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Interpreting METARs and TAFs

By Aaron Flodin

Important Terms
For more information on types of altitude see AirplanesAirspeedsAltitudes - by EricSterns

Introduction
Welcome to the VATSIM PRC ?Interpreting METARs and TAFs? Tutorial. In this tutorial we will cover the many aspects of disseminating the information contained in coded weather reports. Since the beginning of aviation (starting right back with Orville and Wilbur) weather has been a very important factor in flight planning. One must know if thunderstorms are too intense to make a flight, how much fuel to bring along, and many other variables. Weather information is available from thousands of different sources, many of them easily accessible from the internet. Most of these reports however, are published in coded format, and for that reason, we have this tutorial.

This is a long lesson and you will probably not remember everything the first time you read it. I suggest you bookmark this page and refer to it often as you interpret METAR's and TAF's. There are many terms and codes in the following sections that you may not be familiar with, please refer to the "Abbreviations Guide" at the very bottom of the page.

Understanding the METAR

As you saw at the top of this page (I know you read it carefully), METAR stands for ?Meteorological Aerodrome Report?. The standard METAR format is used all over the world and is the only weather report of its kind approved by the World Meteorological Organization. Take a look below at example 1. To the non-aviator this is just a jumble of letters and numbers, but to us, it is an invaluable tool. To help us understand a bit more about the way METAR's work, let's take a look at the example below.

EX.1
KJAX 020256Z 02003KT 10SM TSRA OVC01OCB SCT100 BKN130 18/17 A2996
METAR's will always be published in the same order:

Where:
This is the 4 letter code that is used to identify the airport where the weather report originates.

When:
The first 2 numbers are the day of the month, so in this case ?02?, means that this report was
taken on the second day of the current month. The last 4 digits represent the time when the report
was taken in Universal time (Also called Zulu Time or Greenwich time). In this case the report was taken at ?0256Z?.

Wind:
EX.2
METAR UHPP 060600Z 34003MPS 9999 SHRA OVC009CB 03/02 Q1014 NOSIG
EX.2.A
KPIT 201955Z 22015KT 3/4SM R28R/2600FT TSRA OVC01OCB 18/16 A2992 RMK SLPO13 T01760158
The first 3 digits of this number will always represent the heading that the wind is blowing from. In this case the wind is blowing from ?220 Degrees?. The last 2 numbers represent the velocity of the wind. We measure the velocity of the wind in two different ways.

In example 2, you see that the winds at UHPP are from 340 degrees blowing at a velocity of 3 Meters per second. In example 2.A we see that the winds are blowing from 220 degrees at a velocity of 15 knots.

22015G30 - If you see a number like this with a ?G? in the middle, it means the winds are gusting. In this example the winds are from 220 degrees blowing at a velocity of 15 knots and gusting to 30 knots.

00000KT - If you see all zeroes, the winds are calm

20015KT 180V260 - If you see a report like this one, with the normal winds reported in the beginning and then 2 numbers separated by a ?V? it means the winds are variable. In this example the winds are from 200 at 15 knots. The direction of the wind is variable from 180 to 260 degrees.

VRB - This code represent winds that are less than 6 knots, and variable in direction.

Visibility:
The visibility portion of the METAR can be coded in many different ways.

EX.3
KPIT 151124Z 28016G20KT 2 3/4SM R28R/2600FT TSRA OVC01OCB 18/16 A2992 RMK SLPO13 T01760158
EX.4
EGLL 060326Z 20013G23KT 8000 SCT014 BKN025 Q1013
Visibility can also be reported in fractions of these values. For instance, in example 3, "2 3/4SM" represents 2 and 3 quarters miles visibility.
Here in example 4 is a METAR from London's Heathrow airport, where the visibility is listed in Meters.

Another visibility range that will become more important as you start flying larger aircraft is Runway Visual Range, or RVR. The RVR is the actual distance that you can see looking down the runway. In example 3. R28R/2600FT signifies that the runway visual range for runway 28 Right is 2600 feet.

Weather:
This is the part of the METAR that will include any significant weather in the area. A full list of special weather codes is available at the end of the page. For now we will look at the METAR for Jacksonville listed above in EX.1. The intensity of certain weather phenomena are reported by using the signs: "+","-", and by the absence of a sign.

Clouds:
The identifiers for clouds are as follows. Clouds are categorized based on how many ?Octas? of sky they cover. As you can probably guess, an ?octa? is 1/8 of the visible sky.

Cloud height is measured in hundreds of feet ABOVE GROUND LEVEL or "AGL", so when we see in the example:
This signifies that there is a scattered layer at 10,000 ft.

Keep in mind that only these last two cloud designations (BKN and OVC) constitute ceiling. This is important as you start to learn about VFR cross country planning and weather minimums. In addition to these ?octa? designators, we also have codes for certain types of clouds.

Temp/Dew Point:
Fairly self explanatory, the first set of numbers represents the Air Temperature in Celsius, and the second set of numbers represents the Dewpoint in Celsius.

Altimeter Setting:
This is the Barometric pressure of the reporting station. Depending on where in the world you are flying, this value will be represented in either "Inches of Mercury" or in "hectoPascals" This is the number that you will dial in to the Kollsman window on your altimeter when you are below the ?transition level (or altitude)? for the region you are flying in. (the "Kollsman window is the little dial in the middle of your Altimeter that by default reads "29.92")-(read more about transition levels in ?IFR airspace?.

Understanding the TAF

Ok, take a break, wipe the sweat from your brow, its going to be ok.

Now that you understand the codes associated with the METAR, TAF?s will be simple. The TAF is basically a METAR on a timeline. The TAF provides us with weather forecasts for a particular area. There are a few parts of the TAF that are different from the METAR, mostly in the area of time and probabilities.

Important TAF Terms

Telling TAF Time
TAF's have to be able to give a time for when certain weather patterns are forecast to happen, to do this we have special codes that proceed each weather report.

091720Z
In the example above, the time stamp reads just like a METAR. The time section of the TAF starts with the 2 numbers representing the day of the month, and the last four digits representing the time the report was issued.

041818
In this example, just like the METAR, the first two numbers represent the day of the month. Unlike the METAR, however, the last four numbers represent the time the report was issued, and the time it is valid until. In this case, the report was issued at 1800Z time, and is valid until 1800Z the next day.


As a conclusion to this tutorial let's take a look over a METAR and a TAF that you might see while flying the virtual skies

EX.5
KLAX 060350Z 23004KT 8SM CLR 16/15 A2994
  1. In the first section we see that this report is from Los Angeles International Airport
  2. In the second section we see that this report was taken on the 6th day of the month at 0350Z
  3. In the third section we see that the winds are 230 at 4 knots
  4. We see that visibility is 8 statute miles
  5. Skies are clear
  6. The temperature at KLAX is 16 degrees Celsius, the dewpoint in 15 degrees Celsius
  7. The altimeter is 29.94

EX.6
EGLL 060326Z 060413 20013G23KT 9999 SCT014 BKN025 TEMPO 0413 8000 -RA BKN014 TEMPO 0813 19018G33KT RA
  1. In the first section of the TAF we see that this report comes to us from London's Heathrow Airport.
  2. In the second section we see that this report was taken on the 6th day of the month, at 0413Z.
  3. In the third section we see that the winds are coming from 200 degrees and that the winds velocity is sustained at 13 knots, with gusts to 23 knots.
  4. In section four we see that the visibility is greater than 10 km.
  5. Section 5 lets us know that there are scattered clouds at 1,400 feet and broken clouds at 2,500 feet.
  6. Temporarily, from 0400Z to 1300Z
  7. Visibility is 8,000 meters.
  8. Light rain
  9. A broken Layer at 1,400 feet.
  10. Temporarily, from 0800Z to 1300Z
  11. Winds 190 at 18 knots, gusting to 33 knots.
  12. Moderate Rain.

You've Made it

It's been a long one but you have finally arrived at the end. There are some differences in the way that weather reports are published throughout the world, but if you have the basics, making the transition from one to another should not be difficult. Weather is a huge part of successful flight planning, I hope this tutorial has helped you to better understand a few of the published weather reports available to aviators.


METAR TAF & Abbreviations


KT - Knots
MPS - Meters per second
AO1 - Automated Observation without precipitation discriminator (rain/snow)
AO2 - Automated Observation with precipitation discriminator (rain/snow)
AMD - Amended Forecast (TAF)
BECMG - Becoming (expected between 2 digit beginning hour and 2 digit ending hour)
BKN - Broken
CLR - Clear at or below 12,000 feet (AWOS/ASOS report)
COR - Correction to the observation
FEW - 1 or 2 octas (eighths) cloud coverage
FM - From (4 digit beginning time in hours and minutes)
LDG - Landing
M - In temperature field means "minus" or below Zero
M - In RVR listing indicates visibility less than lowest reportable sensor value (eg. M600)
NO - Not available (eg SLPNO, RVRNO)
NSW - No Significant Weather
OVC - Overcast
9999 - Visibility in meters (9999 means greater than 10 km)
P - In RVR indicates visibility greater than highest reportable sensor value (eg P6000FT)
P6SM - Visibility greater than 6 SM (TAF only)
PROB4O - Probability 40 percent
R - Runway (used in RVR measurement)
RMK - Remark
RY/RWY - Runway
SCT - Scattered
SKC - Sky Clear
SLP - Sea Level Pressure (eg., 1013 reported as 013)
SM - Statute mile(s)
SPECI - Special Report
TEMPO - Temporary changes expected (between 2 digit beginning hour and 2 digit ending hour)
TKOF - Takeoff
T01760158, 10142, 20012 and 401120084 - In Remarks examples of temperature information
V - Varies (wind direction and RVR)
VC - Vicinity
VRB - Variable wind direction when speed is less than or equal to 6 knots
VV - Vertical Visibility (Indefinite Ceiling)
WS - Wind shear (In TAFs, low level and not associated with convective activity)

Descriptors
BC - Patches
BL - Blowing
DR - Low Drifting
FZ - Supercooled/freezing
MI - Shallow
PR - Partial
SH - Showers
TS - Thunderstorm

Weather Phenomena
BR - Mist
DS - Dust Storm
DU - Widespread Dust
DZ - Drizzle
FC - Funnel Cloud
+FC - Tornado/Water Spout
FG - Fog
FU - Smoke
GR - Hail
GS - Small Hail/Snow Pellets
HZ - Haze
IC - Ice Crystals
PE - Ice Pellets
PO - Dust/Sand Whirls
PY - Spray
RA - Rain
SA - Sand
SG - Snow Grains
SN - Snow
SQ - Squall
SS - Sandstorm
UP - Unknown Precipitation (Automated Observations)
VA - Volcanic Ash

Cloud Types
CB - Cumulonimbus
TCU - Towering Cumulus




References:
http://www.dodgenet.com/~weavers/afss/metar.htm∞
http://skylinkweather.com∞



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CategoryLessons
 Comments [Hide comments/form]
Nicely done, Aaron. A couple of comments:

The KJAX METAR doesn't make any sense. If it's really OVC010, there is no way to observe the higher layers from the ground. Coverages, if they increase at all, always increase with altitude.

The visibility section is very US-centric. Most of the rest of the world (certainly all of Europe and the Pacific Basin) measures visibility in meters. You address that only at the very end. It's probably worth, for keeping our non-US bretheren happy, going right into meters in addition to the statute miles.

For winds, Russia and China report winds in meters per second, e.g.

UHPP

METAR

METAR UHPP 060600Z 34003MPS 9999 SHRA OVC009CB 03/02 Q1014 NOSIG
RMK QBB280 QFE 756 SC 045 055 055 S/Z
METAR UHPP 060500Z 36002MPS 9999 SHRA OVC008CB 03/02 Q1014 NOSIG
RMK QBB260 QFE 756 SC 045 055 055 s/z
METAR UHPP 060400Z 34002MPS 9999 SHRA OVC008CB 03/02 Q1014 NOSIG
RMK QBB240 QFE 756 SC 045 055 055 S/Z

and

METAR ZSPD 060600Z 36006MPS 1300 R34/1300N HZ NSC 21/16 Q1013 NOSIG
METAR ZSPD 060500Z 36007MPS 1400 R34/1400N HZ FEW020 21/16 Q1013
NOSIG
METAR ZSPD 060400Z 36006MPS 2000 R34/1400N HZ BKN023 21/16 Q1014
NOSIG

The rule of thumb we use when flying there (besides don't get shot down) is that 1MPS is approximately 2KTS. It's close enough...

There is no link to an abbreviations guide at the bottom as promised early in the article.

The link to dodgenet.com goes some place not particularly relevant. Might want to check that.
-- RichardCritz (2005-11-05 22:49:49)
Good suggestions CZ..Obviously since the only flying i have done has been in the US, the US information will be easier to come by. I will try and find some more international references and put them in......I wasnt sure if we were going to have a seperate page for all of the abbreviations or not so i held off puting them in...Ill add them in for now and if we decide on a seperate section ill take them out.....Thanks for your suggestions, they are greatly appreciated!

Aaron
-- AaronFlodin (2005-11-06 10:46:28)
This is a topic we'll need some help with regional-wise. Thanks for the point-outs, CZ. And Aaron .....wow, what a great lesson. I see your point about amybe break out the abbreviations to a spearte page. That might work out for cleaning up a complex topic and also give people a bookmark to the legend so they can refer back later in their VATSIM flying life.
-- KyleRamsey (2005-11-06 17:26:36)
CZ,

With regards to " The KJAX METAR doesn't make any sense. If it's really OVC010, there is no way to observe the higher layers from the ground. Coverages, if they increase at all, always increase with altitude."

I've seen the odd METAR (usually an auto station) with multiple OVC layers. No real rhyme or reason to it... I think that it has something to do with the sky condition sampling rate of the auto station, during foggy conditions or conditions with multiple 6/8 or 7/8 cloud layers.
-- GregPhelan (2005-11-07 19:34:23)
I too have seen it every know and then. Never occured to me how they knew that until CZ's comment.
-- KyleRamsey (2005-11-07 19:38:47)
Regards to odd METARs, took a look at a few ones this evening in Canada, here are some examples of wierd behaviour

METAR CYYL 080300Z AUTO 19003KT 9SM OVC022 OVC088 M04/M06 A3005 RMK
SLP209=
METAR CYBU 080400Z AUTO 14006KT 9SM SCT016 OVC024 OVC074 M02/M03
A3002 RMK SLP188=
METAR CYPY 080400Z AUTO 11002KT 1 5/8SM -UP OVC007 OVC062 OVC089
M00/M00 A2987 RMK SLP132=

Couldn't find any with a non-OVC layer above an OVC layer, but this is just a sampling of one night's AUTO's on the prairies
-- GregPhelan (2005-11-07 20:31:56)
Makes sense to have 2 overcast layers since the lower can be 7/8 coverage. But it's hard to have it not be increasing coverage as it goes up and be measurable from the ground.
-- RichardCritz (2005-11-07 21:19:01)
I doubt that we will be able to cover every possible scenario, but with a basic knowledge and a good foundation to build on, i dont think these pilots will have any problem interpreting the essential elements of a coded weather report.
-- AaronFlodin (2005-11-08 22:00:19)
Edited to include

-MPS
-Vis section expanded to include more information on meters
-New examples put in
-slight format changes

Great suggeestions, keep them coming.
-- AaronFlodin (2005-11-08 22:36:36)
This one looks done, Aaron. If anyone has a burning desire to make changes in the future we can visit that if it happens.

Mike's going to checkit one last time and lock it down.
-- KyleRamsey (2005-11-09 20:54:46)
Aaron,
The edits I'm making are format changes mostly. All of the lessons will need to match the existing style of the vatsim.net/prc lessons. If any of these changes detract from the lesson, in your or anyone's opinion, please challenge them.

The sections you used "marked text" will not carry over to the HTML PRC pages unless we change the text color. Since I am not really sure what you had in mind, I am leaving those alone for the time being. Let me know.

The section about cloud height measurement in hundreds of feet, might could us a reference to AGL vs MSL considering our audience.

If the edits are half done it's cause I got tired and went to bed. I will finish tomorrow where ever I leave off tonight.

And I just realized I made the first round of edits while NOT being logged in. I have now logged in and changed your ACLs to restrict write access to registered users only.
-- MikeBevington (2005-11-09 22:22:44)
I think changing the color might be a good thing...Nothing drastic, but those are the parts that i wanted to emphasize..i can help make the adjustment, just let me know what you need. I also included the different types of altitude as well as a link to AirplanesAirspeedsAltitudes - by EricSterns
-- AaronFlodin (2005-11-10 18:31:29)
OK Aaron, perfect now in my opinion anyway. I understand your use of marked text and we will adjust that text accordingly when/if we move it from this format to straight HTML and PDF.

I edited a line for clarity by adding BKN and OVC, "Keep in mind that only these last two cloud designations (BKN and OVC) constitute ceiling."

EXCELLENT use of a link to another lesson.

Unless someone has other opinion, I will move this to a "Lessons Complete" list at the end of the weekend.

Great work and thank you.
-- MikeBevington (2005-11-11 22:14:03)
Wind:

EX.2
METAR UHPP 060600Z 34003MPS 9999 SHRA OVC009CB 03/02 Q1014 NOSIG

EX.2.A
KPIT 201955Z 22015KT 3/4SM R28R/2600FT TSRA OVC01OCB 18/16 A2992 RMK SLPO13 T01760158
The first 3 digits of this number will always represent the heading that the wind is blowing from. In this case the wind is blowing from ?020 Degrees?.

The wind is NOT blowing from 020 degrees...it is from 220 degrees
-- RogerCurtiss (2005-11-19 17:47:34)
Thanks Roger, I edited it accordingly Aaron.
-- MikeBevington (2005-11-22 18:15:34)
Australian Information:
http://www.airservicesaustralia.com/publications/current/aip/gen/352535.pdf

Mainly to do with additional codes when only single sensors are used
-- BenIppolito (2005-12-26 18:42:28)
EGLL 060326Z 060413 20013G23KT 9999 SCT014 BKN025 TEMPO 0413 8000 -RA BKN014 TEMPO 0813 19018G33KT RA

In the first section of the TAF we see that this report comes to us from London's Heathrow Airport.
In the second section we see that this report was taken on the 6th day of the month, at 0413Z.

Actually, doesn't the second section say that the report was taken on the 6th day of the month at 0326Z and is valid on the 6th day from 0400 to 1300Z?

Mark Woodhouse
-- MarkWoodhouse (2006-06-07 15:32:08)
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