Forecast Winds and Temperatures Aloft is a forecast of wind direction and speeds and of temperatures at
different altitudes for specific locations. Data for the forecasts are gathered using a small expendable
radiosonde attached to a 2 meter hydrogen or helium balloon.
These balloons are released twice daily. Additional data is collected by commercial aircraft (AMDAR/MDCRS/ACARS), and a network of wind
profiling radars operated by NOAA Global Systems Division (formerly known as Forecast Systems Laboratory).
National Centers for Environmental Prediction (NCEP) produces scheduled wind and temperature aloft forecasts four
times daily for the Continental United States, the Hawaiian Islands, Alaska and coastal waters, and the Pacific
Ocean based on data collected by the weather balloon. There is no requirement to issue amendments to these forecasts.
These reports were known as "FD" in the US, but are becoming known as "FB", following the World Meteorological Organization (WMO)
For each report, three time periods are forecasted. These are known as 6-Hour, 12-hour, and 24-hour forecasts.
For each forecast period, there are two time designations:
Valid time: the specific time for which the winds and temperatures are forecast; and the
For Use time: the time range for which the forecast values may be used.
In the above figure, the Valid time is this first time after the "@", and the
For Use time range is given in the parentheses. The time of the data collection (by
the weather balloons) is given at the bottom of the figure.
Altitudes are true altitude in feet MSL up to 12,000'. Altitudes 18,000 and higher are pressure altitudes. Winds are not forecasted within
1,500' of station elevation. Temperatures are not forecasted within 2,500' of station elevation. Hawaii and Pacific Ocean forecasts include
lower elevation forecasts.
Rules of Thumb
Winds and Temperature Aloft forecasts aids pilots with flight planning in that they forecast the existence (or absence) of head winds or cross winds
which might dramatically change flight times and fuel consumption. Temperatures aloft can show temperature inversions, or unusually warm layers where
climbing performance may be affected.
Winds differ more than 18knts
Jack Williams, coordinator of public outreach for the American Meterological Society and
frequent contributer to AOPA's Flight Training magazine wrote in the December 2007 issue
that anytime the difference between two reporting altitudes is more than 18 knots, "wind
shear could make a flight between those altitudes bumpy." As an aid, AvnWx.com
places a dotted line between such altitudes under the wind data item,
in the Winds Aloft display. You can see
some examples in the above figure, such as between 30000 and 34000 in the 6hr report. It's more than just a simple 18knt difference,
of course -- one has to consider the change in wind direction also. For example: 210 at 23 knts changing to 160 at 22 knts isn't a
1 knt wind shift, it is a 19 knt wind shift!
Note that wind shear can happen anywhere so don't be complacent just because there
isn't a dotted line at your altitude on this website.
Temperature more than 3° per 1000'
Aviation Weather (page 52) gives some guidance regarding atmospheric stability, which can be estimated by observing how
the temperature decreases with altitude:
When temperatures decrease uniformly and rapidly as altitude increases (approaching 3°C per 1000'), you
have an indication of unstable air.
If the temperature remains unchanged or decreases on slightly with altitude, the air tends to be stable.
If the temperature increases with altitude through a layer -- an inversion -- the layer is stable and convection
is suppressed. Air may be unstable beneath the inversion.
When air near the surface is warm and moist, suspect instability. Surface heating, cooling aloft, converging or upslope winds,
or an invading mass of colder air may lead to instability and cumuliform clouds.
Instability is shown in the figure as a dotted line between altitudes
under the temperature data item, when the temperature
decreases more than 3°C per 1000'. See the line, for example, between 24000 and 30000 in the 6hr report.
Note that these are merely a forecast and local wind direction and speed can vary widely. When getting a Weather Brief, you may get more current
information, but also as your briefer for PIREPs which may be directly relevant for your flight path.
AvnWx.com currently provides Winds and Temperatures Aloft data as obtained from Aviation Weather Center NWS Textual FB Winds/Temps Aloft product,
covering only Continental US and Alaska. Hawaii and Pacific Ocean data is under development.
Information on this page is derived from NWSI 10-812, AC 00-45E, and NOAA's Aviation Weather Center website.
For further information, see: