


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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178 FXUS63 KLOT 012021 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 321 PM CDT Tue Jul 1 2025 .KEY MESSAGES... - Noticeably lower humidity but still very warm temperatures are expected away from the lakeshore through Thursday. - Heat and humidity will return for the upcoming holiday weekend. - Isolated gusty storms can`t be ruled out Wednesday and Thursday (20% chance). - Periodic shower and storm chances (30-50%) return Saturday night into early next week. && .DISCUSSION... Issued at 320 PM CDT Tue Jul 1 2025 Through Tonight: Quiescent but warm conditions continue this afternoon with temperatures well into the 80s across much of the area with mid to upper 70s along the lakeshore behind the lake breeze. Any lingering diurnal cumulus will erode with sunset leading to a clear and quiet night. This should allow temperatures to cool readily outside of the Chicago metro with forecast lows in the lower to mid 60s. The urban heat island of Chicago should hold temperatures in the upper 60s to around 70. Wednesday and Thursday: An upper level ridge is progged to amplify across the central CONUS over the next couple of days. This will place the western Great Lakes along the northeast periphery of the ridge where multiple weak disturbances will traverse overhead. This should help to erode any lingering capping by mid-late afternoon on Wednesday. While there is not a lot of moisture through the depth of the column, opted to maintain slight chances (20%) for isolated showers and storms, with perhaps a locally highest potential within the vicinity of the lake breeze or any other subtle convergence axes. We will have to keep an eye out for locally strong wind gusts during this timeframe owing to inverted V soundings supportive of strong downbursts (high DCAPE). The latest SPC outlook brings the Level 1 of 5 risk for severe wind gusts just south of the Wisconsin/Illinois state line which seems appropriate, conditional upon a storm developing. Similar conditions are on tap for Thursday, with perhaps a bit more moisture to work with supportive of isolated to widely scattered shower/storm development during the afternoon into early evening. Friday through Saturday: The upper level ridge axis will shift overhead on Independence Day which will allow more heat and humidity to build into the region through the end of the week. Expect temperatures to warm into the low to mid 90s areawide with upper 90s not out of the question, especially on Saturday, if deeper mixing occurs. At this time, this period of heat doesn`t look as oppressive as the one in June due to daytime dewpoints mixing down into the mid to upper 60s. This should hold peak heat indices generally in the 95-100 degree range. However, given that this will be a busy holiday weekend, those with outdoor plans are encouraged to have a plan in place to avoid heat related illnesses. Strong capping should allow for mainly dry conditions during this time though a stray shower or storm can`t be fully ruled out. Saturday night through Tuesday: The mid-upper ridge begins to flatten out into next week with multiple disturbances forecast to round the ridge over or near the area bringing additional periodic shower and storm chances. While still warm, the increased cloud cover and potential precipitation will bring some relief from the heat. Petr && .AVIATION /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 1234 PM CDT Tue Jul 1 2025 The only aviation weather concern remains the timing an E/NE wind shift at the lake-adjacent terminals this afternoon. A lake breeze is beginning to shift inland across southern Cook county per the TORD. Its current westward motion is set to bring it into the MDW area, with an associated eastward wind shift by 19Z. The north-to-south orientation of the lake breeze will likely keep it focused east of ORD for a period this afternoon. Accordingly, it will take a few more hours this afternoon to make it into the ORD area (likely not until after 22Z). Winds will then become light and variable after sunset, before settling back into an westerly direction overnight. West winds will continue during the day Wednesday, and are likely to become breezy enough (11 kt gusting to 15 to 20 kt) in the afternoon to hold the lake breeze right along the IL lakeshore. While the weather overall looks quiet across the area on Wednesday, there is a low (20%) chance for the development of a few spotty showers and maybe a thunderstorm across parts of northern IL in the afternoon. However, the potential is currently too low to include a formal mention in the TAF at this time. KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago