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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.


Tuesday, August 31, 2021

SPC Aug 31, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1229 PM CDT Tue Aug 31 2021 Valid 011200Z - 021200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID-ATLANTIC... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS... ...SUMMARY... Several tornadoes and scattered damaging winds appear probable across parts of the Mid-Atlantic as the remnants of Ida move through the region on Wednesday. Isolated to scattered severe storms may also occur across portions of the northern Plains. ...Mid-Atlantic into Southern New England... Tropical cyclone Ida will move northeastward from the central Appalachians across the Mid-Atlantic on Wednesday, eventually reaching near the southern New England Coast late Wednesday night. A very moist low-level airmass, with low to mid 70s surface dewpoints, will likely exist ahead of Ida across much of the Mid-Atlantic to the south of a surface boundary. This boundary is forecast to lift northward as a warm front through the day across MD/DE and into parts of southeastern PA and southern/central NJ. Compared to prior days, better diurnal heating should occur across the warm sector as Ida begins to transition to an extra-tropical cyclone. Some guidance suggests the potential for 1000-2000 J/kg of MLCAPE to develop ahead of any ongoing rain bands Wednesday morning as surface temperatures warm into the upper 70s and 80s. The strongest mid-level winds and related deep-layer shear associated with Ida's remnant circulation are forecast to be present across mainly the northern portions of the Mid-Atlantic, from roughly northern VA and MD/DE northward. A broader swath of strong southerly low-level winds should be in place from portions of the central/eastern Carolinas across the Mid-Atlantic. Related enhancement to 0-1 km shear will likely focus from parts of central/northern VA northward to the vicinity of the warm front Wednesday afternoon/evening. Current expectations are for multiple supercells to develop Wednesday afternoon in this favorable thermodynamic and kinematic environment while posing a threat for several tornadoes. This threat appears greatest in the vicinity of the warm front Wednesday afternoon/evening, and tornado probabilities have been increased to account for this potential. Farther south across central/southern VA into the Carolinas, low-level shear is forecast to quickly drop off during the day. Still, multiple clusters of storms that should develop may pose a threat for damaging winds through much of the afternoon, as mid-level flow will remain modestly enhanced. Finally, low probabilities for strong/gusty winds and a tornado or two have been expanded northward into southern New England. A very strong low-level jet across this region Wednesday night and weak boundary-layer instability may support an isolated severe threat as storms move quickly east-northeastward through the end of the period. ...Northern Plains... An upper trough/low is forecast to move from the northern Rockies and adjacent High Plains east-northeastward into central Canada on Wednesday. Downstream upper ridging over much of the Plains should slowly shift eastward through the period. A low-amplitude shortwave trough should move northeastward from the central Rockies across the northern Plains by Wednesday evening, and a surface lee trough is forecast to sharpen across this region. Rather warm mid-level temperatures and a substantial cap will likely inhibit convective development through much of the day along/east of the surface trough. Still, nearly all guidance suggests that isolated to scattered storms will develop Wednesday evening from parts of the NE Panhandle northeastward into western/central SD as a southerly low-level jet strengthens. Steep mid-level lapse rates and a seasonably moist low-level airmass will both contribute to a narrow corridor of at least moderate instability where storms are forecast to develop. Strong deep-layer shear will likely support supercells posing a threat for mainly large hail initially. Some clustering may occur late Wednesday evening, but increasing convective inhibition and tendency for storms to become elevated suggest that the threat for severe wind gusts will probably remain isolated. ..Gleason.. 08/31/2021 Read more LIVE:
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CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)