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Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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316 FXUS63 KLOT 162343 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 643 PM CDT Tue Jul 16 2024 .KEY MESSAGES... - Few early shower/thunderstorm chances this evening - Bit cooler and less humid Wednesday...may some late day showers along lake breeze? - Dry pattern along with cooler than normal temperatures settle in for Thursday through Saturday. && .DISCUSSION... Issued at 331 PM CDT Tue Jul 16 2024 Large scale pattern early this afternoon features an upper low spinning east across northwest Ontario...with troughing extending into the upper Midwest/upper Great Lakes. Expansive upper ridge encompasses the southern third of the CONUS. 17z surface analysis shows at 1002mb low over northwest Quebec with a cold front trailing back to the southwest across Lower Michigan/northern Illinois/ northern Missouri. Drier air is...slowly...filtering southeast behind the front with dew points in the upper 50s/lower 60s across Wisconsin compared to the lower 70s lingering across Illinois. Upper trough will swing across the Great Lakes Wednesday with some weak height falls into Illinois...but more importantly will nudge some cooler temperatures into the area as high pressure settles into the Dakotas/Minnesota for Wednesday...and eventually into the Midwest for Thursday/Friday as a basic ridge west/trough east pattern sets up for the end of the week. Through Wednesday Night: At mid afternoon morning St deck has bubbled up into a scattered-broken Cu field...with mid and high clouds approaching from the west/southwest. Heating and lingering moisture has generated 1000-1500J/kg MLCAPE across northeast Illinois...a few showers have popped in the vicinity of the Wisconsin border (and finally some lightning over Rock County, Wisconsin as of 1911Z) with visual reports of funnel clouds with some of these cells (presumably of the landspout type). As the cold front slowly sinks across the forecast area this evening along with the influence of the lake breeze can`t rule out some convection developing across northeast Illinois especially given current activity. Radar shows several east-west oriented fine lines that could provide a focus as well. Beyond that expect a mid cloud overcast for most of the night...and Wednesday right now looks dry with the only exception possibly being some lake breeze induced convection during the afternoon/evening. Tail end of PV anomaly associated with upper trough crossing the Great Lakes may provide support for this. Should be a bit cooler but noticeably less humid. Thursday through Tuesday: High pressure settling into the region Thursday is expected to provide northern Illinois with a break from the summer heat and humidity. Normal mid July highs are in the mid 80s...but Thursday highs expected to be in the mid 70s give or take a couple of degrees. A gradual air mass moderation is expected heading into the week...but highs Friday in the upper 70s-around 80 expected and probably a couple degrees either side of 80 for Saturday. Dew points should be in the comfortable range as well (50s-lower 60s) so should be a nice stretch of weather. A weakness in the upper level pattern is expected to develop by the end of the weekend over the central Plains. This feature may spin some moisture in our direction to allow for the next chance of widespread rain in the Monday-Tuesday time frame. JPB && .AVIATION /00Z TAFS THROUGH 06Z THURSDAY/... Issued at 640 PM CDT Tue Jul 16 2024 Key Messages: - Lingering spotty showers with ~1hr window for VCTS at ORD Spotty showers have developed across the area with a cluster of more robust showers that developed along the lake breeze in the vicinity of ORD that have produced a few lightning strikes. These will gradually weaken over the next hour or so though a few showers can`t be ruled out through 3Z. Winds have turned northeast at ORD and will be shortly at MDW/GYY. Winds then become light and variable overnight eventually settling into a prevailing northwest by daybreak Wednesday. Winds will turn northeast behind the lake breeze Wednesday afternoon at GYY and could reach ORD/MDW toward early evening. Petr && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago