BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Mon, 18 May 2026 00:17:22 +0000 ----------------------------------------------------------- FOUS30 KWBC 180017 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 817 PM EDT Sun May 17 2026 Day 1 Valid 01Z Mon May 18 2026 - 12Z Mon May 18 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL PLAINS TO THE UPPER MIDWEST... 01Z Update: General model consensus with the expected convective evolution across the Central Plains and Midwest led to a relative continuity in the inherited MRGL risk across the region. Some adjustments were made to reflect where convection has since ended, or trends away from impact overnight allowed for a removal with the biggest change over much of Wisconsin. Environmental conditions are ripe for heavy rainfall within a well-defined warm sector positioned over the Missouri and Mississippi River Basins to the south of a quasi-stationary front draped over the Plains into the Midwest. Northern inflection of the front is situated over eastern SD through northern IA and the WI/IL border. Greatest threat for heavy rainfall is likely in the buoyant environment just=20 downstream of a twin pair of lows analyzed over KS and SD,=20 respectively. HREF neighborhood probabilities maintain moderate=20 values (30-50%) for areas of 2" or greater overnight across the=20 Missouri River basin from southeast NE down through northwest MO,=20 including the KC metro. Upscale growth of thunderstorms=20 materializing over KS and NE will migrate east with the mean flow=20 trajectory signaling a relative east to east-northeast storm motion during the height of the convective impact. Any singular cell=20 generation will likely merge overnight due to cold pool mergers and a maturing LLJ enhancement.=20 Classic quick-moving cells will hopefully limit training=20 prospects, however we will be monitoring the area along I-70 in=20 eastern KS into MO as perhaps the one place where outflow=20 prominence could spur up a period of enhanced low-level convergence that in tandem with the LLJ placement could offer a window for=20 redevelopment over the same areas for a few hours at some point=20 between 00-06z before everything finally kicks eastward or=20 dwindles. The MRGL risk was sufficient at this time as the=20 signature was modest, at best, so decided to maintain general=20 continuity from the previous forecast. MRGL risk over FL from previous update was dropped as cells will decay in intensity with the loss of diurnal heating after 01z leading to a degraded chance for flash flooding for the urban southwest coast of FL. A few cells could still drop a decent amount of rainfall prior, but FFG's remain very high over the region, so everything will be very isolated in general. Didn't think it was necessary to keep the risk with such a short time period of interest.=20 Kleebauer =20 Day 2 Valid 12Z Mon May 18 2026 - 12Z Tue May 19 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL PLAINS TO THE UPPER MISSISSIPPI VALLEY... .19Z Update... The forecast remains on track with another round of heavy rainfall expected to impact areas from the central Plains to the Upper Mississippi Valley where a high-end Slight Risk area remains in the outlook. The highest flash flood risk looks to focus over portions of northern Kansas and Missouri and southern Iowa and Nebraska where backbuilding/repeating storms will be favored. Soils in this area will be thoroughly saturated from rainfall during the Day 1 period, which will increase sensitivity to additional rainfall. Storms will likely produce rainfall rates of 2 inches per hour and could exceed 3 inches per hour, which would exceed flash flood guidance for this area. Dolan .Previous Discussion... Relatively few changes were needed to the outlook for this likely busiest day of the upcoming three. A strong shortwave making up the base of the longwave trough over the Rockies will finally eject out over the Plains on Monday. As that shortwave interacts with plentiful Gulf moisture streaming north up the Plains, renewed lines of showers and storms are expected to develop across the Slight Risk area. Since the storm motion will be towards the northeast, largely parallel to the moisture and instability plume emanating from the Gulf, backbuilding will be a greater possibility than in previous days. Several of the high resolution model guidance show that there could be multiple rounds of storms to impact the area from northeast Kansas through southwestern Iowa, especially in the late afternoon through the first half of the overnight. This area is currently getting very hard-hit with heavy rain from a very slow-moving MCS that has been producing multiple inch per hour rainfall rates and numerous instances of flash flooding. Thus, the soils have become very saturated in some areas. Following potential heavy rain during the day 1/Sunday period, much more rain is expected in this region again on Monday. A higher-end Slight covers the aforementioned region from northeast Kansas through the southwest corner of Iowa. Should multiple inch per hour rates materialize again in this same region, a Moderate Risk upgrade will need to be considered with future updates. Wegman Day 3 Valid 12Z Tue May 19 2026 - 12Z Wed May 20 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE SOUTHERN PLAINS THROUGH THE LOWER OHIO VALLEY... .19Z Update... Forecast remains on track with a Marginal Risk area in effect from the southern Plains to the Mid-Mississippi and Lower Ohio Valleys. The frontal system will push southeast and stall over these regions, with showers and storms capable of producing locally heavy rainfall. Localized flash flooding will be a concern, especially for areas of Central and East Texas where model guidance is starting to indicate the higher rainfall totals may be. Dolan .Previous Discussion... The inherited Slight Risk for the southeastern half of Oklahoma was removed with this update. Guidance has been understandably struggling with the placement of expected rainfall/convection across this region. Since there's excellent agreement that the axis of heaviest rainfall will shift well south of the area expected to be hit with heavy rain in days 1 and 2, the region of greatest impact is an area where soils have dried out and will likely be very receptive to beneficial rainfall. Since guidance is in poor agreement on where the storms will be most persistent, instead broad brushing much of the Marginal Risk area with anywhere from a half inch to 1.25 inches, have opted to leave the large Marginal in place. None of the guidance particularly favors southeastern Oklahoma for any heavier amounts than anywhere else, especially further south into Texas. Expect that should a new Slight be needed with a future update, it will be over a portion and not into Oklahoma, which sits at the back/northwestern edge of the heavier rain axis. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_bmZSIg330EOMTKn2m4hhzj_LUJA0hOYSXx0v6-X-zIV= XPz2GV5O-4EKnuEWStBhjFPUlXuWzc_AQdjeDKfBF5rudww$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_bmZSIg330EOMTKn2m4hhzj_LUJA0hOYSXx0v6-X-zIV= XPz2GV5O-4EKnuEWStBhjFPUlXuWzc_AQdjeDKfBjAN-Olw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_bmZSIg330EOMTKn2m4hhzj_LUJA0hOYSXx0v6-X-zIV= XPz2GV5O-4EKnuEWStBhjFPUlXuWzc_AQdjeDKfBnFz3SOw$=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.28-Linux * Origin: Capitol City Online (1:2320/107) ----------------------------------------------------------- [Voltar]