Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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687 FXUS63 KDVN 202344 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 644 PM CDT Mon May 20 2024 .KEY MESSAGES... - An isolated shower or storm is possible through this evening, but most of the area will stay dry. Scattered showers and storms are possible mainly NW of the Quad Cities late tonight. - There is a Moderate Risk (level 4 of 5) for severe weather on Tuesday. Large hail, damaging winds, and tornadoes will all be possible. Some significant wind gusts over 70 mph may occur. - Drying out Wednesday and Thursday with more seasonable temperatures and humidity. - Shower and thunderstorm chances return Friday through Sunday as a more humid air mass builds back into the region. && .SHORT TERM /THROUGH TUESDAY NIGHT/... Issued at 215 PM CDT Mon May 20 2024 Late Afternoon through Tonight A MCV currently over north-central Illinois and far southern Wisconsin will continue to track to the NE into this evening, taking the majority of the scattered storms with it. A few isolated storms could develop late this afternoon and evening; however, most of the area will stay dry. By late tonight, increasing warm air advection aloft will likely lead to the development of scattered showers and storms across mainly the NW portion of the forecast area. The primary threats from this round of storms are small hail, gusty winds, and heavy downpours. Tuesday A potent shortwave trough is forecast to track from the Central Plains into the Upper Mississippi Valley. The trough will become negatively tilted by the afternoon and evening which will lead to a deepening surface low down to ~988mb as it reaches central Minnesota. This is a classic setup for severe weather locally across portions of Iowa and Illinois as the warm sector pulls northward into the region amidst sufficient deep layer shear for supercells and organized linear convection. There are several potential rounds of storms on Tuesday. The first two rounds during the morning and through mid/late afternoon will likely remain scattered in coverage and favor areas north of I-80. Large hail and damaging winds are the primary threats, with a few tornadoes possible during the afternoon period. The highest confidence on severe storms will be associated with the cold front during the evening into early nighttime period. CAMs indicate either a line of storms or broken line of supercells rolling across the area from west to east. Forecast soundings and HREF environmental parameters are supportive of a higher end severe threat with all hazards possible, including large hail, damaging winds, and tornadoes (a few of which could be strong -- EF2+). CAM forecast soundings display high low- level shear and favorable thermodynamics for tornadic potential with 0-1 km bulk shear near 30 kts, large clockwise hodograph curvature contributing to 0-1 SRH values of 150-250 m2/s2, and reasonably low LCLs under 1000m where moisture pools ahead of the cold front. In addition to the severe threat, a very moist atmosphere with PWATs near 1.75" will support hourly rain rates of 1-2" with the strongest storms. Fortunately, the storms will be moving along at 50 - 60 mph, thereby decreasing the overall threat for flash flooding. We may eventually see a transition in storm morphology from a broken line of supercells to more of a severe QLCS capable of 60 to 80 mph winds, with a continued tornado risk due to embedded supercells and potential for mesovortices with 0-3 km line normal shear near 30 kts. Tomorrow is a day to pay close attention to the weather, have multiple ways to receive warnings, and to take appropriate action if a warning is issued for your location. Timing of Storms: Round 1: Warm air advection driven, mostly elevated storms are possible across the NW portion of the outlook area from late tonight through late Tuesday AM. Round 2: Scattered storms may form during the early to mid afternoon well out ahead of the cold front. Confidence with this round is low, but potential is there for scattered severe storms developing in the open warm sector along a convectively induced warm front. Round 3: The highest severe weather threat is between 6 PM to 11 PM as a cold front and widespread storms track west to east through the outlook area. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Issued at 215 PM CDT Mon May 20 2024 Active weather will continue across the area through the upcoming holiday weekend. The long term period begins on Wednesday with southwesterly flow aloft from the Desert Southwest into the Upper Great Lakes. On Wednesday morning, Tuesdays storms system will be lifting northeastward with a secondary disturbance swinging across the area late Wednesday morning into the afternoon. This will bring lingering showers and storms to the area through the day on Wednesday. High temperatures on Wednesday will be in the lower to mid 70s. After the wave passes on Wednesday, flow aloft becomes split again with the northern US under the influence of the northern branch of the jet stream. High pressure is forecast to lift across the area at the surface and aloft and bring quiet weather to the area Wednesday night through Thursday. High temperatures on Thursday will be warner with temperatures in the mid to upper 70s. Friday through Monday, a series of disturbances will move across the area as shortwave energy from a trough in the Pacific Northwest moves across the area. This will bring daily chances of showers and storms through the holiday weekend, The weekend will not be a total washout but there will be periods of showers and storms. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 638 PM CDT Mon May 20 2024 Late afternoon convection along the frontal boundary from just south of KMLI east across Illinois will dissipate with sunset. Outside of this convection expect VFR conditions through 06z/21. After 06z/21 VFR conditions will continue outside of developing SHRA/TSRA across eastern Iowa. A line of TSRA will sweep across eastern Iowa into southern Wisconsin roughly 12-16z/21 with IFR conditions and wind gusts to 40 knots. After 16z/21 VFR conditions are expected with new TSRA developing after 18z/21. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Uttech LONG TERM...Cousins AVIATION...08