{{refimprove, date=June 2010
SIGWX is a Significant Weather Chart defined by
ICAO
The International Civil Aviation Organization (ICAO ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international sch ...
.
Weather charts being issued by World Area Forecast Centres (from meteorological offices in London and Washington), presenting the most important meteorological phenomena relevant especially for air traffic transport. WAFC publishes them in two formats
*
BUFR The Binary Universal Form for the Representation of meteorological data (BUFR) is a binary data format maintained by the World Meteorological Organization (WMO). The latest version is BUFR Edition 4. BUFR Edition 3 is also considered current for op ...
code
*
PNG
Portable Network Graphics (PNG, officially pronounced , colloquially pronounced ) is a raster-graphics file format that supports lossless data compression. PNG was developed as an improved, non-patented replacement for Graphics Interchange ...
images
Charts are typically being issued every six hours (0, 6, 12, 18
UTC
Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...
). The SIGWX charts only show the forecast for the specific hour, however it is common place for parameters such as the JetStream, CAT & CB to be interpreted +/- 3 hours of the chart validity time. . Prognoses are typically prepared for two ranges of heights:
* SWH - High Level SIGWX (
Flight level
In aviation, a flight level (FL) is an aircraft's altitude as determined by a pressure altimeter using the International Standard Atmosphere. It is expressed in hundreds of feet or metres. The altimeter setting used is the ISA sea level pressur ...
250-630)
* SWM - Medium Level SIGWX (
Flight level
In aviation, a flight level (FL) is an aircraft's altitude as determined by a pressure altimeter using the International Standard Atmosphere. It is expressed in hundreds of feet or metres. The altimeter setting used is the ISA sea level pressur ...
100-450)
Weather phenomena:
* Cloud - including information about cloud type, height of base and top, turbulence and icing risk
* Clear Air Turbulence - including base and top height, strength of turbulence
*
Jet Stream
Jet streams are fast flowing, narrow thermal wind, air currents in the Earth's Atmosphere of Earth, atmosphere.
The main jet streams are located near the altitude of the tropopause and are westerly winds, flowing west to east around the gl ...
- including base and top height, wind speed
*
Tropopause
The tropopause is the atmospheric boundary that demarcates the lowest two layers of the atmosphere of Earth – the troposphere and stratosphere – which occurs approximately above the equatorial regions, and approximately above the polar regi ...
Height
* Tropical Cyclone, Sandstorm
* Volcanoes
* Frontal system
IMPORTANT NOTE: Amendment 74 to
ICAO
The International Civil Aviation Organization (ICAO ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international sch ...
Annex 3 (effective 7 November 2007) Amendment 74 to ICAO Annex 3 /ref> eliminated the requirement for depiction of surface fronts and well-defined convergence zones (e.g. ITCZ) on WAFS SIGWX forecasts (in BUFR-code and PNG chart form). WAFC still publishes frontal bulletins, but they contain no data.