Table-Decoded METAR Report

One of the big problems with the fully-decoded observations, as you have seen in the above example, is that you can't always trust the decoder program. It's useful as a learning tool, until you learn to read the real observations yourself and can easily convert from Fahrenheit to Celsius and back. Push yourself to read the less-intensively-decoded observations: it'll pay off in the long run.

Another major problem with the fully-decoded observations is that it's difficult to read a series of observations. The text alone would take up several pages of the screen, and you'd have to hunt for each weather element buried in the middle of each paragraph.

The cure is what I call "table-decoded" METAR reports. This decoder parses the observations and prints them out in tabular format. It's easy to scan down the individual columns and see how every weather element is evolving.

Here's an example, which includes the same observation from Charlotte:

METARDECODE> clt 7z-18z

STN  TIME VIS PRESS  ALTMR TMP DEW DIR SPD GST WEATHER          CLOUDS                REMARKS

==== ==== === ====== ===== === === === === === ================ ===================== =======

KCLT 0650 0.5 1013.3 29.94  21  20 060   3 -99 FG               BKN001 OVC005         SLP133 T02100196=

KCLT 0719 0.7 -999.9 29.94  21  21 000   0 -99 BR               SCT001 BKN005 OVC022

KCLT 0750 0.7 1013.3 29.94  22  21 060   4 -99 BR               OVC006                SLP133 98059 T02160210=

KCLT 0820 1.5 -999.9 29.94  22  21 080   3 -99 BR               BKN008 OVC014

KCLT 0850 1.5 1013.3 29.94  22  21 080   3 -99 BR               OVC005                SLP133 8/6// T02190206 56003=

KCLT 0950 1.5 1013.3 29.94  22  20 080   4 -99 -RA BR           BKN008 OVC020         RAB45 SLP133 T02170201=

KCLT 1025 1.5 -999.9 29.95  22  20 160   4 -99 BR               FEW005 OVC010         SFC VIS 3=

KCLT 1030 1.5 -999.9 29.96  22  20 240  12 -99 TS BR            FEW005 OVC010         OCNL LTGIC W TSB30 TS W MOV N=

KCLT 1050 1.5 1014.8 29.98  19  19 250  10 -99 +TSRA BR         SCT005 OVC010         FRQ LTGICCG TSB30 TS OHD MOV NE PRESRR SLP148 T01920189=

KCLT 1050 1.5 1014.8 29.98  19  19 250  10 -99 +TSRA BR         SCT005 OVC010         FRQ LTGICCG TSB30 TS OHD MOV NE SHRAB35 PRESRR SLP148 T01920189=

KCLT 1130 2.5 -999.9 30.00  19  19 320  11 -99 TS +SHRA SHRA BR SCT005 SCT010 OVC030  OCNL LTGICCG TS N MOV NE=

KCLT 1150   4 1015.2 29.99  19  19 330   9 -99 TS +SHRA SHRA BR FEW005 SCT010 OVC045  OCNL LTGICCG TS N MOV NE SLP152 60072 70072 8/9// T01850185 10220 20185 53017 K=

KCLT 1150   4 1015.2 29.99  19  19 330   9 -99 -TSRA BR         FEW005 SCT010 OVC045  OCNL LTGICCG TS N MOV NE SLP152 60072 70072 8/9// T01850185 10220 20185 53017=

KCLT 1216   5 -999.9 29.99  18  18 030   5 -99 -SHRA            FEW005 OVC040

KCLT 1216   5 -999.9 29.99  18  18 030   5 -99 -SHRA            FEW005 OVC040         TSE15 MOV E=

KCLT 1250   6 1015.2 29.99  19  18 010   6 -99 -SHRA            FEW005 BKN045 OVC095  TSE15 MOV E SLP152 T01850184=

KCLT 1351  15 1015.2 30.00  19  18 050   5 -99                  BKN045 OVC100         SHRAE30 SLP152 T01940181=

KCLT 1450  15 1014.8 29.98  22  19 040   5 -99                  BKN100                SLP148 60004 8/070 T02200194 58003=

KCLT 1651  15 1013.9 29.96  27  19 080   4 -99                  FEW020 FEW100         SLP139 T02650192=

KCLT 1750  20 1013.4 29.95  28  20 140   4 -99                  SCT030 SCT100 BKN250  SLP134 60004 8/171 T02780199 10278 20183 57012

For this to look good, you'll probably need to make your web browser as wide as possible. This done, you'll find that the data is organized in columns and it is easy to see at a glance what's happened during a given day. In order, the elements are:

• Station ID, which doesn't change.
• Time, in GMT (hours and minutes). Except when there's unusual weather going on, most stations take their observations once an hour, a few minutes before the top of the hour.
• Visibility, in statute miles. This represents the distance to the farthest object that can be seen clearly. It's a function of both the weather and the location. In College Station, the visibility won't exceed ten miles because the ground's so flat that there's nothing tall enough beyond ten miles to be visible.
• Pressure and altimeter. The first is in millibars and the second is in inches of mercury. The changes are more important than the actual values.
• Temperature. In Celsius.
• Dew Point. Also in Celsius.
• Wind Direction, in degrees, with north being 000. A wind direction, for example, of 050, means that the wind is blowing from northeast to southwest and would be called a northeasterly wind.
• Wind Speed and Wind Gust, in knots. If no gust is reported, a -99 is listed in the column.
• Weather. Encoded in a rather complicated fashion. We'll deal with that in a moment.
• Cloud cover. Coverage and height (in hundreds of feet) are given for up to three cloud levels.
• Remarks. This is where much of the interesting stuff is reported, including max and min temperatures, precipitation, and exact temperatures. We'll cover this later too.

This table format makes it possible to see, for example, that except for about an hour and a half near the middle, the winds were light. Also, while we haven't yet learned how to decode the weather symbols, the lack of any weather being reported since 1250 GMT indicates that the rain has stopped. Here's a quick check of your ability to read table-decoded observations (please answer all 4 questions correctly before continuing):

1. During the eleven hours from 0650 UTC to 1750 UTC, what was the warmest temperature reported?

2. When were the strongest winds?

3. According to the most recent observations, is the pressure rising or falling?

4. Are any observations missing?