Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Fri Jul 23 2021 Valid 261200Z - 311200Z ...DISCUSSION... ...Monday/Day 4 to Wednesday/Day 6... The medium-range models keep a large high pressure area in place across much of the western and central U.S. from early to mid week. Northwest mid-level flow is maintained across the Great Lakes and northeastern U.S. At the surface, a moist airmass is forecast to remain in place across the Upper Midwest, where moderate instability appears likely develop each afternoon. Scattered thunderstorms with a severe threat will be possible along the northern edge of the stronger instability each afternoon, from Minnesota and Iowa eastward into the western Great Lakes. The most significant day in the early to mid week time-frame could be from Tuesday into Tuesday night. At that time, the models suggest that a subtle shortwave trough will move southeastward out of southern Canada and into the Great Lakes region. If this happens, the trough could support a more persistent convective cluster during the afternoon and evening, capable of producing wind-damage and isolated large hail. However, uncertainty is considerable at this range due to several factors including timing uncertainties with the shortwave trough. ...Thursday/Day 7 and Friday/Day 8... The large area of high pressure continues to be forecast across much of the central and western U.S. on Thursday and Friday, with northwest mid-level flow located across the Great Lakes. At the surface, a cold front is forecast to move southeastward across the Ohio and Tennessee Valleys. Thunderstorm development will be possible each day along and ahead of the front. Due to a moist and unstable airmass, an isolated wind-damage threat could develop each afternoon. However, deep-layer shear is forecast to be relatively weak suggesting any severe threat would remain localized and could remain marginal. Substantial uncertainty exists concerning the finer-scale details for Thursday and Friday. Read more LIVE: spc.noaa.gov
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