


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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663 FXUS63 KLOT 140223 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 923 PM CDT Sun Jul 13 2025 .KEY MESSAGES... - Shower and thunderstorm chances will increase each day Tuesday through Thursday. && .UPDATE... Issued at 923 PM CDT Sun Jul 13 2025 Couple of minor additions to the forecast for the remainder of the night. First is to had haze on account of wildfire smoke that while mostly aloft, is resulting in some 3-6SM visibility observations and an otherwise hazy abhorrence to the sky where cloud cover is otherwise minimal. Second is to add areas of fog mainly south of I- 80 after midnight tonight where there could be some dense fog, as well patchy fog farther north outside of the core of the Chicago metro. Mid-evenig surface analysis depicts a nearly stationary cold front across central IL/northern IN, in the vicinity of the ILX/LOT border region. Rain along the baroclinic zone has come to an end for the LOT forecast area, in association with a mid- level short wave now moving east of the region across IN. Surface dew points in the vicinity of the surface boundary remain around 70F, which combined with light/variable winds within a weak/baggy surface pressure gradient is likely to allow for fog development overnight south of I- 80, and especially south of the Kankakee/Illinois river valleys. Even farther north, guidance is suggesting patchy fog development away from the core of the Chicago urban area and have included patchy fog there as well. Can`t rule out the eventual need for a dense fog advisory by predawn Monday morning across our southern cwa. Skies have been hazy today from wildfire smoke which has returned to the region behind the cold front and recent mid- level trough passage. Seeing some 3-6SM ASOS/AWOS obs across the region here at mid-evening, along with a generally hazy sky after thicker cirrus has moved out. Thus have added haze mention overnight (outside of fog) with HRRR near-sfc smoke locally focused. Concentrations are forecast to decrease somewhat on Monday, though we`ll keep an eye on the hazy conditions. Ratzer && .DISCUSSION... Issued at 303 PM CDT Sun Jul 13 2025 Through Monday Night: A shortwave trough and its associated weak surface low continue to traverse across eastern MO and central IL this afternoon generating a broad area of scattered showers and embedded thunderstorms as it does so. Thus far the greatest coverage of showers and thunderstorms has remained south of our CWA where the combination of better forcing, moisture, and instability have come together. However, forecast soundings do show some modest (600-800 J/kg of MLCAPE) instability in the presence of upper 60 to near 70 degree dew points south of the Kankakee River which may support at least some scattered showers and perhaps an isolated storm or two. If any showers/storms do materialize the greater coverage should remain along and south of a Pontiac, IL to Rensselaer, IN line with shower/storm coverage expected to gradually diminish after sunset. Elsewhere, the main forecast concern for this evening will be the partly to mostly cloudy skies caused by the cirrus blow off from storms in central IL and some wildfire smoke aloft. Skies are expected to gradually clear out overnight areawide as storms move into IN and OH and the smoke aloft wanes. Therefore, expect a rather pleasant evening with temperatures in the lower 80s to start before cooling into the mid-60s overnight. As for Monday, mid-level height rises are expected to establish overhead which will erode the cloud cover and give a mostly sunny start to the work week. Highs on Monday will be a bit warmer than today with readings in the mid to upper 80s, but the mild humidity will keep heat indices on par with the temperatures. Additionally, a weak lake breeze is forecast to move onshore Monday afternoon which will result in some cooling temperatures along the lakeshore capping highs more into the upper 70s and lower 80s here. The tranquil conditions will extend into Monday night with clear skies and mild temperatures in the mid-60s. Tuesday through Sunday: The weather is expected to become more active heading into the middle and later portions of the week as several disturbances traverse through the Mississippi Valley and Great Lakes. The first disturbance to impact the region will be the ongoing MCV and its associated shortwave in central TX. This MCV and wave are forecast to begin ejecting into the southern Plains on Monday and then into the Mississippi Valley by Tuesday morning. Given that the current guidance consensus is for this disturbance to pivot more into central IL and IN Tuesday afternoon, it seems that the moisture return into northern IL and northwest IN could be more limited. Couple this with the drier mid-level air forecast to be in place, suspect that shower and thunderstorm coverage on Tuesday will likely be somewhat spotty and mainly confined to our southern CWA (namely areas south of I-80). Another convectively enhanced shortwave trough is forecast to develop across the central Plains Tuesday night and move into northern IL on Wednesday. With better moisture expected to be in place in addition to more focused forcing overhead, the coverage of showers and thunderstorms on Wednesday does look to be higher than Tuesday but still in a more scattered nature. Though, the best chances for showers and thunderstorms this week is not expected until late Wednesday night through Thursday as a more amplified trough pivots out of the Mountain West and Upper Midwest and drags a cold front through northern IL and northwest IN. This front looks to keep a decent coverage of showers and storms in play through Thursday night and possibly into Friday pending how quickly the front exits to our south. Furthermore, with PWATs forecast to peak in the 1.7-1.8 inch range the showers/storms will likely be capable of producing heavy rainfall which could result in a flooding threat if storms train along the frontal boundary. While it is still a bit too early to know exact rainfall amounts and location of heaviest rain, this will be a period to monitor over the coming days. Outside of the increasing rain chances, warmer temperatures and increasing humidity will also return Tuesday through Thursday. While forecast air temperatures look to be in the upper 80s to around 90 (warmest Tuesday and Wednesday), the upper 60s to lower 70 degree dew point will support heat indices in the mid to upper 90s during this period. Once the front pushes through the area on Friday, a period of drier and more comfortable conditions is expected to establish for Friday and Saturday with highs in the lower to mid-80s. However, these conditions will be short lived as a northwest flow pattern is forecast to set up late next weekend into the following week which looks to bring another active period of weather to the region. Yack && .AVIATION /00Z TAFS THROUGH 06Z TUESDAY/... Issued at 634 PM CDT Sun Jul 13 2025 Light W/WNW winds at TAF issuance will either become VRB or settle in the SE quadrant this evening as a decaying weak lake breeze shifts across NE Illinois. A surface ridge passing just south of the terminals will then result in generally light winds around 5 knots or less through much of the period. Wind direction will favor SW late tonight through much of Monday, but could become VRB at times given the light flow. A weak lake breeze should then cross the terminals late afternoon or early evening. Upper-level clouds will clear to the east this evening, leaving mostly clear skies through the period. Wildfire smoke aloft tonight and some diurnal VFR cumulus Monday are both represented in the TAF. Some of the smoke is mixing toward the surface, so would not by surprised to see lower VFR visibility with HZ tonight. For the outlying sites (RFD/DPA/GYY), BR/MIFG/BCFG is possible for a few hours around sunrise and may produce MVFR visibility. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago