


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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602 FXUS63 KLOT 030755 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 255 AM CDT Thu Apr 3 2025 .KEY MESSAGES... - Periods of rain, possibly heavy, are expected Friday afternoon into Saturday, with localized flooding possible. && .DISCUSSION... Issued at 255 AM CDT Thu Apr 3 2025 Through Wednesday: A cold front has shifted south and east of the area early this morning with temperatures and dewpoints dropping steadily with each passing hour in its wake. This boundary is forecast to stall generally near the Mid-Mississippi and Ohio River Valleys setting the stage for multiple days of heavy rain leading to potentially significant flooding in those areas. We`ll start the day here locally in the 40s this morning. Increasing cloud coverage through the day combined with continued west northwesterly cold air advection into the region should keep temperatures closer to seasonable in to the mid 50s north of I-80 and upper 50s to near 60 south. High pressure begins to build over the Great Lakes into tonight allowing winds to flop northeasterly. Prevailing onshore/northerly flow will lead to generally cooler than normal temperatures for the next several days in the upper 40s to lower 50s. A few light showers may attempt to lift into southern portions of the area late this afternoon through the early overnight hours (20-30% chance), though the aforementioned surface high should help confine this to areas mainly south of I-80. A weak surface low is forecast to develop and move northeast across central Illinois into northern Indiana late Friday into Saturday. During this time the stalled surface boundary is expected to lift back toward the area, with low level ascent atop the boundary leading to increasing shower coverage (and possibly a few embedded elevated storms) across the area Friday afternoon through Friday night into Saturday. Given anomalously high PWATS >1-1.5" (to potentially near 2" per the 0Z ECMWF), torrential rain will be possible. At this range the highest rainfall amounts currently favors areas south of I-80 where both the GEFS and EPS show a ~30-50% chance of 2" of rain occurring. This matches well with WPC`s latest Day2 Outlook for a level 2 of 4 threat of flash flooding. There has been enough variability over the past several model runs to suggest a northward shift of this axis into more of the Chicago metro area is possible, however. This will remain a period to monitor closely for flooding considering many areas received plentiful rain over the past 24 hours. For now, plan to issue an ESF for areas generally south of I-80 to highlight the increasing flooding threat. A potent short-wave is forecast to dive across the Great Lakes early next week which will bring our next chance for precipitation (likely in the form of snow) on Monday. Ensembles continue to support temperatures dropping into the 20s Monday night. Beyond Monday, an upper level pattern shift supports temperatures gradually moderating through midweek with temperatures in the 50s and lower 60s with occasional low rain chances. Petr && .AVIATION /06Z TAFS THROUGH 12Z FRIDAY/... Issued at 1230 AM CDT Thu Apr 3 2025 Forecast concerns include... Gusty westerly winds through this afternoon. Wind shift to northeast this evening. A cold front has shifted east of GYY early this morning and there may be a few sprinkles and brief mvfr cigs as it continues moving east. Otherwise, westerly winds gusting into the lower/ mid 20kt range will continue through mid afternoon and diminish with sunset. Winds will turn light northwest this evening and then shift to light northeast by mid evening. Some mvfr level cloud cover may spread back across northwest IL and RFD by daybreak and persist through midday. Confidence is low and its also possible this cloud cover may lift to low vfr, 3-4kft by the time it arrives. There is a chance for showers tonight that may spread as far north as GYY but the bulk of this activity is expected to stay south of the terminals and no mention with this forecast. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until noon CDT today for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago