METARs and TAFs

Interpreting METARs and TAFs

 

By Aaron Flodin

Important Terms

  • METAR - Acronym for Meteorological Aerodrome Report
  • TAF - Terminal Aerodrome Forecast
  • AGL - Above Ground Level
  • MSL - Mean Sea level

For more information on types of altitude see AirplanesAirspeedsAltitudes - by Eric Sterns

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.

  • Knots (KT)
  • Meters Per Second(MPS)

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. 

  • Statute miles
  • Meters
  • Runway Visual Range
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.

  • Light "-" /Heavy "+" /Moderate "no sign"
  • TSRA- This part of the METAR code signifies that there are Thunderstorms and Moderate Rain in the area. In this section, intensity identifiers also play a big role.

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.

  • SKC = Sky Clear
  • FEW = 1-2 octas
  • SCT = 3-4 octas
  • BKN = 5-7 octas
  • OVC = 8 octas

Cloud height is measured in hundreds of feet ABOVE GROUND LEVEL or "AGL", so when we see in the example:

  • SCT100

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. 

  • When clouds are made up of towering cumulus or cumulonimbus, TCU or CB will follow cloud height

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.

  • 10/5 - Temperature is 10 degrees celsius, Dewpoint in 5 degrees 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".

  • Standard Altimeter setting in inches of mercury = A2992"
  • "Standard Altimeter setting in hectoPascals = Q1013

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

  • TEMPO - Temporary changes expected
  • BECMG - Becoming
  • PROB - Probability

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