Explanation of Headers



Id      Station 3 letter ID (see list of stations).

Day     Day of the month

Time    Greenwich Mean Time (designated by the trailing Z).

prs     Sea level pressure in millibars times 10.  A reported pressure of
        10132 is 1013.2mb and is equivalent to a mercury barometer
        reading of 29.92 inches.   

tmp     Temperature in degrees Fahrenheit.

dew     Dew point in degrees Fahrenheit.  The relative humidity is 100%
        when the dew point is equal to the temperature.  A dew point that
        is about 20 degrees less than the temperature corresponds to a
        relative humidity of about 50%.

ddd     Wind direction in degrees of the compass.  A wind of 270 is
        a west wind (from 270 degrees, north is 0 degrees).  VRB means 
        that the wind is variable in direction.

ff      Wind speed in knots.  A nautical mile per hour is 1.15 statute
        miles per hour.  A hurricane force wind is at least 75 miles per
        hour and corresponds to a 65 knot wind or greater.

alt     Altimeter setting (in inches of mercury times 100) for aircraft.
        A value of 3012 is 30.12 inches of mercury.

low     First cloud group.  Elevation is hundred's of feet above ground
        level (AGL).  For example, a report of 012 is 1200 feet AGL.
        The amount is coded as:
                       FEW  -  few (1/8 to 2/8 covered)
                       SCT  -  scattered (3/8 to 4/8 covered) 
                       BKN  -  broken (5/8 to 7/8 covered)
                       OVC  -  overcast (100% covered)
                       TCU  -  towering cumulus (appended to the height)
                       CB   -  cumulonimbus (appended to the height)
        note: a report of 120 with no letter code is an observation
              from an automated weather observing station that does
              not observe clouds below 12000 feet.  There may or may
              not be any higher clouds.

mdl     Second cloud group.

high    Third cloud group. 

obs     Obstructions to vision.  This is the reported "weather".  The 
        METAR (Aviation Routine Weather Report) codes are summarized
        in the following table from the Federal Meteorological
        Handbook No.1, Chapter 8:

 - Light
   Moderate
   (see note 2)
 + Heavy
VC In the
   Vicinity
   (see note 3)

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

DZ Drizzle
RA Rain
SN Snow
SG Snow Grains
IC Ice Crystals
PE Ice Pellets
GR Hail
GS Small Hail
   and/or Snow
   Pellets
UP Unknown
   Precipitation

BR Mist
FG Fog
FU Smoke
VA Volcanic Ash
DU Widespread
   Dust
SA Sand
HZ Haze
PY Spray

PO Well-
   Developed
   Dust/Sand
   Whirls
SQ Squalls
FC Funnel Cloud
   Tornado
   Waterspout
   (see note 4)
SS Sandstorm
SS Duststorm

1. The weather groups shall be constructed by considering columns 1 to 5 in the table
   above in sequence, i.e. intensity, followed by description, followed by weather phenomena,
   e.g. heavy rain shower(s) is coded as +SHRA
2. To denote moderate intensity no entry or symbol is used.
3. See paragraph 8.4.1.a.(2), 8.5, and 8.5.1 for vicinity definitions.
4. Tornados and waterspouts shall be coded as +FC.

Further details may be found in the Federal Meteorological Handbook No.1

vis     Visibility in statute miles.

gst     Wind gusts in knots.

pd      Pressure tendency over the previous 3 hours.  If the first number
        is between 0 and 3 the pressure is rising, a 4 is a pressure that
        is the same as 3 hours ago, and a number between 5 and 8 is falling
        pressure.  The units are in millibars times 10 (see prs).


The code of NA is used to denote a missing value.  In most cases the 
parameter is not observed at that station or is not scheduled to be observed
during that hour. A station may transmit a -99 to represent a missing value.

In the remarks section of the undecoded METARS there may be a cloud type group
designated by 8/xxx.  Each of the x's is a place holder for a numbered cloud type
based on the World Meteorological Organization's International Cloud Atlas.  The
first x is for low clouds, the second for middle clouds, and the last x
is for high clouds.  The cloud types are as follows:

        code    low clouds          middle clouds      high clouds
      ------    ------------------- -----------------  -------------------------
          0     no clouds           no clouds          no clouds
                                                                                
          1     Cu (fair weather)   As (thin)          Ci (wispy)
          2     Cu (towering)       As (thick)         Ci (dense)
          3     Cb (no anvil)       Ac (thin)          Ci (dense, often with Cb)
                                                                                
          4     Sc (from Cu)        Ac (patchy)        Ci (thickening)
          5     Sc (not from Cu)    Ac (thickening)    Ci/Cs (low in the sky)
          6     St or Fs (fair wx)  Ac (from Cu)       Ci/Cs (high in the sky)
                                                                                
          7     Fc/Fs (bad weather) Ac (with Ac,As,Ns) Cs (fills entire sky)
          8     Cu and Sc           Ac (with turrets)  Cs (partial)
          9     Cb (thunderstorm)   Ac (chaotic sky)   Cc or Ci/Cc/Cs


        Cu-Cumulus

        Ci-Cirrus
        Cc-Cirrocumulus     Ac-Altocumulus
        Cs-Cirrostratus     As-Altostratus

        Fc-Fractocumulus    Sc-Stratocumulus
        Fs-Fractostratus    St-Stratus

        Ns-Nimbostratus     Cb-Cumulonimbus