Interpreting Metars code

[Corky Scott]

I'm studying up on Aviation Weather Services and am using, among other
things, the FAA's AC 00-45E book.

There is a chapter on how to decode the Metars information and at the
end of the chapter are several sample lines of code and their
decyphered explanation.

On page 2-24 is the following line of code:

METAR KSFO 031453Z VRB02KT 7SM MIFG SKC 15/14 A3012 RMK SLP993 6////
T01500139 56012

Below this line, each parcel of information is explained in longhand.
I'm actually getting to the point where I can read and understand
almost the entire line, except for the last five digits.

56012 is explained as "atmospheric pressure lower since previous 3
hours ago." The problem is I can't tell by looking at 56012 how the
FAA is deriving this information. If it's a code, the code is not
explained on the previous pages. None of the previous samples or the
ones that follow this one have a similar 56012 attached so I don't
know if the number is itself supposed to represent "atmospheric
pressure lower since previous 3 hours ago" or if the number is
actually a code within itself that can be interpreted.

Can anyone explain?

Thanks, Corky Scott

[Roy Smith]

Post by Corky Scott
I'm studying up on Aviation Weather Services and am using, among other
things, the FAA's AC 00-45E book.
There is a chapter on how to decode the Metars information and at the
end of the chapter are several sample lines of code and their
decyphered explanation.
METAR KSFO 031453Z VRB02KT 7SM MIFG SKC 15/14 A3012 RMK SLP993 6////
T01500139 56012
Below this line, each parcel of information is explained in longhand.
I'm actually getting to the point where I can read and understand
almost the entire line, except for the last five digits.

Don't worry about anything that's in the remarks (i.e. from RMK onward).
As long as you can read the stuff before that, you'll be ok.

That being said, I'm embarrassed to admit that I don't know what MIFG
means. I usually get my briefings on DUATS, and on the rare occassions
I don't know an abbreviation, I just use the "plain language translator"
feature. There's also a crib sheet at...

http://www.nws.noaa.gov/oso/oso1/oso12/document/guide.shtml

Hmmmm, MIFG means "shallow fog". Sounds like the kind of thing a pilot
flying in the bay area would be used to seeing. Just make sure you stay
way from those FC's and VA's.

[Ben Jackson]

Post by Corky Scott
METAR KSFO 031453Z VRB02KT 7SM MIFG SKC 15/14 A3012 RMK SLP993 6////
T01500139 56012
56012 is explained as "atmospheric pressure lower since previous 3
hours ago." The problem is I can't tell by looking at 56012 how the
FAA is deriving this information. If it's a code, the code is not
explained on the previous pages.

It's a code. 5 means it's the tendancy, 6 indicates decreasing in a
particular way, and then 012 is the pressure (I think the leading
digit is inferred because 2012 makes no sense).

I'm making an educated guess based on the fact that you already
said what it is, and I know 6xxxx and 7xxxx are similar precipitation
history codes.

Apropos nothing, my own favorite METAR:

KAUS 152340Z 25037G54KT 1/2SM R17L/P6000FT +FC TSRA FG OVC009CB 17/17 A2995 RMK TORNADO B36 AO2 PK WND 24054/2339 PRESRR TORNADO ON GROUND 2WNW MOVG NNE 1/4MI WIDE CONS LTGCGIC ALQDS SEVERE TS ALQDS MOVG NNE

[Brad D.]

Post by Ben Jackson

Post by Corky Scott
METAR KSFO 031453Z VRB02KT 7SM MIFG SKC 15/14 A3012 RMK SLP993 6////
T01500139 56012
56012 is explained as "atmospheric pressure lower since previous 3
hours ago." The problem is I can't tell by looking at 56012 how the
FAA is deriving this information. If it's a code, the code is not
explained on the previous pages.

It's a code. 5 means it's the tendancy, 6 indicates decreasing in a
particular way, and then 012 is the pressure (I think the leading
digit is inferred because 2012 makes no sense).

Actually, 012 means 1.2 millibar change in 3 hours.

In the past three hours, the pressure has changed 1.2 millibars, in
this case code 6 means falling pressure. Any code 6 thru 8 will tell
you pressure is is falling over time (past 3 hours). Codes 1 thru 4 is
pressure rising over time (past 3 hours). Code 5 means pressure has
been steady in the past 3 hours. The 0 in front is a place holder in
the extreme case the pressure rises of falls more than 9.9 millibars
in 3 hours. Code 102 means 10.2 millibars. Pressure tendancy is always
measured in 3 hour increments.

Cheers

Post by Ben Jackson
I'm making an educated guess based on the fact that you already
said what it is, and I know 6xxxx and 7xxxx are similar precipitation
history codes.
KAUS 152340Z 25037G54KT 1/2SM R17L/P6000FT +FC TSRA FG OVC009CB 17/17 A2995 RMK TORNADO B36 AO2 PK WND 24054/2339 PRESRR TORNADO ON GROUND 2WNW MOVG NNE 1/4MI WIDE CONS LTGCGIC ALQDS SEVERE TS ALQDS MOVG NNE

[Bob Gardner]

Don't sweat it. Not everything in a METAR is meant to be relevant to pilots,
just to meteorologists. They use a lot of numerical codes that are not
readily available to the public.

Post by Corky Scott
I'm studying up on Aviation Weather Services and am using, among other
things, the FAA's AC 00-45E book.
There is a chapter on how to decode the Metars information and at the
end of the chapter are several sample lines of code and their
decyphered explanation.
METAR KSFO 031453Z VRB02KT 7SM MIFG SKC 15/14 A3012 RMK SLP993 6////
T01500139 56012
Below this line, each parcel of information is explained in longhand.
I'm actually getting to the point where I can read and understand
almost the entire line, except for the last five digits.
56012 is explained as "atmospheric pressure lower since previous 3
hours ago." The problem is I can't tell by looking at 56012 how the
FAA is deriving this information. If it's a code, the code is not
explained on the previous pages. None of the previous samples or the
ones that follow this one have a similar 56012 attached so I don't
know if the number is itself supposed to represent "atmospheric
pressure lower since previous 3 hours ago" or if the number is
actually a code within itself that can be interpreted.
Can anyone explain?
Thanks, Corky Scott

[Charlie Wendell]

Post by Bob Gardner
Don't sweat it. Not everything in a METAR is meant to be relevant to pilots,
just to meteorologists. They use a lot of numerical codes that are not
readily available to the public.

As noted above .. some data in the METAR is used mainly by forecasters,
the number 5 is just an indicator to signify what type of info is
contained in that group of numbers ..which is the pressure change during
the past 3 hours (in millibars). the number following the 5 indicates if
the pressure has risen or fallen. Figures 0,1,2,3 indicate a rise, 4 no
change, and 5, 6,7,8 indicate a decrease. The various numbers are
suppose to represent what the barograph trace looks like.
If you look at some Surface weather analysis you can see that plotted on
the map ( in the 5 o'clock position around the station. Temperature is at
11 o'clock). The amount of change is indicated in millibars and tenths. The
012 as the last 3 figures mwans a change of 0.12 mb. 120 means 12.0 mb in
3 hours .. a significant change. A reference available to all can be found at

http://weather.unisys.com/wxp/Appendices/Formats/SYNOP.html#111
Hope this may be of some use.
look "way down the page"
--
Cheers, Charlie

[Brad D.]

Tendancy of pressure to change over time is important WRT the strength
of winds. For example, when there is strong pressure rises behind a
front, there is likely a greater chance for stronger winds to develop
there.

Remember the isobars on a surface chart? Remember what they are good
for? If they are close together the winds are strong and conversly if
they are far apart the winds in that area are weak. Pressure change
over a distance is very important for determining wind speeds at a
station in the near future but pressure change over time kind of tells
us this too. Where pressure changes are dramatic in a short time, the
estimate of wind speeds will be higher where this occurs. METARs of
stations upwind sometimes tell us this information and can warn us of
impending dangerous crosswinds developing at an airport downwind based
on pressure gradient as well as pressure tendancy.

METAR remarks often give quite a bit of detail, some useful and some
not so much. Fog bank descriptions, ragged ceilings, thunderstorm
details and even PIREPS can occasionally be found in remarks so
understanding what some of them look like would be useful to a pilot.
It doesn't hurt to look at remarks and if you don't know what
something means, ask someone with more experience before you fly. It
could play a key role in your decision making for a flight.

Cheers




On Fri, 11 Jul 2003 12:00:00 GMT,

Post by Corky Scott
I'm studying up on Aviation Weather Services and am using, among other
things, the FAA's AC 00-45E book.
There is a chapter on how to decode the Metars information and at the
end of the chapter are several sample lines of code and their
decyphered explanation.
METAR KSFO 031453Z VRB02KT 7SM MIFG SKC 15/14 A3012 RMK SLP993 6////
T01500139 56012
Below this line, each parcel of information is explained in longhand.
I'm actually getting to the point where I can read and understand
almost the entire line, except for the last five digits.
56012 is explained as "atmospheric pressure lower since previous 3
hours ago." The problem is I can't tell by looking at 56012 how the
FAA is deriving this information. If it's a code, the code is not
explained on the previous pages. None of the previous samples or the
ones that follow this one have a similar 56012 attached so I don't
know if the number is itself supposed to represent "atmospheric
pressure lower since previous 3 hours ago" or if the number is
actually a code within itself that can be interpreted.
Can anyone explain?
Thanks, Corky Scott