METARs

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KRNO 241155Z 30003KT 10SM SCT200 04/M06 A3012 RMK AO2

Pilots just beginning to learn to fly get to see that for a weather report. I responded with “…what?” and my instructor laughed at me.

This is a METAR, an hourly meteorological observation report. If you aren’t a pilot or don’t want to become one, you will probably never see one of these. If you are a pilot, aspiring or active, these are very important. You should check the METAR before every flight, especially if you live someplace with, shall we say, variable weather.

There are a few tricks. The first is that the first three things on the report are all Ws – Where, When, and Wind.

Where, in this case, is KRNO. That’s the RNO airport, or Reno, in the United States (thus the K at the beginning, which signals the US – each country has its own indicator).

When always has the date first (just the day, though, not the month or year, as the assumption seems to be that you ought to know at least that part of the date) and then the time, hours and minutes, in Zulu, which is aviation and military for Greenwich Mean Time. It’s good to know where you are in relationship to Zulu time so you can tell how recently the METAR report was recorded. You should also be careful, as the relationship with Zulu time changes with Daylight Saving Time. For Pacific Time, Pacific Standard Time is Zulu -8 and Pacific Daylight Time is Zulu -7.

Wind has a few things you might see. In this report, it is 30003KT. The first three numbers, 300 in this case, are the direction of the wind. This could be VRB, which stands for variable, if the wind direction is not consistent. 03KT means the wind is at 3 knots, which is not very much wind. You may also see something like this: 36007G15KT, which would be wind coming from 360 degrees (straight north, for those of you who don’t know the compass headings by heart), with the wind speed at 7 knots gusting (that’s the G) to 15 knots. If the winds are above 6 knots and it’s a day with interesting winds, you might see this: 16018KT 140V250, which indicates that the winds are from 160 degrees at 18 knots, but the direction is actually variable between 140 degrees and 250 degrees. For this to show up, the wind has to have a difference of more than 60 degrees in the variation.

10SM means the visibility is ten statute miles. This is generally the highest number you will see. It can go down to 1/4 of a mile visibility.

SCT200 means there are scattered clouds at 20,000 feet. Always add two zeros to get the altitude of the clouds.

04/M06 is the temperature and dewpoint. The dewpoint is the temperature to which the air must be cooled for condensation to form. These temperatures are in Celsius, and the M means minus.

A3012 means the altimeter shows 30.12 inches of mercury for the pressure.

RMK AO2 means that this is the beginning of the remarks section and that the station is automated and has a precipitation sensor. If it’s AO1, it does not have a precipitation sensor.

Now for the fun part. What if something more dramatic is going on? Here are some of the pieces you may see:

Clouds:
Couds are measured in eighths of the sky, or octas.
SKC Sky Clear
FEW 1-2 octas
SCT 3-4 octas
BKN 5-7 octas
OVC 8 octas – this is short for overcast.

means light.
There is no notation for moderate.
+ means heavy.
C is in the vicinity.

Here are some descriptions:
MI Shallow
PR Partial
BC Patches
DR Low Drifting
BL Blowing
SH Shower(s)
TS Thunderstorm
FZ Freezing

Precipitation is listed like this:
DZ Drizzle
RA Rain
SN Snow
SG Snow Grains
IC Ice Crystals
PL Ice Pellets
GR Hail
GS Small Hail and/or Snow Pellets
UP Unknown Precipitation (I always wondered what could be falling out of the sky to get this notation!)

If the air is not clear, you may see these:
BR Mist
FG Fog
FU Smoke
VA Volcanic Ash
DU Widespread Dust
SA Sand
HZ Haze
PY Spray

This is where it gets fun (or I go find a closet to hide in, which works, too):
PO Well-Developed Dust/Sand Whirls
SQ Squalls
FC Funnel Cloud Tornado Waterspout
SS Sandstorm

If you see any of the last four, I sincerely hope you decide not to fly.

I’m a VFR pilot. I don’t fly in clouds or nasty weather, which is just fine with me. I may eventually get my IFR (instrument) rating, but that will mostly be because I like learning new things, not because I like storms.

Now you have some idea how to read a basic aviation weather report, and I’ve remembered a few things I had forgotten. I think that’s positive all around. At some point I’ll get into SIGMETs and AIRMETs, but that’s a post for another day.