


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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390 FXUS63 KLOT 120805 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 305 AM CDT Thu Jun 12 2025 .KEY MESSAGES... - Today will be very warm and more humid inland of Lake Michigan, though it will be much cooler near the lake. - Shower and thunderstorm chances will continue to remain muted locally through tonight. Greatest shower and storm coverage expected Friday and Saturday. - Seasonable temperatures expected through the weekend, but with notably cooler conditions near Lake Michigan. Temperatures to warm again next week with a return for periods of showers and storms too. && .DISCUSSION... Issued at 305 AM CDT Thu Jun 12 2025 Through Friday: A weak west-to-east oriented cold frontal boundary sagging southward across far northeastern IL early this morning will stall near the I-80 corridor during the day today. North of the boundary, persistent onshore cool northeasterly winds are expected through the day across the southern shores of Lake Michigan. Accordingly, this will foster much cooler temperatures today (a good 15-20F degrees cooler than yesterday), particularly at and near the Lake Michigan shore. Conversely, far interior sectors of northern IL and points south of the frontal boundary will experience another warm early summer day, as highs in these areas look to again top out in the mid to upper 80s. Unlike yesterday, however, more higher level cloudiness will be streaming across our area through the day, thus resulting in partly sunny conditions. The primary focus for showers and thunderstorms early this morning will continue to reside north and northwest of the area across northern IA into southern WI. While this is the case, we certainly cannot rule out a few remnant non impactful showers drifting into parts of the far northern IL counties (areas near the WI state line) over the next few hours this morning before dissipating. Otherwise, we are looking to experience mainly dry conditions through the morning. The threat of showers and thunderstorms will also remain low in our area this afternoon (<20%), owing to continued poor mid- level column moisture and weak flow overhead within a split mid- level flow regime across the central CONUS. However, while largely unfavorable for many storms, we cannot rule out the potential for a couple of isolated storms developing this afternoon (3 to 6 pm). This low potential (~20%) would largely be confined to the vicinity of the surface frontal boundary across the western 1/3 of the CWA where locally higher surface dewpoints pooling along the front during peak heating could contribute to their development. If any storms do develop, weak low to mid-level flow should limit their organization and duration, thus greatly curtailing threat for any severe weather. Any isolated slow moving showers/storms out over the western 1/3 CWA this afternoon will quickly dissipate early this evening. Late tonight, some isolated showers may push into the far southern CWA on the northeastern fringes of closed mid-upper level low pressure moving into the Ozarks. Mid-level overcast will keep overnight temps propped up again, with most spots in the low- mid 60s by early Friday, except upper 50s in far northeast IL farther north of the front. The threat for showers and some thunderstorms will increase into our area during the day Friday. This will particularly be the case for areas along and south of I-80 as the mid and upper- level low tracks into over the Lower Missouri Valley. Severe weather is not expected with this activity, though rather slow storm motions and increasing column moisture could support some locally heavy downpours late in the day into Friday night. More cloud cover and some better chances for rain should result in cooler temperatures areawide on Friday, with highs once again expected to be the coolest (in the low to mid 70s) along the Lake Michigan shore due to continued onshore flow. Farther inland, expect readings to generally be around 80. KJB Friday Night through Wednesday: The upper low currently over eastern TX is expected to be moving into the Ohio River Valley Friday night broadening into an elongated trough as it does so. At the same time, a frontal boundary will be slowly starting to advance southward as a cold front. While scattered showers (and perhaps an isolated storm or two) are expected to be ongoing in association with these two features Friday night, the coverage of showers should be gradually waning from northwest to southeast heading into Saturday as the front progresses through the area. That said, still looks as if a fair coverage of showers and occasional storms will materialize along and east of I-55 for Saturday with lesser coverage to the north and west. Outside of the rain, temperatures on Saturday are forecast to be in the seasonable range with highs in the lower 80s inland but only in the 60s to lower 70s near the lake due to onshore winds. The cold front and the upper trough are expected to move east of the area by Sunday morning which will allow rain to come to a close across northern IL and northwest IN as a surface high moves into the western Great Lakes. However, winds will remain east-northeast behind the front which will continue to support 60s and lower 70 degree readings along the lakeshore while those inland once again warm into the lower 80s. A broad upper ridge is expected to develop across the southwest and central CONUS Sunday into Monday which will gradually begin to advect warmer and more humid air into the Great Lakes from Monday onward. Therefore, expect temperatures to warm through next week with highs back solidly into the 80s (possible even nearing 90s at times) including near the lake. Though, lingering onshore winds on Monday will offer one more day of cooler conditions near the lake with highs in the 70s (mid-80s inland). With the building warmth and humidity will also come more chances for showers and thunderstorms particularly towards the later half of next week as the upper ridge gets moved into the Gulf Coast and a more zonal oriented pattern sets up over the rest of the CONUS with several shortwaves progged to traverse the pattern. Given the high degree of uncertainty with the timing and track of each shortwave, the forecast for next week carries daily chances for showers and thunderstorms. However, suspect that many dry hours will still be seen in between the waves so stay tuned as details get refined in the coming days. Yack && .AVIATION /06Z TAFS THROUGH 12Z FRIDAY/... Issued at 1246 AM CDT Thu Jun 12 2025 Forecast concerns for the terminals... - Frontal boundary to swing into northern IL and northwest IN overnight resulting in a northeast wind shift. - Periods of scattered showers and storms tonight north of the IL-WI line and again Thursday afternoon in western IL, but should remain away from the TAF sites. A frontal boundary will continue to swing into northern IL and eventually northwest IN overnight resulting in a northeast wind shift in its wake. While winds overnight will remain in the 5-7 kt range, a slight increase is expected Thursday afternoon as diurnal mixing allows for occasional mid to upper teen kt gusts before winds ease again Thursday evening. Due to the expected infrequency of the gusts, have decided to maintain a single prevailing group in the TAFs to account for the northeast winds through the day on Thursday. Otherwise, SCT to BKN VFR cirrus will prevail overhead through the forecast period as scattered showers and thunderstorms fester along an elevated frontal zone in southern WI tonight into Thursday morning. While there is still a low chance (<15-20%) for an isolated shower to two to brush far northern IL (including RFD) tonight, current radar trends support showers remain outside of the 10-mile range ring of RFD and thus have left TAF dry. That said, an additional period of isolated to widely scattered showers and storms is forecast to develop across western IL Thursday afternoon. With the aforementioned front expected to be south of the terminals by time showers/storms develop, any activity should remain south and west of the terminals on Thursday and thus have maintained dry TAFs for this period as well. Yack && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago