background image

AIM

10/12/17

7−1−62

Meteorology

7−1−31. International Civil Aviation

Organization (ICAO) Weather Formats
The U.S. uses the ICAO world standard for aviation

weather reporting and forecasting. The World

Meteorological Organization’s (WMO) publication

No. 782 “Aerodrome Reports and Forecasts”

contains the base METAR and TAF code as adopted

by the WMO member countries.

a. Although the METAR code is adopted

worldwide, each country is allowed to make

modifications or exceptions to the code for use in

their particular country, e.g., the U.S. will continue to

use statute miles for visibility, feet for RVR values,

knots for wind speed, and inches of mercury for

altimetry. However, temperature and dew point will

be reported in degrees Celsius. The U.S reports

prevailing visibility rather than lowest sector

visibility. The elements in the body of a METAR

report are separated with a space. The only exceptions

are RVR, temperature, and dew point which are

separated with a solidus (/). When an element does

not occur, or cannot be observed, the preceding space

and that element are omitted from that particular

report. A METAR report contains the following

sequence of elements in the following order:

1. Type of report.
2. ICAO Station Identifier.
3. Date and time of report.
4. Modifier (as required).
5. Wind.
6. Visibility.
7. Runway Visual Range (RVR).
8. Weather phenomena.
9. Sky conditions.
10. Temperature/dew point group.
11. Altimeter.
12. Remarks (RMK).

b. The following paragraphs describe the ele-

ments in a METAR report.

1. Type of report. There are two types of

report:

(a) Aviation Routine Weather Report

(METAR); and

(b) Nonroutine (Special) Aviation Weather

Report (SPECI).
The type of report (METAR or SPECI) will always

appear as the lead element of the report.

2. ICAO Station Identifier. The METAR

code uses ICAO 4−letter station identifiers. In the

contiguous 48 States, the 3−letter domestic station

identifier is prefixed with a “K;” i.e., the domestic

identifier for Seattle is SEA while the ICAO identifier

is KSEA. Elsewhere, the first two letters of the ICAO

identifier indicate what region of the world and

country (or state) the station is in. For Alaska, all

station identifiers start with “PA;” for Hawaii, all

station identifiers start with “PH.” Canadian station

identifiers start with “CU,” “CW,” “CY,” and “CZ.”

Mexican station identifiers start with “MM.” The

identifier for the western Caribbean is “M” followed

by the individual country’s letter; i.e., Cuba is “MU;”

Dominican Republic “MD;” the Bahamas “MY.” The

identifier for the eastern Caribbean is “T” followed

by the individual country’s letter; i.e., Puerto Rico is

“TJ.” For a complete worldwide listing see ICAO

Document 7910, Location Indicators.

3. Date and Time of Report. The date and

time the observation is taken are transmitted as a

six−digit date/time group appended with Z to denote

Coordinated Universal Time (UTC). The first two

digits are the date followed with two digits for hour

and two digits for minutes.

EXAMPLE−

172345Z (the 17

th

 day of the month at 2345Z)

4. Modifier (As Required). “AUTO” identi-

fies a METAR/SPECI report as an automated weather

report with no human intervention. If “AUTO” is

shown in the body of the report, the type of sensor

equipment used at the station will be encoded in the

remarks section of the report. The absence of

“AUTO” indicates that a report was made manually

by an observer or that an automated report had human

augmentation/backup. The modifier “COR” indi-

cates a corrected report that is sent out to replace an

earlier report with an error.

NOTE−

There are two types of automated stations, AO1 for

automated weather reporting stations without a precipita-

tion discriminator, and AO2 for automated stations with a

precipitation discriminator. (A precipitation discriminator

can determine the difference between liquid and

frozen/freezing precipitation). This information appears in

the remarks section of an automated report.