Potential for a large outbreak of severe thunderstorms late Friday into Friday night

THEN HIGH NON-T-STORM WINDS EXPECTED TO SWEEP CHICAGO LATE FRI NIGHT INTO SATURDAY WITH POTENTIAL 50+ MPH GUSTS AND A NEW ROUND OF SIGNIFICANT WIND DRIVEN SNOWS ACROSS THE “NORTH WOODS” OF WISCONSIN AND UPPER MICHIGAN

SEVERE WEATHER CONCERNS REMAIN ELEVATED ACROSS A WIDE SWATH OF THE MIDWEST, INCLUDING CHICAGO, FRIDAY INTO FRIDAY EVENING. The Storm Prediction Center indicates a level 3 to 4 risk on the 5 level scale—which is an elevated level of risk

The 11th atmospheric river/”Pineapple Express” storm since Dec 22nd–a system which has swept off the Pacific into California and now the intermountain West–is behind what looks like some rough weather across the Midwest, including the Chicago area.

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  • Wednesday afternoon GOES EAST satellite view of the incoming storm
  • GOES-18 western view of the storm headed for the central U.S. Satellite images courtesy of CIRA/RAMBB
  • 24 hour T-STORM PROBABILITIES off the SREF model covering the period from 1am CDT Friday to 1am CDT Saturday placing t-storm probabilities for Chicago close to 80%
  • Satellite-derived precip
  • STORM PREDICTED CENTER SEVERE WEATHER RISK assessment for Friday & Friday night
  • TORNADO INGREDIENTS forecast for the period within 6 hours of 10pm CDT Friday night
  • Wed morning 250 mb UPPER AIR ANALYSIS from Environment Canada depicting the powerhouse jet with the Western storm system
  • Closer look at 34,000 ft. level upper air conditions at 7am CDT Wed
  • PROJECTED JET STREAM at 10pm CDT Friday
  • Forecast 18,000 ft. VORTICITY PROG showing the powerhouse short wave reaching Chicago around 10pm Friday evening
  • 5,000 ft. (850 mb) forecast winds 10pm Friday. These winds help transport warm, moist tropical air into the Chicago area from the Gulf of Mexico
  • Area projected likely to see lightning in the 6 hours up to 1am CDT Saturday morning
  • FRIDAY HIGH TEMPS–Chicago is to see its warmest temps to date in 2023
  • Friday predicted high temp departures
  • ESTIMATED TOTAL WATER EQUIVALENT PRECIP from a “blend” of National Weather Service models
  • HEAVY, WIND DRIVEN SNOWS are to accumulate across the Upper Midwest
  • Snowfall 8″ or greater
  • Snow 12″ or greater
  • PRECIPITABLE WATER–The total amount of moisture predicted in the lowest 30,000 ft. of the atmosphere–home to more than 80% of Earth’s atmospheric moisture
  • ACTIVE NWS WATCHES
  • Multi-model forecast of wind velocities and wind gusts at Chicago’s lakeshore. NOTE the spike in wind speeds toward Saturday. Those are projected NON-T-STORM wind gusts which may top 50 mph Saturday across the Chicago area

One the positive side, the storm is finally to bring Chicago 60 to 70-degree warmth which has been sadly lacking to date. More than 60% of Chicago Marches have produced a 70-degree temp by now. In fact there had been three days in the 70s by March 29th a year ago.

But the trade-off with the arrival of the warm, increasingly humid air predicted to reach the city with the incoming storm system’s STRONG frontside south winds is the buoyancy on this air. Warm, moist air (dew points on Friday are predicted to rise to some of their highest levels since last October) wants to rise. And as that happens Friday, that air will ascend into powerful wind fields aloft which are likely to rotate the ascending air threatening to produce supercell t-storms over a broad area of the Midwest as indicated by the risk assessment produced by NWS Storm Prediction Center (SPC) for the Friday/Friday night (Day #3) time frame.

At present, SPC puts the level of risk in Chicago near 3 on its 5 level scale. That’s an eye-catching risk assessment three days out. And the risk is assessed as being even higher in a swath of Illinois just to Chicago’s west back into Iowa and Missouri.

Projected winds speeds at 34,000 ft approaching 175 mph, of 135 mph at 18,000 ft. and approaching 70 mph at the 5,000 ft. level are testament to the sort of wind fields into the ascending air is to rise. The “corkscrew” type spin to which the ascending air and the t-storms it produces doesn’t leave much doubt it won’t be hard to spin up rotating supercell t-storms in such an environment.

PROJECTED JET STREAM at 10pm CDT Friday

Modeling puts t-storm probabilities at 80% in the 24 hour period covering Friday and Friday night and the Storm Prediction Center (SPC) currently places the risk for severe weather as approaching 3 on the 5 level SPC risk scale. It will be interesting to monitor the risk assessment as we get closer to the Friday afternoon/night arrival time of the best supported t-storms. (NOTE: Thunderstorms may occur in clusters Thursday night into Friday ahead of the period most supportive of severe weather later Friday into Friday night).

Forecast Ensemble shows precipitation moving toward the Midwest:

BEYOND THE LATE WEEK STORM, models continue to advertise a very active weather pattern with powerful storms likely to traverse the Midwest in 3 to 4 day intervals in the week and a half which follows.  While much cooler weather sweeps in after Friday’s 60s, additional 60s are on the way next week—most likely Tuesday into Wednesday—and still another set of potential 60s the follow Tuesday and Wednesday based on current computer projections.