AOPA Pilot Magazine - February 2022 - 95

RUDDER & WRENCH
WX WATCH /
Mystery METARS
METARs, by the numbers
BY THOMAS A. HORNE
KPIT 012351Z 15009KT 10SM OVC034 06/04 A2993 RMK A02
RAE45 SLP152 P0002 60003 T00560039 10083 20056 58025
Pittsburgh PA
airport
1 December,
2351Z
observation
2/100 inch of
precipitation
in the last
hour
3/100 inch of
precipitation
in the past
six hours
Hourly
temperature
and dew point
is 5.6° Celsius
and 3.9°
Celsius,
respectively
Six-hour
maximum
temperature
was 8.3°
Celsius
Six-hour
minimum
temperature
was 5.6°
Celsius
Over the past
three hours,
barometric
pressure was
steady or
NOTE
* No " 4 " code, because no snow fell
* No " 7 " code, because precipitation in the
past 24 hours is only reported in 12Z METAR
increasing, then
decreasing; or
decreasing then
decreasing
more rapidly
(8). Amount of
change was
0.075 inHg/2.5
millibars (025)
TEXTBOOKS, SELF-STUDY programs, and
instructors have done a pretty good job
of passing along the basics of METAR
interpretation. Most of us can rattle off
a raw METARs without resorting to the
decoded version of these hourly reports
of the weather at many-not all-airports.
It wasn't always that way. When
METARs replaced the earlier surface
reports (SAs) in 1996 there was a lot of
brouhaha and a steep learning curve.
Same thing with the switch from terminal
forecasts (FTs) to today's TAFs. All of
this in the name of establishing a world
standard of weather reports.
However, most pilots haven't been
educated in some METARs' more infrequently
used coded abbreviations.
Particularly those from sites having automated
weather observing capability. You
know, the additional reporting codes that
follow the core report of date and time,
surface wind, visibility, current weather,
cloud conditions, temperature/dew point,
and altimeter setting. Sometimes instructors
will blow these off by saying, " Oh, you
don't need to know them. It's for meteorologists. "
True, in the strictest sense.
Most of us accept this advice. Others are
curious about these seemingly odd collections
of numbers. So, let's delve into them.
Let's identify them by their prefix letters.
There are the P, 6, 4, T, 1, 2, and 5
groups of codes.
The P-group code gives any hourly
precipitation amounts, in tens, tenths,
and hundredths of an inch since the last
METAR. So, if you see a P0050 code, you
know that a half-inch of rain has fallen. A
trace of rain-meaning an unmeasurable
amount of rain less than 0.01 inch-gets
a P0000 code.
The 6-group reports three- and
six-hour precipitation amounts
at three-hour intervals (shown in
METARs posted for the 03, 09, 15,
and 21 Z observations) and six-hour
intervals (in 00, 06, 12, and 18 Z observations).
Snow gets its own, three-digit
4-group. This shows snow depth in
inches on the ground in six-hour intervals-at
00, 06, 12, and 18 Z. So, a 4021
report means 21 inches of snow fell in
the previous six hours.
The T-group shows the hourly
METARs' temperature and dew point
to the nearest tenth of a degree Celsius.
So, a report of T00710054 translates to a
temperature of 7.1 degrees Celsius and a
dew point of 5.4 Celsius. Temperatures
and dew points below freezing? Then
a " 1 " is posted before the temperature
and dew point numbers.
AOPA PILOT / February 2022
95
LEIGH CAULFIELD
AOPA Pilot Magazine - February 2022

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