The primary objective of the Experimental Warning Program (EWP) is to evaluate the accuracy and the operational utility of new science, technology, and products in a testbed setting in order to gain feedback for improvements prior to their potential implementation into National Weather Service (NWS) operations. A dynamically-adaptive three-dimensional data assimilation (3DVAR) system was introduced real-time as part of the 2011 EWP. During the experiment, NWS forecasters were asked to incorporate the data in conjunction with radar and other multi-sensor products in AWIPS as part of their warning-decision process for both real-time and archive events. Forecasters evaluated the 3DVAR data for wide-range of events across the CONUS including tornadic supercells, severe squall lines, and multicell storms.

The 3DVAR analysis was available to forecasters at 1 km horizontal resolution every 5 min, with a 3-4 min latency, primarily using data from the national WSR-88D network. The products provided included: vertical velocity, simulated reflectivity, vertical vorticity, and 3D wind vectors. Forecasters found the vertical vorticity and updraft products to be the most useful for storm interrogation and quickly visualizing storm trends, often using these tools increase the confidence in a warning decision and/or issue the warning slightly earlier. It was evident to the forecasters that the data was most consistent and reliable when the storm mode was supercellular. Updraft and downdraft intensity and spatial distribution were not as realistic for multicell or shallow convection, particularly when storms were a relatively far distance from a radar. The largest hurdle for realtime use of 3DVAR or similar data assimilation products by forecasters is the data latency, as even 3-5 minutes reduces the utility of the products when new radar scans are already available.