The Aviation Weather Center (AWC) has the responsibility, as part of the World Area Forecast Center, Washington, to provide global weather forecasts of significant weather phenomena. Presently, the AWC produces High Level Significant Weather charts covering two thirds of the globe, both northern and southern hemispheres that are issued four times per day.

More recently the Aviation Weather Center has accepted the responsibility for routinely providing a Mid Level Significant Weather chart, between FL100 and FL450, for the North Atlantic Ocean Region (NAT). The NAT chart implementation is scheduled for Sept 15, 2003 with 0600Z forecast.

The presentation of significant weather on the mid level significant weather chart is similar in many respects to that on High Level Significant Weather charts. The detail required however is more extensive because the bottom of the chart is now at FL100 instead of FL250. Aircraft flying at these lower levels in the atmosphere, below FL250, will more likely encounter larger areas of icing and turbulence.


The North Atlantic Mid Level Significant Weather chart will be transmitted along with the High Level Significant Weather charts. Transmission times for forecast packages are:

Package Issue Time
24 hour forecast package valid at 00Z 08Z
24 hour forecast package valid at 06Z 14Z
24 hour forecast package valid at 12Z 20Z
24 hour forecast package valid at 18Z 02Z

The information placed on the Mid Level Significant Weather chart will be the combination of information imported from the corresponding High Level Significant Weather chart and additional information generated by the meteorologist specifically for the Mid Level chart.

WAFS Significant Weather (SIGWX) Data in BUFR


This document has been prepared by the World Area Forecast Centres (WAFCs) for the purpose of providing guidance to software developers who have the task of constructing WAFS SIGWX BUFR visualisation software. The document is designed to assist developers in the construction of compliant visualisation software that receives its data input from text files obtained from BUFR decoding software.

Forecast Elements

The Mid Level chart will include the following information:
Thunderstorms and Surface frontal positions and movement      a) Thunderstorms and Surface frontal positions and movement;

     b) Jet streams; Jet streams
* Jet Depth: The vertical depths to the 80 knot wind field above and below the jet steam using flight levels. Jet stream vertical depth forecasts are included when the maximum speed is 120 knots or more. More details ...

Tropopause heights      c) Tropopause heights;

     d) Tropical Cyclones; Tropical Cyclones

     e) Moderate or Severe Icing;

     f) Moderate or Severe Turbulence
         (in cloud or in clear air);


Volcanic Eruptions      g) Volcanic Eruptions;

     h) Widespread Sand Storms/Dust Storms; sand or dust storms
     i) Release of Radioactive Materials; Radioactive Materials

To Receive the North Atlantic Mid Level Chart

The Aviation Weather Center provides dissemination via its International Flight Folder Documentation Program. To receive this chart via automated facsimile service call 877-280-2811 and request document number 2135.

You may also provide comments on this sample chart. Send comments to: .

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