The Chicago area is preparing for a round of showers and storms and the possibility of severe weather.

Clusters of fast moving thunderstorms may sweep the area in advance of the late Friday/Friday night time frame —starting as early as later Thursday night and from time to time during the day Friday.

The most favorable conditions for severe weather appear focused on later Friday and Friday night. Modeling put the chances for thunderstorms at some point (and likely on multiple occasions) across the greater Chicago area over the 24 hour period from 1 a.m. Central Time Friday through 1 a.m. Central Time Saturday morning at greater than 80%.

The National Weather Service’s Storm Prediction Center indicates the Severe Weather Risk in Chicago later Friday is to reach level 3 on its 5 level scale–and an even higher assessment of severe weather risk reaching 4 on the 5-level scale–is indicated for the area of Illinois just west of Chicago.

Spring storm is good news/bad news for Chicago area

For those interested, here’s a relatively deep dive into concerns about the late week spring storm headed for the Midwest Friday into Saturday.

The season’s 11th atmospheric river storm to sweep off the Pacific has crossed The Rockies and about to emerge into the Plains. There, it will access warm, moisture-rich tropical air off the Gulf of Mexico and head into the Midwest later Thursday night and during Friday and Friday night. It’s powerhouse backside non-storm winds will follow, sweeping across the region Saturday.

All this sets up a “good news/bad news” scenario for Chicago.

On the positive side, this finally brings Chicago a taste of spring warmth Friday — which has been so lacking to date this year. While a majority of years since the early years of World War II in the 1940s, nearly 60% of them, have already seen one or more 70-deg temps in Chicago (we had recorded three of them by this time last year), this year hasn’t even produced an official 60-deg high in the city. That changes Friday. 60s are on the way — and so are low 60-deg dew points by later in the day, which will lend a “springlike feel” to the air here by Friday afternoon.

But here’s the rub. Warm, moist air is buoyant. It wants to rise through the atmosphere and will be encouraged to do Friday because temps will be dropping rapidly with height. Troublesome is the fact computer modeling suggests this ascending air is to sweep into abnormally powerful winds aloft. This has multiple implications. For one, with upper winds, projected later Friday to reach 175 mph at 34,000 ft. Just west of Chicago in Western Illinois and Missouri, 130 mph at 18,000 ft., 100 mph at 10,000 ft. And over 70 mph 5,000 ft. Aloft—sets up a situation in which thundertorms race along at high speed–probably at 60 to 65 mph, especially Friday afternoon and evening.

Fast moving thunderstorms can be high wind producers, mixing wind energy down to the surface as strong, potentially damaging wind gusts.

Strong winds could produce dangerous situation

Also—the wind profiles through the atmosphere above a wide swath of the Midwest–potentially including the greater Chicago area— later Friday predicted by computer models suggest the ascending air later Friday into Friday night will be rotated in a “corkscrew” fashion. If these projections verify, then rotating supercellular t-storms become a real possibility — the type which can spin up tornadoes in additional to potentially damaging wind gusts.

So this is why there is such attention being paid to the developing Friday afternoon and evening weather situations.

On the cold north side of this storm–a windy snowstorm is projected for the upper midwest and winter storm watches have been hoisted over the north woods region of wisconsin and upper michigan where accumulations are likely to exceed 6″–and even top a foot in sections of michigan’s u.p.