Chicago O'Hare Weather Area Forecast Discussion Monday June 12, 2023

Area Forecast Discussion 
National Weather Service Chicago/Romeoville, IL 
636 PM CDT Mon Jun 12 2023

.SHORT TERM... Issued at 259 PM CDT Mon Jun 12 2023

Through Tuesday night...

Deep upper low (by June standards) remains quasistationary over the western Great Lakes with multiple spokes of higher vorticity pivoting around it. Each small vort max rotating around the main upper low will result in an uptick in precip coverage/chances over the next 24 hours.

The first shortwave is over Wisconsin and will pivot southeast tonight and will likely bring at least some scattered showers into northern Illinois this evening with another wave evident on water vapor imagery over Upper Michigan which could keep showers going overnight or lead to an another increase in coverage overnight into early Tuesday morning. One last wave is just east of Lake Huron, with guidance bring that one around the upper low and into our area Tuesday.

Initially, air mass over the region is very dry, with record low PWAT of only 0.38" on DVN`s 1200 UTC sounding this morning (based on SPC`s newly upgraded SPC sounding climo page)! Water vapor imagery shows moisture being advected north and west around the periphery of this upper low, on a general track toward our area as it pivots around the upper low. PWATs tonight are progged to increase to 0.75-1.00" as moisture streams south from WI into IL. A more substantial increase in moisture, with PWATs near 1.25" is expected by Tuesday afternoon, coinciding with the arrival of the final shortwave.

Rain looks to become fairly widespread in association with this final wave to impact our area Tuesday afternoon into Tuesday evening. Precipitation should be fairly widespread across about the northeast half of the CWA, where localized 24 hour rainfall totals could even reach or slightly exceed a half inch. Over southern and western portions of the CWA, precip Tuesday afternoon should be more showery with lesser coverage.

Temperatures aloft will be quite cold for this time of year, but with dewpoints only expected to be in the 50s tomorrow afternoon, it will likely take some sunshine to heat/destabilize the boundary layer enough for any thunder chances. The best threat of this happen should be in the far southern and southwestern CWA, but it is unclear how much clearing will take place between fairly closely spaced shortwaves late tonight/early Tues and then the next Tues afternoon. Have maintained slight chances for thunder in these areas. Rain should end from NW to SE across the CWA Tuesday evening.

- Izzi

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