1980s, the percentage of precipitation that becomes streamflow in the Upper Rio Grande watershed has fallen more steeply than at any point in at least 445 years, according to a new study led by the National Center for Atmospheric Research (NCAR).While this decline was driven in part by the transition from an unusually wet period to an unusually dry period, rising temperatures deepened the trend, the researchers said.The study paints a detailed picture of how temperature has affected the runoff ratio — the amount of snow and rain that actually makes it into the river — over time, and the findings could help improve water supply forecasts for the Rio Grande, which is a source of water for an estimated 5 million people.The study results also suggest that runoff ratios in the Upper Rio Grande and other neighboring snow-fed watersheds, such as the Colorado River Basin, could decline further as the climate continues to warm.Sandhill cranes in the San Luis Valley of Colorado. The mountains ringing the valley form the headwaters of the Rio Grande River, which flows south into New Mexico and along the border between Texas and Mexico. (Photo courtesy of the National Park Service.)"The most important variable for predicting streamflow is how much it has rained or snowed," said NCAR scientist Flavio Lehner, lead author of the study. "But when we looked back hundreds of years, we found that temperature has also had an important influence  — which is not currently factored into water supply forecasts. We believe that incorporating temperature in future forecasts will increase their accuracy, not only in general but also in the face of climate change."The study, published in the journal Geophysical Research Letters, was funded by the Bureau of Reclamation, Army Corps of Engineers, National Oceanic and Atmospheric Administration (NOAA), and National Science Foundation, which is NCAR's sponsor.Co-authors of the paper are Eugene Wahl, of NOAA; Andrew Wood, of NCAR; and Douglas Blatchford and Dagmar Llewellyn, both of the Bureau of Reclamation.Over-predicting water supplyBorn in the Rocky Mountains of southern Colorado, the Rio Grande cuts south across New Mexico before hooking east and forming the border between Texas and Mexico. Snow piles up on the peaks surrounding the headwaters throughout the winter, and in spring the snowpack begins to melt and feed the river.The resulting streamflow is used both by farmers and cities, including Albuquerque, New Mexico, and El Paso, Texas, and water users depend on the annual water supply forecasts to determine who gets how much of the river. The forecast is also used to determine whether additional water needs to be imported from the San Juan River, on the other side of the Continental Divide, or pumped from groundwater.Current operational streamflow forecasts depend on estimates of the amount of snow and rain that have fallen in the basin, and they assume that a particular amount of precipitation and snowpack will always yield a particular amount of streamflow.In recent years, those forecasts have tended to over-predict how much water will be available, leading to over-allocation of the river. In an effort to understand this changing dynamic, Lehner and his colleagues investigated how the relationship between precipitation and streamflow, known as the runoff ratio, has evolved over time.Precipitation vs. streamflow: Tree rings tell a new storyThe scientists used tree ring-derived streamflow data from outside of the Upper Rio Grande basin to reconstruct estimates of precipitation within the watershed stretching back to 1571. Then they combined this information with a separate streamflow reconstruction within the basin for the same period. Because these two reconstructions were independent, it allowed the research team to also estimate runoff ratio for each year: the higher the ratio, the greater the share of precipitation that was actually converted into streamflow."For the first time, we were able to take these two quantities and use them to reconstruct runoff ratios over the past 445 years," Wahl said.They found that the runoff ratio varies significantly from year to year and even decade to decade. The biggest factor associated with this variation was precipitation. When it snows less over the mountains in the headwaters of the Rio Grande, not only is less water available to become streamflow, but the runoff ratio also decreases. In other words, a smaller percentage of the snowpack becomes streamflow during drier years.But the scientists also found that another factor affected the runoff ratio: temperature. Over the last few centuries, the runoff ratio was reduced when temperatures were warmer. And the influence of temperature strengthened during drier years: When the snowpack was shallow, warm temperatures reduced the runoff ratio more than when the snowpack was deep, further exacerbating drought conditions. The low runoff ratios seen in dry years were two and a half to three times more likely when temperatures were also warmer."The effect of temperature on runoff ratio is relatively small compared to precipitation," Lehner said. "But because its greatest impact is when conditions are dry, a warmer year can make an already bad situation much worse."A number of factors may explain the influence of temperature on runoff ratio. When it's warmer, plants take up more water from the soil and more water can evaporate directly into the air. Additionally, warmer temperatures can lead snow to melt earlier in the season, when the days are shorter and the angle of the sun is lower. This causes the snow to melt more slowly, allowing the meltwater to linger in the soil and giving plants added opportunity to use it.The extensive reconstruction of historical runoff ratio in the Upper Rio Grande also revealed that the decline in runoff ratio over the last three decades is unprecedented in the historical record. The 1980s were an unusually wet period for the Upper Rio Grande, while the 2000s and 2010s have been unusually dry. Pair that with an increase in temperatures over the same period, and the decline in runoff ratio between 1986 and 2015 was unlike any other stretch of that length in the last 445 years.The graph shows changes to runoff ratio in the Upper Rio Grande over time. (Image courtesy Flavio Lehner, NCAR.) Upgrading the old approachesThis new understanding of how temperature influences runoff ratio could help improve water supply forecasts, which do not currently consider whether the upcoming months are expected to be hotter or cooler than average. The authors are now assessing the value of incorporating seasonal temperature forecasts into water supply forecasts to account for these temperature influences. The study complements a multi-year NCAR project funded by the Bureau of Reclamation and the Army Corps of Engineers that is evaluating prospects for enhancing seasonal streamflow forecasts for reservoir management.“Forecast users and stakeholders are increasingly raising questions about the reliability of forecasting techniques if climate is changing our hydrology," said Wood, who led the effort. "This study helps us think about ways to upgrade one of our oldest approaches — statistical water supply forecasting — to respond to recent trends in temperature. Our current challenge is to find ways to make sure the lessons of this work can benefit operational streamflow forecasts.” Because the existing forecasting models were calibrated on conditions in the late 1980s and 1990s, it's not surprising that they over-predicted streamflow in the drier period since 2000, Lehner said."These statistical models often assume that the climate is stable," Lehner said. "It's an assumption that sometimes works, but statistical forecasting techniques will struggle with any strong changes in hydroclimatology from decade to decade, such as the one we have just experienced."Lehner is a Postdoc Applying Climate Expertise (PACE) fellow, which is part of the Cooperative Programs for the Advancement of Earth System Science (CPAESS). CPAESS is a community program of the University Corporation for Atmospheric Research (UCAR).About the articleTitle: Assessing recent declines in Upper Rio Grande River runoff efficiency from a paleoclimate perspectiveAuthors: Flavio Lehner, Eugene R. Wahl, Andrew W. Wood, Douglas B. Blatchford, and Dagmar LlewellynJournal: Geophysical Research Letters, DOI: 10.1002/2017GL073253Writer:Laura Snider, Senior Science Writer and Public Information Officer

Drones need aviation forecasts, too

UAS Weather ForumWhat: An opportunity for stakeholders from the UAS community -- including manufacturers, operators, regulators, and researchers -- to come together to discuss weather effects on drones and the support needed to mitigate those impacts.When: 9 a.m. - 12 p.m., Monday, May 8, 2017Where: XPONENTIAL, Kay Bailey Hutchison Convention Center, Dallas Click here for more information.April 13, 2017 | The possible future uses for drones are spectacularly diverse. Unmanned aircraft systems (UAS) could make door-to-door deliveries, search for a lost hiker, survey agricultural crops, inspect infrastructure, or collect scientific data from difficult-to-reach places, among other things. Already Amazon is experimenting with drone delivery of packages, for example, and BNSF Railway is testing the use of drones to inspect hundreds of miles of railroad tracks.Yet the ultimate success of efforts like these may hinge on a good weather forecast. The National Center for Atmospheric Research (NCAR), long a trusted provider of critical weather information to the aviation industry, is beginning to lend its expertise to the UAS community as well.Staff in NCAR's Research Applications Laboratory are already working with NASA to provide low-level turbulence forecasts for NASA's project to create a UAS Traffic Management (UTM) system, which would be similar to the air traffic control system for crewed airplanes. And in May, the NCAR team is hosting a UAS Weather Forum in Dallas. The forum will be co-located with XPONENTIAL, a conference on "all things unmanned" that is organized by the Association of Unmanned Vehicle Systems International."As the aircraft get smaller and smaller, the challenges of providing the needed weather information increase," said NCAR scientist Matthias Steiner, deputy director of RAL's Aviation Applications Program. "These small UAS's are more sensitive to winds, temperature, turbulence, precipitation — essentially the full range of weather — than larger planes flying at higher altitudes."NASA engineers prepare to launch a remotely piloted aircraft during practice runs for an Unmanned Aircraft Systems Traffic Management test. (Image courtesy NASA.)Weather impacts on dronesDrones, at least the small ones allowed under current Federal Aviation Administration rules, fly in the lowest few hundred feet of the atmosphere, where weather can be highly dynamic and less predictable.This layer of the atmosphere is heavily affected by land surface and topography. Consider, for example, wind as it blows through a city. The buildings force the wind to speed through "urban canyons" and swirl into tight eddies behind structures. Uneven heating — the sunny side of the street warming more than the shady side, for example — can create circulating downdrafts and updrafts.Piloting a drone through a built-up area could be tricky without a detailed understanding of the local atmospheric circulation patterns. And even with that information, it's important to understand how different drones will be affected. The tinier and lighter the drone, the more vulnerable it is to the vagaries of the weather, just as a small Cessna is more vulnerable to turbulence than a giant 747. And the type of drone, such as a fixed wing or a quadcopter, matters as well because each has a different ability to respond.The concern is not just crashing on the ground; severe weather conditions could also lead to a collision in the sky. NASA's UTM project is exploring the possibility of managing a high volume of drones by essentially assigning individual UAS's to a lane of airspace. But weather will affect the ability of a drone to stay in its lane. An abrupt updraft, for instance, could force a drone that is supposed to fly at a lower altitude into the higher-altitude lane assigned to another UAS (or a crewed aircraft in mixed airspace), increasing the possibility of a collision between the two.Weather can have less obvious impacts on drone operation as well. Extremely cold weather, headwinds, or turbulence that requires a lot of flight control adjustments could drain the aircraft's battery more quickly, reducing its range and, potentially, its ability to return home. Facilitating a community dialogueThese kinds of weather challenges would likely not surprise a seasoned aviator. But many of the organizations interested in using drones today come to the UAS community from the technology side, not the aviation side, and may lack a full understanding of the impacts that atmospheric conditions can have on flight.This is where NCAR has expertise to offer. For decades, NCAR has been providing the aviation industry with the tools they need to increase flight safety, including wind shear alerts, turbulence forecasts, and information on inflight icing potential.In an effort to stay on top of the latest weather challenges facing the aviation industry, NCAR launched the Friends and Partners in Aviation Weather Forum in 1997. The meeting, now held twice yearly, is an opportunity for stakeholders from the operational, regulatory, and research sectors to come together."We created these meetings as a means of fostering dialogue," Steiner said. "We want to know: 'What are your operational sensitivities? How can we help you?' Now we are emulating these forums with the UAS community. "The UAS Weather Forum at the XSPONENTIAL conference on May 8 is the first effort at starting a similar meeting—and fostering the dialogue needed to advance drone safety, even in the face of challenging weather conditions."We want drone operators to know NCAR is a partner that can help them address their weather impacts," Steiner said.Writer/contact: Laura Snider, Senior Science Writer and Public Information Officer

Scientists link recent California droughts and floods to distinctive atmospheric waves

BOULDER, Colo. — The crippling wintertime droughts that struck California from 2013 to 2015, as well as this year's unusually wet California winter, appear to be associated with the same phenomenon: a distinctive wave pattern that emerges in the upper atmosphere and circles the globe.Scientists at the National Center for Atmospheric Research (NCAR) found in a recent study that the persistent high-pressure ridge off the west coast of North America that blocked storms from coming onshore during the winters of 2013-14 and 2014-15 was associated with the wave pattern, which they call wavenumber-5. Follow-up work showed that wavenumber-5 emerged again this winter but with its high- and low-pressure features in a different position, allowing drenching storms from the Pacific to make landfall. "This wave pattern is a global dynamic system that sometimes makes droughts or floods in California more likely to occur," said NCAR scientist Haiyan Teng, lead author of the California paper. "As we learn more, this may eventually open a new window to long-term predictability." The high- and low-pressure regions of wavenumber-5 set up in different locations during January 2014, when California was enduring a drought, and January 2017, when it was facing floods. The location of the high and low pressure regions (characterized by anticylonic vs. cyclonic upper-level air flow) can act to either suppress or enhance precipitation and storms. The black curves illustrate the jet streams that trap and focus wavenumber-5. (Image by Haiyan Teng and Grant Branstator, ©UCAR. This image is freely available for media & nonprofit use.)  The finding is part of an emerging body of research into the wave pattern that holds the promise of better understanding seasonal weather patterns in California and elsewhere. Another new paper, led by NCAR scientist Grant Branstator, examines the powerful wave pattern in more depth, analyzing the physical processes that help lead to its formation as well as its seasonal variations and how it varies in strength and location.The California study was published in the Journal of Climate while the comprehensive study into the wave patterns is appearing in the Journal of the Atmospheric Sciences. Both papers were funded by the National Science Foundation, which is NCAR's sponsor, as well as by the Department of Energy, the National Oceanic and Atmospheric Administration, and NASA.The new papers follow a 2013 study by Teng and Branstator showing that a pattern related to wavenumber-5 tended to emerge about 15-20 days before major summertime heat waves in the United States.Strong impacts on local weather systemsWavenumber-5 consists of five pairs of alternating high- and low-pressure features that encircle the globe about six miles (10 kilometers) above the ground. It is a type of atmospheric phenomenon known as a Rossby wave, a very large-scale planetary wave that can have strong impacts on local weather systems by moving heat and moisture between the tropics and higher latitudes as well as between oceanic and inland areas and by influencing where storms occur.The slow-moving Rossby waves at times become almost stationary. When they do, the result can be persistent weather patterns that often lead to droughts, floods, and heat waves. Wavenumber-5 often has this stationary quality when it emerges during the northern winter, and, as a result, is associated with a greater likelihood of persistent extreme events.To determine the degree to which the wave pattern influenced the California drought, Teng and Branstator used three specialized computer models, as well as California rainfall records and 20th century data about global atmospheric circulation patterns. The different windows into the atmosphere and precipitation patterns revealed that the formation of a ridge by the California coast is associated with the emergence of the distinctive wavenumber-5 pattern, which guides rain-producing low-pressure systems so that they travel well north of California.Over the past winter, as California was lashed by a series of intense storms, wavenumber-5 was also present, the scientists said. But the pattern had shifted over North America, replacing the high-pressure ridge off the coast with a low-pressure trough. The result was that the storms that were forced north during the drought winters were, instead, allowed to make landfall.Clues to seasonal weather patternsForecasters who predict seasonal weather patterns have largely looked to shifting sea surface temperatures in the tropical Pacific, especially changes associated with El Niño and La Niña. But during the dry winters of 2013-14 and 2014-15, those conditions varied markedly: one featured the beginning of an El Niño while the sea surface temperatures during the other were not characteristic of either El Niño or La Niña.The new research indicates that the wave pattern may provide an additional source of predictability that sometimes may be more important than the impacts of sea surface temperature changes. First, however, scientists need to better understand why and when the wave pattern emerges.In the paper published in Journal of the Atmospheric Sciences, Branstator and Teng explored the physics of the wave pattern. Using a simplified computer model of the climate system to identify the essential physical processes, the pair found that wavenumber-5 forms when strong jet streams act as wave guides, tightening the otherwise meandering Rossby wave into the signature configuration of five highs and five lows."The jets act to focus the energy," Branstator said. "When the jets are present, the energy is trapped and cannot escape." But even when the jets are present, the wavenumber-5 pattern does not always form, indicating that other forces requiring study are also at play.The scientists also searched specifically for what might have caused the wave pattern linked to the severe California drought to form. In the paper published in the Journal of Climate, the pair found that extremely heavy rainfall from December to February in certain regions of the tropical Pacific could double the probability that the extreme ridge associated with wavenumber-5 will form. The reason may have to do with the tropical rain heating parts of the upper atmosphere in such a way that favors the formation of the wavenumber-5 pattern.But the scientists cautioned that many questions remain."We need to search globally for factors that cause this wavenumber-5 behavior," Teng said, "Our studies are just the beginning of that search."About the articlesTitle: Causes of Extreme Ridges That Induce California DroughtAuthors: Haiyan Teng and Grant BranstatorJournal: Journal of Climate, DOI: 10.1175/JCLI-D-16-0524.1
