METAR Weather Codes Explained

The present-weather group is the part of a METAR that packs the most meaning into the fewest letters. Codes like +TSRA or -FZDZ are not random — they are built from a small set of parts in a fixed order: intensity, then proximity, then a descriptor, then the phenomenon itself. Learn the parts and you can read any combination.

How a weather group is built

Each present-weather group is assembled in this order:

[intensity or proximity] [descriptor] [phenomenon]

For example, +TSRA is + (heavy) + TS (thunderstorm descriptor) + RA (rain). VCSH is VC (in the vicinity) + SH (showers). Multiple groups can appear in sequence when several things are happening at once.

Intensity and proximity

Descriptors

A descriptor modifies the phenomenon that follows it. There are eight:

Precipitation

Obscurations and other phenomena

Putting it together

A full example: METAR KDEN 121853Z 30015G28KT 1/2SM +TSRA GR BKN008CB tells you a heavy thunderstorm with rain and hail is over the field, visibility down to half a mile, with cumulonimbus at 800 feet. That is a stay-on-the-ground report.

Why freezing precipitation matters most

Of all these codes, the freezing descriptor deserves special attention. FZRA (freezing rain) and FZDZ (freezing drizzle) involve supercooled liquid that freezes on contact, producing rapid, dangerous airframe icing. Even "light" freezing precipitation is a serious hazard for most light aircraft.

Descriptors in depth

A few descriptors trip people up. MI (shallow), BC (patches), and PR (partial) only ever attach to fog: MIFG is a shallow ground fog under about two metres deep, BCFG is fog in patches across the field, and PRFG is fog covering part of the aerodrome while the rest is clear. The pair DR (low drifting) and BL (blowing) both describe material lifted by the wind, and the difference is height: drifting stays below eye level, blowing is raised above it. So DRSN is snow snaking along the surface, while BLSN can cut visibility dramatically at eye level.

Using the vicinity flag

VC is easy to misread. It means the phenomenon is happening near the airport — roughly 5 to 10 statute miles away — but not at the station itself. VCTS is a thunderstorm in the vicinity and VCSH is showers in the vicinity. VC is never combined with an intensity sign, because you are not measuring something happening over the field. When you see VC, treat it as a heads-up that conditions could change quickly as the weather moves in.

Recent weather (RE)

A group beginning with RE reports weather that has ended since the last observation but is still operationally relevant. RERA is recent rain, RETS a recent thunderstorm, and REFZRA recent freezing rain. Recent-weather groups appear near the end of the body, and they are a reminder that a runway may still be wet or contaminated even though the phenomenon is no longer occurring.

Combining several groups

When more than one type of weather is present, the station lists each group separately, roughly in order of significance. -SN BR is light snow and, separately, mist reducing visibility. A descriptor such as TS or SH applies to the precipitation that immediately follows it, so SHRA is rain showers while a bare RA is steady rain falling from a layer of cloud rather than a shower.

A second worked report

METAR KBOS 141254Z 04018G26KT 3/4SM +SN BLSN VV007 M04/M07 A2984

Working through the weather groups: +SN is heavy snow, and BLSN is blowing snow lifted above eye level by that 18-knot wind gusting 26. Visibility is down to three-quarters of a mile, the sky is obscured with a vertical visibility of 700 feet, and the temperature is well below freezing. Two weather groups — one for the falling snow, one for the blowing snow — together describe a genuine winter-storm scenario.

Common mistakes

• Reading a missing intensity sign as "none" — no sign means moderate, not absent.
• Assuming SH means light. Showers describe character (brief, from convective cloud), not intensity; a shower can be heavy.
• Treating VC weather as being at the field. It is nearby, not overhead.
• Confusing GR (hail, 5 mm or larger) with GS (small hail or snow pellets, under 5 mm).

Limitations

Automated stations cannot identify every phenomenon. They report UP when they detect precipitation they cannot classify, and they generally do not report hail type, tornadoes, or volcanic ash — those depend on human observers. Absence of a weather group never guarantees the absence of weather nearby; pair the METAR with radar, satellite, and the TAF.

Official sources

• FAA Aviation Weather Handbook (FAA-H-8083-28); AC 00-45 — present-weather notation.
• NWS Aviation Weather Center — aviationweather.gov.