Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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823 FXUS63 KLOT 181948 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 248 PM CDT Tue Jun 18 2024 .KEY MESSAGES... - Hot and muggy conditions will prevail through the end of the week, although cooler conditions are expected near the lake Thursday and Friday. - Periodic chances for thunderstorms will continue, though many hours will remain dry. && .DISCUSSION... Issued at 248 PM CDT Tue Jun 18 2024 Through Wednesday Night: Forecast focus is on thunderstorm potential overnight through Wednesday evening. A cold front will be moving into the northwest cwa Wednesday afternoon. There may be some lingering showers/isolated thunderstorms ahead of this front into far northwest IL around daybreak Wednesday morning. As the front moves further into the area Wednesday afternoon, at least isolated thunderstorms will be possible. Models have a general consensus of a narrow ribbon of instability along/ahead of this front thus still some uncertainty for coverage with the best chance for any thunderstorms generally along/north of I-80. Main severe threat from any the storms would be localized damaging winds. The cold front is also expected to accelerate down Lake Michigan and several of the cams show winds turning northeasterly off the lake by late Wednesday afternoon. This could also serve as an area for development for isolated thunderstorms. Some of the models show a weak wave lifting north across eastern IL and IN late tonight into Wednesday morning, that may bring a few showers/isolated thunderstorms to the southeast cwa by daybreak Wednesday morning. Temperatures have warmed into the lower 90s for most areas, with dewpoints dropping back into the mid/upper 60s this afternoon. This will keep heat index values in the upper 90s to a few locations tagging 100. Lows tonight will be similar to this morning, mid 70s for most locations, warmer in Chicago. Wednesday will be similar to today, with highs back in the lower/mid 90s along with dewpoints in the mid/upper 60s with heat index values again in the upper 90s to 100. With the expected wind shift off the lake late Wednesday afternoon, could see some temps dropping into the 70s for areas near the lake, though overall confidence is low for the timing/speed of the boundary. Lows Wednesday night/Thursday morning are expected to be back into the upper 60s/lower 70s. cms Thursday through Tuesday: The amplified upper level ridge responsible for this ongoing stretch of hot weather will be in the process of flattening out heading into Thursday. This will bring the local area closer to the northern extent of 90 degree temperatures. An associated surface boundary is forecast to stall out somewhere near or just northwest of the local area on Thursday. This will serve as the focus for potential thunderstorm development, particularly across northwest Illinois and southern Wisconsin Thursday afternoon. A further south placement of this boundary would result in increasing chances of showers and thunderstorms into northern Illinois. For now opted to maintain 30-50% chances for areas mainly along and west of the Fox River Valley and north of I-80, though isolated storms can`t be ruled areawide (20% chance). While there are differences in the magnitude of its influence, onshore flow will keep temperatures cooler near the lakeshore, and potentially further inland across northeast Illinois if a backdoor front can make further inroads resulting in high temperatures only in the upper 70s to mid 80s. Otherwise expect 90s yet again for the rest of the area. By Friday this boundary will begin to retreat back to the north and closer to the lakeshore, keeping mainly lake adjacent areas cooler. Accordingly, storm chances are relegated to near and north of the WI/IL stateline, otherwise capping looks to keep most areas dry. Saturday continues to look like the warmest day for most areas late week, including near the lakeshore given strong southerly flow developing in response to a developing surface low across the Northern Plains. This will allow temperatures to warm well into the 90s for all areas, including near the lakeshore. This surface low will eventually swing a cold front through the area Saturday night into early Sunday morning bringing the areas best potential for showers and thunderstorms (50-60% chance). In the wake of this front cooler temperatures will prevail for the start of the week, albeit still warmer than normal, with highs in the mid-upper 80s. There are signs that this break will be short lived, however, with 90s returning to the forecast already by Tuesday as the upper ridge builds back across the central CONUS. Deep mixing each day this week will keep dew points mostly in check this week with heat indices in the 90-100 degree range. While no heat headlines are planned with this update, continue to take steps to beat the heat this week! Petr && .AVIATION /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 1244 PM CDT Tue Jun 18 2024 Main Concerns: - Gusty south-southwest winds into this evening - Chance of TS and a northeasterly wind shift late day Wednesday into Wednesday evening at ORD and MDW South-southwest winds (180-210 deg direction) will gust to 25-30 kt past sunset and then likely ease with only sporadic gusts after midnight. Wind direction will shift to southwest (220-240 deg) Wednesday morning with gusts in the 15-20 kt range developing by around 12z. Late in the day Wednesday, isolated to widely scattered SHRA/TS may encroach upon the Chicago area. In addition, a cold front approaching from the north will likely cause a wind shift to northeast by/during Wednesday evening. Due to timing and coverage uncertainty regarding the TS and timing uncertainty with the anticipated wind shift, deferred any TS and wind shift inclusion in the ORD and MDW TAFs to later updates. VFR conditions can be expected through the current TAF period. Castro && .CLIMATE... Issued at 305 AM CDT Tue Jun 18 2024 With a high temperature of 97 degrees recorded at O`Hare Airport yesterday, Chicago broke its daily high temperature record of 96 degrees for June 17th, which was previously set in 1887 and 1957. A few additional temperature records (primarily some of the record warmest low temperatures for both Chicago and Rockford) may be threatened over the next few days. Here are the daily high and warmest low temperature records for Chicago and Rockford for each day through Saturday, June 22nd: Chicago --------------------------------------- Day: 6/18 6/19 6/20 6/21 6/22 --------------------------------------- Record High: 98 102 104 101 97 Record Warm Low: 77 78 78 74 76 Rockford --------------------------------------- Day: 6/18 6/19 6/20 6/21 6/22 --------------------------------------- Record High: 99 99 101 100 97 Record Warm Low: 74 76 73 71 73 Ogorek && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...Air Quality Alert from midnight tonight to midnight CDT Wednesday night for INZ001-INZ002-INZ010-INZ011. LM...Small Craft Advisory until 10 PM CDT this evening for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago