BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Sun, 17 May 2026 15:42:34 +0000 ----------------------------------------------------------- FOUS30 KWBC 171542 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1142 AM EDT Sun May 17 2026 Day 1 Valid 16Z Sun May 17 2026 - 12Z Mon May 18 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL PLAINS TO THE UPPER MIDWEST AND FOR SOUTHWEST FLORIDA... .16Z Update... A Marginal Risk area was introduced for Southwest Florida with this issuance. Numerous thunderstorms are expected to develop near the=20 western coast along the sea breeze boundary this afternoon and=20 evening, and elevated moisture in a southeasterly flow regime will=20 support locally heavy rainfall that could lead to flash flooding in urban areas. The RRFS shows modest probabilities (30-50%) of=20 rainfall rates greater than or equal to 3 inches per hour in=20 Southwest Florida later today, which would meet/exceed current=20 flash flood guidance. A Marginal Risk area remains in effect from the central Plains to the Upper Midwest where several upper level shortwave troughs will interact with a low pressure system and lifting warm front to=20 produce numerous thunderstorms across the region. The environment=20 looks to be favorable for backbuilding storms over northern Kansas=20 overnight tonight, and the Marginal Risk area was expanded to=20 cover more of northeastern Kansas to account for model trends with this activity. The heaviest rainfall totals from storms in Kansas tonight should be displaced to the south of where the heaviest rainfall fell with the earlier MCS this morning, which should help limit the flood potential.=20 Dolan .Previous Discussion... A pair of shortwave troughs tracking northeast on the downwind side of a slow moving longwave trough over the Intermountain West will provide upper level forcing for several rounds of thunderstorms to impact a large area from Kansas through the upper Great Lakes. A fully open Gulf and associated moisture plume will continue to advect northward up the Plains and Mississippi River. This will keep PWATs consistently above 1.25 inches, with many areas above 1.5 inches. This influx of moisture will support and instability will support both storms capable of heavy rainfall, as well as development and redevelopment of storms in this favorable weather regime. For the most part, due to fast upper level flow, the storms will likely organize into fast moving lines/segments, which should work to keep rainfall totals manageable in any one area. The greatest area of concern stretches from southeastern Nebraska east along the Iowa/Missouri border, where multiple inches of rain have fallen overnight last night. Thus, any backbuilding or holdups in any lines of storms could have outsized flooding impacts. A short- fused Slight may be needed once again in this general area if rainfall totals today come up further. For southeastern Louisiana, the inherited MRGL was removed. Nearly all of the guidance shows only light showers expected to impact that area, with only a one or two showing one isolated storm. Further, high FFGs should preclude any flooding even if that one storm does form. Wegman 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... 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... 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 that 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!6ffwsWSe2i506eDRm3DuRAd_aBbde4w1MouAVCXpzajo= 5svASE_qr7TBXf7Q5jysKPlepIg6BIUtK6s_RC6h9oUSpuU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6ffwsWSe2i506eDRm3DuRAd_aBbde4w1MouAVCXpzajo= 5svASE_qr7TBXf7Q5jysKPlepIg6BIUtK6s_RC6h2M3HvH0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6ffwsWSe2i506eDRm3DuRAd_aBbde4w1MouAVCXpzajo= 5svASE_qr7TBXf7Q5jysKPlepIg6BIUtK6s_RC6hEHfbiJQ$=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]