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Weather conditions directly above are near Lakefront. Top tabs refer to O'Hare (official).

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.

Friday, August 26, 2022

SPC Aug 26, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Fri Aug 26 2022 Valid 262000Z - 271200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NEW ENGLAND... ...SUMMARY... Isolated to widely scattered strong to severe thunderstorms remain possible possible across parts of the Northeast and northern High Plains this afternoon and evening. ...20Z Update... Severe probabilities have been trimmed behind ongoing convection across New England. Both isolated large hail and scattered damaging winds will remain possible with this activity as it spreads eastward towards the Atlantic Coast over the next few hours. For more information on the near-term severe threat across this area, see Mesoscale Discussion 1723. Across the northern High Plains, the Marginal Risk was expanded westward to include more of eastern MT to account for ongoing strong thunderstorms that have developed this afternoon. Even with deep-layer shear remaining fairly modest over this region, convection should pose an isolated severe risk through this evening as it encounters greater low-level moisture along/near a surface trough across eastern MT/WY into the western Dakotas. Recent visible satellite and radar imagery shows a well-defined MCV over northeastern SD and southeastern ND. This feature is forecast to continue moving slowly northeastward toward MN this afternoon and evening. While a conditional severe threat remains evident across east-central SD given a favorable shear profile through mid levels, the prospect for surface-based thunderstorms still appears rather low. Have therefore not included a Marginal Risk with this update. ..Gleason.. 08/26/2022 .PREV DISCUSSION... /ISSUED 1111 AM CDT Fri Aug 26 2022/ ...Northeast this afternoon/evening... Embedded speed maxima will progress eastward from the lower Great Lakes to New England, within the southern portion of a broad belt of cyclonic mid-upper flow over southeast Canada. Likewise, a weak surface cyclone will move eastward from the Saint Lawrence Valley to ME by early tonight, as a trailing cold front moves southeastward across PA/NY/Southern New England. Scattered, slightly elevated thunderstorms are ongoing this morning over eastern NY in association with a lead shortwave trough. Surface heating and boundary-layer dewpoints in the mid 60s east of this convection and a pre-frontal trough will result in destabilization and will support surface-based thunderstorm development by early afternoon. Clusters and short line segments will subsequently spread eastward across New England in an environment of moderate buoyancy (MLCAPE of 1000-2000 J/kg) and vertical shear (effective bulk shear of 30-35 kt with modest hodograph length/low-level clockwise curvature). Occasional damaging gusts will be the main threat, though marginally severe hail and an isolated tornado will be possible. Isolated strong cells may occur farther west across NY this afternoon, near and east of the cold front, with more veered low-level flow and weaker vertical shear. ...Northern High Plains late this afternoon/evening... A weak midlevel trough will continue moving eastward over MT through this evening, and it will be preceded by a convectively-enhanced trough/MCV moving east-northeastward over SD. The southern fringe of the SD MCV will coincide with a corridor of boundary-layer dewpoints in the 60s along a warm front, but it is not clear that additional (surface-based storms) will form this afternoon across eastern SD. Otherwise, surface heating and residual 55-60 F dewpoints along a weak lee trough (in the zone of ascent downstream from the midlevel trough) will support afternoon/evening thunderstorm development from eastern MT into northeastern WY. Steepening low-midlevel lapse rates and deeper mixing across WY/MT will support the potential for isolated severe outflow winds/hail. Convection will tend to become elevated and will weaken with time while moving eastward into weakening buoyancy and larger convective inhibition across the Dakotas late this evening into tonight. Read more CHECK UPDATE ZOOM GRAPHIC
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