Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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647 FXUS63 KLOT 141719 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1119 AM CST Thu Nov 14 2024 .KEY MESSAGES... - Dreary morning expected, as showers transition to a period of drizzle and fog. - Temperatures will be near to above average through early next week. - A cooler weather pattern, potentially accompanied by periodic showers, may materialize mid-late next week and continue toward the end of the month. && .DISCUSSION... Issued at 259 AM CST Thu Nov 14 2024 Through Friday: Scattered showers continue to develop and stream northward across our area just in advance of a sharp mid-level trough/low centered across far southeastern IA as of this writing. This feature, and its associated surface low, will quickly slide eastward across northern IL through daybreak, then across northern IN through the remainder of the morning. As it does, expect developing showers to continue for the next few hours (through 5 or 6 am), before the primary focus begins to shift to the east. While no longer formally mentioned in the forecast, we still cannot totally rule out a few lightning strikes with some of this activity early this morning, but any threat for this will be short lived. Otherwise, expect a rather dreary morning across the area this morning as very low clouds, fog and areas of drizzle persist under the low. Winds will turn northwesterly with the eastward passage of the surface low this morning. While a gradual visibility improvement is expected through the morning, it appears cloud cover will hang on across the area today. Accordingly, temperatures are expected to remain fairly steady in the low to mid 50s. Drizzle and rain chances will end for most by this afternoon. However, a low potential (~20% chance) for some light lake effect showers will continue tonight across parts of northeastern IN. Cloud cover may end up lingering across much of northeastern IL and northwestern IL tonight into the day on Friday as low-level moisture looks to become trapped under a subsidence inversion developing off the surface. For this reason it remains a bit unclear as to how quickly conditions may scatter out on Friday as a weak surface high shifts overhead. As a result, temperatures are expected to hold in the low to mid 50s for Friday. KJB Friday Night through Thursday: Heading into this weekend, the synoptic weather pattern will feature upper-level troughing over the western half of the CONUS and upper-level ridging over the eastern half of the CONUS. This upper-level flow configuration will help spawn an initial weak surface low over the northern Plains late Friday into early Saturday that will then wander off to the northeast into Ontario on Sunday, remaining well to our north. Low-level flow to the south of the low and on the backside of a departing surface high will be out of the south to southwest, helping high temperatures to climb into the mid-upper 50s and possibly even low 60s on Saturday. In spite of increasing cloud cover, continued modest warm air advection should cause Sunday`s highs to end up being a few degrees warmer than Saturday`s, so long as the cold front associated with the aforementioned low slows its southeastward progress as much as most of the latest forecast guidance says it will. A ribbon of isentropic ascent ahead of this front could help generate a few showers in or near our forecast area on Sunday, though with little additional forcing support, the overall coverage and duration of any showers should be limited. Early next week, the primary western CONUS trough will lift northeastward towards the Midwest, accompanied by a low pressure system at the surface. While uncertainty remains in how this trough will interact with another upper-level trough swooping in from the Pacific Northwest and how quickly the attendant surface cyclone will occlude and where, every single member of both the 00Z EPS and 00Z GEFS outputs QPF in our forecast area late Monday into Tuesday. This lends high confidence to rain occurring during this time frame regardless of exactly how the upper-level trough and surface low evolve, though the exact timing, duration, and quantity of rainfall all remain points of uncertainty in our forecast that will need to be refined in forthcoming forecast updates. The finer scale details of the synoptic pattern evolution will be of greater relevance for the forecast for Wednesday through the end of the week, which remains quite uncertain at this time. While it may still be a few days before we have a better idea on how all of the puzzle pieces will come together, there is a fairly strong signal in ensemble guidance that these pieces will come together in some way that will establish mean upper- level longwave troughing over the northeastern quadrant of the CONUS from late next week through possibly the end of November. If such a pattern were indeed to be established, then cooler temperatures would be favored to prevail across the region. These cooler temperatures would potentially be accompanied by periodically showery conditions as well, including showers that wouldn`t necessarily be of the liquid variety... Ogorek && .AVIATION /18Z TAFS THROUGH 00Z SATURDAY/... Issued at 1119 AM CST Thu Nov 14 2024 IFR to MVFR cigs are expected to prevail through much of the afternoon before rising and settling near 2000 to 2500 feet overnight into tomorrow. Timing out when cigs will scatter/erode is always tough in the current regime (moisture trapped beneath an inversion, relatively low sun angle), so for now, will offer a pessimistic forecast with MVFR prevailing through the entire TAF. Northwest winds will remain generally between 5 to 10 kt through much of the TAF period before becoming light and variable tomorrow evening. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago