Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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799 FXUS63 KLOT 280856 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 356 AM 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. && .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. 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 /06Z TAFS THROUGH 12Z MONDAY/... Issued at 1235 AM CDT Sun Apr 28 2024 Key Aviation Messages: - Increasing shower/storm coverage tonight through mid morning - SSW winds tonight (variable in and near TS), may turn SE toward daybreak then return to gusty SSW in the afternoon - Another round of TSRA late Sunday evening and overnight Clusters of showers and thunderstorms currently along/south of I-80 will continue to lift northeast across the Chicago area terminals over the next hour or two (later at RFD). The trend in model guidance has slowed the exit of showers into the morning hours and have accordingly extended the VCTS mention through 14Z. Winds prevail SSW overnight through may be variable at times in and near any TS. Will keep an eye on a southward moving outflow boundary from earlier storms in SE Wisconsin that may try to briefly turn winds NW at ORD but the current expectation is for it to stall just to the north. There remains a signal that winds turn east to southeast due to remnant outflow in the wake of the AM showers/storms before then returning to a gusty SSW by the afternoon as the boundary retreats back to the north. There may be a 2-3 hour window that gusts occasionally exceed 30kt in the afternoon before easing again toward sunset. Spotty showers and storms may try to redevelop by the afternoon, especially toward RFD though confidence is not high enough to include with this update. There is a better signal for widespread showers and storms moving through during the late evening and overnight hours from west to east with associated vsby/cig reductions. Petr && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago