Derivation of Composite Soundings for Severe Weather and Special Weather Statement (SPS) Conditions to Improve the Wind Gust Potential at WFO Miami

The strong wind gusts generated from a severe thunderstorm pose a risk not only to life and property, but to aviation as well. This study analyzes three years of sounding data at WFO Miami and shows that the inclusion of composite soundings for specific conditions (e.g. severe and non-severe) should be used at the time of the convective assessment at WFO Miami to improve the prediction of days with severe wind gusts. This study categorizes the 12z sounding data into (1) days for which the WFO Miami issued Special Weather Statements (SPS) with no severe wind gusts reported by the surface observing networks in the office forecast area, and (2) days that reported severe wind gusts. For the days that reported severe wind gusts, two composite soundings were constructed: one for days observing wind gusts below 58 mph and a second one for days observing wind gusts of 58 mph or greater. The composite soundings were constructed for both the warm and cool season separately. The composite soundings were generated from the average of different soundings into a single sounding. The results of the analysis show distinct differences and characteristics of the upper-air conditions for each of the composite soundings. The comparison of the severe/SPS composite soundings reveals that dry air above 500 mb is needed to generate severe wind gusts in South Florida. In addition, the 800 to 600 mb lapse rate is steeper in the severe composite sounding. For instance, the difference in lapse rates between severe cases with reported winds greater than 70 mph and non-severe cases (gusts <58 mph) is 0.7 C/km. The difference in lapse rates between the days reporting gusts between 58 to 70 mph and the non-severe cases (<58 mph) is 0.5 C/km. Small differences in South Florida are significant when it comes to the convective assessment and are important to forecasters. The composite sounding for the severe cases shows that westerly winds are an important ingredient for the generation of severe wind gusts in South Florida. A detailed analysis of the different convective parameters for each of the composite sounding is presented in this work.