Notice of Intent to Change MRF MOS Guidance
Effective with the 0000 UTC forecast cycle on May 9, 2001, guidance for the probability of
thunderstorms will be added to the MRF MOS messages. These messages are identified with
WMO headers FEPA20, FEUS21-FEUS26, and FEAK37-FEAK39, and are stored as MEX
products in the AWIPS text data base. The probability of thunderstorm guidance provides
forecasts of the probability of a thunderstorm in a 12- or 24-h period. Because the thunderstorm
guidance was developed from lightning strike data extracted from the National Lightning
Detection Network, guidance is only provided for sites in the contiguous United States (CONUS). The 12-h
probabilities labeled as T12 are valid for periods of 12-24, 24-36, 36-48, ..., and 180-192 hours
after 0000 UTC. The 24-h probabilities are labeled as T24 and are valid 12-36, 36-60, 60-84, 84-108, 108-132, 132-156, and 156-180 hours after 0000 UTC.
During the development, the lightning data were placed on a 48 km grid, and all of the strikes that occurred anywhere in the 48 km grid box were assigned to the center point of the grid box.
This is an areal forecast covering the grid box, and the forecast verifies when a thunderstorm occurs anywhere in the grid box. For the text messages, a nearest neighbor approach was used to match each CONUS MOS site to the closest thunderstorm grid point. More details on the guidance may
be found at the following web sites:
Please note that the techniques used in developing the MRF MOS thunderstorm guidance are
analogous to those used in developing the thunderstorm guidance from the AVN model.
Page updated May 9, 2001