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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 24, 2021

SPC Sep 24, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0249 PM CDT Fri Sep 24 2021 Valid 242000Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN MA NORTHWARD NEAR THE NH/ME BORDER...AND ACROSS INTERIOR SOUTHERN CA... ...SUMMARY... Isolated wind damage and a brief tornado may occur this afternoon from eastern Massachusetts northward near the New Hampshire/Maine border. Isolated strong-severe wind gusts will also be possible this afternoon across interior southern California. ...20Z Update... ...Eastern MA to the NH/ME border vicinity... Shortwave trough continues to move away from the region while a cold front slowly pushes eastward. Area VAD profiles continue to show strong low to mid-level flow. Buoyancy is weak, but the threat for a few weakly rotating storms capable of damaging wind gusts and/or a brief tornado will persist for the next few hours. ...Interior Southern CA... A few stronger storms have already occurred thus far today, and that trends is expected to continue as storms move southwestward across the higher terrain of southern CA. Primary threat will continue to be strong outflow winds. ..Mosier.. 09/24/2021 .PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Sep 24 2021/ ...Eastern MA to the NH/ME border through mid afternoon... A midlevel shortwave trough will continue moving north-northeastward over NY/western New England through this afternoon, as an associated surface cold front drifts slowly eastward across MA/NH. A narrow warm conveyor belt with some embedded convection will persist through early-mid afternoon from eastern MA northward to near the NH/ME border. Boundary-layer dewpoints in the upper 60s to lower 70s and pockets of surface heating will maintain MLCAPE of 500-1000 J/kg through this afternoon. Effective bulk shear of 30-40 kt and effective SRH near 150 m2/s2 within the warm conveyor belt will be sufficient for embedded/weakly rotating storms. Low-level shear will gradually diminish from south-to-north through the afternoon as the midlevel trough moves northward, with phasing of vertical shear and buoyancy becoming less favorable for rotating storms by later this afternoon/evening. In the meantime, a brief tornado and isolated wind damage will still be possible. ...Interior southern CA this afternoon... A weak midlevel low will drift west-southwestward over southern CA today, and low-midlevel moisture will likewise spreading westward with the midlevel low. Some elevated convection is ongoing this morning from southwest AZ into southeast CA, and scattered thunderstorms are expected this afternoon over southeast CA and interior southern CA, especially over the higher terrain. Typical inverted-v profiles and DCAPE in excess of 1000 J/kg could support isolated strong-severe outflow gusts this afternoon. ...Upper Midwest late this afternoon into early tonight... An midlevel trough over the northern Plains will continue to dig southeastward over the upper MS Valley/upper Midwest through tonight, as an associated surface cold front progresses east-southeastward. Moisture return in advance of the front is quite limited as a result of a prior frontal passage down to the Gulf coast. The threat for damaging winds appears to be quite low as a result of very weak surface-based CAPE in a narrow zone along the cold front this evening from WI into northern IL, and wind profiles will not be particularly strong where buoyancy is relatively larger. Likewise, an isolated strong gust could occur early tonight along the east shore of Lake MI where static stability is a bit lower due to the relatively warm lake waters, but the overall threat for damaging thunderstorm winds is still too low for an outlook area. 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)