751 FXUS63 KLOT 160921 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 421 AM CDT Sun Oct 16 2022 .SHORT TERM... Issued at 317 AM CDT Sun Oct 16 2022 Through Tonight... A dry cold front passage is underway early this morning, with the front aligned roughly from Mendota to Batavia to Winnetka as of 3am. The front will clear the CWA by around daybreak with little fanfare. Blustery WNW winds gusting 25mph+ are expected this afternoon as CAA commences under initially mostly sunny skies. Diurnal heating combined with steepening low-level lapse rates and a lifting inversion will support the development of a robust stratocumulus deck from north to south through the afternoon. Cloud depths should become sufficiently deep to generate some sparse sprinkles across far northeast Illinois late afternoon, though better precip chances will remain well northeast of the area. Strong CAA will take hold late this afternoon through tonight, during which 850/700 hPa temps will drop as much as 10/15C. NW winds will continue to gust to 25 mph through the night, and possibly to 30mph by daybreak Monday. With the loss of daytime heating and drier upstream profiles, the forecast area should remain precip free tonight with the exception for a few lake effect showers clipping extreme northeast Porter County. Persistent stratus and gusty winds will limit radiational cooling, with a vast majority of cooling occurring from advection. Temps will fall into the low 30s for much of the interior CWA for a few hours late tonight. Given the marginal freeze conditions, no expected frost due to strong winds, and much colder conditions in the forecast for Monday night and Tuesday night, opted to hold off on a Freeze Warning. Kluber && .LONG TERM... Issued at 317 AM CDT Sun Oct 16 2022 Monday through Saturday... For all intents and purposes, Monday's weather could easily be a forecast any given day in January! After Monday's preview of winter weather, gradually moderating temperatures are expected through the week and could culminate with June-like weather by next weekend! Gusty northwest winds will continue to supply a feed of unseasonably cold temperatures into the area Monday. Given the continued cold air advection and 925mb temps around 0C, should see temps struggle to reach 40F with strong winds resulting in wind chills in the 20s most of the day. While temps will be unseasonably cold and could threaten records, of greater concern is the sharp low/mid level trough axis progged to rotate around the backside of the big closed low and across our area during the late afternoon/early evening. Significant tropopause fold associated with this trough will result in dramatic lowering of the tropopause along with a significant steepening of mid-level lapse rates. There is strong model agreement in depiction of that scenario unfolding (pardon the pun), but there is model disagreement in extent of mid-level moisture and saturation. The NAM and especially the ECMWF are on the moist side of the model spectrum with the GFS and GEM somewhat drier. Low level lapse rates will already be quite steep in the strong cold air advection regime, so as mid-level lapse rates steepen up with the approaching trough, potentially convectively unstable layer deepens considerably. If the more moist mid-level profiles in the NAM and ECMWF verify, then it seems likely that there will be scattered snow showers around Monday afternoon (mainly late) into early Monday evening. The best chances should be in the Chicago metro area, but some potential exists, albeit lower, even farther west into our CWA. While surface temps may reach into the lower 40s, wetbulb temps through the column should be near/below freezing, so any showers would likely be all snow as column wetbulbs down to freezing. Given the convective nature of the precip, we could certainly see some graupel as well. Should the drier solutions verify, then we may not see any precip or just a couple flurries. Given the uncertainty, maintained just chance pops for now, but am concerned that we could see some robust and potentially impactful snow showers during Monday afternoon/evening rush hour. In the wake of this trough, winds look to increase further, with gusts of 35 to 40 mph possible Monday evening. Along the northwest Indiana shore, where winds will be blowing off the lower friction and much more unstable surface of Lake Michigan, it is possible winds could reach wind advisory criteria (gusts >=45 mph) Monday night. A veering of the low level flow behind the trough could also send lake effect precip backing west into Porter county Monday night. If the more vigorous lake effect does make it into Porter County, then there could even be some minor accumulations on grassy surface inland a bit from the relatively warmer lake. Something that will require a closer look in coming forecast cycles. After Monday night, the weather should quickly quiet down for the remainder of the long term period. Temperatures will moderate through the week and into the weekend. In fact, latest operational runs of the GFS and ECMWF would support high temps well into the 70s to possibly 80F next weekend! NBM temps aren't quite that warm, but if current trends in guidance continue, would anticipate our forecast highs temps for the weekend trending considerably warmer in coming days. - Izzi && .CLIMATE... Issued at 235 PM CDT Sat Oct 15 2022 Here are the current records in place for Monday and Tuesday. Most records appear to be safe, with the record cold max for Rockford for Monday 10/17 being the most likely record to be threatened. Though temperatures will not be all that much above the other records... October 17 October 18 Record Cold Record Low Record Cold Record Low Maximum Maximum Chicago 40 (1880) 26 (1948) 38 (1930) 20 (1948) Rockford 44 (2002) 24 (1992) 41 (1972) 19 (1952) Petr/Izzi && .AVIATION... For the 06Z TAFs... Cold front will move across the terminals prior to sunrise this morning resulting in a wind shift to the northwest. Northwest winds expected to gradually increase and become gusty later this morning after sunrise. Gusty northwest winds expected to continue through the afternoon and into tonight. Expect a low end VFR BKN deck to overspread the area later this morning. Some potential for this deck to build down to higher end MVFR tonight. Otherwise, no impactful weather expected for aviation. - Izzi && .MARINE... Issued at 421 AM CDT Sun Oct 16 2022 Northwest gales are expected to develop late tonight and especially Monday afternoon into Tuesday morning from strong cold- air advection between a 1034mb high over Manitoba and a 997mb low over Georgian Bay. The strongest gales to 40 knots are expected Monday evening as a secondary trough shifts across Lake Michigan. A brief period of gales to 45 knots is possible in the Indiana nearshore during this time. Winds will only slowly diminish through the day Tuesday, with some gale gusts to 35 knots remaining possible into Tuesday evening. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743...3 PM Sunday to 1 PM Monday. Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743...1 PM Monday to 10 AM Tuesday. Small Craft Advisory...LMZ744-LMZ745...3 PM Sunday to 4 AM Monday. Gale Warning...LMZ744-LMZ745...4 AM Monday to 10 AM Tuesday. && $$ Visit us at weather.gov/chicago Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSChicago www.twitter.com/NWSChicago www.youtube.com/NWSChicago