Exploring the Accuracy of the North American Mesoscale Model during Low-Level Jet Influenced Convection in Iowa

摘要

This study analyzed low-level jet (LLJ) influenced overnight convection cases over Iowa. There are two main regimes for LLJ development over the Great Plains. One is when there is an upper-level trough in the western United States, while the other is dominated by an upper-level anticyclone. The forecasts of the twelve kilometer North American Mesoscale model (NAM) were analyzed for accuracy in both regimes and overall. The variables examined were the LLJ peak magnitude, timing, location, and total rainfall produced in Iowa from 0000UTC-1200UTC the day of an event. Although weak underforecasting was found regarding the magnitude of the LLJ with both models, there were no significant shortfalls regarding magnitude, timing, or location for either regime. However, the model runs significantly underforecasted the magnitude and area of rainfall, as all but one model run produced a rainfall maximum that was underforecasted in both LLJ regimes.