FXUS63 KLOT 310157 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 757 PM CST Mon Jan 30 2023 .UPDATE... Issued at 756 PM CST Mon Jan 30 2023 Arctic high pressure of 1036 mb was centered over western Iowa early this evening, and the eastern periphery of surface ridging will extend east into northern Illinois overnight. The combination of largely clear skies, fresh snow cover and diminishing winds will allow for strong radiational cooling overnight especially across northern parts of the forecast area. Temperatures had already fallen into the single digits above zero across much of the forecast area after sunset and should continue to dip below zero overnight. Going forecast already undercuts guidance across the snow pack roughly north of I-80 by several degrees, and current temperatures have been tracking nicely with our forecast hourly values so far. Thus have no significant changes planned for the evening update. Farther to the south, forecast lows in the lower positive single digits appear on track as well, with lack of snow cover and some lingering cloud cover still gradually decreasing there. Surface winds were still 5 to 10 mph in some areas especially across eastern/southern parts of the cwa, though with the ridge axis spreading in would expect winds to be nearly calm later tonight and early Tuesday morning when the coldest temperatures occur. Thus am fine with continuing to hold off on wind chill advisory headlines. Ratzer && .SHORT TERM... Issued at 210 PM CST Mon Jan 30 2023 Through Tuesday night... A large center of high pressure encroaching from the northwest will keep the short term forecast quiet, but awfully cold. The persistent cold advection from said high has prevented temperatures today from warming more than a few degrees from early this morning, even in the northwest CWA where they've been gifted with a fair amount of sunshine so far today. Early this afternoon, the area is sitting in the upper single digits and teens. However, a decent breeze out of the northwest is keeping wind chills in the single digits below zero across most areas. The aforementioned sunshine is slowly creeping across the CWA this afternoon as a pesky stratus deck is taking its time sneaking out of here. The southern CWA may not even see clearing until after sundown. Nonetheless, the area should see mostly clear skies through evening and night, aiding in the bitter cold conditions in store for tonight and early tomorrow. Temperatures around daybreak tomorrow are forecast in the single digits south of I-80 down to the double digits below zero in spots across the Rockford metro and surrounding areas. With the high centering itself over northern Illinois tomorrow morning, winds tonight into the morning should be very light, if not calm for several hours over the northwest CWA. Therefore, wind chills shouldn't depart too far from actual temperatures. Minimum wind chills are forecast to drop near -20 degrees in spots across the northwest CWA. Opted out of a wind chill advisory for tonight given the overall lack of wind and widespread wind chills expected to be slightly warmer than advisory criteria. Tomorrow will see similar temperatures to today with highs in the teens. Wind chills through the better part of the day are expected to be in the single digits on either side of 0. Modest warm air advection in the return flow of the departing high will bring slightly warmer conditions for tomorrow night. Lows will be in the single digits to slightly below zero with wind chills as low as the teens below zero. Doom && .LONG TERM... Issued at 210 PM CST Mon Jan 30 2023 Wednesday through Monday... Wednesday and Thursday look comparatively "milder" as we briefly emerge into a warm advection regime on the backside of a departing 1030 mb arctic high. Southwesterly breezes look to develop on Wednesday and with things generally looking pretty sunny, insolation and developing WAA may help push our temperatures a bit above the NBM offering of low 20s even with our newly-minted snowpack across northern Illinois. A reinforcing surge of notably colder temperatures will arrive Thursday night into Friday as a 1040+ mb arctic high slides east across the Upper Midwest. With this high center expected to remain mainly to our north, we should maintain some decent northerly/northwesterly winds into Friday, so depending on just how cold we get, could be flirting with Wind Chill Advisory criteria (wind chills -20 F or below) during the morning. Friday looks pretty unpleasant into the daytime hours with a lingering northerly breeze which will likely hold wind chills in the single digits above zero. We briefly get into the right entrance region of a very sharp jet streak that's slated to nose across the UP of Michigan and this likely will set off some loosely-organized arcs of modest f-gen through the day. Soundings look quite dry below about 800 mb in the wake of the front, so at this point it seems like the only impact from all of this would be a gradual increase in mid-level cloud cover. Renewed thrust of cold temperatures will drive an increase in lake effect snow showers on Friday. Prevailing wind direction should focus most activity just east of the region and a good deal of dry air aloft will likely cut down on LES production overall, but still seems like a scenario worth carrying some slight chance PoPs across parts of Porter and eventually Lake counties in NW Indiana. Winds eventually shift out of the southeast Friday night which may shove lingering LES into NE Illinois, but too far out to pinpoint any of this in the gridded database. Series of fast-moving disturbances will move across the region over the weekend, driving another period of robust warm advection which should pretty quickly dislodge this latest bout of cold. Lots of variability across the guidance suite regarding degree of moistening associated with the first shortwave Saturday night. Dry forecast for now is the way to go, but note that there is a signal for some light precip in ensemble guidance during this time frame. Another disturbance--this one with a bit more jet support--may arrive during the Monday - Tuesday period next week although temperatures initially may be warm enough to support just plain rain ahead of the cold front. Carlaw && .AVIATION... For the 00Z TAFs... 534 PM...No forecast concerns this period. Northwest winds around 10kts to start will diminish this evening and turn more westerly by morning with speeds possibly back to 10kts Tuesday afternoon. One mid deck has pushed southeast of the area with another mid deck across southern IA that may spread across the area later tonight, but confidence is low. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...IN nearshore waters until 3 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