A - 107 Weather Reports Review

Weather

Weather can be broken down into two different categories: qualifiers and weather phenomenon (+TSRA BR). First, the qualifiers of intensity, proximity and the descriptor of the weather will be given. The intensity may be light (-), moderate (no entry or symbol) or heavy (+). Proximity only depicts weather phenomena that are in the airport vicinity (VC).

Forecast Significant Weather

Weather phenomenon is coded in the TAF reports in the same format as the METAR. If no significant weather is expected during the forecast time period, the denotation "NSW" will be included in the "becoming" or "temporary" weather groups.

Report Type

A TAF can be either a routine forecast (TAF) or an amended forecast (TAF AMD).

METARS

An aviation routine weather report, or METAR (Message D'Observation Mèteòrologique Pour L'Aviation Règulière), is an observation of current surface weather reported in a standard international format.

TAF Publication

A TAF is a report established for the 5 statute mile radius around an airport. Weather within 10 SM will sometimes be included, and will be coded as VC for vicinity. TAFs are issued every six hours (0000Z, 0600Z, 1200Z, 1800Z). TAFs will often be issued a short time prior to the scheduled forecast time. While TAFs are valid for up to 24 hours, they are replaced by the next one issued.

Ceiling Cloud Coverage

A ceiling, for aviation purposes, is the lowest layer of clouds reported as being broken or overcast, or the vertical visibility into an obscuration like fog or haze.

Forecast Change

Change— For any weather change forecast to occur during the TAF time period, the expected conditions and time period are included in this group. This information may be shown as From (FM), Becoming (BECMG), and Temporary (TEMPO).

Remarks

Comments may or may not appear in this section of the METAR. The remarks section always begins with the letters "RMK." The information contained in this section may include wind data, variable visibility, beginning and ending times of particular phenomenon, pressure information and various other information deemed necessary.

METAR and TAF on DOSS IFS Website

Doss main page --> Weather planning --> METAR/TAF

Station Identifier

Each station is identified by a four-letter code as established by the International Civil Aviation Organization (ICAO). In the 48 contiguous states, a unique three-letter identifier is preceded by the letter "K." Eg: KCOS, KDEN, KPUB, etc

Forecast Sky Condition

Forecast sky conditions are given in the same manner as the METAR. ONLY cumulonimbus (CB) clouds are forecast in this portion of the TAF report.

SPECI METARS

Generated when: - There is a change in wind direction by 45 degrees or more in less than 15 minutes with a steady speed of 10 knots or more - A thunderstorm forms or dissipates - A layer of clouds or obscuring phenomenon aloft forms below 1,000 feet AGL

METAR Publication

Information for METAR reports is observed hourly between 45 minutes after the hour until the top of the hour. The observation is made by either a person or automated equipment. While the exact time may vary from one reporting station to the next, a routine METAR will be reported between 50 minutes after the hour until the top of the hour. If there is a significant change in the weather during the hour prior to a new METAR being reported, then a special report will be made. This is called a SPECI report.

Example METAR

METAR KBTR 161753Z 14021G26 3/4SM -RA BR BKN008 OVC012 18/17 A2970 RMK PRESFR Type of Report: Routine METAR Location: Baton Rouge, Louisiana Date: 16th day of the month DOSS IFS Academic Lesson Reading 1 Jan 2014 A107-4 Time: 1753 Zulu Modifier: None shown Wind Information: Winds 140 degrees at 21 knots gusting to 26 knots Visibility: 3/4 statute mile Weather: light rain and mist Sky Conditions: Skies broken 800 feet, overcast 1,200 feet Temperature: Temperature 18° C, dewpoint 17° C Altimeter: 29.70 in. Hg Remarks: Barometric pressure is falling.

Modifier

Modifiers denote that the METAR came from an automated source or that the report was corrected. If the notation "AUTO" is listed in the METAR, the report came from an automated source. It also lists "AO1" or "AO2" in the remarks section to indicate the type of precipitation sensors employed at the automated station.

Sky Condition

Sky condition (BKN008OVC012CB) is always reported in the sequence of amount, height and type or indefinite ceiling/height (vertical visibility). Broken clouds at 800ft AGL, overcast at 1200ft AGL, with cumulonimbus. FEW = 1/8 - 2/8 cloud cover SCT = Scattered (3/8 - 4/8 cloud cover) BKN = Broken (5/8 - 7/8 cloud cover) OVC = overcast (8/8 cloud cover)

TAFs

Terminal Aerodrome Forecasts are always produced by a human forecaster. For this reason there are far fewer TAF locations than there are METAR locations. TAFs take into account local, small-scale, geographic effects. While this information may be included at military installations and on international TAFs, the National Weather Service (NWS) does not include temperature, icing or turbulence information.

BECMG Group

The "becoming" designator is used for gradual changes in weather taking place over a longer time frame—usually two hours.

FM Designator

The FM change group is for significant and rapid change to a new set of prevailing weather conditions

Temperature and Dew point

The air temperature and dew point are always given in degrees Celsius (18/17). Temperatures below 0° are preceded by the letter "M" to indicate minus. EG: (4/M2) 4 degrees Celsius current temp, dew point at -2 degrees Celsius.

Altimeter Setting

The altimeter setting is reported as inches of mercury in a four-digit number group (A2970). It is always preceded by the letter "A." Read as "two niner seven zero"

Date and Time of Report

The date and time (161753Z) are depicted in a six-digit group. Created on the 16th day of the month at 1753 Zulu time

Types of METARS

The first is the routine METAR report that is transmitted every hour. The second is the aviation selected special weather report (SPECI).

Forecast Visibility

The forecast visibility is given in statute miles and may be in whole numbers or fractions. If the forecast is greater than 6 miles, it will be coded as "P6SM."

Visibility

The prevailing visibility (3/4 SM) is reported in statute miles as denoted by the letters "SM." It is reported in both miles and fractions of miles. The maximum visibility reported in a METAR is 10 SM. If the visibility is less than 10 SM, the reason for the reduced visibility is given.

IACO Station Identifier

The station identifier is the same as that used in a METAR.

Forecast Wind

The wind direction and speed forecast are given in a five digit number group. The first three indicate the direction of the wind in reference to true north. The last two digits state the wind-speed in knots as denoted by the letters "KT."

TEMPO Group

There is a date and time breakdown for temporary weather conditions. TEMPO refers to any change in wind, visibility, weather, or sky condition that is expected to last for "generally less than an hour at a time, and is expected to occur during less than half the time period."

Time of Origin and Valid Time Period

Time and date of TAF origination is given in the six-number code with the first two being the date, the last four being the time. The valid forecast time period is given by a six digit number group. The first two numbers indicate the date, followed by the two digit beginning time for the valid period, and the last two digits are the ending time. EG: 2418/2524. This means that the TAF is valid from day 24 of the month at 1800Z to day 25 of the month at 2400Z.

Wind Shear

Wind shear is forecast of non-convective low level winds (up to 2000 feet AGL) and is entered after the sky conditions when wind shear is expected. Encoded with WS followed by a three-digit height, slant character, and direction and velocity format like surface winds Example: WS010/18040KT - Low level wind shear at one-thousand, winds one-eight-zero at four-zero knots

Wind

Winds are reported with five digits (14021) unless the speed is greater than 99 knots, in which case the wind is reported with six digits. Winds at 21kts from 140. (34008G15) Winds from heading 340 at 8 kts gusting to 15 kts. If winds are variable then VRB precedes the wind speed. EG: (VRB06KT)