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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.


Wednesday, June 30, 2021

SPC Jun 30, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0251 PM CDT Wed Jun 30 2021 Valid 302000Z - 011200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR EASTERN NY INTO PARTS OF NEW ENGLAND... ...SUMMARY... Scattered damaging winds are expected from eastern Ohio into Pennsylvania, New York and New England through the afternoon and evening. ...Discussion... Only minimal changes have been made to the previous convective outlook and each of these changes are related to convection moving through an area and associated convective overturning/stabilization. ..Smith.. 06/30/2021 .PREV DISCUSSION... /ISSUED 1130 AM CDT Wed Jun 30 2021/ ...Northeast this afternoon/evening... A midlevel trough over QC/ON is in the process of digging southeastward, as a series of embedded speed maxima eject eastward through the base of the trough, from the upper Great Lakes to northern New England. An associated surface cold front will move slowly southward into northern NY/New England, but the primary foci for thunderstorm development this afternoon will be a differential heating zone and pre-frontal trough from NY into New England. This corridor will lie along the southern periphery of the stronger (40-50 kt) midlevel flow, where surface heating will boost afternoon temperatures near or above 90 F with boundary-layer dewpoints in the upper 60s to lower 70s. Though midlevel lapse rates will not be steep, MLCAPE will still reach or exceed 1500 J/kg with minimal convective inhibition by early-mid afternoon. Thunderstorm development is expected by midday into mid afternoon along the aforementioned boundaries, as well as along an outflow boundary across down east ME. The combination of moderate buoyancy, steep low-level lapse rates, and moderately strong midlevel flow with straight hodographs (effective bulk shear of 35-45 kt) will favor a mix of supercells and organized clusters capable of producing damaging winds, as well as isolated large hail. The convection will spread east-southeastward across NY/New England through the afternoon, prior to the severe threat gradually diminishing late this evening into early tonight. Farther southwest into PA/OH, a little weaker flow/shear and similar buoyancy will support occasional damaging gusts with multicell clusters as the main severe threat this afternoon/evening. ...Southern Upper MI/northeastern WI this afternoon... Strong surface heating is underway with associated destabilization, and a weak midlevel trough is pivoting southeastward toward this area. At least isolated thunderstorm development is expected this afternoon in the corridor of greatest destabilization, and in association with a weak surface trough and local lake breeze boundaries. Buoyancy and vertical shear could be large enough to support low-end supercells and an attendant threat for isolated damaging gusts/marginally severe hail. Read more LIVE:
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