Impact of Microphysical Uncertainty on the Practical Predictability of the 10 August 2020 Midwest Derecho with the Assimilation of All-Sky Infrared Radiances

The 10 August 2020 midwest derecho is the costiliest severe thunderstorm events in United States history. This study examines the impact of using different microphysics schemes during the EnKF cycles that assimilates all-sky infrared radiances from GOES-16 and the subsequent forecasts on the forecast errors of the derecho and associated hazards. Because the different partitioning of hydrometeor types and different behaviors between these hydrometeors, the vertical distributions of ice and liquid hydrometeors show vast differences across the microphysics schemes, when all of them show similar (indistinguishable) cloud features after the assimilation of the all-sky infrared radiances. These differences also lead to changes in the structure of the derecho, particularly the structure of the leading convective line and the depth and strength of the cold pool, which lead to different characteristics of the rear-inflow jet and subsequently the severity of the surface gusts. When different microphsyics schemes are mixed during the data assimilation stage and the forecast stage, it shows that the microphysical uncertainties during the data assimilation stage is the more important contributor to the subsequent forecast errors, while varying the microphysics schemes based on the same data assimilation analyses lead to relatively smaller changes in the forecasts. The results suggest the importance of considering and quantifying the impact of microphysical uncertainties in future data assimilation applications when all-sky infrared and microwave radiances are used.