Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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843 FXUS63 KLOT 252010 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 310 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 /18Z TAFS THROUGH 00Z MONDAY/... Issued at 112 PM CDT Sat May 25 2024 Forecast concerns for the terminals... - Lake breeze turning winds easterly at the Chicago terminals this afternoon - Couple rounds of showers and thunderstorms possible Sunday, first round in the morning with a second round in the late afternoon/evening High pressure will continue to build into the area this afternoon which will keep sunny skies and light winds in place. However, a lake breeze is surging inland across northeast IL and is expected to reach ORD around 19z and MDW between 18z and 1830z. Behind the lake breeze winds will become easterly with a slight uptick in wind speeds into the 8 to 10 kt range. Elsewhere, winds will maintain a north-northwest direction through this afternoon before turning southeasterly overnight. Heading into Sunday, a line of showers and thunderstorms is expected to develop across the central Plains and advance across northern IL Sunday morning through early afternoon. While initially these showers and storms should arrive in a decaying state, instability is forecast to be gradually increasing through the morning as the showers/storms approach the Chicago terminals (around 16-17z). Therefore, confidence remains modestly high that showers and storms will impact the terminals Sunday morning and have maintained the prevailing SHRA and VCTS mentions. Though, have left GYY dry as the storms are not expected to reach the airport until after 18z which beyond their respective TAF period. Depending on how quickly this initial line of showers/storms exits the area Sunday afternoon will determine how much destabilization occurs and whether or not a second round of storms develops late Sunday afternoon/evening (similar to yesterday`s forecast). Guidance is unfortunately showing little agreement on whether or not the environment will recover and therefore confidence is lower on any impacts at the terminals. However, felt there was still a sufficient signal to warrant the addition of a PROB30 to the 30-hour TAF sites to account for this potential. Yack && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago