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Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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597 FXUS63 KLOT 152343 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 643 PM CDT Mon Jul 15 2024 .KEY MESSAGES... - Strong to severe thunderstorms expected late this afternoon into tonight. Locally heavy rainfall possible, which could lead to additional flooding. - Additional thunderstorm chances continue Tuesday, mainly south of I-80/east of I-55. - Pattern breaks by Wednesday, with dry weather and seasonable temperature and humidity through the weekend. && .MESOSCALE... Issued at 546 PM CDT Mon Jul 15 2024 Explosive severe thunderstorm development has taken place across Iowa, with storm tops exceeding 65kft. Special soundings from DVN and ILX both show extreme instability and moderate deep layer shear, though sufficient shear to support storm scale organization in light of the extreme instability. Already seeing signs of amalgamating cold pools/downdrafts with convection over Iowa with radar showing some developing rear inflow jets. The evolution of the convection so far continues to fit the expectations for today with evolution to QLCS well underway. As cold pool strengthens, would anticipate a QLCS to begin accelerating eastward with increasing damaging wind threat as storms approach and cross the Mississippi River. Strengthening low level jet this evening over northern Illinois should result in a ramping up of low level shear and coincident increasing threat of QLCS tornadoes with bowing segments and/or line embedded supercells. Given the shear/instability combo, threat is certainly there for a large number of QLCS tornadoes this evening over northern IL. Recent satellite/radar imagery shows some cells developing over far northern Winnebago County near the Wisconsin line. This could be the beginnings of a "warm air advection" wind ahead of the Iowa QLCS, which if it is and continues to fill in this could result in a potential significant/high end flash flood threat in our CWA if storms drift south of the IL/WI border. Given the vulnerability of the Rockford area due to nearly 10" of rain over the past 48 hours, this will be something that we will be monitoring extremely closely. - Izzi && .DISCUSSION... Issued at 247 PM CDT Mon Jul 15 2024 Through Tuesday Night: Showers and storms may linger into the morning hours, especially across the southern portion of the CWA. There is a chance that the cold front associated with the storms may set up in a west to east fashion and stall out across the southern portion of the area, which could lead to storms persisting into the evening over this area. However, most of the 12Z CAMs show this scenario playing out south of the area. Although the chances of this seem to be on the lower side, did include chance PoPs across the southern CWA through Tuesday afternoon to account for this possibility. With the cold front moving through the area, Tuesday will be cooler than today with temperatures in the mid-to-upper 80s. Dew points will still be around 70 degrees, so it may still feel a bit on the humid side, but peak heat indices will only be in the 90-95 degree range. Carothers Wednesday through Monday: The main upper trough axis is expected to shift east across the forecast area Wednesday. Despite steep low-level lapse rates depicted in forecast soundings, warm mid-level temps (700-600 mb) look to provide a capping inversion with respect to surface based convective development. Therefore, forecast for Wednesday is dry at this point. Broad surface high pressure then builds across the area through the end of the week, setting the stage for a well-deserved period of dry and seasonably mild but less- humid weather conditions, downstream of a high-amplitude upper ridge which develops over western North America. Ratzer && .AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/... Issued by National Weather Service Gaylord, MI 643 PM CDT Mon Jul 15 2024 The primary aviation weather concerns for the 18Z TAF period include: * Severe squall line this evening * Period of MVFR ceilings (at least?) ahead of and behind a cold front expected to pass through in the 12z-18z time frame. QLCS has developed as expected and pressing across the Mississippi River as of this writing. Storms expected to reach KRFD around 01z and into the Chicago metro in the 02-03z time frame with strong wind gusts in excess of 40 knots anticipated. Still looks to be a period of MVFR ceilings in the wake of this evening`s convection into Tuesday morning though flight conditions are expected to improve toward midday with a wind shift to the northwest behind a cold front (and likely a lake breeze impacting KORD/KMDW during the afternoon). JPB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Flood Watch until 3 AM CDT Tuesday for ILZ003-ILZ004-ILZ005- ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020- ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105- ILZ106-ILZ107-ILZ108. Heat Advisory until 7 PM CDT this evening for ILZ008-ILZ010- ILZ011-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039- ILZ106-ILZ107-ILZ108. IN...Flood Watch until 3 AM CDT /4 AM EDT/ Tuesday for INZ001- INZ002-INZ010-INZ011-INZ019. LM...None. && $$ Visit us at weather.gov/chicago