Winds aloft, officially known as the winds and temperatures aloft forecast, (known as "FD" in the US and Canada, but becoming known as "FB", following the

World Meteorological Organization The World Meteorological Organization (WMO) is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics. The WMO originated from the Internati ...

MOnomenclature), is a forecast of specific atmospheric conditions in terms of

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...

and

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...

at certain

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

s, typically measured in feet (ft) above

mean sea level There are several kinds of mean in mathematics, especially in statistics. Each mean serves to summarize a given group of data, often to better understand the overall value (magnitude and sign) of a given data set. For a data set, the '' ari ...

(MSL). The forecast is specifically used for aviation purposes. The components of a winds and temperatures aloft forecast are displayed as DDss+/-TT: * Wind direction (DD) and wind speed (ss), displayed as a 4-digit number, e.g. 3127, indicating a wind direction of 310 degrees

true north True north (also called geodetic north or geographic north) is the direction along Earth's surface towards the geographic North Pole or True North Pole. Geodetic north differs from ''magnetic'' north (the direction a compass points toward t ...

and a wind speed of 27

knots A knot is a fastening in rope or interwoven lines. Knot may also refer to: Places * Knot, Nancowry, a village in India Archaeology * Knot of Isis (tyet), symbol of welfare/life. * Minoan snake goddess figurines#Sacral knot Arts, entertainme ...

. Note that wind direction is rounded to the nearest 10 degrees and the trailing zero is excluded. * Temperature (TT), displayed as a +/- two-digit number, indicating temperature in degrees Celsius. Above 24,000 feet, the format changes by omitting a +/- sign on temperature. Temperatures at high aviation altitudes are below zero Celsius.

Example

FBUS31 KWNO 190440 DATA BASED ON 190000Z DATA VALID 190600Z FOR USE 0600-1200Z. TEMPS NEG ABV 24000 FT 3000 6000 9000 12000 18000 24000 30000 34000 39000 ABR 1027 1326+01 1428-03 1431-09 1639-21 1749-34 175849 175957 174758 ABI 2849+04 2857-02 2760-07 2670-20 2682-32 760344 760648 259451 ABR, ABI, and ALS are the weather station abbreviations used in this report. Wind speeds over 99 knots are extracted by subtracting 50 from the direction and adding 100 to the speed. Thus, for example, the wind forecast for Abilene (ABI) at 30,000 feet, shown above as 7603, indicates a forecast wind of 260 degrees at 103 knots (76-50=26 or 260, and speed became 100+03=103). This forecast is now made four times a day based on 0000Z, 0600Z, 1200Z, and 1800Z data (the Z stands for Zulu and indicates

Coordinated Universal Time Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently use ...

). The forecasts are valid 6 (FD1/8), 12 (FD2/9), and 24 (FD3/10) hours after the observation date/times of 0000Z and 1200Z upon which they are based. Depending on station elevation, FD1/2/3 wind forecasts are issued for the following levels: 3, 6, 9, 12, 18, 24, 30, 34, and 39 thousand feet. The first level for which a wind forecast is issued is 1,500 feet or more above the station elevation. Temperature is forecast for all wind levels, except the 3,000 foot level, that are 2,500 feet or more above the station. As indicated in the third line of the forecast, the temperatures at all levels above 24,000 feet are generally negative and the minus sign is excluded. FD8/9/10 are for the 45,000 and 53,000 foot levels. Light and variable winds (which by definition have speed close to zero and also lack specific direction) are coded as 9900.

References

NATIONAL WEATHER SERVICE INSTRUCTION 10-812
– Aviation Wind and Temperature Aloft Forecasts Instructions
NOAA's National Weather Service
– Forecast Winds and Temps Aloft Help

External links

Forecast winds and temps aloft
NOAA's National Weather Service, Aviation Weather Center, ADDS Wind Temp Data page, featuring graphical and other optional presentation formats {{DEFAULTSORT:Winds Aloft Weather forecasting Aviation meteorology