Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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591 FXUS63 KLOT 221730 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1230 PM CDT Wed May 22 2024 .KEY MESSAGES... - Westerly winds will gust to around 30 mph today - A line of showers and storms is expected on Friday - Another chance for storms Sunday into Monday next week && .DISCUSSION... Issued at 241 AM CDT Wed May 22 2024 Through Thursday: A cold front, seen as a well defined fine line on the terminal doppler radars, is in the process of moving across the Chicago metro area as of this writing (0730 UTC). Passage of the cold front should put an end the very impressive synoptic winds that have occasionally gusted to near 60 mph since early last evening. It will remain breezy behind the front through the day today, but not nearly as windy as what we are seeing/saw ahead of the cold front. Will trim away at the remaining wind advisory as the front clear the area. Other than westerly winds gusting to around 30 mph today, really not expecting any impactful weather through Thursday. After some morning cloudiness, expect skies to gradually clear out this afternoon. While much cooler than yesterday, temps should be seasonably mild today. Thursday will be sunny and seasonably warm, though a lake breeze will develop in the afternoon knocking temps back into the 60s at the lakeshore. - Izzi Thursday Night through Tuesday: As the next upper level wave trough ejects out of the Rocky Mountains early on Thursday, a new surface cyclone will develop over the Great Plains and travel northeastward. The good news is a.) all model indications are that this low will be weaker than Tuesday and b.) it will take a more northerly track, closer to Minnesota. Regardless, a trailing cold front is schedule to arrive Friday morning and pass across the forecast area through Friday. Being so far removed from the low, models are developing a more marginal set up. There is a good consensus among models for mid level lapse rates around 7.5C/km, over 2000 J/kg of CAPE above the inversion, as well as a nice veering wind field through the column. Two main inhibiting factors will be tied to wind shear and forcing. Models have consistently over the last several days been projecting fairly weak shear, only 30 knots up to 6km and less than 20 knots below 3km. The jet streak wrapping around the upper level trough appears to be too far north to assist with any synoptic lift, so most of the forcing will have to come from the front itself. However, with afternoon temperatures expected in the 80s, there should be enough to tap into the instability aloft and scattered thunderstorms. With model soundings projecting around 800-1100 J/kg of DCAPE, if there was a severe threat, it could come with gusty winds as the line passes through. Better height rises and cold air advection behind the front will lead to a pleasant Saturday with temperatures in the 70s under clearer skies. As the next upper level trough moves over the Plains, another surface low will move northeastward from Missouri on Sunday into Monday. However, models are all over with the exact track, but it seems like Chicago continues to be the proverbial "fork in the road" with the low avoiding the city to the north or south depending on which model and which model run you look at. Since a majority of models are taking the southerly track toward northern Indiana, its no surprise that the NBM has higher Pops through Sunday into Monday for areas south of I-80. But given that it is five days away, confidence will remain in that showers and thunderstorms are expected, but the details can be ironed out closer to Sunday. Beyond Monday, ensemble upper level patterns develop more northwest flow over the area and the previous trough moves to the east. As it exits, it could send some weak lobes of vorticity over the area mid week for another chance for showers over the area, but confidence being low, PoPs in the extended were capped at just a chance. But with cooler air filtering in from the northwest, high temperatures next week should be around seasonal norms. DK && .AVIATION /18Z TAFS THROUGH 00Z FRIDAY/... Issued at 1230 PM CDT Wed May 22 2024 Main Concern: - Timing of likely lake breeze wind shift on Thursday afternoon Quiet VFR conditions are in store through this TAF cycle. Gusty west winds will ease with sunset and become light southwest to variable overnight. Weak winds aloft on Thursday are expected to allow a lake breeze to push inland across ORD and MDW (and GYY beyond its current TAF period), shifting winds to easterly near 10 kt. Indicated a 20z timing of the wind shift at ORD and MDW, which will be refined as needed in subsequent updates. Castro && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 6 PM CDT this evening for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago