winter weather

Cold, hard facts

Bob Henson • January 6, 2014 | It’s hard to escape the cold weather now plowing into the eastern United States—especially if you turn on a TV or log onto Facebook. The big freeze is a compelling news story, with truly dangerous temperatures and wind chills extending into large swaths of the nation. Yet we’ve had worse: in some ways, this cold snap serves to illustrate how rare such intense events have become. Amid all the hype, what stands out about this early winter onslaught? Back to the 20th century—but not that far back.  Many cities in the Midwest and mid-South are experiencing temperatures unseen since the turn of the new century. As a whole, though, this cold wave won’t rival the worst of those seen up through the 1990s. This morning, January 6, Indianapolis dipped to –14°F, the city’s coldest reading since January 1994. (During that same month, temperatures reached –27°F, the city’s all-time low.) The storm has also delivered 10 to 20 inches of snow from eastern Missouri to Michigan, with several cities having some of their heaviest 24-hour snowfalls on record. The frigid Midwestern air mass should move east quickly, but there will be a number of daily records set for cold nights and cold days along its path. Winds ripping around a polar vortex arc from central Canada across the Midwest and back into northeast Canada, as analayzed at 300 millibars (about six miles above sea level) at 18Z (noon CST) on Monday, January 6, 2014.  Jet-stream winds topped 150 knots (172 mph) in the brighest purple band, stretching from Mississippi to Quebec. (Image courtesy NCAR/RAL Real-Time Weather Data.) A fast mover. Part of the reason this cold front may not set many all-time record lows is because it’s moving so quickly. To get the air temperature to sink to record lows, it helps to have a calm, clear night, ideally with a deep snowpack. Just two days ago, the air mass now in the Midwest was nestled in northern Canada. A powerful dip in the jet stream pulled the frigid air south so quickly that it’s had little time to modify. (You may hear this pattern being referred to as a displacement of the polar vortex; here’s an excellent explainer from the National Weather Service.) Such setups can produce extremely low wind chills and very cold daytime readings. At noon today (January 6), Chicago was hovering near –14°F, one of the 10 coldest noontime readings ever reported there. Many other Midwest cities are having their coldest afternoon temperatures in decades. But the conditions that foster the coldest nighttime readings may not cover as wide an area. Ups and downs. Sometimes it’s not just the cold but the rapid swings between cold and warm that cause trouble. In between an Arctic blast during New Year’s week and the latest one, a swath of mild, humid air rocketed northward across the South and into New England, producing roller-coaster temperature swings that are quite rare in those parts of the country. The mercury dipped to 9°F in Salisbury, Maryland, on Saturday morning, January 4. By late Sunday night, it had jumped to 64°F.  By Tuesday morning, it could be back down near 10°F. Saranac Lake, New York, vaulted from –24°F late Friday night to 49°F early Monday morning. In Melbourne, Florida, readings will plummet from 79°F this afternoon to a predicted 33°F by tomorrow morning. * Update | 7 January: Salisbury reached an overnight low of 10°F, while Melbourne dipped to 38°F on its hourly measurements. The OWLeS field project is analyzing some of the nation's most intense snowfalls, which occur regularly along the south and east shores of Lake Ontario and on top of New York's nearby Tug Hill region. On the night of December 12, 2013, a University of Utah student launches a radiosonde (weather balloon) in snowfall rates of 4 inches per hour. (Photo courtesy Peter Veals, University of Utah.) Lake effect in overdrive. When cold air sweeps over the relatively warm Great Lakes, huge snowfalls can occur along and near the downwind shoreline. This week, the contrast between the largely-unfrozen lake water and the frigid incoming air is about as strong as it gets. Between now and Wednesday, more than five feet of snow could fall on the Tug Hill region, just north of Syracuse, New York. Fortuitously, OWLeS, the Ontario Winter Lake-Effect Systems field project, is under way, with Doppler on Wheels radars and other equipment on hand to document the massive snowfall. NCAR is managing a field catalog for the project, and Jim Steenburgh (University of Utah) is blogging from the scene. So far this winter, the warm extremes have it. The U.S. Records site, maintained by NOAA’s National Climatic Data Center, tells us that—believe it or not—the nation saw four times more daily record highs (999) than record lows (254) for the 30 days ending on Sunday, January 5.  The same period saw seven monthly highs but no monthly lows. Where has it been so warm? Largely toward the Southeast, with occasional surges up the East Coast. South Florida had one of the mildest Decembers in its history, and Baltimore experienced a low on December 22 of 62°F, its warmest on record for any day in meteorological winter (December through February). During November 2013, North America was one of the few land masses on the globe with temperatures running below the 1961–1990 average, as shown in this map of anomalies (cool colors = cooler than average, warm colors = warmer than average). It was the warmest November globally in records that extend back 134 years. (Image courtesy NOAA National Climatic Data Center.) Climate change hasn’t stopped. Globally, we’ve just seen the warmest November in more than a century of recordkeeping. (See this post on the longer-term “pause” in global warming, which has some interesting features of its own.) This week, the cold is mostly concentrated in North America. Australia is smashing heat records, with temperatures reaching 118°F. Many Eurasian cities are well above average too: this week will see Moscow hovering in the 30s Fahrenheit, and Warsaw is expecting 40s with periods of rain. According to Pravda, some Russians would be happy to trade places with North Americans right now: “Many people find the current winter in Russia extremely dull and depressing.”

Predicting snow in the Anchorage Bowl

Researchers and forecasters work together to improve forecasts where the mountains meet the sea. November 17, 2011  • Local geography, such as a mountain range or large body of water, can greatly affect snowfall amounts. This is especially true in Anchorage, Alaska, nestled between the Chugach Mountains and Pacific Ocean. Anchorage, Alaska. (Photo by Frank K., Wikipedia Commons.) Thanks to a recent partnership between the University of Alaska Anchorage and the National Weather Service (NWS), Anchorage residents may get better forecasts of winter snowfalls. The research was facilitated by UCAR’s COMET Program, which focuses on education and training for the environmental sciences. The Anchorage Bowl, as it's known, averages about 70 inches (178 centimeters) of snow per year, most of it falling between December and February. Forecasting for the area can be difficult due to the region’s varied and rugged geographical features. This is especially true when a low pressure system builds over nearby Prince William Sound (PWS). These lows, which bring warm air and moisture into the bowl, have been anecdotally associated with major snowstorms in Anchorage. The goal of the research project was to examine the relationship between significant snowfall events in Anchorage and the presence of PWS lows, in hopes of improving weather forecasts. The research team, led by the University of Alaska’s Peter Olsson and the NWS’s James Nelson, compiled a climatology of significant snowfall events (defined as storm totals greater than 6 in, or 15 cm) in Anchorage between January 1997 and December 2006. They then narrowed this down to events associated with PWS lows. A potent setup for snowfall in Anchorage occurs when energy moving along the upper-level jet stream (purple) triggers formation of a surface low-pressure center (red) that moves into Prince William Sound (PWS). The mountains lining the sound (see photo, above) help force air upward. However, a small difference in the track of the PWS low can greatly affect how much snow falls. If the low moves toward the west side of the sound, more than a foot of snow may occur in and near Anchorage in less than 24 hours. These amounts are greatly reduced if the low tracks toward the east side of the sound. Scientists are gaining traction on predicting the behavior of PWS lows through a study facilitated by UCAR's COMET Program and carried out by the University of Alaska Anchorage and the National Weather Service. (Illustration ©UCAR.) The results show that snowfalls characterized by PWS lows comprised just over half of all significant storms for Anchorage for the study period; the contribution of PWS lows to the total snowfall for the study period was 24%. The team’s next step was to focus on a particular storm that occurred on February 9, 2005, as a case study to see if weather models could reproduce the event. The storm, which occurred during a PWS low, produced about 7 in (18 cm) of snow in Anchorage. The researchers used the NCAR-based Weather Research and Forecasting model to simulate the storm and verify the results against real-world weather data from the event. The model captured the presence of the PWS low and accurately portrayed winds, though it overproduced precipitation. Nelson says that the project has helped the Anchorage NWS office better understand PWS lows and their potential to produce significant snowfall for the area. “The study should help us predict PWS snowfall events with greater accuracy for both onset and amount of precipitation, so that we can provide better service to local officials and the public,” he says. The University of Alaska benefited from the partnership as well, as its researchers became familiar with accessing NWS weather data and then analyzing it with NCAR Command Language (a data analysis and visualization tool) and VAPOR (a 3-D visualization software developed at NCAR). “This combination of access to regional datasets and new analysis tools will help us approach a variety of research questions,” Olsson says. He adds that university researchers are interested in pursuing future research projects with the NWS on additional weather phenomena in the Anchorage area, including high wind events, wind shear, and turbulence. Vickie Johnson (©UCAR.) Bringing forecasters and researchers together The Anchorage snowfall project was facilitated by COMET’s Outreach Program, whose goal is to improve local forecasts and warning services by providing financial support for applied research that fosters relationships between academic researchers and operational forecasters. The program, which gets its financial support from the NWS, has sponsored more than 300 research projects since 1989, involving more than 80 universities and 100 forecast offices. “We get really positive feedback about the Outreach Program,” says COMET’s Vickie Johnson. “The forecasters enjoy working on research, and they receive assistance on projects that will help them forecast better. On the university side, the researchers experience what it's like to forecast in the real world.” Nearly all Outreach Program projects involve university students, she adds. “The students enjoy doing research that lets them see the applications,” she says. “Many have gone on to have careers at the NWS after working on these projects.” >>>COMET Outreach Program

Canadian forecasters sharpen winter skills

   UCAR's COMET Program partners with the Canadian Meteorological Service for   expert training. November 17, 2011  • In October, an international group of weather forecasters convened in Boulder, Colorado, to hone their skills at predicting winter weather. The annual two-week course, which is delivered through a partnership between the UCAR COMET Program and the Meteorological Service of Canada (MSC), aims to build stronger links between atmospheric research and operational forecasting. Course topics ranged from the structure of wintertime cyclones to lake-effect snowfall, mountain precipitation, radar and satellite applications, and more. Forecasters from across Canada attended the training, along with meteorologists from the U.S. National Weather Service, U.S. Navy, and several European countries. The course was taught with the help of several scientists, representing both academic and operational backgrounds, from Canada and the United States. In addition, Brad Snyder and James Cummine from MSC worked with the COMET staff to facilitate the course. “The ultimate goal of the course is for the forecasters to increase their understanding of atmospheric processes associated with winter weather,” says COMET meteorologist Dave Linder, who helped lead the course. “We want them to retain the knowledge, apply it, and share it with their fellow forecasters after the course.” >>>Winter weather training: The COMET Program Matt Albers, Meteorological Service of Canada.   Paul Greeley, Meteorological Service of Canada.

Winter driving: Where the rubber meets the road

What if the vehicles ahead of you could send weather data to a smart system, warning you of ice or fog just ahead? November 17, 2011  • There's nothing unusual these days about using a mobile device to check for traffic jams or road closures ahead, especially when winter weather creates chaos out of a daily commute. But new technology being developed at NCAR might take this vital information to another level. Alerting drivers. The prototype Vehicle Data Translator aims to improve driving safety by warning motorists about nearby hazards. Information about adverse conditions would be automatically transmitted from vehicles to a remote data processing system. The system would incorporate weather information from other sources, including radars and satellites, and then send alerts to drivers in the area. (©UCAR. Illustration by Lex Ivey. This image is freely available for media & nonprofit use.*) “What you really want to know isn't just the general weather conditions in the 20-mile zone around you," says NCAR scientist Sheldon Drobot. “You want to know what’s going on at the next street corner, and should you go left or right at the light.” Drobot manages a research program on surface transportation in NCAR’s Research Applications Laboratory. For the past few years, he and his colleagues have been developing and testing an innovative technological system that will eventually help protect drivers from being surprised by black ice, fog, and other hazardous weather conditions. The prototype system, which is called the Vehicle Data Translator and sponsored by the U.S. Department of Transportation’s Connected Vehicle and Road Weather Management Programs, gathers detailed information about weather and road conditions from moving vehicles. Within the next decade, it should enable motor vehicles equipped with wireless technology to transmit automated updates about local conditions to a central database, which will then relay alerts to other drivers in the area. “The goal is to reduce crashes, injuries, and deaths by giving drivers information about nearby hazards,” Drobot says. “The system will tell drivers what they can expect to run into in the next few seconds and minutes, giving them a critical chance to slow down or take other action.” Field testing In 2009, the research team tried out the system in the Detroit area, where test drivers in 11 cars equipped with sensors sought out adverse winter road conditions. The NCAR team then analyzed the reliability of the system by comparing data from the cars with weather observations from radars and satellites, and used the information to build the algorithms, or mathematical formulas, for the Vehicle Data Translator software. This winter, the team is taking the project to Minnesota and Nevada, where they will outfit state Department of Transportation snowplows and supervisor trucks with sensors. Eighty vehicles in Minnesota and 16 in Nevada will measure temperature, pressure, humidity, and other weather variables as their drivers go about their routine jobs. The researchers are also keeping sensors on hand at NCAR’s headquarters in Boulder, Colorado, so that they’re ready to drive up Vail Pass when storms hit. The pass maintains a road weather station that will give the team another baseline for verifying the vehicle sensors. The science behind precision forecasting The way the system will work, once operational, is that an onboard digital memory device will collect both weather data, such as temperature, and indirect indications of road NCAR researchers Sheldon Drobot, Michael Chapman, and Brice Lambi install a sensor in a vehicle as part of testing for the Vehicle Data Translator system. (©UCAR. Photo by Carlye Calvin.) conditions, such as windshield wipers being switched on or the activation of antilock brakes. This information will be transmitted to a central database, where it will be integrated with other local weather data and traffic observations, along with details about the road's surface material and alignment. Drobot explains that incoming data would be anonymous to protect the privacy of drivers, and drivers would likely have the option to opt out. The processed data would then be used to warn motorists about upcoming hazards—everything from icy roads to a nearby vehicle that’s driving erratically—and even suggest alternative routes. The system would also alert emergency managers to hazardous driving conditions and help road crews clear snow more efficiently. One of the team’s biggest challenges is figuring out how to process the enormous amounts of data that could be generated by about 300 million motor vehicles. NCAR has worked with the Department of Defense, the aviation industry, and other organizations to analyze complex weather observations. But the new system incorporates information from far more sources—and those sources are constantly on the move. The team is refining its algorithms and other techniques for accurately interpreting data and eliminating misleading indicators. If a driver, for example, turns on the windshield wipers in clear weather to clean the windshield, the system will identify that action as an outlier rather than issuing a false alert about precipitation. "It's not enough to process the information almost instantaneously," says NCAR program director William Mahoney. "It needs to be cleaned up, sent through a quality control process, blended with traditional weather data, and eventually delivered back to drivers who are counting on the system to accurately guide them through potentially dangerous conditions." The next step The research team will use the data from this winter’s tests in Minnesota and Nevada to continue to develop the software. They're hoping to have a program ready for operational field testing by winter 2012–13, according to Drobot. In 2013, the National Highway Traffic Safety Administration plans to use the results of pilot tests to determine whether the technology is mature enough to encourage vehicle manufacturers to include the equipment in new passenger vehicles. For example, manufacturers could earn higher government safety ratings for vehicles that support the technology. The NCAR-developed software would then be made available to private vendors, according to Drobot. "We have a long history of transferring technology to public use. We want to see our efforts implemented in the real world," he says. >>>Surface transportation - weather decision support (NCAR Research Applications Lab)

Where snow is born: Getting on top of winter storms

PLOWS campaign opens a window on how snow develops in clouds. November 17, 2011  •  If you’ve ever flown above the vast cloud deck of a winter storm, then experienced a few jolting seconds as you descended into it, you already know something about cloud-top instability. It turns out that small pockets of rising air near the tops of winter storms may play a large role in generating snowfall on the ground. The view from the NSF/NCAR C-130 as it flew above a thick, snow-producing cloud deck while taking measurements for the PLOWS project on December 14, 2009. (Photo by Andrew Rosenow, University of Illinois at Urbana-Champaign.) Researchers with the PLOWS project (Profiling of Winter Storms), which involved several UCAR member universities, are now in the thick of data analysis. The results from the NSF-funded project are giving scientists a richer three-dimensional understanding of how snow takes shape inside winter storms. In time, the insights could also help forecasters analyze how a storm is evolving and what people on the ground can expect. “We’ve made a number of fundamental discoveries,” says PLOWS leader Bob Rauber (University of Illinois at Urbana–Champaign). He and several students are among the PLOWS participants now working on papers to be submitted over the next few months. “We’re still on a pretty steep learning curve, but we’re getting close,” Rauber says. At two recent conferences held by the American Meteorological Society, Rauber and colleagues presented striking preliminary results from the data they gathered across the Midwest in 2009–10 and 2010–11. Where snow is born One of the most illuminating cases captured by PLOWS was a winter storm that dropped 12 to 15 inches (30–38 centimeters) of snow across parts of Iowa and neighboring states on December 9, 2009. The top part of the graphic below is a composite of images from standard, ground-based Doppler radars that shows the classic comma shape of a mature winter storm. “Our longstanding interpretation of winter storms is based on what you see in that top panel,” says Rauber. But as he and colleagues found out, there’s more going on than meets the eye on ground-based radar. The new perspective came largely from research radar and lidar (laser-based radar) flown into snowstorms aboard the NSF/NCAR C-130 aircraft. The Wyoming Cloud Radar gathered data with a razor-sharp resolution of 15 meters (about 50 feet). Vertical profiling of the storms with this radar allowed the investigators to see storm features invisible to the standard WSR-88D radars used in daily forecast operations, which have much lower resolution and sensitivity. Two views of a winter storm. A composite of ground-based Doppler radar data (top) shows the classic comma shape of a well-developed storm. As the NSF/NCAR C-130 flew along a path shown by white dotted lines in the top image, its upward- and downward-pointing cloud radar detected narrow cloud-top streamers toward the north end of the storm (top left of bottom image) and deep convective towers toward the south end (right edge of bottom image). (Images courtesy Bob Rauber.) The aircraft’s track allowed for a cross-sectional view as it passed through the storm, as shown by the dashed white line in both the top and bottom images. As it looked upward, the radar detected a set of narrow, feathery streamers (blue and green) descending from cells near the top of the storm (at top left of bottom image). Each streamer is about 1.3 miles (2 kilometers) tall and anywhere from a half-mile to a few miles wide. That’s about the size of an ordinary cumulus cloud you might see in midsummer, when sunshine heats the ground and columns of warm, moist air rise (a process called convection). In this case, however, it’s December, and the clouds are at altitudes where the air is typically colder than –22°F (30°C), so the pockets of convection came as more of a surprise. Rauber and his collaborators aren’t yet sure what is driving the apparent cloud-top instability. However, it appears to be different from other forms of instability long associated with winter storms. It’s also surprisingly common, says Rauber: “These features are ubiquitous. We saw them in almost every case.” Preliminary results suggest that the broad field of snow falling through a winter storm’s comma cloud originates in the cells that produce the narrow streamers. Updrafts in these cells can reach about 7 mph (3 meters per second)—quite strong for a winter system. Once the streamers descend into the heart of the storm, they appear to merge into a broader area where smaller snowflakes collide and coalesce into larger flakes. Rauber and his research team are focusing on understanding these cloud-top features, a new aspect of winter storm dynamics made evident through PLOWS. A better handle on thundersnow Where there’s instability and precipitation, there’s often thunder. Some of the PLOWS cases involve reports of lightning during snow. However, the 3-D structure of these electrified snowstorms isn’t yet known. For example, one of the graduate students on Rauber’s team is examining data from a ground-based electric field mill, airborne and ground-based radars, and lightning detectors to see how variations in electric field correspond to other aspects of storm development. Forecasters can already recognize when highly unstable air might lead to thundersnow—for instance, it’s relatively common during the most intense nor’easters along the mid-Atlantic, such as the “Snowtober” storm that occurred in late October 2011. However, PLOWS may help forecasters better understand borderline cases where the chance of thundersnow is less clear. Left: PLOWS lead investigator Bob Rauber (right) prepares a radiosonde with graduate student Melissa Peterson (both from the University of Illinois at Urbana-Champaign) on January 16, 2010, in Moulton, Alabama. Right: Along with studying winter weather, PLOWS participants had to deal with it themselves. (Left photo by Joe Wegman; right photo by Bob Rauber.) Rauber has already shared some of the findings from PLOWS with NWS forecasters, who’ve given him an enthusiastic reception. ”The initial reaction of the nearby office in Lincoln, Illinois, was, You’ve got to show this to everybody in the Midwest,” says Rauber. That office quickly arranged a teleconference to do just that with all the NWS science and operations officers (better known as SOOs) from the Midwest. Instruments and collaborators for PLOWS came from the University of Missouri, University of Alabama at Huntsville, and University of Wyoming. The project also employed NCAR’s Mobile Integrated Sounding System, a vehicle equipped to launch and capture data from weather balloons, in addition to the C-130 aircraft. >>>Snow gaze: PLOWS scoops up insight (UCAR Magazine report from 2009 field phase)PLOWS field support (NCAR's Earth Observing Lab)PLOWS - University of Illinois
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