A four year climatology of simulated convective storms from NSSL WRF

A ~4 year (June 2009 thru April 2013, 12z-12z) climatology of simulated convective storms is constructed from the experimental National Severe Storms laboratory (NSSL) WRF using an object based approach. A limited sensitivity analysis is conducted to test composite reflectivity (CREF) thresholds and storm areas. Choosing slightly higher thresholds (34 vs 30 dBz) reduces storm size but increases the number of storms; however this has very little effect on storm-size spectra for those storms containing hourly maximum updraft helicity values at or exceeding 25 m^2/s^-2. This is indicative of identifying more storm cores using higher thresholds.

Storm attributes are codified in terms of the maximum convective available potential energy (CAPE) and maximum 0-6km shear in the hour preceding the storm. Two-dimensional histograms are constructed in the CAPE-shear parameter space to examine characteristics of the model environment relative to severe weather proxy variables used in the NOAA Hazardous Weather Testbed Spring Experiment. The relationship between hourly maximum variables including updraft helicity (UH), 10-m wind speed, vertically integrated graupel (GR), and updraft speed (UP) are quantified.

Preliminary results indicate that updraft helicity >= 25 m^2s^-2 in individual storms is present nearly fifty percent of the time when simulated storms have 10-m wind speeds >= 20 ms^-1, updraft speeds >= 26 ms^-1, GR >= 35 kg m^-2, and CREF >= 55 dBz. Additionally, storms meeting this UH threshold frequently occur in high deep-layer shear environments (>20 ms^-1) with relatively lower dependence on CAPE. This relationship is modified somewhat for GR and UP where there is more dependence on CAPE especially above 1800 J kg^-1.