World Area Forecast System (WAFS) - upcoming changes

World Area Forecast Centre (WAFC) London, the UK Met Office, and WAFC Washington National Oceanic and Atmospheric Administration (NOAA) are constantly looking at ways in which the WAFS data sets can be improved and evolve to meet the changing needs of the aviation industry.  These new and improved data sets will contribute towards limiting the environmental impact of air travel, cope with increased traffic and capacity demands and help air traffic management strategies to mitigate against and avoid hazardous weather conditions.      

In addition, with the increasing volumes of weather data and rapid advancement in technology that are taking place, it is essential that meteorological information, including the WAFS data sets can be effectively delivered to, and used by, the aviation community. These changes are largely driven by ICAO’s Global Air Navigation Plan (GANP) and the Aviation System Block Upgrades (ASBU)

WAFS SIGWX Forecasts 

IMPORTANT: There will be changes to the T+24 SIGWX forecasts in November 2024, notably the removal of embedded cumulonimbus clouds and in particular Isolated embedded cumulonimbus (ISOL EMBD CB).

Please read the What will happen to the existing T+24 SIGWX charts and BUFR files and FAQs for further information.

Both WAFC London and WAFC Washington have been working closely together to develop the next generation of WAFS SIGWX forecasts.  This will introduce multi-timestep SIGWX forecasts that span T+6 to T+48 at 3-hourly intervals, and which are produced four times daily.  The SIGWX forecasts will span FL100 to FL600.  Beta data sets are now available on the SADIS API so that users can start getting their systems set up to process and visualise the data. 

SIGWX plot

Benefits of the new SIGWX forecasts

  • Forecasts that extend out to 48 hours ahead to assist with flight planning and situational awareness
  • The ability to see how features move and evolve at 3 hour intervals
SIGWX animation 1 SIGWX animation 2

Labels are not shown on these animations so the movement of features can be seen.  Moderate turbulence areas are light grey, severe turbulence is darker grey.  Moderate icing is light purple, severe icing is darker purple. Cumulonimbus areas (OCNL and FREQ) are the red scalloped areas.  Tropopause contours are in blue (note these are still undergoing final optimisation)”.


  • Forecasts for the time at which a flight is taking place produced from a more recent model run.
WAFS timeline

The diagram above shows how for a flight taking off at 14:00 on 2nd February

  • (A) With the existing SIGWX, you would be limited to using a T+24 forecast, based off the 12Z model on the 1st February.  The forecast would be issued at 18:50 on the 1st February.

  • (B) With the new SIGWX, it would be possible to use the T+6 and T+9 forecasts based off the 06Z model on the 2nd February run.  This forecast would be issued at around 11:30 on 2nd February.

  • (C) With the new SIGWX having forecasts available out to T+48, the first SIGWX forecasts that cover the period of the flight would have been issued at approx. 23:30 on 31st January (based off the 18Z model run on the 31st). 


  • SIGWX forecasts that are fully consistent with the WAFS gridded data.
  • Areas of icing that cover the entire globe (instead of only regionally).

What will the new SIGWX data contain:

The new SIGWX data will be produced in a new IWXXM format (a form of XML) and will contain the following features:

  • Jet streams
  • MOD and SEV turbulence areas, with information on upper and lower flight level affected. The turbulence areas will be based on the WAFS turbulence severity data set.
  • MOD and SEV icing areas, with information on upper and lower flight level affected.
  • OCNL and FRQ cumulonimbus areas, with information on the flight level of the cumulonimbus top.
  • Tropopause height contours
  • Erupting volcano, tropical cyclone, and nuclear release markers.

These forecasts will become operational in November 2024.  Test data sets are available on the SADIS API right now so that meteorological visualisation systems and flight planning software can be set up to process and display the new SIGWX forecasts.

What will happen to the existing T+24 SIGWX charts and BUFR files?

  • The T+24 Medium Level and High Level SIGWX charts will continue to be published until November 2028 on SADIS FTP, after which they will be retired.  The WAFC’s will create them from the new SIGWX data sets.
  • The T+24 BUFR files will be retired in November 2026.
  • There will be some changes to the appearance of the T+24 SIGWX charts:
    • Embedded cumulonimbus areas will not be included, and only areas with a cumulonimbus coverage of 50% or greater (i.e. OCNL and FRQ) will be included. This means that "ISOL EMBD CB" (isolated embedded cumulonimbus) will not be included.
    • Tropopause information on the WAFC produced charts will be shown as contours at 5000ft vertical intervals, instead of as spot heights.
    • On the medium level SIGWX the combined in-cloud turbulence and icing areas will become solely icing areas.
    • Turbulence areas will look a little different as the drawing style will change, and will be based on the WAFS gridded turbulence data set.
  • The BUFR files will remain largely the same, although for the medium level data the “coverage area” of the data may change.  Test data sets will be provided.


This flyer summarises all the upcoming changes. Please share this flyer with users of the WAFS SIGWX charts to make them aware of the changes. 

SIGWX Performance Metrics

Performance metrics for the new SIGWX are currently being compiled, and will be shared in due course.  Please check back in June. WAFC London Performance metrics and WAFC Washington Performance metrics for the underpinning WAFS gridded data sets that the SIGWX is using are already available.

FAQs about the SIGWX data

  • Why are embedded (EMBD) cumulonimbus (CB), and in particular “ISOL EMBD CB” not included in the SIGWX forecasts any more.

The WAFCs do not have meteorological model output that indicates whether cumulonimbus clouds are embedded in other cloud or not. Whether a cumulonimbus is embedded is also a very subjective field, and depends on the pilots viewpoint and flight level.

For this reason the WAFCs will be filing a difference against ICAO Annex 3 to facilitate this change in the SIGWX content.  This means that ISOL EMBD CB will not be provided at all as “isolated” cumulonimbus clouds (less than 50% coverage) are not a criteria for the SIGWX forecast as per Annex 3. Areas where the cumulonimbus clouds are more concentrated with more than 50% coverage  (being OCNL or FRQ in nature) will still be included.

With Amendment 82 to Annex 3 in November 2025 the requirement for EMBD CB in the SIGWX will be removed.

WAFC forecasts are primarily for en-route activities, and modern aircraft have on board radar systems that can identify location of larger precipitation sized water droplets that can indicate the location of heavy rain or thunderstorms in a larger mass of cloud.

The WAFS gridded cumulonimbus data sets should be the primary tool used to identify where thunderstorms may be expected to occur.   

  • Why are cumulonimbus bases not included/shown?

Cumulonimbus bases are almost always below flight level 100 (FL100), and would therefore be below the base that the SIGWX forecast is valid for and marked as “XXX”.  The decisions aviation users make are unlikely to change on the odd occasion that the cumulonimbus base might be FL110 or FL120 , so this field is not part of the new SIGWX data set.

  • Why has CAT changed to turbulence – what is the difference?

The WAFCs upgraded the way in which turbulence is forecast in the gridded WAFS data sets in November 2020, and the algorithm used is able to forecast both clear air turbulence (CAT) and orographic turbulence types. 

  • Where did the in-cloud turbulence field go?

The in-cloud turbulence field was retired as a WAFS data set in early 2021 as its forecast skill was low.  Therefore, there is no WAFS gridded in-cloud turbulence field that can be used in the creation of the SIGWX forecasts.

  • Why is the new SIGWX spanning FL100 to FL600 and not split into medium and high level versions?

The new SIGWX features all contain vertical information and users could, via their meteorological or flight planning software provider, filter the information vertically when creating charts/visualisations from it if they chose to.  This approach gives the maximum flexibility to end users.

  • What will the differences between the EGRR (WAFC London) and KKCI (WAFC Washington) versions of SIGWX be?

Each WAFC uses their own wind and tropopause data in the creation of the jet stream and tropopause height features.  The cumulonimbus, icing and turbulence features are created from the WAFC  blended hazard data sets, and if the blending has successfully taken place those SIGWX features should be identical.  Each WAFC producing their own set of SIGWX products allows resilience in the production system.

  • Why aren’t we providing briefing quality charts on for the new SIGWX forecasts?

For each issue of the T+24 SIGWX products 18 different briefing quality charts are produced.  This would not be sensible for the new SIGWX forecasts which have 15 different forecast timesteps and would require 270 different charts to be handled.  By providing digital data it enables meteorological or flight planning software to display and then create customised charts that suit their user needs in terms of colour schemes, map areas and map projections. 

  • What is IWXXM?

IWXXM is an information model designed for the operational exchange of meteorological information for aviation, which is specified in ICAO Annex 3.  A World Meteorological Organisation task team created the schematron for SIGWX in conjunction with the WAFC’s, and WMO are responsible for the release and publication of the IWXXM schematrons.  They are published by WMO here:  The schema being used for SIGWX can be found in the 2023-1 directory, and is called the “WAFSSigWxFC” schema. 

Probabilistic WAFS forecasts

The WAFC’s are planning to introduce probabilistic WAFS hazard data sets in November 2027, which will then become fully operational in November 2028. 

They are expected to consist of the following:

  • Probability that the Turbulence Severity will have an Eddy Dissipation rate higher than some set thresholds (equating to moderate or greater in intensity)
  • Probability that the Icing Severity will be Moderate or greater in intensity
  • Probability that the cumulonimbus cloud tops will exceed particular height thresholds.
  • Initially there will be 6 turbulence levels, and 5 icing levels provided at a horizontal resolution of 0.5 degrees.  Data will be provided for the 6-hour to 48-hour forecast period at 3-hour intervals.

Some preliminary example plots are shown below:

1) Probability that the Turbulence Severity Eddy Dissipation rate will exceed 0.2.

Probabilistic turbulence

2) Probability that the Icing Severity will be moderate or greater in intensity

Probabilistic turbulence

3) Probability that the cumulonimbus cloud tops will exceed 35,000ft.

Probabilistic CB

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