Aviation Weather Services

Aviation Routine Weather Report (METAR) 4. Modifier—denotes that the METAR/SPECI came from A METAR is an observation of current surface weather an automated source or that the report was corrected. If reported in a standard international format. While the the notation “AUTO” is listed in the METAR/SPECI, METAR code has been adopted worldwide, each country is the report came from an automated source. It also lists allowed to make modifications to the code. Normally, these “AO1” (for no precipitation discriminator) or “AO2” differences are minor but necessary to accommodate local (with precipitation discriminator) in the “Remarks” procedures or particular units of measure. This discussion of section to indicate the type of precipitation sensors METAR covers elements used in the United States. employed at the automated station. When the modifier “COR” is used, it identifies a METARs are issued on a regularly scheduled basis unless corrected report sent out to replace an earlier report significant weather changes have occurred. A special that contained an error (for example: METAR KGGG METAR (SPECI) can be issued at any time between routine 161753Z COR). METAR reports. 5. Wind—reported with five digits (14021KT) unless Example: the speed is greater than 99 knots, in which case the METAR KGGG 161753Z AUTO 14021G26KT 3/4SM wind is reported with six digits. The first three digits +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK indicate the direction the true wind is blowing from in PRESFR tens of degrees. If the wind is variable, it is reported as “VRB.” The last two digits indicate the speed of A typical METAR report contains the following information the wind in knots unless the wind is greater than 99 in sequential order: knots, in which case it is indicated by three digits. If the winds are gusting, the letter “G” follows the wind 1. Type of report—there are two types of METAR speed (G26KT). After the letter “G,” the peak gust reports. The first is the routine METAR report that is recorded is provided. If the wind direction varies more transmitted on a regular time interval. The second is than 60° and the wind speed is greater than six knots, the aviation selected SPECI. This is a special report a separate group of numbers, separated by a “V,” will that can be given at any time to update the METAR for indicate the extremes of the wind directions. rapidly changing weather conditions, aircraft mishaps, or other critical information. 6. Visibility—the prevailing visibility (¾ SM) is reported in statute miles as denoted by the letters “SM.” It is 2. Station identifier—a four-letter code as established by reported in both miles and fractions of miles. At times, the International Civil Aviation Organization (ICAO). runway visual range (RVR) is reported following the In the 48 contiguous states, a unique three-letter prevailing visibility. RVR is the distance a pilot can identifier is preceded by the letter “K.” For example, see down the runway in a moving aircraft. When RVR Gregg County Airport in Longview, Texas, is is reported, it is shown with an R, then the runway identified by the letters “KGGG,” K being the country number followed by a slant, then the visual range designation and GGG being the airport identifier. in feet. For example, when the RVR is reported as In other regions of the world, including Alaska and R17L/1400FT, it translates to a visual range of 1,400 Hawaii, the first two letters of the four-letter ICAO feet on runway 17 left. identifier indicate the region, country, or state. Alaska identifiers always begin with the letters “PA” and 7. Weather—can be broken down into two different Hawaii identifiers always begin with the letters “PH.” categories: qualifiers and weather phenomenon Station identifiers can be found by calling the FSS, a (+TSRA BR). First, the qualifiers of intensity, NWS office, or by searching various websites such proximity, and the descriptor of the weather are given. as DUATS and NOAA's Aviation Weather Aviation The intensity may be light (–), moderate ( ), or heavy Digital Data Services (ADDS). (+). Proximity only depicts weather phenomena that are in the airport vicinity. The notation “VC” indicates 3. Date and time of report—depicted in a six-digit group a specific weather phenomenon is in the vicinity (161753Z). The first two digits are the date. The last of five to ten miles from the airport. Descriptors four digits are the time of the METAR/SPECI, which are used to describe certain types of precipitation is always given in coordinated universal time (UTC). and obscurations. Weather phenomena may be A “Z” is appended to the end of the time to denote reported as being precipitation, obscurations, and the time is given in Zulu time (UTC) as opposed to other phenomena, such as squalls or funnel clouds. local time. 13-6