SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0255 PM CDT Mon Jul 26 2021 Valid 262000Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF EAST-CENTRAL MINNESOTA AND NORTHERN WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF VIRGINIA/NORTH CAROLINA... ...SUMMARY... Supercells and bowing structures with large hail and damaging winds are expected this afternoon/evening from eastern North Dakota into northern Minnesota. Other locally severe storms capable of damaging winds will affect portions of Virginia and North Carolina. ...Discussion... Only change this outlook update is to include 5-percent wind probabilities in central OK into far south-central KS. The 18z Lamont, OK raob showed a very unstable airmass with an 18 g/kg lowest 100 mb mean mixing ratio and 3300 J/kg MLCAPE. Despite very weak flow through the troposphere and indicative of a pulse thunderstorm mode, the steepened 0-2 km lapse rates and high PW will favor water-loaded wet microbursts (localized gusts up to 65 mph) with the most intense cores. This activity will diminish by early/mid evening. ..Smith.. 07/26/2021 .PREV DISCUSSION... /ISSUED 1148 AM CDT Mon Jul 26 2021/ ..Eastern ND/MN/northern WI/Upper MI this afternoon into tonight... A broad upper ridge is prominent across much of the CONUS today, with stronger westerly flow stretching from MT to the Great Lakes region. At the surface, a moist air mass with dewpoints in the mid 60s extends as far north as ND/MN, where strong daytime heating will yield MLCAPE values of 1500-2500 J/kg. Deep-layer shear profiles will also be quite strong across this region, with effective shear values around 40 knots. These parameters will result in a conditionally favorable environment for supercells and bowing storm complexes capable of very large hail and damaging winds. The primary forecast uncertainty involves the timing and placement of storms later today. 12z CAM guidance shows considerable diversity, and given the subtle/weak forcing mechanisms, confidence in the 30% hail area is not particularly high. Nevertheless, a few HREF members continue to indicate an active convective day over the SLGT/ENH risk area, so will leave risk areas mostly unchanged. ...VA/NC... A hot and very humid low-level air mass is present today over southern VA and northern NC, with dewpoints in the mid 70s. Strong heating will result in an axis of MLCAPE over 2500 J/kg from western NC into south-central VA, where scattered afternoon thunderstorms are expected. Vertical shear is not particularly strong, but may be sufficient for a few convective clusters to become organized and pose a risk of damaging winds and hail. Activity will persist into the early evening and the onset of diurnal cooling. ...Northern New England... Moderately strong west-northwesterly mid-level flow stretches across the northeast states today, where mostly clear skies are present. This will allow for the development of relatively steep low-level lapse rates. Isolated thunderstorms are expected to form over the region, and across eastern ON/QB and move across the MRGL risk area. The strongest cells could produce locally gusty winds. ...NV/UT... The corridor of enhanced mid-level winds has shifted northward into NV/UT today. Yesterday's convection over this region may limit high temperatures somewhat and lessen the damaging wind potential. But given the mostly clear skies and consistent forecast of an axis of thunderstorm development later today, will add a MRGL risk for locally damaging winds.
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