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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.

Thursday, September 16, 2021

SPC Sep 16, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1222 AM CDT Thu Sep 16 2021 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF MINNESOTA...SOUTHEAST SOUTH DAKOTA...AND NORTHERN NEBRASKA... ...SUMMARY... Scattered storms, some producing severe hail and wind, are possible from late afternoon through early tonight across Minnesota and into parts of Nebraska. ...Synopsis... A strong positive-tilt upper trough will move across MT and ND during the day, and toward northern MN overnight. A broad belt of 50+ kt southwesterlies will spread across the Dakotas and MN during the day, along with cooling aloft. At the surface, low pressure is forecast to develop over western NE, with a trough extending northeastward into eastern SD and central MN by 21-00Z. Strong heating will occur south of this boundary, especially over NE and south-central SD, with 60s F dewpoints spreading north across the MO Valley. South/southwest 850 mb flow of 40-50 kt will maintain a warm/moist boundary layer through the period, until the cold front eventually surges southward overnight. Elsewhere, generally rising heights aloft will occur across the Mid Atlantic, with a surface high centered over the Northeast. A few non-severe, afternoon storms are possible over parts of VA and MD where shear will be very weak. ...MN...SD...NE...IA...WI... Early day storms are possible across northern MN toward Lake Superior on the nose of the low-level jet. Elevated MUCAPE in excess of 1500 J/kg is forecast, which may support sporadic hail. Later in the day, heating will occur ahead of the front, maximized from southern SD into NE. A capping inversion will likely inhibit convection across MN for much of the day, but the cap is forecast to break from north to south across MN after 21Z. Storms will form close to 00Z farther southwest into NE. Some of the storms may begin as high based due to the strongly mixed boundary layer, but wind profiles will also be marginally favorable for supercells. Large hail and a few damaging gusts appear likely along the length of the front. Given the steep lapse rates and 200+ m2/s2 effective SRH, a brief tornado or two will be possible in the early stages of development before outflows merge and surge. ..Jewell/Bentley.. 09/16/2021 Read more LIVE: spc.noaa.gov