Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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956 FXUS63 KLOT 180138 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 838 PM CDT Mon Jun 17 2024 .KEY MESSAGES... - Hot and muggy conditions will prevail through the end of the week. - Periodic chances for thunderstorms will continue, though many hours will remain dry. && .DISCUSSION... Issued at 255 PM CDT Mon Jun 17 2024 Through Tuesday Night: Isolated thunderstorms will be possible through sunset. The focus appears to be a weak boundary lifting north, currently between I-55 and I-57. As this boundary lifts north, isolated thunderstorms will continue to be possible. Otherwise, it remains hot with temps in the lower/mid 90s. Southwest winds gusting as high as 30 mph have allowed dewpoints to mix out, in some areas into the lower 60s. This is keeping the heat index values generally in the mid/upper 90s with a few locations tagging 100. Winds will diminish with sunset this evening but may remain gusty at times, especially in the metro area as low level winds increase this evening. Combined with dewpoints likely rising back into the upper 60s/lower 70s, low temps tonight will likely be in the mid 70s for most locations, upper 70s/near 80 for Chicago. The next chance for thunderstorms will be overnight through mid/late morning Tuesday as a weak wave lifts north across the area. Confidence remains low for coverage, especially at that time of day and its possible precip may be in form of showers, vs thunderstorms. Kept pops in the slight chance (20%) range for now but as trends emerge tonight, these may need to be increased. Isolated thunderstorms are possible again Tuesday afternoon, but could be dependent on morning coverage and then most of Tuesday night looks dry for now. Did not make any changes to high temps on Tuesday, which is mainly lower 90s areawide. However, these are generally above most guidance highs. Possible cloud cover and precip in the morning, if it occurs, could keep high temps lower. Though if clouds clear out during the afternoon, highs may still reach the lower 90s. Southwest winds gusting into the 25-30 mph range may once again keep dewpoints in the 60s with heat index values only in the upper 90s. cms Wednesday through Monday: The focus mid to late week remains the continued hot and humid conditions and periodic shower and thunderstorm chances. The amplified upper level ridge across the eastern CONUS will begin to flatten out some across the Great Lakes region with the heat dome still locked in place. Forecast high temperatures Wednesday through Saturday are in the mid-upper 90s which is 10-15 degrees above the 30-year normals for this time of year. Dew points likely mix out enough each day to keep our max heat indices in check in the 95-100 degree range which remains below our local heat headline criteria. However, given this is the first prolonged stretch of heat this year we will continue messaging heat safety related information. A backdoor front looks to keep wind directions onshore Thursday and Friday which will likely hold high temperatures near the lake in the 80s. As for shower and thunderstorm chances, a stalled surface boundary will be near to just northwest of the area as early as Wednesday morning that could serve as a focus for thunderstorm development through Wednesday, particularly northwest of Chicago toward the Rockford area. Given lingering uncertainties with the timing and placement of this boundary precip chances remain capped at 30-50% for areas northwest of I-55. For areas southeast of I-55 isolated showers and thunderstorms can`t be ruled out each afternoon. A shortwave moving across the Northern Plains/Canadian border and associated surface low will eventually swing a cold front across the area during the Saturday night into Sunday period. This will bring shower and thunderstorm chances and at least a temporary reprieve from this current heat wave with highs back in the 80s early next week. Petr && .AVIATION /00Z TAFS THROUGH 06Z TUESDAY/... Issued at 640 PM CDT Mon Jun 17 2024 Ongoing showers and thunderstorms near GYY should continue to move offshore and away from the terminals over the next hour, though trends (including any signs of redevelopment of thunderstorms out of cumulus clouds extending along Interstate 80 upstream of DPA/ORD/MDW) will be watched with an eagle eye over the next few hours. Otherwise, breezy southwest winds at press time should ease in magnitude after sunset, though occasional gusts up to 20kt may prevail through the overnight hours. Scattered high-based cumulus should become replaced by thickening upper-level clouds overnight. Toward or just after daybreak, an MCV currently located near the bootheel of Missouri will arrive over northeastern Illinois or northwestern Indiana. At least scattered showers but possibly also scattered thunderstorms may accompany the MCV, though confidence in the exact track of the circulation, let alone coverage of any shower or thunderstorm, is not high enough to warrant any mention of such in the outgoing TAF package. In addition, local pockets of MVFR cloud cover may accompany the MCV, but confidence is likewise not high enough to advertise more than a period of SCT025. Adjustments to the TAF at 03Z or 06Z may be warranted as the circulation lifts through central Illinois and forecast confidence increases in where it will go. Southwest winds will increase in magnitude after sunrise and gust 25-30kt through the morning. Depending on the thickness of cloud cover tomorrow, rising mixing heights may allow for a period of wind gusts over 30kt tomorrow afternoon. Finally, like today, isolated thunderstorms cannot be ruled out in the afternoon with a probability of occurrence at any given point somewhere around 20% or lower. Borchardt && .CLIMATE... Issued at 441 AM CDT Mon Jun 17 2024 Several temperature records will be threatened over the next few days. The records that appear to be in greatest jeopardy are today`s (June 17) record high for Chicago and several record warmest low temperatures for both Chicago and Rockford through Saturday, June 22nd. Here are the daily high and warmest low temperature records for Chicago and Rockford for each day through June 22nd: Chicago -------------------------------------------- Day: 6/17 6/18 6/19 6/20 6/21 6/22 -------------------------------------------- Record High: 96 98 102 104 101 97 Record Warm Low: 78 77 78 78 74 76 Rockford -------------------------------------------- Day: 6/17 6/18 6/19 6/20 6/21 6/22 -------------------------------------------- Record High: 99 99 99 101 100 97 Record Warm Low: 75 74 76 73 71 73 Ogorek && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Air Quality Alert until midnight CDT tonight for ILZ005-ILZ006- ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-ILZ106- ILZ107-ILZ108. IN...None. LM...None. && $$ Visit us at weather.gov/chicago