Prioritize...
When you've completed this page, you should be able to decode a METAR observation. In particular, focus on the station ID, time and date, wind observations, present weather, sky coverage, hourly temperature / dew point observations, the T-group, the 1-group, 2-group, and 6-group.
Read...
Throughout the certificate program, you've surely come across METAR observations at least a few times. But, you never actually had to know how to decode them. You might be wondering, "Why do we need to know how to decode METARS? We can get already decoded versions lots of places online!" That's certainly true, but by looking at raw METARS, you can glean more information than from the standard decoded versions (many decoded versions don't include the complete observation). Plus, if you become well-versed decoding raw METARS, you'll find that you can actually gather information from the coded versions much more quickly since the data is presented in a denser format. So, by knowing how to decode raw METARS, you can more easily and quickly see how your forecasts are doing, and gather data as you prepare your forecast for the next day!
Note that this page is quite long, but I don't intend for you to read every single part of it in detail. Focus on the sample METAR observations below and the parts emphasized in the Prioritize statement (they're in red as you go down the page). Also, focus on the Key Skill and Quiz Yourself sections, because they'll outline important things you'll need to know and give you some practice. Consider the rest of the page as a reference guide for times when you need to look up the meaning of a specific code or remark.
Let's get right to it. Here are a couple of METAR observations from Concord, New Hampshire on May 13, 2006.
- METAR KCON 131151Z AUTO 09009KT 1 3/4SM +RA BR OVC010 09/07 A3005 RMK AO2 CIG 007V013 SLP177 P0015 60056 70066 T00890072 10094 20089 53018
- METAR KCON 131751Z AUTO 00000KT 2SM +RA BR OVC013 08/06 A3012 RMK AO2 SLP202 P0017 60115 T00780061 10089 20072 53004
What do all of these letters and numbers mean? Let's break it down and decode the first METAR (you may want to open this link and refer to it as you go down the translation):
- METAR - METAR is a French acronym that, loosely translated, means "routine aviation weather observation." But sometimes you'll see "SPECI", which translates to a special (unscheduled) report.
- KCON is the four-character ICAO (International Civil Aviation Organization) identifier for Concord, New Hampshire. You can use the station list at the National center for Atmospheric Research to help you decipher any identifier.
- 131151Z is the observation date and time. The observation was taken on the 13th (May, 2006) at 1151Z (the month and the year are not part of the report, so it's important to know whether you're looking at a current or past observation).
- AUTO indicates a fully automated report with no human intervention. If an observer takes or augments observations, this tag does not appear. Sometimes you might see COR, which indicates a corrected observation.
- 09009KT indicates wind direction and speed. Here, the wind blew from 90 degrees (an easterly wind) at 9 knots. What happens if winds are gusty? Let's look at a METAR from Mount Washington in New Hampshire (see photograph below) at the same time as the first METAR from Concord:
KMWN 131147Z 13043G58KT 1/16SM FZRA PL FZFG VV001 M01/M01 RMK PLB40 VRY LGT GICG 60074 70148 931000 10017 21013
Winds were blowing from 130 degrees sustained at 43 knots and gusting to 58 knots. That's just a ho-hum "breeze" compared to the world-record setting 231 miles an hour clocked at the summit on April 12, 1934! Yes, Mount Washington is a windy place indeed.
Mount Washington, New Hampshire, in December, 2005. If you look closely, you can see the Mount Washington Observatory.Credit: Mount Washington ObservatoryIn stark contrast to windy Mount Washington, a METAR entry of 00000KT represents a calm wind. When the wind is light (a speed of six knots or less) and it varies in direction with time, the data encoded on a METAR might look like VRB004KT (variable direction blowing at four knots). If the wind speed is greater than six knots and the wind direction varies, the data encoded on a METAR might look like "32014KT 290V350". Translation: the wind direction was 320 degrees and the wind speed was 14 knots, but the direction varied from 290 to 350 degrees. Such a varying wind direction might occur in the immediate wake of a cold front. Variable wind directions are always encoded in the clockwise direction (just for the record).
- 1 3/4SM translates to a horizontal visibility of one and three-fourths statute miles. Visibilities below one fourth of a mile appear as M1/4SM in METARS from automated stations.
- +RA BR is the present weather in this case. "+RA" represents heavy rain, while "BR" is the METAR code for mist. You should become familiar with the other codes for precipitation and restrictions to visibility.
| QUALIFIER | WEATHER PHENOMENA | |||
|---|---|---|---|---|
| INTENSITY OR PROXIMITY 1 |
DESCRIPTOR 2 |
PRECIPITATION 3 |
OBSCURATION 4 |
OTHER 5 |
| - Light Moderate2 + Heavy VC In the Vicinity3 |
MI Shallow PR Partial BC Patches DR Low Drifting BL Blowing SH Shower(s) TS Thunderstorm FZ Freezing |
DZ Drizzle RA Rain SN Snow SG Snow Grains IC Ice Crystals PE Ice Pellets GR Hail GS Small Hail and/or Snow Pellets UP Unknown Precipitation |
BR Mist FG Fog FU Smoke VA Volcanic Ash DU Widespread Dust SA Sand HZ Haze PY Spray |
PO Well- Developed Dust/Sand Whirls SQ Squalls FC Funnel Cloud Tornado Waterspout4 SS Sandstorm SS Duststorm |
| 1. The weather groups shall be constructed by considering columns 1 to 5 in the table above in sequence, i.e. intensity, followed by description, followed by weather phenomena, e.g. heavy rain shower(s) is coded as +SHRA 2. To denote moderate intensity no entry or symbol is used. 3. See paragraph 8.4.1.a.(2), 8.5, and 8.5.1 for vicinity definitions. 4. Tornados and waterspouts shall be coded as +FC. |
||||
On with the rest of our METAR translation:
- OVC010 represents the current sky condition, which, at this time, was overcast at 1000 feet (the three-digit code corresponds to the ceiling (or cloud base) in hundreds of feet). In general, please note that METARS can list data about more than one layer of clouds. Moreover, when the sky is obscured, METARS should include the vertical visibility in hundreds of feet. For example, VV004 corresponds to an obscured sky with a vertical visibility of 400 feet.
- A3005 is the altimeter setting - in this case, 30.05 inches of mercury.
- 09/07 represent the temperature and the dew point reported to the nearest degree Celsius (more precise data sometimes appear near the end of METARS - more in a bit). In this observation, the temperature was 9 degrees Celsius and the dew point was 7 degrees Celsius.
- RMK stands for "Remarks." There are a multitude of possible remarks, but I'll only go over the ones in this particular METAR. In this case, A02 indicates that the automated station has a precipitation sensor (A01 means that the automated station does not have a precipitation sensor).
- CIG 007V013. When the ceiling (as measured by a ceilometer, which uses a laser or other light source to determine the height of a cloud base) is less than 3000 feet and variable, this group typically appears in METARS. In this case, the ceiling was variable between 700 and 1300 feet.
- SLP177 indicates the sea-level pressure in millibars, using the same convention as on a standard station model (1017.7 mb, in this case).
- P0015 is the hourly liquid precipitation (in hundredths of an inch). In this case, 0.15 inches of rain fell in the hour ending at 12Z.
- 60056 represents the three- or six-hour total liquid precipitation (in hundredths of an inch). In this case, 0.56 inches of rain fell in the six-hour period ending at 12Z. For the record, six-hour totals appear at 00Z, 06z, 12Z and 18Z. Three-hour totals appear at 03Z, 09Z, 15Z and 21Z. 60000 translates to a trace of liquid precipitation during the three- or six-hour period.
- 70066 indicates the total 24-hour liquid precipitation ending at 12Z (in hundredths of an inch). In this case, 0.66 inches fell at Concord from 12Z on May 12 to 12Z on May 13.
- T00890072, the T-group, indicates the hourly temperature and dew point to the nearest tenth of a degree Celsius. The "0" after the "T" indicates that the temperature is greater than or equal to 0 degrees Celsius (a "1" will follow the "T" when the temperature is lower than 0 degrees Celsius). After the three digits for temperature, a "0" indicates that the dew point is greater than or equal to 0 degrees Celsius (a "1" indicates that the dew point is less than 0 degrees Celsius). In this case, the 12Z temperature at Concord was 8.9 degrees Celsius (48 degrees Fahrenheit) and the dew point was 7.2 degrees Celsius (45 degrees Fahrenheit).
- 10094, the 1-group, indicates the highest temperature, in tenths of a degree Celsius, during the previous six-hour period. If the digit following the "1" is a "0", then the temperature is higher than 0 degrees Celsius (a "1" following the first "1" indicates that the temperature is less than 0 degrees Celsius). So the highest temperature at Concord between 06Z and 12Z on May 13, 2006, was 9.4 degrees Celsius (49 degrees Fahrenheit). Note that the "1" group is only reported at 00Z, 06Z, 12Z and 18Z.
- 20089, the 2-group, indicates the lowest temperature during the previous six-hour period. If the digit following the "2" is a "0", then the temperature is higher than 0 degrees Celsius (a "1" following the "2" indicates that the temperature is less than 0 degrees Celsius). So the lowest temperature at Concord between 06Z and 12Z on May 13, 2006, was 8.9 degrees Celsius (48 degrees Fahrenheit). Like the "1" group, the "2" group is only reported at 00Z, 06Z, 12Z and 18Z.
- 53018 indicates the pressure tendency (the "5 group"). The digit following the "5", which can vary from 0 to 8, describes the behavior of the pressure over the past three hours (for guidance, consult the table below). The last three digits represent the amount of pressure change in tenths of a millibar. Thus, the pressure at Concord increased 1.8 mb in the three-hour period ending at 12Z on May 13, 2006.
| Primary Requirement | Description | Code Figure |
|---|---|---|
| Atmospheric pressure now higher than 3 hours ago. |
Increasing, then decreasing. | 0 |
| Increasing, then steady, or increasing then increasing more slowly. | 1 | |
| Increasing steadily or unsteadily. | 2 | |
| Decreasing or steady, then increasing; or increasing then increasing more rapidly. | 3 | |
| Atmospheric pressure now same as 3 hours ago. |
Increasing, then decreasing. | 0 |
| Steady | 4 | |
| Decreasing then increasing. | 5 | |
| Atmospheric pressure now lower than 3 hours ago. |
Decreasing, then increasing. | 5 |
| Decreasing, then steady, or decreasing then decreasing more slowly. | 6 | |
| Decreasing steadily or unsteadily. | 7 | |
| Steady or increasing, then decreasing; or decreasing then decreasing more rapidly. | 8 |
I realize that translating one METAR hardly qualifies as an entire lesson, but at least you now know the general guidelines and where to find information in case you run across a METAR that gives you pause. I encourage you to expand your aptitude for decoding METARS - they hold a lot of information! If you want to completely master METAR code, you can study Chapter 12 of the Federal Meteorological Handbook No. 1, which is basically the METAR "bible" (section 12.7 in particular covers the wide variety of "remarks" that can appear). If you have aspirations for becoming an official weather observer, you may be interested in checking out the entire handbook (it's very long, but there is a table of contents to help you find specific topics).
Key Data Resources
You can access METAR observations taken at ASOS and AWOS sites at this interactive FAA Web site or the NCAR surface observation site (which also includes plots of regional station models).
What are the key take-away points from this section? The Key Skill box below highlights some key data groups with which you must become proficient in this course, and the Quiz Yourself section will give you a chance to get a little practice, too. Once you get the hang of it and memorize the general format and some common codes, it's a snap!
All of these observations we've been talking about, over long periods of time, constitute a station's climatology, and good forecasters investigate the climatology of the location they're forecasting for. We'll take a look at common climate data and what components are needed for a good understanding of a city's climatology next.
Key Skill...
This semester, you'll need to work with some METAR data groups repeatedly, so you must be proficient in translating them and applying them to forecasts and verifications. Forgetting about them can easily lead to an incorrect forecast verification, or perhaps making your next day's forecast with the wrong impression of today's observations! When interpreting METAR data, keep the following important points in mind:
Observation times: As you may remember from your previous studies, a certain hour's observation is typically issued several minutes before the hour. So, our KCON observation example on this page came from 1151Z, but that's actually the official 12Z observation.
Temperature observations: Many METARS have two temperature (and dew point) observations -- one that's rounded to the nearest degree Celsius, and a more precise version to the nearest tenth of a degree Celsius in the T-group. Make sure you use the T-group for conversions to Fahrenheit (if it's available). Using the less precise values rounded to the nearest degree Celsius can lead to incorrect Fahrenheit conversions!
Verifying high and low temperatures: We can't just use T-groups to determine the highest and lowest temperatures over a given period of time because they only tell us the precise temperature right at the observation time. They don't tell us anything about what happened in between observations, so you must look at the 1-groups and 2-groups at specific synoptic times in order to determine six-hour maximum and minimum temperatures, respectively. For example, if you wanted to determine a station's maximum and minimum temperatures over a 24-hour period from 06Z to 06Z, you would need to evaluate the 1- and 2-groups at 12Z, 18Z, 00Z, and 06Z to cover the entire 24 hour period.
Verifying total liquid precipitation: The "P" groups give us total liquid precipitation that has fallen in the past hour, but summing the "P" groups to get a liquid precipitation total for a longer period of time can be fraught with error--especially when "P" groups get reported with special observations in-between the hourlies. Thus, it's easiest to look at the 6-groups at specific synoptic times, and add them together in order to determine the total liquid precipitation over a period of time. For example, if you wanted to determine a station's total precipitation over a 24-hour period from 06Z to 06Z, you would need to evaluate the 6-groups at 12Z, 18Z, 00Z, and 06Z to cover the entire 24 hour period (each would give a six-hour total). You would ignore the 6-groups at 09Z, 15Z, 21Z, and 03Z because those three-hour totals would be redundant in this scenario.
Verifying maximum sustained wind: Hourly METARS only show us sustained winds at the time of the observation, but of course sustained wind speeds will vary (perhaps greatly) over the course of each hour. So, the maximum sustained wind speed will not likely occur exactly at the time of the hourly observations (we often can't verify maximum sustained wind speed from hourly METARS). For major stations, the National Weather Service tracks sustained wind speeds continuously and publishes the maximum sustained wind speed for each calendar day in its Daily Climate Summary.
Quiz Yourself...
Quickly gathering information from coded METARS is a useful skill for forecasters. To give you some practice in gathering the types of information you'll regularly need to gather in this course, here's 24-hours of METARS from Cheyenne, Wyoming, spanning 06Z December 30 through 06Z December 31, 2014. Older observations are toward the bottom, while more recent ones are toward the top.
Question #1
During this 06Z - 06Z period, what was the maximum temperature observed at KCYS? What data group confirms it?
Answer: -18.9 degrees Celsius (-2 degrees Fahrenheit) as evidenced by the 1-group in the 12Z observation (11189). The 1-groups give us six-hour maximum temperatures at the synoptic times (12Z, 18Z, 00Z, and 06Z). So, we can quickly tell the maximum temperature during this period by merely looking at the 1-groups at the synoptic times and determining which one shows the highest temperature. There's no need to look at the temperature reported in every single observation.
Question #2
During this 06Z - 06Z period, what was the minimum temperature observed at KCYS? What data group confirms it?
Question #3
The temperatures reported in the 22Z and 23Z observations were both "M21". Were the temperatures actually the same at each time?
Question #4
How much liquid precipitation fell during this 06Z - 06Z period?
Explore Further...
While METARS are typically published every hour, the observations are being recorded continuously, and you can find some sites on the Web that provide more frequent METAR data. For example, here are translated 5-minute METAR observations for Los Angeles International Airport (if you want to see the actual encoded 5-minute METARS, just click on "Raw Observations"). By the way, if you want to view a different station, just change the "KLAX" in the URL to your desired station ID.
However, I urge caution when interpreting translated 5-minute METARS. The raw 5-minute METARS typically lack a T-group, which means decoders get the temperature in degrees Fahrenheit from rounded values in Celsius in the raw 5-minute METAR. That sometimes results in incorrect Fahrenheit conversions, so the temperatures you see in degrees Fahrenheit can sometimes be a degree off from the actual observation. Be careful with 5-minute METARS!