Aviation weather reports are designed to give accurate depictions of current weather conditions. Each report provides current information that is updated at different times. Some typical reports are METAR, PIREPs, and radar weather reports (SDs).

12.4.1 Aviation Routine Weather Report (METAR) #

A METAR is an observation of current surface weather reported in a standard international format. While the METAR code has been adopted worldwide, each country is allowed to make modifications to the code. Normally, these differences are minor but necessary to accommodate local procedures or particular units of measure. This discussion of METAR will cover elements used in the United States. METARs are issued hourly unless significant weather changes have occurred. A special METAR (SPECI) can be issued at any interval between routine METAR reports.

Example: METAR KGGG 161753Z AUTO 14021G26 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

A typical METAR report contains the following information in sequential order: 1.

Type of report—there are two types of METAR reports: the routine METAR report transmitted every hour, and the aviation selected SPECI, a special report that can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information. 2.

Station identifier—a four-letter code as established by the International Civil Aviation Organization (ICAO). In the 48 contiguous states, a unique three-letter identifier is preceded by the letter “K.” For example, Gregg County Airport in Longview, Texas, is identified by “KGGG.” In other regions, including Alaska and Hawaii, the first two letters indicate the region/country/state (Alaska “PA,” Hawaii “PH”). 3. Date and time of report—a six-digit group (161753Z): the first two digits are the date, the last four are the time, always in coordinated universal time (UTC), denoted by a “Z.” 4.

Modifier—denotes that the METAR came from an automated source (“AUTO,” with “AO1″/”AO2” in remarks) or that the report was corrected (“COR”). 5.

Wind—reported with five digits (14021), or six if speed is greater than 99 knots. The first three digits indicate the direction the true wind is blowing in tens of degrees (“VRB” if variable); the last two indicate speed in knots. Gusts are shown by “G” followed by the peak gust (G26). If the wind varies more than 60° and the speed is greater than six knots, the extremes are given separated by a “V.” [Figure 12-7]

6.

Visibility—the prevailing visibility (¾ SM) reported in statute miles (“SM”). Runway visual range (RVR) may follow, shown as R, the runway number, a slant, then the visual range in feet (R17L/1400FT). 7. Weather—qualifiers (intensity light (-), moderate, heavy (+); proximity “VC”) and weather phenomena (+TSRA BR). Descriptors describe certain types of precipitation and obscurations. [Figure 12-8] 8. Sky condition—reported as amount, height, and type, or indefinite ceiling/vertical visibility (BKN008 OVC012CB). Cloud base heights are in hundreds of feet AGL; clouds above 12,000 feet are not reported by automated stations. Towering cumulus (TCU) or cumulonimbus (CB) are reported with their height. Sky coverage is reported in eighths. [Figure 12-9] 9. Temperature and dew point—given in degrees Celsius (18/17); temperatures below 0 °C are preceded by “M.” 10. Altimeter setting—reported as inches of mercury in a four-digit group preceded by “A” (A2970). 11. Zulu time—UTC. 12. Remarks—begins with “RMK”; may include wind data, variable visibility, beginning/ending times of phenomena, pressure information (e.g., “PRESRR”/”PRESFR”), and equipment-maintenance notes.

Explanation of the example: Routine METAR for Gregg County Airport for the 16th day of the month at 1753Z, automated source. Winds 140° at 21 knots gusting to 26. Visibility ¾ statute mile. Thunderstorms with heavy rain and mist. Ceiling broken at 800 feet, overcast at 1,200 feet with cumulonimbus clouds. Temperature 18 °C and dew point 17 °C. Barometric pressure 29.70 “Hg and falling rapidly.

12.4.2 Pilot Weather Reports (PIREPs) #

PIREPs provide valuable information regarding the conditions as they actually exist in the air, which cannot be gathered from any other source. Pilots can confirm the height of bases and tops of clouds, locations of wind shear and turbulence, and the location of inflight icing. If the ceiling is below 5,000 feet, or visibility is at or below five miles, ATC facilities are required to solicit PIREPs from pilots in the area. When unexpected weather conditions are encountered, pilots are encouraged to make a report to a FSS or ATC. PIREPs are easy to file and a standard reporting form outlines the manner in which they should be filed. Figure 12-10 shows the elements of a PIREP form. Item numbers 1 through 5 are required information when making a report, as well as at least one weather phenomenon encountered.

Example: UA/OV GGG 090025/TM 1450/FL 060/TP C182/SK 080 OVC/WX FV 04R/TA 05/WV 270030/TB LGT/RM HVY RAIN. Explanation: Type—routine pilot report; Location—25 NM out on the 090° radial, Gregg County VOR; Altitude/Flight Level—6,000 feet; Aircraft Type—Cessna 182; Sky Cover—8,000 overcast; Visibility/Weather—4 miles in rain; Temperature—5 °C; Turbulence—light; Icing—none reported; Remarks—rain is heavy.

12.4.3 Radar Weather Reports (RAREP) #

Areas of precipitation and thunderstorms are observed by radar on a routine basis. Radar weather reports (RAREPs) or storm detections (SDs) are issued by radar stations at 35 minutes past the hour, with special reports issued as needed.

RAREPs provide information on the type, intensity, and location of the echo top of the precipitation. [Figure 12-11] These reports may also include direction and speed of the area of precipitation, as well as the height and base of the precipitation in hundreds of feet MSL. RAREPs are especially valuable for preflight planning to help avoid areas of severe weather. However, radar only detects objects in the atmosphere that are large enough to be considered precipitation; cloud bases and tops, ceilings, and visibility are not detected by radar.

A typical RAREP will include: location identifier and time of radar observation; echo pattern—Line (LN, a line of precipitation echoes at least 30 miles long, at least four times as long as wide, with at least 25 percent coverage), Area (AREA, a group of echoes of similar type not classified as a line), or Single cell (CELL, a single isolated convective echo such as a rain shower); area coverage in tenths; type and intensity of weather; azimuth (referenced to true north) and range in nautical miles from the radar site of points defining the echo pattern; dimension of echo pattern; cell movement (coded only for cells); maximum top of precipitation and location (coded “MT” or “MTS”); the contraction “AUTO” if automated from WSR-88D data; and a final section used primarily to prepare radar summary charts (the higher the number, the greater the intensity).

Example: TLX 1935 LN 8 TRW++ 86/40 199/115 20W C2425 MTS 570 AT 159/65 AUTO ^MO1 NO2 ON3 PM34 QM3 RL2=. Explanation: The report is automated from Oklahoma City and was made at 1935 UTC. The echo pattern indicates a line of echoes covering 8/10 of the area. Thunderstorms and very heavy rain showers are indicated. The azimuths defining the echo are 86° at 40 NM and 199° at 115 NM, 20 NM wide. The cells within the line are moving from 240° at 25 knots. The maximum top, as determined by radar and satellite, is 57,000 feet, located on the 159° radial, 65 NM out. The last line indicates precipitation intensity (e.g., in grid QM the intensity is 3, heavy; 1 is light and 6 is extreme).