922 FXUS63 KLOT 101143 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 643 AM CDT Wed Oct 10 2018 .SHORT TERM... 337 AM CDT Through tonight... The main forecast concern continues to focus on the showers and thunderstorms expected to impact the area today ahead of an approaching cold front. Gusty west-northwest winds then become the primary focus by this evening following the passage of a strong cold front. Early this morning, a line of showers, and some thunderstorms, extends north-to-south generally along the entire Mississippi River Valley from the southern Gulf Coast up into MN. This line of showers is only slowly working eastward into western portions of IL at this time. This activity will be gradually working eastward over north central IL through the morning hours. Meanwhile, additional showers and storms, currently developing to our south over southern IL and western portions of TN and KY, will work there way northward into portions of eastern IL and northwestern IN later this morning and early this afternoon. In between these two areas of showers, it appears that several areas of northeastern IL will remain dry, at least for some time this morning, before the threat of rain increases by midday. While there will be a period of showers and possibly a few embedded storms across the area this morning, the main threat for possible strong storms with strong gusty winds looks to be this afternoon. This potential will be driven by the arrival of a strong cold front, associated with a dynamic area of low pressure over IA and southeastern MN. Overall this low is expected to continue to deepen into a sub 1000 mb low today as a potent negatively tilted mid-level disturbance ejects northeastward over the a Upper Midwest. The low is expected to drive the cold front eastward across northern IL through the afternoon. Along and ahead of this frontal boundary some enhanced forced ascent will likely drive a redeveloping area of potentially stronger showers and storms. As has been mentioned in previous discussions over the past couple of days, this will be a low CAPE, but high wind shear environment, which is not all that atypical for this time of year. While this will be the case, it does continue to appear that a period of strong dynamically forced ascent just ahead of the approaching surface front should help compensate for the weaker instability. Strong damaging wind gusts look to be primary concern from these afternoon showers and storms. The storms will come to an end from west to east late this afternoon and early this evening as the cold front shifts across the area. Gusty west-northwest winds are then likely to onset across the area early this evening following the frontal passage. It appears that wind gusts could, at least briefly, gust up close to 40 mph immediately following the frontal passage. Otherwise, expect wind gusts of 30 to 35 mph through the night as cold air moves into the area. After highs in the 70s today, lows tonight will fall into the upper 30s to low 40s under these gusty winds. KJB && .LONG TERM... 337 AM CDT Thursday through Tuesday... The main forecast concern during the extended period will be the increasing possibility of widespread frost across the area by the end of the week. Gusty west-northwesterly winds will continue on Thursday, and this will continue to usher in much colder weather. In fact, temperatures on Thursday are likely to remain in the upper 40s to low 50s area-wide in spite of mainly sunny skies during the afternoon. Temperatures Thursday night then look to fall into the lower to mid 30s with this cold airmass in place. There continues to be some concerns on the extent of frost across the area Thursday night, due mainly to the likelihood of a continued northwest wind of 5 to 10 mph through the night. However, with the possibility of some areas in north central IL and into the Fox Valley falling to near freezing, I have continued the mention of frost in the forecast to heighten awareness. Friday will be another cold day across the area, with upper 40s far north, to low 50s south. Model guidance has been indicating that a mid-level short wave disturbance will shift from the Dakotas to the southern Great Lakes during the day Friday. While this has been the case, guidance has been struggling on if there will be enough available moisture to support precipitation over the area as this disturbance moves overhead. With the uncertainty still apparent, I choose to run with the blended solution that gives some lower end chances for precipitation Friday afternoon and evening. Interestingly, some of the guidance indicating precipitation with this disturbance Friday evening are also cold enough to support some wet snowflakes. While this could be possible given the cold airmass in place, I have left the mention of snow out of the forecast at this time. Surface high pressure will be building in across the Mid- Mississippi Valley in the wake of this disturbance Friday night. If skies are able to clear late Friday night, we could see yet another night of temperatures falling down around freezing and potentially widespread frost over the area, assuming any lingering winds remain light enough. Temperatures look to remain chilly Saturday, but may warm a couple of degrees on Sunday, before another cold front pushes over the area later in the day. There still will be a chance of precipitation over the area late Sunday and Sunday night as forecast guidance continues to advertise another disturbance shifting across the central CONUS, but confidence remain low with the timing of this next system. KJB && .AVIATION... For the 12Z TAFs... Dry/VFR conditions with southerly winds continuing at this time, as surface low pressure and front remain just to the west of the terminals. Expect these features and associated precip to reach RFD here shortly but do think thunder will be limited at first, with latest obs indicating this trend. Do think there will be an increase in thunder potential through mid/late morning though. Along with increasing precip/thunder chances during this time, will also see VFR ceilings fall to MVFR. It's possible to observe IFR ceilings today, however, confidence remains low and have continued MVFR. After this initial wave of precip this morning, will likely see a broken line of showers and thunderstorms develop by midday/early afternoon and then move east through northern IL and northwest IN through the afternoon. This should end any precip chances for the period, though some scattered showers may continue for a couple of hours into the late afternoon. Will see a trend back up to VFR ceilings by the evening, with these conditions persisting through the end of the period. Southerly winds will likely continue for most of today, but anticipate a trend to the south southwest this afternoon, and then eventually more west southwest with FROPA. This shift to the west will also usher in much stronger winds, with gusts up to around 30 kt possible at times this evening. Could see a period of stronger winds with FROPA, and will need to monitor the possibility of higher speeds/gusts for a time this evening. Rodriguez && .MARINE... 342 AM CDT A strong weather system will move across the region today and tonight. In response to this, south winds later today will be near Small Craft Advisory, and there could be some gusty showers and storms as well, especially in the afternoon. A strong cold front will pass early this evening. Directly following this 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. For now we will hold with the gale watch. MTF/KB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...LMZ742-LMZ743-LMZ744-LMZ745...9 PM Wednesday to 4 AM Friday. Gale Watch...LMZ740-LMZ741...9 PM Wednesday to noon Thursday. && $$ 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