


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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159 FXUS63 KLOT 221651 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1151 AM CDT Sun Jun 22 2025 .KEY MESSAGES... - Dangerously hot and humid conditions will continue through at least Monday evening. A Heat Advisory remains in effect through Monday evening for the entire CWA except Cook County IL where an Extreme Heat Warning is in effect. - The magnitude of heat should lessen by Tuesday, though heat indices will still be in the upper 90s to near 100 through much of the week. Heat headline extensions are not currently planned. - Shower and storm chances increase incrementally Monday evening through the end of the week. Some may be severe with damaging winds and flash flooding. && .DISCUSSION... Issued at 327 AM CDT Sun Jun 22 2025 Through Monday: Conditions are awfully warm out there early this morning. As of around 3 AM, temperatures are still sitting in the upper 70s and lower 80s around the area. Otherwise, skies are nice and clear and marginally breezy southwest winds are gusting to 20 to 25 mph semi-frequently. Very little has changed in our expectations for the second day of this heatwave. Synoptically, the upper high responsible for the heat will propagate from the TN Valley northeast into the OH Valley during the day today lifting 500mb heights overhead to an impressive 5960m! From a heat index standpoint, today should feel very similar to yesterday. The consensus is pretty strong among models that today should generally be just a couple of degrees warmer than yesterday, from largely lower 90s to now closer to middle 90s expected this afternoon. Conversely, dewpoints look to mix out slightly lower than yesterday, into the lower 70s as opposed to middle 70s. These sort of readings should again yield afternoon heat indices between 100 and 105F, possibly a little higher in spots. Today will also be another breezy day, although not nearly as windy as what we saw yesterday. Those aforementioned gusts that we`re seeing are the result of a low level jet seated right off the deck that we`ve been occasionally mixing into. This jet will actually be weakening through the morning, but we`ll see gusts at the surface pick up as mixing into the jet deepens. We`re expecting gusts in the ballpark of 25 to 30 mph from late morning into early evening mainly near and north of I-80 with slightly lesser winds anticipated farther south. The gusts will ease for the night before picking back up to 20 to 25 mph for Monday. Conditions will again remain warm during the night tonight with lows forecast in the middle to upper 70s. Unless the forecast proves several degrees too cool, it looks likely that Chicago and Rockford will be breaking their warm low temperature record for today, just as they both did for yesterday (see climate section of AFD for details.) The oppressive heat will continue into Monday. Temperatures are expected to be a tad warmer than today with highs forecast to make a run at upper 90s in a few spots. Slightly cooler midday dewpoints in the upper 60s to around 70 degrees should produce peak heat indices over 100 to around 105F. A rather sharp cold front will approach the area from the northwest late Monday afternoon, but unfortunately will not arrive in time to cool things off during the day. More on this front and associated rain and thunder chances can be found in the long term discussion below. Doom Monday Night through Saturday: The extended forecast period features a shift to a more active pattern lead to episodic shower/storm chances and continued warm and humid conditions. Convection will likely be ongoing northwest of the area Monday evening along a cold front extending across Iowa into southwest Wisconsin. Instability is maximized along and south of this boundary (MUCAPE >2000 J/kg), which combined with ~25-30kt of effective bulk shear would be supportive of severe convection capable of damaging winds and hail. The big question mark at this time is how far southeast this activity can reach before dissipating after sunset. Have maintained low chances (~20-30%) generally near and north of a Dixon to Waukegan line, highest northwest of Rockford, though it is quite possible the entire area ends up dry. Nevertheless, remnant outflow winds could make inroads across northern Illinois, resulting in a gusty northwest wind shift and cooling things off a bit. The rest of the area will remain warm and humid through Monday night with lows still in the mid-upper 70s. The upper level ridge responsible for the early week heat wave begins to flatten out toward midweek with the baroclinic zone (stalled surface boundary) setting up near and over the area. As weak disturbances move within the mid-upper flow paired with diurnal heating, expect regular shower and thunderstorm chances through the end of the week. While the jet stream will remain well north of the area at the top of the ridge (and with it the better shear), ample instability south of the surface boundary will still be supportive of strong to severe storms capable of damaging winds. High PWATs and weaker flow aloft also suggest there could be a localized flooding threat. There will be plenty of dry hours but pinpointing when those occur remains low confidence at this range. While warm and humid conditions likely continue through the end of the week, it won`t be as oppressive as experienced earlier in the week, with highs in the upper 80s to lower 90s and heat indices in the 90s to locally near 100. Onshore flow at times should help cool temperatures off near the lakeshore. Petr && .AVIATION /18Z TAFS THROUGH 00Z TUESDAY/... Issued at 1151 AM CDT Sun Jun 22 2025 Southwest winds will remain breeze through the TAF period, with gusts in excess of 25k kt during the afternoon easing and becoming more sporadic during the overnight hours. Otherwise, there are no other aviation concerns. Borchardt && .CLIMATE... Issued at 327 AM CDT Sun Jun 22 2025 Temperatures early this week will threaten record highs and record warm lows for Chicago and Rockford. Here are the current records: Chicago High Warm Low Sunday 6/22 97 (1988) 76 (1923) Monday 6/23 97 (1930) 79 (1923) Rockford High Warm Low Sunday 6/22 97 (1923) 73 (1908) Monday 6/23 97 (1923) 74 (1908) NWS Chicago && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Heat Advisory until midnight CDT Monday night for ILZ003- ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013- ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ106- ILZ107-ILZ108. Extreme Heat Warning until midnight CDT Monday night for ILZ103-ILZ104-ILZ105. IN...Heat Advisory until midnight CDT /1 AM EDT/ Monday night for INZ001-INZ002-INZ010-INZ011-INZ019. LM...Small Craft Advisory until 10 PM CDT this evening for the IL and IN nearshore waters. Small Craft Advisory from 8 AM to 9 PM CDT Monday for the IL nearshore waters. && $$ Visit us at weather.gov/chicago