247 FXUS63 KLOT 102000 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 300 PM CDT Wed Oct 10 2018 .SHORT TERM... 206 PM CDT Through Tonight... Numerous showers, moderate to heavy at times, are expected through the afternoon. There could be a few thunderstorms, but with only 500 J/kg per the latest RAP analysis, storms should be few and far between. Shear still looks favorable, but all other parameters are not favorable for severe storms, so I'm not expecting any severe storms. Showers shift east ahead of the approaching cold front ending from west to east early this evening. The front is over the Mississippi River and will shift overhead late this afternoon into tonight. Winds will become west and gust to 30 MPH immediately behind the front. Gusts increase to around 35 MPH this evening as we mix higher into the column. If mixing is greater than currently expected, gusts could be higher. Most areas have reached their high temp for the day and temperatures will continue to fall into the upper 30s to low 40s overnight. Windchills will be in the low 30s Thursday morning. JEE && .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 18Z TAFs... Showers with a few embedded thunderstorms will continue through the late afternoon. I have low confidence in the number of storms as there is very little convective energy to work with. However, based on past observations, stronger showers and storms could bring visibilities down to IFR. Cigs should be mainly MVFR although a few patches of IFR cigs persist over northwest Indiana. Showers end ahead of the approaching cold front. The front is currently over the Mississippi River and will move through the terminals late this afternoon and early evening. There may be a very brief period of VFR conditions just ahead of the front, but MVFR cigs will return immediately behind the front. Winds will become west with gusts up to 25 kt initially. Better mixing behind the front may produce near 30 kt gusts by mid evening through Thursday morning. Gusts could be higher if mixing is deeper. West winds slowly diminish with gusts up to 25 kt expected in the late aftn as clouds slowly scatter out from south to north. JEE && .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...None. IN...None. LM...Gale Warning...LMZ740-LMZ741...9 PM Wednesday to 10 AM Thursday. Small Craft Advisory...LMZ742-LMZ743-LMZ744-LMZ745...9 PM Wednesday to 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