May 22, 1996 A Controller's View of METAR

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by	Brian Fallon
	New York TRACON Associate Editor, THE NATCA VOICE

The results of the New York TRACON's Safety Survey "Are You Ready for METAR?" are in, and the results are unanimous: No one around here knows anything about METAR!

Well, in the interest of safety, the mystery of METAR can now be revealed.

METAR is the ICAO (International Civil Aviation Organization) meteorological format for Aviation Routine Weather Reports. In order to enhance safety, the U.S. agreed to modifying its domestic weather codes to match ICAO's standards.

This isn't exactly late-breaking news. The first changes began happening in 1993! Although these changes were mostly transparent to domestic operations, the FAA made it known to aviation user groups early-on that the changes would be coming and several prominent aviation magazines have run articles describing in general the format changes. And yet, no one thought to tell the controllers. Not until the change was almost here, that is.

The good news is that METAR was NOT implemented on the originally-planned date of January 1, 1996. The FAA and NWS just weren't ready in time, lucky for us. The new implementation date is July 1, 1996, at 0800Z.

Here is the sequence of elements in a METAR report:

1. Type of report

2. Station designator

3. Time of report

4. Wind

5. Visibility

6. Weather and obstructions to visibility

7. Sky condition

8. Temperature and dew point (in CELSIUS!)

9. Altimeter setting

10. Remarks

Here is a quick overview of each of the elements and what's new and different about them:

1. Type of report:

There are two types of report: (a) the METAR, which is a routine observation report, and (b) the SPECI, which is a Special METAR weather observation.

2. Station designator:

The METAR codes uses ICAO 4-letter station identifiers. In the contiguous 48 states, the 3-letter domestic station identifier is prefixed with a "K", i.e. the domestic identifier for Newark is EWR while the ICAO identifier is KEWR.

3. Time of report:

The time is the time the observation was taken in UTC, as it is now, but will also be preceded by the day of the month and followed by the letter "Z", e.g. 091250Z.

4. Wind:

In METAR reports, the wind will be the first weather element. Also, the wind will be reported with three digits for the direction and two digits for the speed (3 digits if needed). If the wind is gusty, it is reported after the speed with a "G", followed by the highest gust reported (in 2 or 3 digits). It will be appended with the abbreviation "KT" to denote the use of knots for wind speed.

Example:

Winds now reported as 1308 will be shown as 13008KT. Winds now reported as 0832G45 will be shown as 08035G45KT.

Also, if the winds are variable, the information will immediately follow the wind group instead of being in the Remarks.

Example:

32015G22KT 280V350

If you think about it, this actually is an improvement to the way winds are now done.

5. Visibility:

Visibility is reported in statute miles with "SM" appended to it. If Runway Visual Range is reported, it will immediately follow, in the format: R(Runway)/(Visual Range)FT. The 'R' identifies the RVR group.

Example:

1/2SM R22R/1200FT

Again, this is all pretty much straight forward and shouldn't be too hard to get used to.

6. Weather:

Now this is where things start to get confusing. All of the weather abbreviations will be in two letter codes, and some of the codes don't exactly lend themselves to immediate understanding. The big ones are pretty easy, such as Thunderstorm = TS and Rain = RA, but some are just weird, like Hail = GR and Smoke = FU. The NWS folks say these are derived from the French words, but personally, I think there are some 'inside jokes' behind those two.

Also, weather will be broken down into sub-categories and will be reported in the following format:

• Intensity

• Proximity

• Descriptor

• Precipitation

• Obstructions to Visibility

• Other

Intensity:

This will apply ONLY to the first type of precipitation reported. A minus sign (-) denotes light, no sign denotes medium, and a plus sign (+) denotes heavy.

Proximity:

Applies to and reported ONLY for weather occurring in the vicinity of the airport (5-10 NM). It is denoted by the letters "VC".

Descriptors:

The standard METAR format has these seven descriptors that apply to the precipitation or obstruction to visibility:

• TS = Thunderstorm

• DR = low drifting (i.e. scud)

• SH = showers

• MI = shallow (i.e. fog)

• FZ = freezing

• BC = patches

• BL = blowing (i.e. snow)

Precipitation:

There are six types of precipitation in the METAR code:

• RA = rain

• DZ = drizzle

• SN = snow

• GS = small hail/ice pellets

• SG = snow grains

• IC = ice crystals

Obstructions to Visibility:

There are eight types of obstructing phenomena in the METAR code:

• FG = fog (vsby less than 5/8 mile)*

• HZ = haze

• FU = smoke

• PY = spray

• BR = mist (vsby 5/8-6 miles)*

• SA = sand

• DU = dust

• VA = volcanic ash

*NOTE: Fog (FG) is forecast only when the visibility is less than 5/8 mile; otherwise mist (BR) is forecast.

Other:

There are five categories of Other Weather Phenomena which are reported when they occur:

• SQ = squall

• SS = sandstorm

• DS = duststorm

• PO = dust/sand whirls

• FC = Funnel cloud/Tornado/Waterspout

7. Sky Condition:

The sky condition as reported in METAR represents a significant change from the way sky condition is presently reported. In METAR, the sky condition is reported in the following format:

• Amount

• Height

• Type (or Vertical Visibility)

Amount:

The amount of sky cover is reported in eights of sky cover, using the contractions:

• SKC = Sky clear

• SCT = Scattered (1/8-4/8)

• BKN = Broken (5/8-7/8)

• OVC = Overcast (8/8)

Now, what is interesting is that there is no ceiling layer designated in the METAR code. For aviation purposes, the ceiling is the lowest reported broken or overcast layer, or vertical visibility into an obscuration. Also, there is no provision for reporting thin layers.

One more oddball detail: automated weather reporting stations report CLR (meaning sky clear below 12,000 feet) instead of SKC. Go figure!

Height:

Cloud bases are reported with three digits in hundreds of feet.

Example:

SCT011 OVC015

Sky conditions are 1100' scattered, ceiling 1500' overcast.

Type:

If towering cumulus (TCU) or cumulonimbus (CB) are present, they are reported after the height which represents their base. This is a nice feature of the METAR format. It really helps you develop a good visual picture of what the weather is doing.

Vertical Visibility:

Total obscurations are reported in the format "VVhhh", where VV denotes Vertical Visibility and the hhh is the vertical visibility in hundreds of feet. There is no provision in METAR to report partial obscurations:

Example:

1SM FG VV003

Prevailing visibility is 1 statute mile in fog, with a vertical visibility of 300 ft.

8. Temperature and Dew Point:

Here's the part that will probably cause the most grief. The temperature and dew point will be reported in a two digit form in Celsius. Also, temperatures below zero will be prefixed with an "M".

9. Altimeter:

Minor changes here. The altimeter will be reported in a full four digit format prefixed with an "A".

10. Remarks:

This is where the U.S. domestic METAR will deviate significantly from the rest of the world. Normally, remarks in METAR are limited to reporting operational significant weather (i.e. lightning: LTGICCCCA), the beginning and ending times of certain weather phenomena, and low-level wind shear reports. Until we get the full training packages, we can't be exactly sure what's going to be in the Remarks. In any case, the contraction "RMK" will precede the remarks themselves. "RE" stands for "Recent Event" (not "Rain Ended"). "WS is for "Wind Shear", followed by "TKO" (take-off) or "LDG" (landing), and "RWxx" which will denote the runway affected.

Example:

RMK REFZDZB45 WS TKO RW04L

Remarks: Recent Event: Freezing Drizzle, Began 45 minutes past the hour; Wind Shear: On Take-off, Rwy 041.

This should give you a pretty good overview of what to expect. Also, don't sweat trying to memorize all the new weather codes. There's a nifty METAR/TAF quick refererence card that you can print out and use as a crib sheet.

Once everyone gets comfortable with the new format, I think most will find it simple to understand and may actually be able to better visualize what the weather is doing. There are some weather abbreviations that we'll never see around here, and the commonly used ones will become second nature soon enough. And if you do see one of the strange ones, chances are you'll have plenty of pilots to tell you what it is, because that's what they're trying to avoid. Think about it: if you've got "VA" in the weather sequence at your primary airport, you've got bigger problems to worry about than learning a new weather code.

No one need to get too uptight about METAR. It's just winds, temp. and weather, after all. All the same things are there, it's just the way they're being presented that's new. Happy vectors, and always remember:

SAFETY FIRST!