FXUS63 KLOT 011756 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1156 AM CST Sun Nov 1 2026 .KEY MESSAGES... - Periods of showers or sprinkles today. - Additional periods of wet weather are likely especially mid- week. - Warmer than average temperatures early in the week are expected to eventually trend slightly below average by next weekend. && .DISCUSSION... Issued at 213 AM CST Sun Nov 1 2026 Scattered small clusters of convective showers and isolated thunderstorms were lifting across eastern portions of the forecast area early this morning. This weak convection was occurring in association with a sheared northwest-southeast area of mid-level vorticity, coincident with a layer of steep lapse rates roughly in the 800-500 mb layer, as noted in current RAP soundings. Though model sounding ELs are just shy of -20C, MRMS isothermal reflectivity does indicate the tallest updrafts reaching the -20C level with some 40-45 dBZ cores. The expectation is that these scattered showers and isolated thunderstorms will continue to lift across far northeast IL and northwest IN (mainly east of the I-55 and I-355 corridors) prior to sunrise before the sheared vort lobe moves northeast of the forecast area. Another weak mid-level short wave was noted across the mid- Missouri Valley early this morning, and is progged to track east across the area later this morning and afternoon. The strongest forcing and juxtaposition of the low-level baroclinic zone to our south suggests greater potential for measurable rain remains largely south of our forecast area across central IL/IN, the presence of the mid-level trough, weak warm advection and reasonably moist profiles should support occasional spotty light showers or sprinkles across the CWA during the day. Have maintained a 15-20% chance mention, highest generally along/south of I-80. Short-wave mid-level ridging is then indicated across the area tonight, in the wake of today's short wave passage. Attention then turns to our west, focused on the evolution and eastward progression of a complex long-wave upper trough and it's associated deep surface low. Guidance has come into better agreement with the upper trough axis (and embedded closed upper low) propagating east of the Rockies and onto the Plains late Monday, with a deepening sub-995 mb surface low developing into eastern South Dakota by early evening. This is forecast to induce strong southerly return flow into the Midwest within a tightening surface pressure gradient. For northern IL/IN, the main impacts Monday look to be the development of somewhat breezy southerly winds (though forecast soundings depict fairly shallow mixing, supporting gusts around 20 mph during the afternoon), the potential for low stratus to advect in from the southwest, and perhaps some scattered showers as isentropic ascent increases with an elevated warm frontal zone lifting across the area. While warmer temperatures are expected, the shallow mixing may limit this somewhat with forecast highs Monday are in the mid-upper 60s. A strong mid-level short wave (currently off the northern Baja coast) is progged to wrap around the south/southeastern periphery of the larger scale upper trough late Monday/Monday night, further deepening the closed upper low over the Central Plains. This results in new surface low development (or redevelopment) southeastward across IA, eventually slowing as the system begins to become more vertically stacked on Tuesday. Forecast sounding and time/height sections indicate development of a ~45 kt low-level jet into the forecast area Monday night into Tuesday/Tuesday night ahead of the deepening system. Strengthening south winds will likely keep Monday night temps very mild with lows in the 55-60 degree range. Winds may gust in excess of 30 mph during the day Tuesday, with temperatures potentially topping out in the low-mid 70s. Deeper moisture feed during this process is initially focused west of the Mississippi River, due to the southwestern periphery of high pressure ridging from the Gulf Coast to the mid- Atlantic region. This moisture eventually looks to reach our area late Tuesday/Tuesday night however, with the greatest potential for showers and perhaps a few thunderstorms in this moisture axis ahead of the system's occluding cold front. The extent of thunderstorm coverage is a little uncertain, with models indicating a pinching off of the MUCAPE axis to the north of the surface frontal occlusion Tuesday night. Confidence in forecast details then decreases mid-week, due to model differences in the further evolution of the slow-moving upper low across the region - complicated somewhat by the degree of phasing with a northern stream short wave across the upper Midwest/northern Lakes. Overall, the Wednesday-Friday period continues to look unsettled as the closed upper low and occluded surface system track slowly east across the region, though some timing differences linger in the guidance at this distance. While no strong intrusion of colder air is evident at this time, temperatures do look to eventually cool to/slightly below average on the back side of this departing system. Ratzer && .AVIATION /18Z TAFS THROUGH 00Z TUESDAY/... Issued at 1156 AM CST Sun Nov 1 2026 Spotty light SHRA from a mid-level cloud layer will continue into early afternoon, followed by perhaps a couple instances of sprinkles into mid-evening. Otherwise, VFR conditions will persist through at least the early morning hours as winds under 10 knots favor directions in the SE quadrant. Winds will then settle SSW/S while increasing to over 10 knots for much of the day Monday. As mid-level moisture exits the area to the northeast overnight, low-level moisture will gradually advect northward across Illinois. Low-level MVFR ceilings are expected to shift over the Chicago terminals within an hour or two on either side of sunrise Monday. Ceilings may lower into IFR levels during the morning and early afternoon, with cloud depths also becoming sufficiently deep for DZ. Confidence was low enough to limit the mention of lower conditions to a PROB30 at the Chicago terminals. IFR ceiling and DZ potential will increase with westward extent, so have prevailed lower conditions at RFD during most of the morning. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago