The impact of MODIS SST composites on short-term regional forecasts

The NASA Short-Term Prediction Research and Transition (SPoRT) Center seeks to accelerate the infusion of NASA Earth science observations, data assimilation and modeling technologies into NWS forecast operations and decision-making at the regional and local levels. The SPoRT Center produces 1 km Moderate Resolution Imaging Spectroradiometer (MODIS) sea surface temperature (SST) composites, which can be used in numerical weather prediction (NWP) models. Current operational NWP models use the Real-Time Global SST (RTG-SST) field, which is produced at approximately 50 km resolution. Mesoscale features, such as precipitation and cloud fields, are observed along strong SST gradients off the Florida coast. These gradients are better defined in the high resolution MODIS SST composites. The scientific hypothesis of this project is that accurate specification of the lower-boundary forcing (i.e., the specification of localized SST gradients and anomalies) within the Weather Research and Forecasting (WRF) prediction system will result in improved land/sea fluxes and hence, more accurate evolution of coastal mesoscale circulations and the sensible weather elements (i.e., low-level horizontal transport, temperature trends, clouds, and precipitation) associated with them. The region of study includes the coastal zones of Florida and Northern Gulf of Mexico.

The WRF domain uses a 500x500 2 km grid centered on the Florida peninsula. A 20 km Forecast Systems Laboratory (FSL) Rapid Update Cycle (RUC) analysis is used as the background field for the Advanced Regional Prediction System (ARPS) Data Analysis System (ADAS). ADAS creates an analysis using the Bratseth successive correction technique, and this analysis initializes a 3h WRF forecast. During these three hours, the WRF boundary layer adjusts to the underlying SSTs. The 3h forecast becomes the new background field for an ADAS analysis, which provides the initial conditions for a 24h WRF forecast. This cycle is completed daily for the month of May 2004. Each day contains both a control forecast using the RTG-SST field and one with the MODIS SST composite.

This presentation will show the verification of the 24h WRF forecasts. Specific areas of interest will include the timing and position of sea breeze circulation using both subjective and objective techniques. Satellite imagery and radar data will be compared to forecasted clouds and precipitation both inland and over SST gradients. The height of the marine boundary layer will be examined to determine the impact of the modified SSTs. Finally, buoy observations of air temperature and winds will verify forecasts over the ocean. Both general results for the month of May 2004 and specific examples will be included.