A Controller’s View of METAR

It isn't just pilots who are concerned about the changeover to METAR and TAF weather reporting. Air traffic controllers are scrambling to learn how to break the new code, too. New York TRACON's resident expert on METAR shows how the new weather reports aren't really as tough to figure out as they look ... and are actually better than the old familiar SA reports in a number of important respects.

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The results of the New York TRACON’s Safety Survey “Are YouReady 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 nowbe revealed.

METAR is the ICAO (International Civil Aviation Organization)meteorological format for Aviation Routine Weather Reports. Inorder to enhance safety, the U.S. agreed to modifying its domesticweather codes to match ICAO’s standards.

This isn’t exactly late-breaking news. The first changes beganhappening in 1993! Although these changes were mostly transparentto domestic operations, the FAA made it known to aviation usergroups early-on that the changes would be coming and several prominentaviation magazines have run articles describing in general theformat 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-planneddate of January 1, 1996. The FAA and NWS just weren’t ready intime, 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 newand different about them:

1. Type of report:

There are two types of report: (a) theMETAR, 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-letterstation identifiers. In the contiguous 48 states, the 3-letterdomestic station identifier is prefixed with a “K”,i.e. the domestic identifier for Newark is EWR while the ICAOidentifier is KEWR.

3. Time of report:

The time is the time the observationwas taken in UTC, as it is now, but will also be preceded by the day of themonth and followed by the letter “Z”, e.g. 091250Z.

4. Wind:

In METAR reports, the wind will be the first weatherelement. Also, the wind will be reported with three digits forthe 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 willbe appended with the abbreviation “KT” to denote theuse of knots for wind speed.

Example:

Winds now reported as 1308 will be shown as 13008KT.Winds now reported as 0832G45 will be shown as08035G45KT.

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

Example:

32015G22KT 280V350

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

5. Visibility:

Visibility is reported in statute mileswith “SM” appended to it. If Runway Visual Range isreported, it will immediately follow, in the format: R(Runway)/(VisualRange)FT. The ‘R’ identifies the RVR group.

Example:

1/2SM R22R/1200FT

Again, this is all pretty much straight forward and shouldn’tbe 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 immediateunderstanding. The big ones are pretty easy, such as Thunderstorm= TS and Rain = RA, but some are just weird, like Hail = GR andSmoke = 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 willbe reported in the following format:

  • Intensity

  • Proximity

  • Descriptor

  • Precipitation

  • Obstructions to Visibility

  • Other

Intensity:

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

Proximity:

Applies to and reported ONLY for weather occurringin the vicinity of the airport (5-10 NM). It is denoted by theletters “VC”.

Descriptors:

The standard METAR format has these sevendescriptors that apply to the precipitation or obstruction tovisibility:

  • 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 inthe 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 obstructingphenomena 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 lessthan 5/8 mile; otherwise mist (BR) is forecast.

Other:

There are five categories of Other Weather Phenomenawhich 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 METARrepresents a significant change from the way sky condition ispresently reported. In METAR, the sky condition is reported inthe 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 designatedin the METAR code. For aviation purposes, the ceiling is the lowestreported broken or overcast layer, or vertical visibility intoan obscuration. Also, there is no provision for reporting thinlayers.

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 hundredsof 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 youdevelop 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 thehhh is the vertical visibility in hundreds of feet. There is noprovision in METAR to report partial obscurations:

Example:

1SM FG VV003

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

8. Temperature and Dew Point:

Here’s the part that willprobably cause the most grief. The temperature and dew point willbe reported in a two digit form in Celsius. Also, temperaturesbelow zero will be prefixed with an “M”.

9. Altimeter:

Minor changes here. The altimeter will bereported in a full four digit format prefixed with an “A”.

10. Remarks:

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

Example:

RMK REFZDZB45 WS TKO RW04L

Remarks: Recent Event: Freezing Drizzle, Began 45 minutes pastthe 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 cardthat you can print out and use as a crib sheet.

Once everyone gets comfortable with the new format, I think mostwill find it simple to understand and may actually be able tobetter visualize what the weather is doing. There are some weatherabbreviations that we’ll never see around here, and the commonlyused ones will become second nature soon enough. And if you dosee one of the strange ones, chances are you’ll have plenty ofpilots to tell you what it is, because that’s what they’re tryingto avoid. Think about it: if you’ve got “VA” in theweather sequence at your primary airport, you’ve got bigger problemsto 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 justthe way they’re being presented that’s new. Happy vectors, andalways remember:

SAFETY FIRST!