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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.

Wednesday, September 15, 2021

SPC Sep 15, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0244 PM CDT Wed Sep 15 2021 Valid 152000Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF NEW ENGLAND...NEW YORK...AND PENNSYLVANIA... ...SUMMARY... Severe thunderstorms capable of damaging winds, severe hail and an isolated tornado or two are expected across the Northeast States and New England. An isolated tornado risk will also exist across parts of the middle Gulf Coast. ...20Z Update... ...Northeast... Potential for strong to severe thunderstorms continues ahead of the cold front moving across the Northeast. Latest surface analysis places this front from northwest ME southwestward across northern NH, central VT, central NY, and central PA. As mentioned in MCD 1756, a narrow corridor of increasing severe potential exists from far northern NJ into MA ahead of ongoing strong/severe convection further to the north/northwest. Severe Thunderstorm Watch 503 was recently issued to cover this threat. Primary severe threat is damaging wind gusts. The severe threat continues in the eastern portions of Severe Thunderstorm Watches 501 and 502 (i.e. western ME into central PA), with damaging wind gusts remaining the primary severe threat. ..Mosier.. 09/15/2021 .PREV DISCUSSION... /ISSUED 1107 AM CDT Wed Sep 15 2021/ ...Northeast... Water vapor imagery shows a low-amplitude and progressive upper trough moving across the Great Lakes region toward the northeast states. An associated cold front currently over parts of eastern OH/KY will sweep eastward today, providing the focus for numerous showers and thunderstorms. Relatively strong daytime heating is occurring ahead of the front, where dewpoints in the mid/upper 60s and afternoon temperatures in the 80s will yield MLCAPE values of 1000-2000 J/kg. Forecast soundings show deep and strong southwesterly flow, aiding in the organization and intensity of storms. Present indications are that primary severe threat will begin soon (refer to WW 501) and spread across parts of PA/NY and New England through the afternoon and early evening hours. Damaging winds will be the main threat with the line of storms, but severe hail is also possible given the favorable CAPE fields. A tornado or two is also possible - mainly over New England - where low level wind shear is forecast to be strongest. Storms should weaken after dark as they move into southern New England. ...Lower MS Valley... The remnant circulation of Nicholas is moving slowly eastward across southern LA. Scattered convection to the east of the low is in a region of moderate low-level vertical shear, with local VAD profiles indicating 0-3km SRH values of 150-250 m2/s2. This may be sufficient for a few rotating cells this afternoon and evening, posing a risk of a tornado or two. Read more LIVE: spc.noaa.gov