Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Thu Jul 16 2020 Valid 171200Z - 181200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF SOUTHEAST ND...FAR NORTHEAST SD AND WESTERN/CENTRAL MN... ...SUMMARY... Severe thunderstorms are expected across portions of the northern Plains into the Upper Midwest Friday afternoon into early Saturday morning. At this time, damaging wind gusts and hail appear to be the primary hazards associated with this activity. A more conditional threat for a few tornadoes also will exist. ...Northern Plains into the Upper Midwest... Forecast guidance has been fairly consistent the past several cycles bringing a compact shortwave impulse embedded in a larger-scale upper trough across the northern Plains and Upper Midwest Friday afternoon into early Saturday. At the surface, low pressure will develop eastward across the Canadian prairies and a trailing cold front will shift eastward from eastern MT into the Dakotas and MN during the forecast period. Ahead of the surface front, strong southerly low level flow will transport rich boundary layer moisture poleward. Combined with evapotranspirative process, surface dewpoints in the mid 60s to low 70s seem reasonable. A plume of steep midlevel lapse rates will also overspread the region, and aided by strong boundary layer heating, MLCAPE values from 3000-4000 J/kg appear likely. Vertically veering wind profiles will result in 35-45 kt effective shear. Vigorous thunderstorm development is expected by mid-to-late afternoon across central ND, quickly becoming well-organized and severe. Storm mode, at least initially, remains a little uncertain. Shear and thermodynamic profiles will support supercells, but how long convection remains discrete is in question. Forecast soundings indicate large, curved hodographs with effective SRH between 250-300 m2/s2 and mean mixing ratio values greater than 16 g/kg. Any discrete supercells that do develop, and maintain discrete characteristics certainly would pose a threat for damaging wind, large hail and a few tornadoes. Eventually, upward development into a forward-propagating bow is expected, given strong frontal forcing and an increasing southwesterly low level jet during the evening. This should result in a move widespread damaging wind threat as convection tracks east/southeast along the instability gradient from the eastern Dakotas into MN. Widespread severe gusts are possible given the forecast extreme instability, steep low level lapse rates amid PW values from 1.5-2.0 inches, and model indications of a well-developed cold pool. ..Leitman.. 07/16/2020Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_0600.html
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