Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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428 FXUS63 KLOT 281759 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1259 PM CDT Tue May 28 2024 .KEY MESSAGES... - Scattered thunderstorms expected this afternoon into early this evening, the strongest of which may produce locally gusty winds to 50 mph and hail to the size of a penny. - Cool, but dry, weather expected Wednesday and Thursday, followed by moderating temperatures back into the lower 80s by early next week. && .UPDATE... Issued at 1026 AM CDT Tue May 28 2024 As yesterday`s upper level wave has moved to the southeast, clearer skies have developed over northeastern Illinois prompting a downward adjustment to the sky cover forecast for the short term. But all eyes are on satellite and radar as the next wave is clearly visibly moving southeast out of Minnesota and western Wisconsin. For now, there has not been any indication of lightning with this broken line of showers. However, as they move down, they will be able to interact with just over 1000 J/kg of MUCAPE that recent mesoanalysis displays over northern Illinois. Time of arrival still looks good for around 3 PM around the Wisconsin/Illinois border, with numerous showers expected and the chance for thunderstorms through this evening with the potential for stronger wind gusts and maybe some penny size hail. DK && .DISCUSSION... Issued at 307 AM CDT Tue May 28 2024 Through Wednesday: Water vapor imagery early this morning depicts our mid-level impulse responsible for yesterday afternoons scattered thunderstorms currently sliding east-southeastward right across southeastern WI/ and far northeastern IL. The lingering showers associated with this impulse will continue to hug the southeastern WI shores of Lake Michigan through sunrise. Most of our area remains dry this morning, but cannot rule out a few of the ongoing showers in southeastern WI briefly shifting into parts of Lake county IL during the predawn hours, before the focus quickly moves offshore. Following a quiet and dry morning, the focus for this afternoon and evenings weather quickly shifts to the next impulse currently noted in the water vapor imagery across the eastern Dakotas. This feature will be the driver for yet another round of afternoon and early evening thunderstorms as it digs southeastward into our area. Similar to yesterday, low-level moisture is expected to remain marginal through afternoon, as dewpoints remain in the lower 50s. Accordingly, MLCAPE values will remain lackluster, with values only peaking in the 500-800 j/kg range. Deep layer shear is also not expected to be overly favorable for organized severe storms as a result of the stronger mid-level flow remaining displaced to the west and southwest of the area. Nevertheless, unseasonably cold temperatures aloft (e.g. 500 mb temperatures around -20C) are expected to again foster rather steep low to mid- level lapse rates as surface temperatures warm into the low 70s this afternoon. This may thus act to compensate for the meager MLCAPE values and poor shear to at least support some low threat for a few isolated pulse-type storms and loosely organized multi- cell clusters that could become capable of producing a few instances of locally gusty winds to 50 mph and possibly some small hail. The threat of storms will wane shortly afternoon sunset, though some lingering showers could persist through the evening. The weather will quiet down for Wednesday, but temperatures will be below average. Expect high temperatures Wednesday to only be in the 60s to low 70s. The coolest temperatures will be near the lake due to the persistent breezy onshore flow. Dangerous swimming conditions are also expected along Lake Michigan beaches on Wednesday due to enhanced wave action from the breezy northerly flow down the lake. KJB Wednesday Night through Monday: The windward side of a departing upper trough will spread surface high pressure across the Great Lakes late Wednesday and remain in the region into early Friday. This should keep conditions quiet and clear Wednesday night and Thursday. We can expect seasonably mild temperatures on Thursday with highs forecast to reach the lower and middle 70s for most of us. Light onshore flow will keep areas near the lake several degrees cooler. The high will begin moving away to the east early Friday and the mild return flow will help pull highs into the middle and upper 70s to close out the work week. Clouds are anticipated to build during the day as moisture is advected in aloft ahead of an approaching shortwave disturbance. This wave is expected to bring a push of showers across the region late Friday and Saturday. There is spread on the timing and magnitude of the wave with the GFS being the most aggressive with forcing. In any case, while embedded thunderstorms look very achievable, really no guidance is hinting at an overly supportive thunderstorm environment. At this point, the greatest precip potential for us here looks to be late Friday night through Saturday morning meaning we`ll hopefully spend the bulk of Saturday rain-free. There is rather poor agreement among medium-range guidance on the regional synoptic pattern beginning early next week. It does look to be a moderately unsettled one with various disturbances floating around causing models to spit out sporadic rain and storm chances Sunday through Tuesday. The GFS and Euro over several runs have been bringing a cold front through the region sometime between late Sunday and early Tuesday with an appreciable thunderstorm environment building ahead of it. We`ll continue to monitor this potential as model confidence for this period builds. There is considerable agreement among deterministic and ensemble guidance in a warmup to more early summer-like conditions early next week just in time for the dawn of meteorological summer! Doom && .AVIATION /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 1259 PM CDT Tue May 28 2024 Forecast concerns for the terminals... - Lake breeze may impact the Chicago terminals early this afternoon - Scattered showers and thunderstorms this afternoon and evening - Period of low-end VFR to MVFR ceilings late tonight into Wednesday morning Scattered to broken VFR clouds will continue to develop this afternoon with otherwise light northwest winds around 6 to 8 kts. However, a lake breeze is trying to surge inland across northern IL and northwest IN this afternoon which may result in an easterly wind shift at ORD and MDW. Given that winds with the lake breeze are equal to the prevailing winds, confidence is low as to whether or not the boundary will actually surge through ORD and MDW or stall just east of the airports. Therefore, have decided to forgo a formal mention of an easterly wind shift at ORD, but since the lake breeze is almost to MDW did add a wind shift at 1830z. Regardless, winds at the Chicago terminals should turn back northwest as showers arrive later this afternoon. Scattered showers and thunderstorms are expected to develop across northeast IL and northwest IN this afternoon as an upper- level disturbance pivots through the area. While instability continues to look modest, shower and storm coverage is forecast to be more robust than yesterday thus confidence on storms is higher today especially in the 22z to 00z timeframe. Additionally, there is the potential that the strongest storms may produce locally gusty winds and small hail but widespread severe weather is not expected. Showers and storms will come to an end this evening (likely by 02z at the latest) with dry conditions expected for the rest of the period. However, guidance continues to hint that some 2000 to 3000 ft ceilings may try to develop overnight and linger into Wednesday morning. While most guidance is in good agreement on the ceilings, ensemble probabilities are only around 30% for MVFR conditions tonight so have decided to maintain the SCT020 mention for now. Any MVFR ceilings that develop tonight will erode by midday with otherwise northwest winds becoming northeasterly Wednesday afternoon. Yack && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago