SR SSD 2000-20

Technical Attachment


Scientific Services Division*
NWS Southern Region

Medium Range (MRF) Model.

On July 19, 2000, PoP and QPF guidance forecasts were added to the new MRF MOS messages. These messages are identified with WMO headers FEPA20, FEUS21-FEUS36, and FEAK37-FEAK39, and are stored as MEX products in the AWIPS text data base.

The probability of precipitation (PoP) guidance provides forecasts for 12- and 24-hr periods. Except for the stations in the FEPA20 message, the 12-hr PoPs (labeled as P12) are valid for periods of 12-24, 24-36, 36-48, ..., and 180-192 hours after 0000 UTC. For the FEPA20 sites, the 12-hr probabilities are valid for periods of 18-30, 30-42, 42-54, ..., and 186-198 hours after 0000 UTC. The 24-hr probabilities for all sites (labeled P24) are valid 24-48, 48-72, 72-96, ..., and 168-192 hours after 0000 UTC.

The precipitation amount (QPF) guidance forecasts are labeled Q12 and Q24, for the 12- and 24-hr periods, respectively. These catgorical forecasts of amount categories are for the same projections as PoP, except the last forecast period for QPF ends at 156 hr after 0000 UTC. QPF categories are:

0 no precipitation
1 0.01 to 0.09 in
2 0.10 to 0.24 in
3 0.25 to 0.49 in
4 0.50 to 0.99 in
5 1.00 to 1.99 in
6 2.00 inches or greater.

More details may be found at:

Aviation (AVN) Model.

On July 18, 2000, guidance forecasts for ceiling height and total sky cover were added to the new AVN MOS messages. WMO headers for the products are FOPA20, FOUS21-FOUS26, and FOAK37-FOAK39, and they are stored as MAV products in the AWIPS text data base. The guidance provides forecasts of categories of ceiling height and sky cover valid every 3 hr from 6- to 60-hr after 0000 or 1200 UTC, and at the 66- and 72-hr projections. Categories are:


Total Sky Cover

1 less than 200 ft CL-clear
2 200 to 400 ft SC-greater than 0 to 4 octas
3 500 to 900 ft BK - greater than 4 to less than 8 octas
4 1000 to 3000 ft OV - 8 octas
5 3100 to 6500 ft
6 6600 to 12000 ft
7 greater than 12000 ft or unlimited

More details on the new guidance is at:

Also in July, equations to predict the conditional probability of precipitation type (freezing, frozen, or liquid) were implemented, but guidance forecasts will not be displayed in the MOS message until September 1. Details will be provided prior to that time.


* This summary was compiled from information provided by the Techniques Development Lab at NWS Headquarters.