Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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892 FXUS63 KLOT 281739 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1239 PM CDT Sun Apr 28 2024 .KEY MESSAGES... - Waves of showers and thunderstorms through Monday. Localized flooding remains possible early this morning, and there is a low (~15%) chance for an isolated severe thunderstorm or two to occur later this afternoon or evening. - After a break on Tuesday, a stormy pattern returns midweek along with continued unseasonably warm temperatures. && .UPDATE... Issued at 1036 AM CDT Sun Apr 28 2024 An area of showers continues to lift across northern IL into southern WI this morning along a warm front which will provide a brief reprieve for most of the area. However, additional showers and thunderstorms are expected to redevelop across eastern IA and western IL this afternoon and evening as the upper low pivots into the upper Midwest. There continues to be some uncertainty as to how much destabilization will occur before storms develop this afternoon due to the expectation for mid-level stratus to persist overhead which will play a role in storm coverage and intensity. Though, recent satellite trends do show pockets of clearing occurring across eastern MO and adjacent areas in IL which could drift into our area and provide some sun to help destabilize the environment. If sufficient instability can materialize as guidance suggests, the presence of 30 to 40 kts of deep shear should allow for some storms to organize and contain a threat for severe weather primarily in the form of gusty winds and hail. Additionally, hi-res forecast soundings do show some modest low-level shear near the aforementioned warm front which could support a low-end tornado threat across northern IL this afternoon into early evening. Given that instability is expected to wane quickly after sunset I suspect the main window for any severe weather will be confined to the 3 to 8 PM timeframe and largely be focused near I-39. While the severe threat will conclude this evening, showers and possibly a storm or two are expected to continue through tonight into Monday as a cold front advances through the area. Otherwise, seasonably warm and breezy conditions can be expected with gusts of 30 to 35 mph this afternoon. Temperatures will top out in the mid to upper 70s this afternoon for most, but areas along the Lake County, IL lakeshore will remain cooler due to onshore winds. Yack && .DISCUSSION... Issued at 356 AM CDT Sun Apr 28 2024 Through Monday: It`s been a rainy and stormy early morning for much of the area as a low-level jet has been funneling a persistent stream of moisture our way. MRMS and radar estimates indicate that, through 345 AM, between about 1 and 2.5 inches of rain has fallen across a corridor from the southwest Chicago suburbs towards Peoria, with lower totals elsewhere. With the low-level jet still going strong, rainfall is expected to continue over the next few hours and may ultimately culminate in some minor flooding of fields, ditches, and areas of poor drainage, mainly in the aforementioned corridor. Fortunately though, radar trends suggest that the instability reservoir in the region has gradually become depleted as a result of the widespread convection, and rainfall rates should continue to taper off as we approach daybreak. The shower/storm activity is expected to diminish over the course of this morning as the low-level jet weakens, paving the way for much of our forecast area to see plenty of dry time during the daytime hours today. However, with isentropic upglide continuing along the eastern periphery of a low pressure system situated beneath the upper-level trough over the Great Plains, additional rain showers will be funneled northward along the Mississippi River Valley throughout the day. Some of these showers will likely trickle into western portions of our forecast area this afternoon, though overall coverage is expected to be no more than scattered. The northward transport of warmth and moisture will also likely support MLCAPE recovering to around 500-1000 J/kg this afternoon in the zone of shower activity, so it`s very much possible that a few storms develop within this corridor as well. Shear profiles actually look fairly decent given the overhead placement of both the low- and upper-level jets, so if some deeper convection can get going, it could take on supercellular characteristics and become capable of producing damaging winds and/or hail. A brief tornado also couldn`t be ruled out with any organized storm that crosses the warm front near the Illinois/Wisconsin state line. Confidence in this outcome playing out is relatively low, and even if it came to fruition, the severe weather threat would remain isolated, so the Storm Prediction Center`s Day 1 Marginal Risk covers this possibility well. This afternoon, several storms are also expected to develop along a frontal zone to our west/southwest in Iowa and Missouri and will probably consolidate into a more linear multicell cluster that will propagate towards our forecast area this evening. Similar to yesterday evening, these storms are likely to lose steam as they encounter increasing quantities of convective inhibition with time and eastward extent. Consequently, the likelihood of severe weather occurring tonight as these decaying storms roll through is quite low, but if they managed to maintain their intensity, then some strong to marginally severe wind gusts couldn`t be ruled out. Tonight`s band of showers/storms will likely depart our forecast area early Monday morning as a mid-level dry slot barges into the region. With low-level cold air advection yielding steepened low-level lapse rates and the continued presence of the nearby upper-level trough providing forcing support, isolated to scattered low-topped convective showers may develop during the daytime on Monday. However, the quality and depth of moisture trapped beneath a low-level temperature inversion doesn`t look great overall and could potentially prevent these showers from developing altogether or, at the very least, limit their overall coverage. Have slashed PoPs a good bit for Monday as a result, keeping the highest probabilities focused in our southeastern CWA, where the influence of the dry slot won`t be as great as farther northwest and higher inversion heights will provide a better chance for clouds to grow deep enough for showers to redevelop. A cold front is then expected to pass through the area during the latter half of the afternoon into the evening, effectively shutting off shower chances behind it. Ogorek Monday Night through Saturday: Heading into Monday night most of the area will be dry, though a slower eastward push of the surface cold front would result in showers and storms potentially lingering into early Monday evening across portions of northwest Indiana. Modest upper- level height rises are expected in the wake of the aforementioned front which will promote a period of dry weather through the daytime hours on Tuesday. The reprieve looks to be short lived, however, as a series of shortwave troughs are forecast to traverse across the north- central CONUS. This will result in periods of showers and thunderstorms beginning Tuesday night and persisting through at least the end of the week. The details on timing and coverage of showers and storms will continue to be refined with later updates. Temperatures will remain unseasonably warm with afternoon highs in the mid to upper 70s through Thursday then turning a bit cooler and less humid heading into next weekend. Yack/Petr && .AVIATION /18Z TAFS THROUGH 00Z TUESDAY/... Issued at 1239 PM CDT Sun Apr 28 2024 Key Aviation Impacts for the current TAF period: - Scattered showers northwest of Chicago with the potential for some thunderstorms around KRFD this afternoon - Widespread showers and thunderstorms expected this evening and through Monday morning After a brief window of drier, VFR conditions, the next round of showers moves into the area this afternoon ahead of a front tonight. The risk for thunder was low enough around Chicago terminals to leave it out of the TAF currently; however, a TEMPO for -TSRA was placed into the KRFD TAF given the higher instability aloft expected to the west. Winds are slowly becoming out of the southwest as the warm front drifts northward. As cloud cover erodes, stronger gusts around 25 knots are expected to return to area terminals, though the occasion gust up to 30 knots is not out of the question. After 00Z, a cold front will start its movement eastward over Illinois through the overnight hours. This will bring a renewed threat of showers and thunderstorms at terminals that will provide another opportunity for MVFR/IFR conditions from lower cigs and vis. Current expectation is for the cold front, and associated heaviest rain, to be over the lake after 12Z Monday morning. However, post frontal showers are expected to linger through the morning hours. While there is lower confidence on the exact timing for when rain cuts off, drier conditions are expected Monday afternoon as southwest winds gust around 20 knots and gradually become slightly more west to southwest by the late afternoon. DK && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago