How to Decode PART of a METAR Weather Observation - v.971117
When looking at weather observations, it is important to realize that
a single weather observation represents the conditions existing during
one particular time at one specific location. For a routine weather
observation the time period is from 15 minutes before the hour to the
transmission time (usually about 5-10 minutes before the hour). Most
observations are routine. Any other transmission time (see below)
indicates a "special" observation. Reported conditions may or may not
be regional in scope. For instance, rainfall reported at KLAX is not
necessarily the same as the amount received in the Los Angeles region.
It is just what was received in a six inch wide circle (a rain gauge)
at Los Angeles International Airport (KLAX).
A METAR observation (an "obs") can be as simple as:
KSBP 231447Z 00000KT 25SM SKC 05/04 A3027=
Or it can be more complicated:
KPIT 211151Z 25009KT 1 1/2SM -SN FEW021 BKN027 OVC035 M12/M15 A3014 RMK
A02 SLP236 8/546 P0000 60000 T11171150 11106 21131 51016=
It consists primarily of four parts, the last of which (Remarks) doesn't
Part 1 Identification: KPIT 211151Z
KPIT This is the International Civil Aviation Organization
(ICAO) identifier for Pittsburgh International Airport.
(See the ICAO Identifier Table for cross reference.)
21 Observation is for the 21st day of the month.
1151Z The time the observation ended (and was transmitted)
in this case 1151 UTC (this is the 12Z or 12 GMT obs).
Note: If "AUTO" appears just after the time group,
the observation is from an automated station.
Part 2 Observations: 25009KT 1 1/2SM -SN FEW021 BKN027 OVC035
25009KT Wind is coming from 250 degrees from true north
(250 degrees clockwise from true north) at 009
nautical miles per hour (knots). (1 kt = 1.15 mph)
If this wind had been gusting to 20 knots, it
would have been coded 25009G20KT.
1 1/2SM The visibility is reduced to 1 1/2 (or 1.5)
statute miles (SM) because of light snow (-SN).
(Any visibility less than 7 statute miles must
indicate what is causing the reduction.)
The visibility will occassionally be followed by
something like R28L/2000FT. This is a "runway
visual range" (runway visibility) observation.
The RVR reading above says "runway 28L visibility
is 2000 feet. M2000 says "less than 2000" (minus)
and "P2000" says "greater than 2000" (plus).
-SN Present weather is light snow. (See table 3 below.)
FEW021 The lowest cloud layer is at 2,100 feet (021)
BKN027 AGL (AGL means "Above Ground Level"), the next
OVC035 is at 3,500' AGL (035), and so on. (See table 1
below for further explanation.)
Part 3 Gauge Readings: M12/M15 A3014
M12 The air temperature is -12 C (+10 F).
M15 The dew point temperature is -15 C (+5 F).
(The dew point is a measure of atmospheric
moisture and the relative humidity is computed
using the air temperature and dew point.)
A3014 The altimeter setting (a measure of barometric
pressure) is 30.14 inches of mercury.
Part 4 Remarks and Coded Data: This can be lots of things (snow
depth, amount of precipitation, pressure tendency,
etc.) with most in code. It is preceeded by "RMK".
A01/A02 This is from an automated station. A01 does not
have the capability to detect precipitation. A02
has a "precipitation discriminator".
P0000 The total precipitation received during the last
hour. P0000 indicates 0/100's of an inch and
P0017 would indicate 17/100's of an inch.
T11171150 The hourly air and dewpoint temperatures to the
nearest 1/10 C degree. 1117 is -11.7 C (coded
M12 above) and 1150 is -15.0 (coded M15 above).
A positive number is preceeded by a 0 instead of
a 1 (0117 would be +11.7 C).
SLP236 The sea level pressure (SLP) is 1023.6 mb
(millibars or 102.36 pascals). This is another
measure of atmospheric pressure. A low number
(like 236 [23.6]) must be added to 1000 millibars
(indicating 1023.6 mb) while a high number must be
added to 900 mb (so 978 [97.8] indicates 997.8 mb).
11106 The 6 hour maximum temperature (the highest air
temperature recorded during the previous six
hours) is -10.6 C. The first 1 is the group
identifier, the second is the sign (0 for + or
1 for -), and the final three digits are the
temperature (106 is 10.6).
21131 The 6 hour minimum temperature (-13.1 C) coded
as above. Here, the 2 is the group identifier.
4/001 The total snow depth on the ground in inches.
Usually found in the 06 and 18Z observations.
411061131 A nine digit group beginning with a 4 as the
group identifier would contain the 24 hour
maximum and minimum temperatures, in that order,
coded as in the "T" group above. Usually found
in the 08Z observation.
51016 The "5" group is the 3 hour pressure tendency
and amount of change. The the second digit is
the tendency (coded, where 0-3 are going up, 4
is steady, and 5-8 are going down) and the last
three digits are the change (016 is 1.6 mb).
60000 3 and 6 hour precipitation amounts encoded as
above. 60217 would indicate 2.17 inches. The
3 hourly precip is reported in the
70025 The 24 hour total precipitation (this will be
liquid equivalent for frozen precip) in 1/100s
of an inch. 70025 would be 0.25 inch. This
is usually found in the 12Z observation.
8/546 This identifies the low, middle, and high cloud
types using WMO code. (See table 2 below.)
933125 Liquid water equivalent of the snow on the
ground in 1/10s of an inch. 933125 says the
SWE is 12.5 inches. Usually in the 18Z obs.
98096 Duration of sunshine in minutes. 98096 means
there were 96 minutes of sunshine during the
day. Usually in the 08Z observation.
Plus a lot of other information that can be encoded or
given in plain language (ex: volcanic eruptions, wind
shifts, precipitation beginning or ending, lightning
type and direction, etc.).
Note: (1) Sky Cover:
SKC/CLR Clear (no clouds)
FEW Few clouds (1 to 2 eighths [1/8 to 2/8] of the
sky is covered with clouds at this level).
SCT Scattered (3/8 to 4/8 cloud cover).
BKN Broken (5/8 to 7/8 cloud cover).
OVC Overcast (8/8 or all the sky is covered).
Note: (2) Cloud Types:
Code Low Clouds Middle Clouds High Clouds
---- --------------- --------------- ---------------
0 None None None
1 Cu (fair wx) As (thin) Ci (filaments)
2 Cu (towering) As (thick) Ci (dense)
3 Cb (no anvil) Ac (thin) Ci (often w/Cb)
4 Sc (from Cu) Ac (patchy) Ci (thickening)
5 Sc (not Cu) Ac (thickening) Ci/Cs (low in sky)
6 St or Fs (fair) Ac (from Cu) Ci/Cs (hi in sky)
7 Fc/Fs (bad wx) Ac (w/Ac,As,Ns) Cs (entire sky)
8 Cu and Sc Ac (w/turrets) Cs (partial)
9 Cb (T-storm) Ac (chaotic) Cc or Cc/Ci/Cs
Ac-Altocumulus, As-Altostratus, Cb-Cumulonimbus,
Cc-Cirrocumulus, Ci-Cirrus, Cs-Cirrostratus, Cu-Cumulus,
Fc-Fractocumulus, Fs-Fractostratus, Ns-Nimbostratus,
Sc-Stratocumulus, St-Stratus (wx = weather)
Note: (3) Weather:
- Light intensity (moderate is blank)
+ Heavy intensity
VC In the vicinity
MI Shallow PR Partial
BC Patches DR Low drifting
BL Blowing SH Showers
TS Thunderstorm FZ Freezing
RA Rain DZ Drizzle
SN Snow SG Snow Grains
IC Ice Crystals PE Ice Pellets
GR Hail GS Small Hail
UP Unknown Precipitation
FG Fog VA Volcanic Ash
BR Mist HZ Haze
DU Widespread Dust FU Smoke
SA Sand PY Spray
SQ Squall PO Dust or Sand Whirls
DS Duststorm SS Sandstorm
FC Funnel Cloud (Tornado or Waterspout)
This METAR decode was prepared by the Climate Research Division
of Scripps Institution of Oceanography. Anyone having corrections
or comments please contact Larry Riddle (firstname.lastname@example.org).