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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, July 25, 2023

SPC Jul 25, 2023 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1258 AM CDT Tue Jul 25 2023 Valid 251200Z - 261200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF THE NORTHERN PLAINS AND THE MID ATLANTIC... ...SUMMARY... Scattered severe wind/hail-producing thunderstorms are possible across parts of the Northern Plains and the Northeast this afternoon and evening. Isolated severe gusts are also possible over portions of the Interior West. ...Synopsis... A stationary upper ridge will center over the southern Rockies today, with multiple mid-level troughs expected to traverse the periphery of the ridge, supporting regimes favoring strong to severe storms. Monsoonal moisture trapped near the upper ridge over the Interior West will support scattered thunderstorm development by afternoon peak heating. Storms along the periphery of the ridge over the central/northern Rockies will benefit from stronger upper flow from a passing mid-level trough, with isolated strong to severe storms possible. Farther east across the northern Plains, a small but pronounced mid-level trough will rapidly approach the Upper MS Valley, supporting the development of severe thunderstorms amid a buoyant and sheared airmass. Finally, strong to potentially severe thunderstorms may also develop across portions of the Northeast ahead of an upper trough. ...Northern Plains... With afternoon heating, surface temperatures are expected to exceed 90 F amid upper 60s to near 70 F dewpoints. When overspread by 8+ C/km mid-level lapse rates, MLCAPE may exceed 3000 J/kg on a widespread basis. However, given a somewhat dry surface-700 mb layer, stronger than -100 J/kg of MLCINH will also be present, with most of the CAPE (albeit wide) constrained above 700 mb. Nonetheless, persistent warm-air advection and deep-layer ascent from the rapidly approaching mid-level trough will support convective initiation across portions of the central and northern Plains by afternoon peak heating. Elongated hodographs suggest that multicellular clusters should be the dominant mode of convection, though a couple of supercells are also possible. Large hail will be possible with the initial modes of convection. Low-level shear is not expected to be overly strong, and storm/cold-pool mergers may support the development of one or more MCSs by evening. Should this occur, severe wind gusts will become the primary concern. ...Mid-Atlantic into New England... A mid-level trough will gradually overspread the East Coast through the day, with surface lee troughing becoming established east of the Appalachians by afternoon peak heating, serving as the impetus for convective initiation. Across the Mid Atlantic, a plume of steeper (i.e. 7+ C/km) mid-level lapse rates will reside ahead of the surface lee trough, fostering over 2000 J/kg MLCAPE amid elongated hodographs. Organized multicells and perhaps supercells should develop, accompanied by a severe wind/hail threat. Farther northeast into parts of the Hudson Valley and New England, mid-level lapse rates should be less steep (i.e. 5.5-6 C/km), supporting tall and thin CAPE profiles. Nonetheless, the troposphere should be relatively uncapped in the presence of elongated hodographs. Multicells will be possible from the Hudson Valley and points northeast, where a couple of damaging gusts may accompany the stronger storms by afternoon peak heating. ...Utah to Montana... Stronger mid-level flow traversing the periphery of the upper ridge will support elongated hodographs from portions of western Utah into central Montana by afternoon. Storms developing from the heating of monsoonal moisture in this regime will have the potential to become somewhat organized and longer lived compared to storms meandering in the weaker tropospheric flow farther southeast. A couple of severe gusts may accompany the stronger, longer-lived storms, warranting the introduction of Category 1 (Marginal Risk) probabilities. ..Squitieri/Broyles.. 07/25/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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