This study addresses a goal of MPEX to explore the impacts of assimilating afternoon pre-convective upsonde observations on the analysis of the mesoscale environment, as well as their impacts on subsequent short-term (0-9 h) convection-permitting forecasts. For eight MPEX cases, ensemble data assimilation is performed on a mesoscale (15-km) grid and the resulting analyses are downscaled to produce forecasts on a convection-permitting grid (3-km). The ensembles of forecasts are evaluated through their depiction of radar reflectivity compared to observed radar reflectivity.
Examination of fractions skill scores over eight cases shows that, for four of the cases (18 May, 23 May, 31 May, and 8 June), assimilation of radiosonde observations nearby to subsequent convection has positive impacts on the initiation and early evolution during the first 3 to 4 h of the forecasts (and longer for the 18 May case), even for the smallest resolvable scales of the 3-km grid. For the four cases in which positive impacts near the smallest resolvable scales of the grid are not seen (19 May, 20 May, 27 May, 28 May), analysis of the changes to the pre-convective environment suggests that sub-optimal locations of the soundings compared to the location of convective initiation are to blame. Regardless, aggregate positive impacts on forecasts of convection is apparent when spatial scales larger than individual thunderstorms are examined.
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