Expires:No;;141374 FXUS63 KLOT 040511 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1111 PM CST Tue Dec 3 2024 .KEY MESSAGES... - Scattered gusty snow showers/squalls Wednesday afternoon and evening. - Conditions turn sharply colder with sub-zero wind chills behind an arctic front Wednesday night. && .DISCUSSION... Issued at 300 PM CST Tue Dec 3 2024 Through Wednesday Night: An area of high pressure continues to drift across the Ohio River Valley this afternoon which has resulted in dry conditions over northern IL and northwest IN. While there was some sun earlier, an axis of stratus has developed over western IL and will continue to spread eastward across the rest of the area this evening. That said, temperatures are not expected to warm much above their current readings but the increasing clouds and southerly winds tonight should aid in keeping temperatures in the mid-20s overnight. Finally, there remains a low chance (<15%) for some freezing drizzle to develop in central IL and IN late tonight into Wednesday morning as the warm advection interacts with some moisture trying to surge northward. Given that the moisture profile in forecast soundings looks to be very shallow (<1000 ft) confidence on the drizzle developing in our area remains low and therefore have left out a formal mention in the forecast. Though, we will continue to monitor areas south of a Paxton to Rensselaer line in the off chance something does materialize. The main forecast concern for the day on Wednesday will be a strong arctic cold front that will sweep across the region Wednesday afternoon and evening. While precipitation chances along the front look minimal, guidance continues to show a decent set up for scattered snow showers and squalls to develop behind the front as an upper-level shortwave and associated jet streak pivot overhead. However, moisture continues to look modest especially within the DGZ which may limit the coverage and/or intensity of such showers should they develop. That said, if the steep low-level lapse rates can overcome the lacking moisture, the snow showers/squalls will have the potential to produce sharply reduced visibilities, snow accumulations (generally under 0.5 inches), and slippery travel conditions for the evening commute. Given the convective nature of these showers confidence on the exact location of any shower is low and therefore have maintained a broad 20-40% chance for such across the area. Though the greatest coverage in hi-res guidance does seem to be favoring areas along and north of a Dixon to Rensselaer line. Aside from the snow showers, temperatures on Wednesday are expected to be warmer than today prior to the frontal passage with highs in the mid to upper 30s. However, once the front passes temperatures will quickly cool into the low teens to near signal digits by Thursday morning. Couple these falling temperatures with the increasing west-northwest winds and conditions will be in place for wind chills to dip into the sub- zero range Wednesday night. Furthermore, wind gusts Wednesday afternoon and night may also have the potential to exceed 45-50 mph if sufficient mixing is achieved. Since confidence on the degree of mixing is somewhat low have decided to cap wind gusts in the 35-45 mph range for now, but if confidence grows then we may need to consider a Wind Advisory for this period. Yack Thursday through Tuesday: Bitterly cold temperatures and sub-zero wind chills are expected at the start of the morning on Thursday. While wind gusts will gradually ease through the day as the surface pressure gradient begins to relax, continued cold air advection into the region should hold highs in the 20s with wind chills in the low-teens. Most of the area is expected to be dry under clear skies, with the exception of northeast Porter County where lake effect snow showers could linger through the day and result in additional snow accumulations. A series of weak disturbances will move within the broader northwest flow aloft through the end of the week but any precipitation associated with these features looks to remain mainly outside of the area. As broad surface high pressure shifts to the south of the area, southwest flow will return late Friday ushering a gradual warming trend into early next week with highs back into the mid-upper 40s by Sunday. There remains variability in the handling of a cut-off low forecast to stall over the desert southwest which eventually ejects northeast sometime early next week. This will bring increasing precipitation chances during the Sunday night through Tuesday period as it lifts across the region. At this range the higher probabilities for rain lie southeast of I-55 (40-60%) with further refinement in the details expected over the coming days. A period of cooler temperatures returns in the wake of these systems midweek next week. Petr && .AVIATION /06Z TAFS THROUGH 12Z THURSDAY/... Issued at 1111 PM CST Tue Dec 3 2024 Main Aviation Concerns: - Breezy SW wind gusts in excess of 22-28kts continue overnight through Wednesday morning, with increase expected Wednesday afternoon in excess of 35-40kts from the WNW/NW. - Areas of MVFR ceilings 1200-1500ft continue for the next few hours, before a break clearing of the low levels. Additional MVFR ceilings expected to arrive early Wednesday morning. - Potential remains in forecast for convective snow showers Wednesday afternoon through evening, with possible IFR visby's and minor accumulations. Breezy S/SW winds continue overnight, with gusts in the 22-28kt range. Wednesday morning starts breezy from the WSW, however sustained winds and gusts increase substantially through the afternoon from the west. Behind fropa during the mid afternoon, winds rapidly change to the WNW/NW with gusts in excess of 35-40kts (isolated higher). Gusty winds remain through the end of the period from the NW, as blustery air invades the region into Thursday morning. Ceilings are forecast to remain MVFR with a cover of secondary stratus clouds shifting into the western terminals. With both layers of cloud coverage, expecting MVFR to continue over the next couple of hours before VFR returns near 08z. Additional MVFR ceilings arrive near the 13-15z time frame from NW to SE, and remain overhead throughout much of the period. Still watching model depiction of snow showers Wednesday afternoon through the evening across the region. Winds ramp up in this time period, along with ceilings around 2kft and visby's reduced to 1SM, creating squall activity near the surface. There is potential for lower visby's (<1SM) and ceilings (<2kft), however at this time confidence is not high enough to include in forecast. Baker/DK && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 3 PM CST Wednesday for the IL and IN nearshore waters. Gale Warning from 3 PM Wednesday to 9 AM CST Thursday for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago