####018006222#### FXUS63 KDVN 190019 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 719 PM CDT Sun May 18 2025 .KEY MESSAGES... - Active pattern set to develop late tonight through Wednesday with periods of showers and storms. High likelihood of rainfall of greater than 1 inch (60-90% chance) with locally heavy rainfall greater than 2 inches possible (30-60% chance). - Conditional severe weather threat (level 1/2 out of 5) modulated by the location of a warm front late Monday PM/night, with large hail and damaging winds the primary threats, currently forecast for southern portions of the CWA. - A sharp temperature gradient is expected, especially near Interstate 80, with cool conditions north, and milder air to the south through Tuesday, followed by widespread cool weather Wednesday. && .SHORT TERM /THROUGH TONIGHT/... Issued at 207 PM CDT Sun May 18 2025 Spectacular Sunday weather will continue into this evening, with clear skies gradually filling in with mid clouds and an noticeable east wind by sunset. A back door push of colder air is expected tonight, as flow begins to interact with developing Plains low pressure. Colder air, flowing south through Lake Michigan is set to drop into northwest Illinois by mid evening, and spread over the remainder of the CWA overnight, as lows drop to the lower 40s northeast to lower 50s south. This cool low level air should create a stable air mass for any storm arriving late tonight, and at the very least, limit impacts of downdrafts. Most models are now showing convective debris and dissipating rainfall arriving from the west late tonight, and continuing Monday morning in that dissipation mode. The exception to that would be the NAM which has a MCS moving through our area. Thus, we'll need to watch convective trends, and see if the farther north NAM scenario gains traction tonight. Either way, the stable boundary layer remains forecast. Monday, we're expecting many more dry hours than earlier forecasts, but still seeing cloudy skies and east winds. Temperatures in the upper 50s to low 60s are expected north of I-80, and mid 60s to near 70 farther south. Some passing showers are possible at any time, mainly from elevated WAA processes. The main focus for storms and heavy rain sets up Monday evening, as a large area of showers and storms spreads across northwest Missouri and Iowa, spreading widespread moderate to heavy rain into our area through the night. PWATs in the 1.30 to 1.8 range are forecast to converge into our region, resulting in widespread rainfall of 1-2 inches Monday night through Tuesday morning. The heaviest rains continue to be forecast in our southwestern counties in this period, with lowest amounts northeast, but still over 0.5. This initial round of rain should be absorbed mostly, with developing drought conditions in much of the area. We can't rule out some localized water issues, especially with any high rainfall rates convectively enhanced and/or repeated heavy rain or convection with the main concern should this occur in any urban areas. Severe weather remains conditional, as ample shear exists for updraft organization, but this is well north of the surface warm front. Thus, some storms may provide a large hail threat Monday night, in our souther counties, but wind and tornado threats appear low given the stable boundary layer. If the depth of this stable layer is thin enough, some isolated strong/severe gusts would be possible in the south, but that is far from certain. && .LONG TERM /MONDAY THROUGH SUNDAY/... Issued at 207 PM CDT Sun May 18 2025 The storm system continues Tuesday into Wednesday night. Tuesday, the latest guidance suggest the boundary will lift up near I-80 while low pressure rides east through the CWA from central Iowa. At this time, instability appears weak, but certainly enough to bring slow moving showers and thunderstorms along and north of the front. While overall QPF is lower in the Tuesday night and Wednesday period, convection will be very slow moving, and a narrow axis of heavy rain is possible, right now forecast near I-80 in Iowa and Illinois. This seems to be a period where we could see some isolated flash flooding develop. As stated above, temperatures appear quite cool Tuesday north, and mild south, then cool in all areas Wednesday, as the fully occluded system continue to spread showers and weaker storms over the area. Looking beyond, into next weekend, pleasant temperatures are forecast as the upper low shifts towards the eastern CONUS. Though a few showers could occur in northwest flow, the dry air in place would keep the threat for rainfall low. Highs in the 60s to 70s are forecast. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 715 PM CDT Sun May 18 2025 The main concerns for aviators are a gusty east winds on Monday and rain showers and any thunderstorm potential on Monday, although low confidence on shower coverage. A quiet rest of the Sunday evening with a gradually increasing wind. Gusts should be frequent by shortly after daybreak Monday and persist through the day, occasionally exceeding 25 kt. Overall confidence in wind direction and speed is high. Showers and storms over the Central Plains tonight will move toward the TAF sites but fade in both intensity and coverage. This casts some doubt on timing and duration of morning showers in the TAFs. Highest confidence is for BRL, even where there could be some thunder in the morning and some showers or storms persisting into the afternoon. Finally, more persistent MVFR clouds are likely to spread into the area just after the current TAF time. BRL is where they could move in prior to the end of the daytime Monday. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Ervin LONG TERM...Ervin AVIATION...Friedlein