Development of a radar based thunderstorm climatology for North Dakota

Traditionally thunderstorm climatologies have been derived using either surface station data or damage reports from the National Climatic Data Centre's (NCDC) storm events database. The use of either of these sources of information tends to lead to results that are biased towards either the surface station locations or areas where there are concentrations of population, such as large urbanized centres. In an attempt to eliminate some of these shortcomings we explore the use of WSR-88D radar data to develop a thunderstorm climatology for the state of North Dakota that allows both temporal and spatial variations to be explored as a precursor to developing a thunderstorm risk model for the area. Level III storm structure data files for the period 2002-2006 for the three WSR-88D radar stations in North Dakota at Bismarck (KBIS), Grand Forks (KMVX) and Minot AFB (KMBX) were downloaded from the NCDC's HDSS mass storage system and processed to create separate thunderstorm cell databases for all three stations, as well as a combined database.

Analysis of the resulting individual and combined databases found very clear seasonal and diurnal variations in the observed thunderstorm cell characteristics, including the frequency, duration, intensity as measured by the maximum reflectivity, and heading. Comparison with surface data from eight ASOS stations in North Dakota over the same time period showed a good match with those seasonal and diurnal parameters that were directly comparable such as frequency. Although the hope was that by using radar data more insight into the spatial variability of thunderstorms in North Dakota could be obtained, the results were somewhat inconclusive and require further study to determine how much of the resulting variability is due to limitations in the radar data itself and how much is due to the underlying climatology of thunderstorms in this area.