Chicago O'Hare Weather Forecast Beginning Wednesday June 21, 2023

Area Forecast Discussion 
National Weather Service Chicago/Romeoville, IL 
113 PM CDT Wed Jun 14 2023

.SHORT TERM... Issued at 250 AM CDT Wed Jun 14 2023

Through Thursday...

Pretty quiet in the short term here with the pesky cutoff upper low finally headed eastbound. Cloud cover should gradually thin through the morning, although stratus will likely hang on a bit longer across far NE IL and NW IN. The only minor change to the forecast today was to add in some very low chances for a few showers this afternoon. Guidance is generally in pretty good agreement suggesting upper 50s dewpoints will pool inland of the lake breeze today which may be just sufficient to result in things becoming uncapped to surface-based parcels with diurnal heating. With a lack of notable large scale forcing present, looks like any coverage should be extremely limited today. Finally, seeing a smattering of MVFR visibility reports (Haze) across northern Minnesota, probably in association with wildfire smoke. With the greatest concentrations of near-surface smoke readings per RAP/HRRR output forecast to remain north and west of us today, suspect most smoke will remain aloft and have reflected this with some increased cloud cover (outside of thicker diurnal cumulus fields).

A low amplitude shortwave will scrape across the southern parts of Lake Michigan tonight and noting a decent response along the 300-305 K theta surfaces in the form of increasing isentropic upglide. A few pieces of guidance show the 800-700 mb layer moistening just enough to support some freely-ascending parcels forced above 700 mb. At this point, think things will remain dry overnight across NE IL and out over the lake with the greatest mid-level moisture displaced a bit farther north.

The main story on Thursday will be another robust lake-charged cold front and--depending on where you are--some significant afternoon cooling. While timing differences on the order of 2-3 hours remain across the guidance suite, the general idea is for FROPA near the lake late Thursday morning/midday before pushing southward through the afternoon. Small timing shifts will result in a big temperature bust potential, mainly north and east of I-90/right at the lake (slower arrival will allow temperatures to rocket notably higher than currently advertised). Temperature drops on the order or 15 degrees in an hour will be possible with the frontal passage.

Continue to suspect this will be a largely dry FROPA as dewpoints don`t look particularly high, and may attempt to mix down some during the late morning and afternoon, limiting the reservoir of uncapped surface based instability. There is some indication that pockets of higher dewpoints may attempt to pool immediately ahead of the surging boundary though, and for this reason have elected to maintain a slight chance of showers/storms through the afternoon.


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