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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.


Friday, September 8, 2023

SPC Sep 8, 2023 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0742 AM CDT Fri Sep 08 2023 Valid 081300Z - 091200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MID-ATLANTIC TO NEW ENGLAND AND PARTS OF THE SOUTH-CENTRAL STATES... ...SUMMARY... Scattered damaging winds and isolated large hail will be possible across parts of the Mid-Atlantic States into New England from mid-afternoon into this evening, and across parts of the South-Central States in multiple rounds through tonight. ...Mid-Atlantic States to New England... Abundant insolation east of the Appalachians combined with a pervasive plume of 60s to low 70s surface dew points will yield a pronounced west/east-oriented gradient in MLCAPE across the region, with peak values approaching 2500-3000 J/kg over the coastal plain. Scattered thunderstorms are expected to develop within the MLCAPE gradient from near the WV/VA border northeast into parts of western New England. With forecast soundings suggesting nearly unidirectional southwest flow will weaken with height from the mid to upper-levels, multicell clustering will dominate. 700-mb winds in excess of 30 kts should be confined from eastern NY to ME should support slightly more organized clustering. Steeper low-level lapse rates from VA to the DE Valley should compensate for the weaker flow and support relatively more prolific downburst potential. In aggregate, scattered damaging winds along with isolated severe hail are expected, mainly from mid-afternoon into the evening. ...Red River and the Sabine Valleys... Elevated convection has persisted for the past several hours in the Ozarks vicinity. During the past few hours, storm-scale consolidation has yielded small cluster growth across western AR. How this activity evolves through late morning into the afternoon is still uncertain. Increasingly negative low-level theta-e advection may be sufficient to decay convection, a signal consistently pronounced within HRRR runs prior to 11Z. Meanwhile, multiple other 00Z HREF members and earlier RRFS runs suggest convection will not weaken and should actually intensify as downstream diurnal heating ensues on a plume of PW values from 1.7-1.9 inches. The 11Z HRRR and 10Z RRFS have trended towards somewhat greater consistency with the 06Z NAM-Nest in suggesting that outflow from this morning's activity will be the main impetus for downstream development across western LA into far southeast TX this afternoon. Scattered damaging winds and isolated large hail will be the main threats. Farther to the northwest along the Red River Valley, record hot temperatures and a deep-mixed boundary layer should support sporadic downbursts from late afternoon to early evening with isolated thunderstorms near the surface front. Some of this activity may try to congeal and grow upscale south-southeast in east TX during the evening into tonight within the persistent northwest flow regime atop the low-level moisture gradient. But low confidence exists in this scenario, with potential effects of the daytime round of storms modulating the downstream environment and ascent. ...Northern High Plains to Black Hills vicinity... A low-amplitude shortwave impulse along the international border over the northern Rockies will move east today. Ascent attendant to this wave will support isolated to scattered thunderstorms focused primarily across southern MT. While there will be MLCIN concerns to the north and east, 35-45 kt effective bulk shear should support a few organized cells capable of isolated severe wind and hail. A more favorable supercell wind profile should exist near the Black Hills, but pronounced MLCIN may inhibit sustained storm development. ...North to central FL... A mid-level low near the FL/GA border should slowly weaken as it drifts south today. Relatively cold mid-level temperatures sampled by the 12Z JAX sounding of -13 C at 500 mb should support enhanced CAPE profiles between 700-300 mb yielding pronounced vertical growth. Effective bulk shear will tend to remain weak, especially near the cold core, suggesting the potential for organized storms is limited. Still, sporadic occurrences of marginally severe hail and wind are possible, mainly this afternoon. ..Grams/Mosier.. 09/08/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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