


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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687 FXUS63 KLOT 132003 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 303 PM CDT Sun Jul 13 2025 .KEY MESSAGES... - Scattered showers and isolated thunderstorms to remain possible through sunset, mainly along and south of a Pontiac, IL to Rensselaer, IN line. - Shower and thunderstorm chances will increase each day Tuesday through Thursday. && .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 /18Z TAFS THROUGH 00Z TUESDAY/... Issued at 1219 PM CDT Sun Jul 13 2025 Key messages for the 18Z TAF period include: * Fog possible outside of Chicago late tonight into early Monday. Westerlies between 5 and 10 kt this afternoon will go light and variable overnight, then back to westerly below 10 kt during the day on Monday. A lake breeze will attempt to move across the Chicago sites and GYY Monday afternoon, but the expectation is that it will hold off and prevailing winds will remain some form of westerly until Monday evening, just beyond the current TAF period. Additionally, instances of fog are expected around the area late tonight into early Monday, primarily outside of Chicago. Most model camps limit vis reductions to high MVFR, and a 5SM BR TEMPO group can be found in the RFD, DPA, and GYY TAFs accordingly. Doom && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago