Acronyms are pronounced as if they were words, and so do not take an article in front of them (FEMA, NASA, COSMIC, etc.). "NCAR" is a pronounced acronymn. Initialisms that require each letter to be sounded out separately usually take an article (the IMF, the EPA).
We make some exceptions for frequently used initialisms: we drop the article in front of division and section abbreviations and in front of NSF, for example. Read on for more specifics.
Do not give an abbreviation or acronym for a term that is only used once unless the acronym is better known than the full spelling (e.g., FAA).
Our field is laden with acronyms, so it's not unusual to find a short article strewn with "alphabet soup." To avoid the soup as much as possible, consider whether your article will contain more than two mentions of the noun your acronym represents. If it's two and only two, consider using the full spellout for those two occasions.
It is also a best practice to avoid the acronym by using "the center," "the foundation," etc., as the second through nth reference when there is only one center or one foundation in your article and hence the reference would be unequivocal. Note that only the full name is capitalized; shorter versions generally take lower case, as in UCAR Board of Trustees . . . the board ruled that. . . .
If you'll be making at least three mentions or your case was not covered above, read on. [02/2008; 06/2011]
If an abbreviation or acronym is used very soon after the use of the full term (e.g., in the same paragraph), it is not necessary to give the acronym in parentheses. For example: "John Doe, a visitor at NCAR from the Federal Aviation Administration, reports that the FAA will spend $1.2 million on the program over the next five years." Likewise, if the acronym is used first and the spellout follows soon after, it is not necessary to repeat the acronym in parentheses.
Exception to the same-paragraph rule: If the spellout itself is predominantly lower case (e.g., advanced fiber-optic Echelle spectrograph), then do include the acronym in parens immediately following first use (assuming the one-or-two-use rules have been met): The advanced fiber-optic Echelle spectrograph (AFOE), was deployed . . . . [02/2008]
When the above-listed conditions have been satisfied, at the first appearance in text of a term that is commonly abbreviated or that you wish to abbreviate, write it out and give the abbreviation in parentheses immediately thereafter. Use the abbreviation throughout the rest of the text, except in very long documents, in which you should give the full spelling several times (for example, once per chapter).
It is acceptable to give the abbreviation or acronym first (with the whole name in parentheses) if the acronym is much more familiar than the whole name or the structure of the sentence works better that way. Also, if the acronym first arises in a quote (and the speaker uses the acronym rather than the full name), keep the speaker's terminology intact and put the full spelling immediately after the abbreviation, in brackets.
Use of periods: yes for abbreviations of two letters; no for three letters or more: U.S., U.N., but UNEP.
Units of measure: Do not abbreviate any units on first use in nontechnical writing; treat them as regular abbreviations. In technical contexts, follow SI usage (see list in Chicago, 14th ed., p. 478, section 14.41). Units are spelled out when not used with numerals (e.g., hundreds of kilometers). Do not abbreviate day, month, or year.
See also "metric units."
NCAR or UCAR: almost never spelled out. The same for "NASA," which itself has stopped using the spellout in most cases. Staff Notes and the Quarterly have additional exceptions (e.g., NOAA, NWS, NSF), but all other acronyms must be spelled out. If you're not sure what one stands for, look it up in the Acronym List.
Labs and Divisions: We follow common NCAR usage concerning articles before acronyms: Do not use "the" before the acronym for any NCAR division or section. Do not use "the" before NSF, NOAA (and its subunits), NASA, NWS, acronyms of most experiments and research programs, WMO, NAS, NMC, ML, FL.
Do use "the" before EAC, EPA, FAA, AMS, CCM, GCM, and other acronyms that are not pronounceable as words (exceptions noted above). Do use "the" when any acronym serves as an adjective (the NASA program). [03/2000]
Use the English-equivalent spellout; when translation is not available use the foreign-language acronym plus an English description of the institution in parens.