Embedded Files
Read through this section now, but it's mostly useful as a reference. When you encounter something in a METAR report you don't understand, see if it's here. And when you encounter an abbreviation that doesn't seem to have any letters in common with the word it stands for, it's probably an abbreviation of the French.
Weather
Intensity: - = light, nothing = Moderate, + = heavy
Modifiers: SH = shower, TS = thunderstorm, FZ = freezing, MI = shallow, PR = partial, BC = patches, DR = low drifting, BL = blowing
Precipitation: RA = rain, SN = snow, DZ = drizzle, SG = snow grains, IP = ice pellets, IC = ice crystals, GR = hail, GS = small hail or snow pellets, UP = unknown precipitation type (automated report)
Obscuration: FG = fog, BR = mist (light fog), HZ = haze, FU = smoke, SA = sand, DU = dust, VA = volcanic ash, PY = spray.
Other: FC = funnel cloud or tornado, PO = dust devils, DS = dust storm, SS = sandstorm, SQ = squalls.
Sky Cover
SKC (manual) or CLR (automated) : no clouds
FEW : Up to 1/4 of the sky obscured by clouds.
SCT : Up to 1/2 of the sky obscured by clouds.
BKN : More than 1/2 of the sky obscured by clouds.
OVC : All of the sky obscured by clouds.
Other Stuff
Sometimes you'll see Runway Visual Range (visibility along a particular runway) reported after the regular visibility group. It will be a long string of characters beginning with an R, for example: R11/P6000FT. This is not terribly difficult to decode, and is of great importance to pilots and aviation forecasters. The R stands for Runway, followed by the runway this observation is valid for. Runways are named by their direction, in tens of degrees. In this case, Runway 11 is aligned at 110 degrees. After the slash, either a M or a P follows, indicating the RVR is lower than the lowest reportable sensor value, or higher than highest reportable sensor value, respectively. A V could also appear, indicating that there is variability. The following number is the visibility, reported in hundreds of feet (FT). Sometimes, the FT is followed by another slash, and then a D, U or N, denoting a downward trend, upward trend, or no change, respectively. It should be noted that RVR is only reported if the prevailing visiblity is ≤ 1 mile or the RVR is ≤ 6000 feet.
The rest of this stuff is in the remarks, and is only reported if it's appropriate. Peak wind: PK WND, followed by the wind direction and speed, a slash, and the time of occurrence. Wind shift: WSHFT, followed by the time of occurrence. Useful for detecting fronts and such. Lightning: LTG, preceded by frequency (OCC, FRQ, etc), followed by location (NE, etc.). Virga: VIRGA (precipitation visible but not reaching the ground). Sea level pressure: SLP, followed by encoded pressure group: tenths of millibars, only last three digits reported.
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