Expires:No;;889500 FXUS63 KLOT 062338 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 638 PM CDT Sun Apr 6 2025 .KEY MESSAGES... - Isolated to scattered (mainly non-accumulating) gusty snow showers Monday into Monday evening. - The next chances for precipitation return late Tuesday night through Wednesday night, with some snow possible at times. && .DISCUSSION... Issued at 249 PM CDT Sun Apr 6 2025 Through Monday Night: A surface ridge will remain overhead this evening which will continue to promote dry conditions. While a band of clouds remains across portions of east-central IL an northwest IN, they should gradually erode this evening leaving us with mostly clear skies overnight. The clear skies in combination with light winds and dry dew points will allow temperatures to efficiently cool into the low to mid-30s areawide by daybreak Monday. At the same time, the stout shortwave trough noted on water vapor imagery in northern Quebec will pivot into the Great Lakes late tonight through Monday morning. This will force a cold front through northern IL and northwest IN Monday morning and lead to the development of snow showers. While the near freezing surface wet bulb temperatures may allow for some accumulation (generally less than 0.20 inches) on grassy surfaces, the increasing northwest winds behind the front and the convective nature will result in reduced visibilities and in slowed travel for the morning commute. That said, the snow is only expected to last 2-3 hours at any one location and will move out of the area by midday. However, confidence is growing that a band of lake effect snow will develop Monday afternoon. While forecast soundings show sufficient lake effect ELs in the 9000 to 10000 ft range, the strength of the surface convergence along a lake induced boundary is more modest which may limit the overall coverage of the lake effect. That said, any lake effect that does develop will generally remain east of a McHenry to Kankakee line and should gradually shift into northwest IN through the afternoon. Similar to the aforementioned snow showers, accumulations from the lake effect are expected to be minimal with amounts generally under a couple tenths and mainly confined to grassy surfaces. Though reduced visibilities will be a concern. The lake effect will gradually taper Monday evening leaving the area under mostly clear skies for Monday night. With the blustery winds expected to diminish as well, temperatures should dip into the lower to mid-20s areawide by Tuesday morning with the potential for more sheltered/cold spots to see some upper teen readings. Yack Tuesday through Sunday: Light winds and mainly clear skies under a Canadian high will result in a cold start to the day Tuesday morning. Temperatures are expected to bottom out in the low to mid 20s in most areas. Quiet and sunny weather will then persist under this surface high during the daylight hours of Tuesday, but temperatures will remain rather cool for early April, with highs only slatted top out in the 40s (coldest near the lake). The next shortwave impulse, and associated surface low, is slatted to shift eastward across NE into the mid Missouri Valley region Tuesday night. As it does, an intensifying southwesterly low-level jet, impinging upon a strong baroclinic zone draped from north-to-south over the Midwest, will foster a wing of robust warm air advection (isentropic upglide) into our region late Tuesday night. Increased ascent and moistening within this warm air advection wing will support an eastward expanding area of precipitation into northern IL and northwestern IN late Tuesday night into Wednesday morning. Initially, the column could be cold enough across parts of northeastern IL and far northwestern IN to result this precipitation onsetting as wet snow, before changing to rain by mid to late Wednesday morning. Some slushy wet snow accumulations (less than an inch) are possible on grassy surfaces early Wednesday, particularly across northeastern IL into northwestern IN. Ensemble guidance continues to display some spread in the exact track and strength of the surface low across our area late Wednesday. However, the general consensus at this time favors an eastward track around, or a south of the I-80 corridor. If this occurs, northern IL and northwestern IN north of the surface low track will end up experiencing the snow changing over to a cold rain during the day Wednesday. At this time, we cannot rule out the possibility of the rain mixing with some more wet snow before ending Wednesday night, particularly near the WI state line, but this is of low confidence. Either way, this it is looking like Wednesday will be a wet and raw day for much of far northern IL. Broad troughing will linger overhead through the end of the week, although the introduction of drier air largely looks to suppress precipitation chances late in the week. KJB && .AVIATION /00Z TAFS THROUGH 06Z TUESDAY/... Issued at 638 PM CDT Sun Apr 6 2025 Expect VFR conditions through tonight. SE winds around or less than 10 knots will shift SW by late evening as a weak surface ridge crosses the area. A cold front quickly tracking southward Monday morning will bring a period of MVFR ceilings and a brief band of snow as winds quickly shift NNW and gust to around 25 knots. Accumulations are not expected with this snow, though MVFR visibility is likely and IFR visibility is possible. Ceilings will lift into low-end VFR levels by late morning. A resurgence of cold air on NNE winds combined with growing cloud depths will result in the redevelopment of MVFR ceilings and isolated to scattered non-accumulating snow showers by mid afternoon. Some of the showers could produce IFR visibility mid afternoon through around sunset before intensity wanes later in the evening. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory from 4 AM Monday to 7 AM CDT Tuesday for the IL nearshore waters. Small Craft Advisory from 4 AM Monday to 4 PM CDT Tuesday for the IN nearshore waters. && $$ Visit us at weather.gov/chicago