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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 22, 2023

SPC Sep 22, 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 1246 AM CDT Fri Sep 22 2023 Valid 221200Z - 231200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHERN AND CENTRAL HIGH PLAINS...AND OVER THE SOUTHERN COASTAL MIDDLE ATLANTIC... ...SUMMARY... Severe thunderstorms are possible across parts of the central and northern High Plains, mainly this afternoon and this evening. A few tornadoes are also possible along the Mid-Atlantic Coast early Saturday morning in association with the approaching potential tropical system. ...Northern/Central High Plains... Strong upper low that has settled into the northern Great Basin will advance into western WY by late afternoon as a 70kt 500mb speed max rotates through the base of the trough to near WY/UT/CO border by 23/00z. Seasonally cold mid-level temperatures (-20C at 500mb beneath the upper low) will spread east in association with this feature, and the exit region of aforementioned jet will overspread the High Plains of eastern WY by early afternoon. Latest model guidance suggests boundary-layer flow will remain decidedly easterly across NE and the Dakotas into eastern WY. As a result, strongest boundary-layer heating will be noted across the higher plateau region of WY immediately ahead of the approaching trough. Forecast soundings suggest convective temperatures will be breached by 19z, and thunderstorms should develop shortly thereafter. Soundings across eastern WY exhibit substantial SBCAPE with steep lapse rates through 8km. NAM 21z forecast sounding for LUS strongly favors supercells with 60kt surface-6km bulk shear. Very large hail may accompany some of this activity as it spreads toward the southern Black Hills region/northwestern NE. Additionally, relatively moist boundary-layer conditions and low LFCs suggest some tornado threat. It's not clear how far this activity will spread east before weakening, as the updrafts will likely decouple from the boundary layer due to much cooler surface temperatures and weaker low-level lapse rates. For this reason have focused higher severe probabilities across the High Plains where stronger surface heating is expected. ...Potential Tropical Cyclone Sixteen... PTC 16, currently located well southeast of the Carolina Coast, is forecast to move north-northwest over the next 24hr, likely intensifying as it approaches the NC Coast early Saturday. As this system intensifies, low-level shear will increase markedly across the southern Middle Atlantic Coast. Probabilities for supercells will increase late, especially after 06Z, along with some risk for tornadoes, primarily east of the low track. Reference for more information on this developing system. ..Darrow/Moore.. 09/22/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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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)