Weather Information : C - Aviation Weather Reports and Observations Flashcards
What is a METAR and what are the two types?
A METAR is an hourly surface observation of conditions observed at an airport. There are two types of METAR reports—a routine METAR report that is transmitted every hour and an aviation selected special weather report (SPECI). This is 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.
(AC 00-45)
Describe the basic elements of a METAR.
a. Type of reports—the METAR, and the SPECI (aviation special weather report).
b. ICAO station identifier—4-letter station identifiers; in the
conterminous U.S., the 3-letter identifier is prefixed with K.
c. Date and time of report—a 6-digit date/time group appended with Z (UTC). First two digits are the date, then two for the hour, and two for minutes.
d. Modifier (as required)—if used, the modifier AUTO identifies the report as an automated weather report with no human intervention. If AUTO is shown in the body of the report, AO1 or AO2 will be encoded in the remarks section to indicate the type of precipitation sensor used at the station.
e. Wind—5-digit group (6 digits if speed is over 99 knots); first three digits = wind direction, in tens of degrees referenced to true north.
Directions less than 100 degrees are preceded with a zero; next two digits are the average speed in knots, measured or estimated (or, if over 99 knots, the next three digits).
f. Visibility—surface visibility in statute miles, space, fractions of statute miles (as needed), and the letters SM.
g. Runway visual range (RVR), as required.
h. Weather phenomena—broken into two categories: qualifiers, and weather phenomena.
i. Sky condition—amount/height/type (as required) or indefinite ceiling/height (vertical visibility)Heights are recorded in feet AGL.
j. Temperature/dew point group—2-digit format in whole degrees Celsius, separated by a solidus (/). Temperatures below zero are prefixed with M.
k. Altimeter—4-digit format representing tens, units, tenths, and hundredths of inches of mercury prefixed with A. The decimal point is not reported or stated.
l. Remarks (RMK), as required—operational significant weather phenomena, location of phenomena, beginning and ending times, direction of movement.
Example: METAR KLAX 140651Z AUTO 00000KT 1SM
R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2
(AC 00-45)
Describe several types of weather observing programs available.
a. Manual Observations—with only a few exceptions, these reports are from airport locations staffed by FAA personnel who manually observe, perform calculations, and enter their observations into the communication system.
b. AWOS—Automated Weather Observing System; consists of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcast local, minute-by-minute weather data directly to the pilot. Observations will include the prefix AUTO in data.
c. AWOS Broadcasts—Computer-generated voice is used to automate the broadcast of minute-by-minute weather observations.
d. ASOS/AWOS—Automated Surface Observing System/Automated Weather Observing System (AWOS); the primary U.S. surface weather observing systems. Both systems provide continuous minute-by-minute observations that generate METARs and other aviation weather information. Transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID, and receivable to a maximum of 25 NM from the station and a maximum altitude of 10,000 feet AGL. Observations made without human intervention will include themodifier “AUTO” in the report data. A maintenance indicator ($) is coded when an automated system detects that maintenance is needed on the system.
What are PIREPs (UA), and where are they usually found?
A pilot report (PIREP) provides 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. There are two types of PIREPs: routine or “UA,” and urgent or “UUA.” PIREPs should be given to the ground facility with which communications are established (i.e., FSS, ARTCC, or terminal ATC). Altitudes are MSL, visibilities SM, and distances in NM. PIREPs are available from an FSS and on the internet via the ADDS web page at: aviationweather.gov/airep.
(AC 00-45)
