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Friday, July 9, 2021

SPC Jul 9, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 AM CDT Fri Jul 09 2021 Valid 111200Z - 121200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY ACROSS PARTS OF THE SOUTHERN APPALACHIANS INTO THE LOWER OHIO VALLEY...MIDDLE AND LOWER MISSISSIPPI VALLEY AND SOUTHERN GREAT PLAINS...AS WELL AS ACROSS PARTS OF THE SOUTHERN ROCKIES.... ...SUMMARY... Strong storms may impact a corridor from the southern Great Plains into the lower Ohio Valley, portions of the southern Appalachians, as well as the southern Rockies on Sunday, accompanied by at least some risk for severe weather. ...Discussion... The stronger westerlies will remain confined to latitudes near and north of the Canadian/U.S. border, and appear likely to include one modest wave, with several embedded perturbations, progressing east of the Canadian and adjacent northern U.S. Rockies during this period. In the more stagnant southern mid- and subtropic latitudes, it appears that a mid-level high centered near Bermuda may become increasingly prominent, with ridging continuing to build along an axis to its northwest, across the Mid Atlantic Coast states. This will occur downstream of amplified mid-level troughing over the Mississippi Valley, which likely will include one short wave impulse pivoting around the northeastern periphery of a prominent cyclonic circulation centered over Missouri, and another perturbation progressing around the circulation's southwestern/southern periphery. However, there probably will be little net eastward progression of the larger-scale troughing. At the same time, little movement to a persistent, prominent upstream high centered near/east of the southern Sierra Nevada is forecast, though another significant impulse progressing around its periphery across the southern Rockies may contribute to some suppression Sunday through Sunday night. In association with this regime, steep lapse rates will be maintained across the southern Rockies, but the eastward advection of warm well-mixed air off the Rockies and Mexican Plateau will remain cut off. However, a seasonably deep, moist boundary-layer within the warm sector of a weak cyclone associated with the mid-level troughing may still support moderately large mixed-layer CAPE (in excess of 2000 J/kg) with daytime heating. In the presence of modest southwesterly lower/mid-level wind fields, particularly across parts of the southern Great Plains into the lower Ohio Valley, this could contribute to an environment supportive of developing and organizing storm clusters. Severe weather potential, though, will probably hinge considerably on sub-synoptic/mesoscale developments characterized by low predictability at this time frame. ..Kerr.. 07/09/2021 Read more LIVE: spc.noaa.gov