Evaluating the usage, performance, and limitations of the WSR-88D Doppler radar system in Alaska

Very little research has been done regarding the use of weather radars in Alaska, not only to localize them for the unique set of environmental phenomena found in Alaska, but also to evaluate their feasibility as reliable data sources in observation-deficient areas. This project sought to help isolate specific areas where the Alaskan radar network has performed well, where its data quality is suspect, and where improvement of the system is desired. Several interviews were conducted with forecasters at all three Alaskan National Weather Service forecast offices, as well as the Alaska River Forecast Center and Alaska Region Headquarters, to learn about perspectives on the radar network. The radars were perceived to excel at detecting weak or otherwise difficult to define boundaries important for forecasting in coastal areas, as well as providing an excellent, real-time capability to monitor volcanic eruptions and their associated ash clouds. Areas where improvement was desired included increasing radar areal coverage, the ability to archive Level II radar data for research purposes, and questionable precipitation estimates. Due to time limitations, the area chosen for the most investigation was the precipitation amount estimates given by various radars. Specific excessive rainfall and flooding cases recommended by local forecasters were evaluated, using three of Alaska's Doppler radars. One-hour, radar-derived precipitation estimates were compared to observed hourly rain gauge data, and WRF model simulations using reanalysis data were also used to “estimate” precipitation from these events. It can be shown that, for river forecasting and flash flooding purposes, radar-derived precipitation estimates very often, though not always, substantially improve upon model forecast estimates. However, even with this improvement, it was found that radar-derived precipitation estimates were rarely accurate within their scale of resolution as compared to rain gauge data, and the error was not consistent from site to site or from event to event. Possible reasons for these errors, particularly with regards to the Alaskan environment, are discussed, as are questions that would require future research.