


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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492 FXUS63 KLOT 070503 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1203 AM CDT Mon Jul 7 2025 .KEY MESSAGES... - Scattered showers and thunderstorms will continue through early evening before shifting south and diminishing in coverage late this evening and overnight. The main concern will be torrential rain with localized flooding possible. A few strong wind gusts are possible, primarily south of a Pontiac to northern Jasper County line. - Dangerous swimming conditions at Lake Michigan beaches this through midday Monday. - A period of dry and slightly cooler weather is on track to start the upcoming week, though isolated showers and storms cannot be ruled out in the Tuesday night through Thursday timeframe (20-40% chance or so each day). && .DISCUSSION... Issued at 241 PM CDT Sun Jul 6 2025 Through Monday: Shower and thunderstorm coverage continues to increase across much of the forecast area as diurnal heating has left the boundary layer uncapped this afternoon. Three forcing mechanisms are responsible for the ongoing convection. First is a cold front aligned from south of Rockford to south of Waukegan. The second area is a residual outflow boundary from Dixon to northern Cook County associated with early morning convection over southern Wisconsin. The front will gradually overtake the outflow boundary, with recent radar trends depicting an increase in shower coverage between the two features. The congealed line will drift southeastward across the Chicago metro through 6-7pm, with perhaps an increase in lightning coverage after 3pm. Poor mid-level lapse rates, weak shear, and a moisture-laden profile suggest a prevalence of low-centroid showers with embedded lightning, localized torrential rainfall rates, and brief non-severe gusty winds. The third area is tied to a sheared and weakening mid-level trough extending from northwest Indiana toward central Illinois. Less cloud cover south of this area has allowed more destabilization this afternoon. But given the weak mid-level forcing, higher coverage has struggled to materialize. As the features across northern Illinois track southward through the afternoon, the added surface-based forcing should allow coverage of convection to increase primarily, south of a line from Pontiac to northern Jasper County by early evening. Though deep-layer shear remains quite low, slightly higher mid-level lapse rates and the additional destabilization noted above could support a couple multicell clusters capable of producing strong to marginally severe wind gusts. Activity will quickly decrease with loss of heating after mid-evening. All activity should end across the remainder of the CWA by around daybreak Monday as the front clears to the southeast. Beside ongoing convection, N/NNE winds gusting to 30 mph behind the cold front this afternoon will generate high waves and dangerous swimming conditions that will persist through Monday. A Beach Hazards Statement remains in effect until 4pm CDT Monday. Kluber Monday Night through Sunday: Monday night through Wednesday, the overarching upper-level pattern from the northern Plains to the Great Lakes is expected to be characterized by broad/disorganized northwesterly flow. Ensemble model guidance suggests a shortwave moving along the US/Canadian border, perhaps augmented by upstream convection in the Plains, will move into the Great Lakes region sometime in the Tuesday night to early Wednesday timeframe. If such timing were to hold (definitely no guarantees), any convection that develops Tuesday afternoon across Iowa would be prone to weakening by the time it reaches our area Tuesday night. Tuesday otherwise looks like a nice day with highs in the mid to upper 80s Wednesday and Thursday, upper-level ridging will build northward toward Hudson Bay atop weak troughing across the Gulf Coast. Such a regime will lead to mid-level heights "spreading out" across the Mississippi River Valley, altogether leading to somewhat benign weather. Healthy cumulus fields each day may sprout an isolated storm or two, particularly near daily lake breezes where localized convergence will be maximized. With little to no flow through the meager convective layer, any storm that manages to develop would be fairly short-lived with threats for occasional lightning strikes and downpours. Will maintain the NBM PoPs of 20 to 40% through the period, keeping in mind they are likely overdone for many areas. Highs both days should be in the mid to upper 80s, with cooler readings in the upper 70s in the wake of the aforementioned lake breezes. Friday into the weekend, the upper-level low currently stalled in the Gulf of Alaska is expected to swing southeastward and track along the US/Canadian border. At the same time, the upper- level low meandering off the California coast is expected to swing east-northeastward atop a strengthening ridge over the southwestern US, placing it in line to interact with the approaching trough from the northwest. If and how both interact will be something to watch as we get closer. Regardless, the general idea is that chances for showers and storms should return to the general region sometime next weekend. Borchardt && .AVIATION /06Z TAFS THROUGH 12Z TUESDAY/... Issued at 1202 PM CDT Mon Jul 7 2025 Northeasterly winds will continue to advect MVFR stratus off Lake Michigan and over the terminals through the overnight hours. Using the RAP 925mb RH as a proxy for moisture in the stratus layer, will advertise improvement/erosion of cigs a few hours after sunrise from north to south. Occasional holes may develop from time to time beforehand, however. Once stratus erodes tomorrow morning, VFR conditions (and continued northeasterly winds) are expected to prevail. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Beach Hazards Statement through Monday afternoon for ILZ006- ILZ103-ILZ104. IN...Beach Hazards Statement through Monday afternoon for INZ001- INZ002. LM...Small Craft Advisory until 9 AM CDT Monday for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago