High resolution assimilation of CASA X-band and NEXRAD radar data for thunderstorm forecasting

During 2006 a network of four X-band radars were deployed in central Oklahoma as the first integrated project (IP1) of the Collaborative Adaptive Sensing of the Atmosphere (CASA) Engineering Research Center (ERC). The CASA IP1 network has an average radar spacing of about 27 km and is situated midway between the Oklahoma City and Frederick, Oklahoma WSR-88D radars of the NWS/FAA/DoD NEXRAD operational radar network.

In the spring of 2007 the CASA radar data will be combined with other high resolution data, including mesonet observations and satellite imagery, in a near-real-time data assimilation experiment. The CAPS ADAS radar analysis program, including a complex cloud analysis with latent heating adjustment will be used to generate analysis increments on a 2-km resolution grid to be assimilated in the CAPS ARPS non-hydrostatic model using an incremental analysis updating (IAU) assimilation procedure in four consecutive 10-minute cycles (Fig. 1). The afternoon or early-evening starting time of the model will be adapted to the weather, beginning at the time of first echo in the network for systems that develop within the network, or at the time of initial approach to the CASA network for traveling weather systems. A 5.5-hour forward forecast will be made following the data assimilation and compared to actual radar echoes from the CASA and NEXRAD radar networks. Forecasts with CASA and NEXRAD radar data will be compared to those using only NEXRAD radar data and only CASA radar data.

The complete program plan, summary of the weather forecasts, and initial comparative results will be presented at the conference.

Figure Caption: Figure 1. Assimilation timeline for a sample case of storm initiation around 22:00 UTC. Radar and other high resolution data are inserted using IAU every 10 minutes.