Title: Tropospheric Waveguide Teleconnections and Their SeasonalityAuthors: Grant Branstator and Haiyan TengJournal: Journal of the Atmospheric Sciences, DOI: 10.1175/JAS-D-16-0305.1Writer:David Hosansky, Manager of Media Relations

UCAR praises passage of Weather Research and Forecasting Innovation Act

Update: April 18, 2017Today President Donald Trump signed H.R. 353, the "Weather Research and Forecasting Innovation Act of 2017," into law.BOULDER, Colo. — With the unanimous passage of legislation to improve weather research and prediction, Congress has taken a major step today toward strengthening the nation's resilience to severe weather and boosting U.S. economic competitiveness."This landmark legislation will save lives and property while providing business leaders with critical intelligence," said Antonio J. Busalacchi, president of the University Corporation for Atmospheric Research (UCAR). "Today's bipartisan vote underscores the enduring value of scientific research to our nation."The Weather Research and Forecasting Innovation Act is the first major weather legislation since the early 1990s. It calls for more research into subseasonal to seasonal prediction, a priority for business and community leaders who need more reliable predictions of weather patterns weeks to months in advance. The bill also will strengthen short-term weather forecasts and smooth the way for research findings to be adopted by forecasters and commercial weather companies.Antonio J. Busalacchi. (©UCAR. Photo by Carlye Calvin. This image is freely available for media & nonprofit use.)Improved short- and long-term weather predictions have major implications for public safety and the economy. The nation experienced 15 weather and climate disasters last year that cost $1 billion dollars or more, including tornadoes and widespread flooding that left dozens dead. Even routine weather events can affect transportation, supply chain management, consumer purchasing, and other sectors, with a collective impact of hundreds of billions of dollars on the U.S. economy.Scientists at the National Center for Atmospheric Research, which is managed by UCAR on behalf of the National Science Foundation, have estimated that weather forecasts provide an annual benefit to the American public of more than $30 billion, compared with about $5 billion spent on generating U.S. weather forecasts."Research into the atmosphere provides an enormous return on investment," Busalacchi said. "Weather affects all of us, and being able to make plans based on forecasts of likely weather conditions is literally worth many billions of dollars to households and businesses."Decades of investments by federal agencies in weather research, observing systems, computer models, and supercomputing resources are dramatically advancing our understanding of how our atmosphere works. Five-day weather forecasts now are as reliable as two-day forecasts used to be, hurricane forecasts will soon extend out to seven days, and scientists are starting to find ways to project certain events, such as droughts and heat waves, a month or longer in advance.The Weather Research and Forecasting Innovation Act is designed to strengthen:forecasts of tornadoes, hurricanes, and other severe stormslong-range prediction of weather patterns, from two weeks to two years aheadcommunication of forecasts, which influences subsequent decisions by public safety officials, businesses, and the publictsunami warningsthe process of moving research into operations and commercializationThe legislation (HR 353) was introduced by Rep. Frank Lucas of Oklahoma and Sen. John Thune of South Dakota. Co-sponsors include Sen. Brian Schatz and Reps. Jim Bridenstine, Lamar Smith, Dana Rohrabacher, Chris Stewart, Aumua Amata Coleman Radewagen, and Suzanne Bonamici.The bipartisan bill authorizes spending increases at the National Oceanic and Atmospheric Administration (NOAA) for weather research focused on observations, models, and more powerful computing resources. It authorizes spending for COSMIC-2 an innovative suite of micro-satellites that will provide critical atmospheric observations, with multiagency support provided by UCAR, NOAA, the U.S. Air Force, the National Science Foundation, and Taiwan's National Space Organization. The legislation also expands commercial opportunities to provide weather data while increasing the efficiency of NOAA's weather satellite programs."We are very appreciative of the work by Senator Thune, Representative Lucas, and the many co-sponsors in the House and Senate," Busalacchi said."As the United States faces an increasingly competitive global marketplace, it needs more accurate and longer-term weather forecasts," he added. "At UCAR we look forward to working with NOAA, the Department of Defense, and the other federal agencies; the private sector; and the university community to build off of the National Science Foundation investment in basic research in this essential area."

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