Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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371 FXUS63 KLOT 252346 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 646 PM CDT Sat May 25 2024 .KEY MESSAGES... - Periods of showers and thunderstorms on Sunday, with pockets of gusty winds and isolated large hail in the morning and a highly conditional risk for storms with large hail, damaging winds, and tornadoes late afternoon into the evening. - Widely scattered afternoon and early evening showers (and possibly a few non-severe storms) Memorial Day and again Tuesday - Gradual warming and drying conditions for the end of the week && .DISCUSSION... Issued at 310 PM CDT Sat May 25 2024 Through Sunday Night: High pressure crossing the area this afternoon as led to a dry and sunny day with temperatures mostly in the 70s away from Lake Michigan. Thickening upper-level cloud will shift across the area tonight as the low and mid-levels remain quite dry. Focus then turns to potential severe weather in and around our region for Sunday. A lot needs to unfold with regards to expected convection from southern Nebraska into northern Oklahoma late this afternoon into this evening. Per recent observational trends and morning CAM guidance, clusters of convection ahead of a lead wave ejecting from New Mexico into eastern Colorado will likely enhance the wave with a couple embedded MCVs while tracking toward the Mississippi River Valley late tonight. Ongoing elevated linear convection should near the western CWA in the 6 or 9am window. The overall evolution beyond that point becomes less clear as sufficient low-level moisture may not advect northward early enough to take advantage of impressive 8+C/km mid-level lapse rates. Given recent guidance, the convection should remain mostly sub-severe through much of the CWA, with the primary hazards being locally large hail and perhaps some pockets of strong gusty winds. However, if this decaying storm complex slows by as little as a couple hours, the low-level environment will become increasingly favorable for surface- based convection due to additional heating and increasing moisture with a warm front lifting northward. In this scenario, all hazards are possible roughly east of I-57 early in the afternoon. After the low-level environment attempts to recover in the wave of the morning convection, a conditional severe weather risk with all hazards exists early to mid-evening. Given sufficient heating, isolated to scattered discrete convection could develop along the cold front as deep-layer shear increases ahead of a stronger mid-level wave. Current trends suggest this will be a low probability (<30%) chance as airmass recovery will occur too late for sustaining stronger updraft cores before the loss of daytime heating. If the initial wave in the morning trends even faster than expected, severe storm chances would be notably higher across much of the area through at least mid-evening. Kluber Monday through Saturday: As the front moves east, drier conditions are expected on Monday, even if momentarily. Another short wave trough descends down the longer wave aloft on Monday providing another chance for showers in the late afternoon and early evening. Moisture is limited, lapse rates aloft are not particularly robust and wind shear through the column is fairly weak. However, there is a little instability aloft that could make some rumbles of thunder. Better chances are for areas closer to the Wisconsin state line, but kept at least minimum slight chances for the entire forecast. As an almost repeat event on Tuesday, the final short wave trough descends down out of Wisconsin for the chance for showers and storms Tuesday afternoon. Precipitable water amounts are projected to be even less than Monday afternoon with weaker instability. Current projections have the wave hugging the lake as it descends, so there are better probabilities for showers closer to the lake. Beyond Tuesday, an upper level ridge begins to grow over the Plains and drift east over Illinois. With heights rising and mid level subsidence developing, a gradual warming trend with drier conditions are expected for the end of the week, with a chance for temperatures away from the lake to start creeping back into the 80s by Friday and Saturday. DK && .AVIATION /00Z TAFS THROUGH 06Z MONDAY/... Issued at 646 PM CDT Sat May 25 2024 Forecast concerns include... Chance of thunderstorms Sunday morning. Chance of thunderstorms Sunday afternoon/evening. Gusty southeast winds Sunday. Mvfr cigs Sunday night. Convection developing over the central Plains this evening is expected to continue through the night and reach northwest IL around daybreak Sunday morning, likely in a slowly weakening phase but continue across all of the terminals by early Sunday afternoon. Adjusted timing a little earlier, starting 16z for the Chicago terminals, but further refinement will be needed once trends emerge overnight. After this activity moves east, there may be a lull for a few hours in the mid/late afternoon and then there will be a chance for at least isolated thunderstorms late Sunday afternoon into early Sunday evening. There is still uncertainty for timing and coverage but prob mention seems reasonable at this time. Southeast winds under 10kts will continue tonight and then increase to 10-15 kt Sunday morning with gusts into the 20kt range developing by late morning. Winds will likely turn more southerly mid/late Sunday afternoon and then southwesterly Sunday evening, but there remains quite a bit of uncertainty for specific wind directions during this time. Gusts should diminish with sunset Sunday evening. While mvfr cigs will be possible with any thunderstorms, prevailing low mvfr cigs may develop Sunday evening or early Monday morning as cooler air spreads into the area behind a cold front. Low confidence for mvfr cigs but scattered mention seems reasonable from this distance. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago