Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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145 FXUS63 KLOT 021939 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 239 PM CDT Thu May 2 2024 .KEY MESSAGES... - Scattered showers and thunderstorms will increase in coverage this afternoon, and continue through the overnight hours. - A few storms may be severe this afternoon with hail up to 1 inch in diameter, 60 mph winds, and soaking downpours. The severe threat should wane after sunset. - Periodic chances for showers and thunderstorms will continue from this weekend onward, with some potential for severe weather on Tuesday. && .DISCUSSION... Issued at 239 PM CDT Thu May 2 2024 Through Saturday night: Showers and thunderstorms are off to an early start along the I-55 corridor, seemingly due to the interaction with an eastward-moving mid-level gravity wave and the northward-moving warm front. Additional showers and storms are expected to develop throughout the afternoon and especially after sunset as the right entrance region of an upper-level jet streak moves over the Great Lakes. As we already saw with the first batch of showers and thunderstorms, a few may pulse to severe levels with 1" hail and 60 mph "splat" downbursts through about midnight thanks to MLCAPE 1000-1250 J/kg and meager deep layer shear. With that said, widespread severe weather is not expected today, and the threat should wane with the loss of heating after sunset (though a few non-severe thunderstorms may continue through the overnight hours). Showers will likely continue through daybreak Friday as a cold front sweeps across the area. Chances for rain will then end from west to east Friday morning behind the front as drier air works into the region. Clearing skies and highs in the lower 70s are expected tomorrow afternoon, though stout northerly winds off Lake Michigan will keep lakeshore locations some 10 to 15 degrees colder, particularly in northwestern Indiana. As a surface high pressure system slides overhead tomorrow night, slacking winds and clear skies will allow for efficient radiational cooling. Overnight lows should dip into the upper 40s with locally cooler readings in typical cold spots. If drier guidance verifies (allowing for even more efficient radiational cooling), some lower 40 degree readings cannot be ruled out. Borchardt Sunday through Thursday: Coming Soon... NWS Chicago && .AVIATION /18Z TAFS THROUGH 00Z SATURDAY/... Issued at 1237 PM CDT Thu May 2 2024 Key Messages: - Southerly wind shift expected at the terminals by 20z this afternoon. - Isolated to widely scattered late afternoon and early evening thunderstorms around the terminals after 21z. - A period of more widespread showers (and a few storms) expected mid to late this evening through early Friday morning. - West-southwesterly winds shift northerly by daybreak Friday, then northeastward through the day. A couple periods of active weather are expected later today and tonight as a storm system tracks north-northeastward from IA into the Upper Great Lakes. In the near term, a southerly wind shift is expected in the 19 to 21z timeframe as a surface warm front lifts northward across the terminals. Once this occurs, a warm and moist airmass will allow for the development of some isolated to widely scattered thunderstorms later this afternoon. While it remains a bit unclear if these storms will move over a given terminal late this afternoon, there is moderate confidence that a few will be around the area. For this reason, we continue to advertise this potential in a tempo group in the 22 to 24z timeframe. More widespread showers (with some embedded storms) are expected to develop/shift eastward across the terminals tonight as a cold front approaches. The best timing for the Chicago terminals looks to be in the 04 to 09z timeframe, and more in the 03 to 08z period at KRFD. A period of MVFR CIGs and VSBYs may also accompany some of the rain overnight. MVFR CIGs may linger for a few hours following the end of the rain late tonight, but conditions should improve back to VFR through the morning following the cold front. Winds will shift north-northwesterly late tonight following the cold frontal passage. Directions will then settle into a northeasterly direction during the day Friday. KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago