877 FXUS63 KLOT 110752 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 252 AM CDT Thu Oct 11 2018 .SHORT TERM... 252 AM CDT Through tonight... The primary forecast concerns revolve around temperatures, especially the next couple of nights, which are likely to drop to near, or just below freezing across, at least portions of the area. Due to the likelihood for freezing conditions tonight across north central IL we have issued a freeze warning, which goes as far east as the Fox Valley. Elsewhere, with the exception of Porter County IN, a frost advisory has been issued for tonight. Surface low pressure will continue to deepen today as it moves over eastern Ontario and into western Quebec. Meanwhile, much colder air continues to stream in over the Midwest and Great Lakes Region in the wake of this departing low. Westerly winds have been gusty up around 35 mph through the night, and it appears that these gusty winds will continue into this afternoon before abating by early this evening. A large deck of MVFR stratus, indicative of the cold air advection regime across the region, will also continue to hang on across the area into this afternoon, before skies begin to gradually scatter later this afternoon. Temperatures today will remain quite cool, with highs likely only hovering around 50 degrees in most areas. These cold daytime highs today will then set the stage for a cold night across the area tonight. Surface high pressure is expected to build eastward today from the Dakotas to Iowa by tonight. With this being the case, it is likely that most areas will continue to experience a light 5 to 7 mph wind speed overnight. Typically, winds of this magnitude are not the best to support widespread frost development. However, in spite of this concern, due to the fact that surface temperatures are likely to fall to near freezing, we felt that it is worth issuing the respective frost and freeze headlines. KJB && .LONG TERM... 233 PM CDT Thursday through Wednesday... No significant weather impacts appear to be in store through mid next work week. However, the big story will be the sudden flip from summer-like to late fall-like weather. On Thursday, strong cold air advection will support fairly deep mixing, thus brisk west-northwest winds will gust to 25-35 mph. As mentioned in short-term AFD, after 2 days with highs in 80s this week and 70s today, wind chill values for the Thursday morning commute will be in the lower to mid 30s, quite a change. Broken to closed cell stratocumulus will gradually erode during the afternoon, with highs only in the upper 40s to lower 50s for most, except possibly mid 50s far south. Mostly clear to partly cloudy skies and diminishing winds Thursday night into early Friday should set the stage for lows in the lower to mid 30s outside of Chicago. With winds unlikely to drop to calm, a bit hard to say how much true frost development is in store, though do have areas to widespread mention outside of downtown Chicago. Would anticipate a decent chance for frost/freeze headlines being needed, unless clouds increase quicker in advance of the next wave approaching from the west. Models vary on precip coverage and northward extent on Friday afternoon, with current focus of chance PoPs currently more so south of I-80, though with latest ECMWF favoring northward, this forecast is subject to change. Highs Friday will only be in the mid 40s to lower 50s, again well below the normal lower to mid 60s. Surface high will quickly move in Friday night into Saturday and center just south of us. This will likely be close enough for sufficiently light winds for good radiational cooling and lows 30-35 outside of Chicago (possibly a few upper 20s in typical cool spots per MET MOS guidance), assuming skies do clear as expected. Depending on how cold it gets, this has the potential to be a killing freeze for sensitive outdoor plants. After highs mainly in the 50s Saturday and a bit milder readings Saturday night, another cold front will move across the area Saturday night into Sunday with a small chance for light rain. Looking ahead to later Sunday into Monday, ECMWF had been indicating a strong upper jet interacting with lower-level baroclinic zone to blossom an area of light precip much farther north than other guidance. Latest run did back off a bit on this while other guidance keeps the rain south. In deference to ECMWF and given the uncertainty, did maintain some PoPs. Monday will have highs in the 40s likely for all or most locations north of I-80 and another near freezing night outside Chicago Monday night. The long-wave trough responsible for the cool weather and possible reinforcing cold shot by around mid week may lose its grip later next week beyond day 7. Castro && .AVIATION... For the 06Z TAFs... Dry conditions expected this forecast period, however, will continue to see MVFR ceilings this morning through midday/early afternoon. A slight rise in ceiling heights may occur this morning, but once again, think mainly MVFR ceilings. Expect skies to scatter later today, with clearer skies then anticipated this evening. West winds/gusts will persist this morning into this afternoon, but a diminishing trend will then occur this evening through the end of the forecast period. Rodriguez && .MARINE... 206 PM CDT A strong cold front will pass early this evening. Following the frontal passage this evening, wind gusts may briefly gust to near 35 kt gales, especially along the IL near shores, before gradually settling down to near 30 kt overnight and into Thursday. I think there will be a few gale force gusts, so I opted to go with a Gale Warning. However, winds should diminish below gales by mid Thursday morning. MTF/KB/JEE && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Freeze Warning...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011- ILZ012...1 AM Friday to 9 AM Friday. Frost Advisory...ILZ006-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021- ILZ022-ILZ023-ILZ032-ILZ033-ILZ039...1 AM Friday to 9 AM Friday. IN...Frost Advisory...INZ001-INZ010-INZ011-INZ019...1 AM Friday to 9 AM Friday. LM...Gale Warning...Winthrop Harbor to Northerly Is. until 10 AM Thursday. Small Craft Advisory...Northerly Is. to Michigan City IN until 4 AM Friday. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO