Mesoscale Discussion 1675 NWS Storm Prediction Center Norman OK 0753 PM CDT Sat Sep 05 2020 Areas affected...Southern MN...Northern/Eastern IA Concerning...Severe potential...Watch likely Valid 060053Z - 060300Z Probability of Watch Issuance...80 percent SUMMARY...Deep convection will develop across southern Minnesota over the next few hours. Large hail is likely with the strongest storms. Severe thunderstorm watch will likely be issued by 03z. DISCUSSION...Early-evening water-vapor imagery clearly depicts a mid-level vorticity max over southeast SK, now digging southeast after topping the western US Ridge. This short-wave trough will provide large-scale background support for organized convection later this evening. 00z soundings from MPX and ABR were quite dry this evening with meager buoyancy, but strongly sheared. However, OAX exhibited 1.3 inch PW with a 14C 850mb dew point. 20kt southwesterly 850mb wind should increase into southern MN by 04z as LLJ strengthens to near 40kt in response to the approaching short wave. Substantial moisture advection will be both necessary and likely over the next few hours before elevated convection materializes. While it's not entirely clear when elevated convection will develop, latest thinking is thunderstorms will likely develop quickly as moisture rushes northeast ahead of the digging mid-level speed max, possibly as early as 03z. Steep lapse rates and long, straight hodographs favor large hail. ..Darrow/Hart.. 09/06/2020 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DVN...ARX...MPX...DMX...FSD... LAT...LON 45659540 44799281 42719065 41739220 44279655 45659540Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/md/md1675.html
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