6.5 Revisiting sensitivity to horizontal grid spacing in convection-allowing models over the central–eastern United States using a large dataset.
Schwartz, Craig S., and Ryan A. Sobash, National Center for Atmospheric Research
This presentation
will describe results from 497 retrospective, deterministic, 36-h WRF-ARW model
forecasts with 3- and 1-km horizontal grid spacing over the conterminous United
States (CONUS) east of the Rockies, with a focus on next-day precipitation and
tornado forecasts. The 497 cases were chosen based on observed severe weather
events occurring between 2010–2017 and spanned both the warm and cool seasons.
Model surrogates of low-level rotation (such as updraft helicity) indicated
1-km forecasts yielded more accurate next-day tornado forecasts than 3-km
forecasts. Furthermore, 1-km model climatologies of precipitation generally
aligned better with those observed than 3-km climatologies. Regarding
precipitation placement, during the cool season and spring, when large-scale
forcing was strong and precipitation entities were large, 1-km precipitation
forecasts were more skillful than 3-km forecasts. Conversely, during
summertime, when synoptic-scale forcing was weak and precipitation entities
were small, 3- and 1-km precipitation forecasts had similar skill.
These collective results differ substantially from previous work finding 4-km
forecasts had comparable springtime skill as 1- or 2-km forecasts over the
central–eastern CONUS, and hypotheses regarding this disparity will be
described.