


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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286 FXUS63 KLOT 292046 CCA AFDLOT Area Forecast Discussion...CORRECTED National Weather Service Chicago/Romeoville, IL 346 PM CDT Sun Jun 29 2025 .KEY MESSAGES... - Isolated gusty thunderstorms will persist through tonight, with gusty winds possible with any thunderstorm through this evening. - At least scattered thunderstorms are likely on Monday ahead of a cold front, with the strongest storms capable of producing localized damaging winds. - Heat and humidity will return for the 4th of July holiday weekend, along with thunderstorm chances, particularly on Saturday-Sunday. && .DISCUSSION... Issued at 332 PM CDT Sun Jun 29 2025 Through Tonight: Isolated showers and widely isolated thunderstorms continue to bubble across most of the area this afternoon, particularly on the periphery of Lake Michigan, east of I-55, and south of the Kankakee River Valley. The environment remains uncapped, but little mid to upper-level forcing exists. Where surface forcing via an outflow-reinforced lake breeze as well as weak outflow boundaries are present, isolated convection has been persistent. This is especially true as slightly more-favroable low-level moisture has advected northward across areas east of I-55. A washed out mid-level front is also providing subtle support from around Kankakee and east. Farther west, little to no forcing has resulted in very sparse and brief shower activity, with the mid-level front supporting a slight increase in cumulus coverage around the Illinois River. The ongoing trends so far this afternoon should persist into early evening, with isolated convection exhibiting a short life cycle while cascading downstream to generate additional brief single or multicell. Decent mid-level dry air and negligible deep-layer shear has kept the overall coverage in check. A pair of mid-level waves currently crossing southeast Minnesota and central Wisconsin have generated robust convection from Green Bay to northeast Iowa. appreciable forcing will remain north of the area with an associated rapid decrease in deep-layer shear toward the IL/WI line this evening. Have maintained chance PoPs north of I-88 mid-evening through the early overnight hours as a few decaying multicell clusters could extend this far southwest. Cannot rule some stronger wind gusts toward the Rockford metro mid-evening before low-level stability increases with time through the night. Elsewhere south of the I-88 corridor, any coverage of precip will likely be quite sparse through the night, with much of the area remaining dry and seasonably mild. Kluber Monday through Monday night: The muggy air mass stationed over the region today will still be in place at the beginning of the day tomorrow, which will result in tomorrow being another hot and humid day across northern Illinois and northwest Indiana. While persistently ample low-level moisture and sufficiently steep mid-level lapse rates could allow for some convective remnants and associated cloud cover from overnight to linger past sunrise, the relative dearth of synoptic-scale forcing early in the day (possibly coupled with modest subsidence on the backside of a departing weak MCV) suggests that most of our forecast area should remain dry through at least mid-morning. If the spatial footprint of convection and the associated cloud cover during the morning indeed ends up being as muted as the latest CAM guidance indicates, then ample diurnal heating should occur through the morning, setting the stage for a likely greater coverage of showers and thunderstorms in our forecast area later on in the day. Much like today, air mass convection could get going as early as the late morning/early afternoon as convective temperatures in the mid-upper 80s are breached. A sharpening lake breeze and/or any remnant outflow boundaries from the overnight convection in the region could serve as potential foci for convective development. With the stronger tropospheric flow not expected to arrive until later on in the afternoon, any earlier convection that manages to get going would have a similar pulse- like character to what has been exhibited by the convection that has occurred in our area in recent days with attendant threats for strong to locally severe downburst winds, torrential rainfall, and lightning. Showers and thunderstorms should then become increasingly numerous across our forecast area as the afternoon goes on as an incoming mid/upper-level trough swings into the western Great Lakes and an associated cold front approaches from the northwest. It also appears increasingly likely that an MCV originating from widespread convection across the central Plains tonight will arrive in the region during the afternoon as well. The exact track that this MCV takes and the extent to which it can maintain its integrity as it tracks farther to the east will likely play a key role in dictating whether convection tomorrow will end up being relatively scattered in coverage or whether a more widespread coverage will end up being realized with most of our forecast area getting in on the showers and thunderstorms at some point during the afternoon or evening. With deep-layer shear increasing closer to 30 kts as stronger wind fields on the southern periphery of the aforementioned trough spread over the area, loosely-organized multicell clusters should tend to become the more predominant storm mode with time. Climatologically high precipitable water values peaking in the 1.5-2" range would support a continued threat for water-loaded downbursts with the most robust convection. MLCAPE values as high as 2000-2500 J/kg and 0-3 km theta-e deficits in the 20-30C range suggest that some of these downbursts could be strong enough to produce wind damage, though subpar mid-level lapse rates may play a role in keeping this damaging downburst threat more isolated than widespread. The Marginal (level 1/5) Risk for our forecast area in the latest Day 2 Convective Outlook from the Storm Prediction Center continues to look appropriate based on our latest forecast thoughts and expectations. Ogorek Tuesday through Sunday: After Monday, a three-day break in the humidity looks to follow with drier northwest flow, so highs in the mid-upper 80s away from any lake cooling will be more tolerable. The nighttime periods during the middle of the week should be pleasant as well. Turning ahead to the 4th of July holiday weekend, medium range guidance remains in good agreement in the heat and humidity returning (highs near to a bit above 90F with dew points increasing back into the 70s). Convective chances may end up somewhat minimal (better focus north) on the day and evening of the 4th, with signs then pointing toward a potentially more stormy Saturday-Sunday period (PoPs still in the chance range for now). Castro/Ogorek && .AVIATION /18Z TAFS THROUGH 00Z TUESDAY/... Issued at 1229 PM CDT Sun Jun 29 2025 Concerns: - Widely scattered thunderstorm development possible along a lake breeze this afternoon and also SW of the terminals. - Additional chances for showers/storms late this evening into the early overnight, and another slightly higher chance Monday afternoon. - East wind shifts a potential in/around any storms at the near-lake terminals. - Potential shift to east winds ahead of a cold front on Monday Cumulus development is ongoing area wide. The lake breeze boundary has sharpened up a bit in the vicinity of ORD/MDW, mainly just to the east. Therefore the currently favored area for TS would be for MDW, GYY, and then along the east gates at ORD. With very little flow in place, wherever storms form they will not move much and would produce locally heavy rain and some brief erratic/gusty winds. As storms move off the lake breeze they would like tend to collapse fairly quickly. Another area of isolated thunderstorms would also be favored to the SSW of the C90 area. If storms form in this area, they could also slowly drift NW toward the terminals as well. Additional isolated-scattered showers and storms may develop late this evening and overnight. While the signal for TS continues to remain nebulous during this period, enough of a signal exists to continue the PROB30 groups at all the terminals, though admittedly confidence is medium-low. Another round of storms appears plausible as a cold front shifts through the airspace on Monday. This is the most likely period for thunderstorms during the TAF cycle. There could be some showers prior to the afternoon, but we tried to hit the most likely time windows in the TAF for now, which will also likely need refinement based on the frontal timing. One complicating factor tomorrow is if the4 frontal timing is a bit slower, a lake breeze may make it to ORD and MDW and shift winds to east for a few hours Monday afternoon. This is not depicted in the ORD TAF, but is in the MDW TAF, and therefore will be an aspect of the forecast to monitor. KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago