Distribution of Warm Season Precipitating Storms in the Southern Great Plains

We use a multisensor gridded precipitation product to examine the interannual and intraseasonal variability of precipitating storms during the months of April - September of 1996 -2006 in the Arkansas-Red River Basin. We are able to divide the precipitation field into individual storms by designating regions of contiguous precipitation (in space and time). We thus have a record of the size and lifespan of storms responsible for individual precipitation events. Our data set has a total of 519,562 storms whose numbers vary by year and month. Storms are most numerous in the eastern and western extremes but the central part has the most precipitation. We find that the average storm is small with a maximum size under 500 km2 and a lifetime between 1 and 1.5 hours. Storms in August are smaller but longer lasting than those in April. The linear correlation between mean storm size and number of storms per year is -0.77. Assuming all storms to be convective, we can divide the storms into single ordinary thunderstorms, multiple thunderstorms (includes supercells), and Mesoscale Convective Systems (MCS). The MCS are between 1 and 1.5% of all storms but account for about 85% of the precipitation. Nevertheless, the linear correlation between the number of MCS in each six month period and the total amount of precipitation in the period is only 0.42 We looked at the characteristics of storms which occurred in years with modest as well as abundant precipitation. We did not find any specific characteristics common to either years with less precipitation or years with more. A combination of factors controls interannual precipitation variability. In future work we plan to examine the special density of these storms in more detail as well as the initiation and termination times of the storms. We are also interested in storm movement and how it changes over the storm lifetime.