Wednesday, 15 May 2002: 9:45 AM
Cloud/hydrometeor initialization in the 20-km RUC using GOES and radar data
Accurate initialization of cloud and hydrometeor fields can have a significant effect not only on cloud and explicit icing forecasts, but also on precipitation, precipitation type, and even surface temperature. One of the main innovations in the 20km RUC, being implemented at NCEP in early 2002, is the inclusion of assimilation of GOES cloud-top pressure to modify RUC 1-h hydrometeor forecasts. Close scrutiny of real-time test RUC20 forecasts during 2001 led to important modifications upon the RUC cloud analysis technique reported on at previous Aviation conferences. These include techniques for rederiving cloud-top pressure in the lower troposphere using RUC 1-h temperature profiles, establishing marine stratus in a more accurate manner, and a more correct treatment for scattered convective clouds. All of these techniques were designed to handle limitations in the GOES cloud-top product. The RUC cloud analysis was also changed to handle single field-of-view data, now used instead of the previous 3x3 field-of-view data. The RUC is the first NCEP operational model to include clearing and building of explicit hydrometeor fields in its assimilation.
Current verification of RUC-20 and RUC-40 (without cloud assimilation) cloud forecasts shows a fairly consistent improvement for the RUC-20 not only for very short-range 1-3h forecasts but also at the 12-h range.
In the paper, the RUC cloud analysis technique will be carefully described, and recent verification results and case studies will be presented. Finally, initial results from addition of radar reflectivity to the RUC cloud/hydrometeor analysis will be shown.