Hydrometeor assimilation using hourly-updated satellite cloud retrievals over North America in the Rapid Refresh

A 3-d hydrometeor assimilation technique developed originally for the Rapid Update Cycle has now been improved and applied over all of North American in the Rapid Refresh, the new hourly-updated assimilation/model in real-time testing toward the planned replacement of the RUC at NCEP in 2010.

As of early August 2009, GOES-based cloud retrievals from NASA Langley Research Center including cloud-top pressure, cloud-top pressure, liquid water path, and ice water path covering North America are assimilated, along with METAR multi-level cloud, visibility, and current weather observations, and 3-d radar reflectivity, correcting a previous 1-h forecast of 3-d multi-species hydrometeor fields. These initial tests as of early August are in an experimental RUC, and will now very soon be applied to the experimental Rapid Refresh, where CONUS-domain GOES cloud retrievals have been assimilated since early 2008. The North American GOES cloud data completely cover the RUC domain, and will cover about 90% of the Rapid Refresh domain. Quality checks for the cloud-top data using 1-h skin temperature forecasts are being modified for application to the arctic region to allow “warm stratus” in which cloud radiative temperatures are much warmer than the underlying surface, a situation not usually observed in the RUC domain over CONUS and southern Canada.

Further improvements to the RR/RUC hydrometeor assimilation were implemented into the operational RUC at NCEP in March 2009, with improved retention of observed hydrometeor data in short-range forecasts. These improvements and current status of hydrometeor assimilation in the Rapid Refresh within the NCEP Gridpoint Statistical Interpolation (GSI) assimilation system will be described in the conference.