BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Sat, 30 May 2026 15:55:03 +0000 ----------------------------------------------------------- FOUS30 KWBC 301554 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1154 AM EDT Sat May 30 2026 Day 1 Valid 16Z Sat May 30 2026 - 12Z Sun May 31 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF MONTANA... 16Z Update... ...Tennessee Valley... Current radar and RAP mesoanalysis show a weak 925 mb circulation over central TN that is caught between the front to the north and the low- level WSWrly over MS/AL. The 12Z BMX sounding shows the atmosphere remains weakly capped with a 1.9" PW, and >500 MLCAPE, RH at low=20 and mid levels >90%, and a warm cloud layer approaching 12,000ft=20 in depth. A nearby outflow boundary is also moving south into=20 southern TN this morning and is likely to trigger additional heavy thunderstorms this afternoon. There is not much in the way of=20 vertical wind shear, so storms will be fairly short lived. But up=20 to 2.5"/hr rainfall rates this afternoon and evening atop soils=20 that remain quite saturated led to an extension of the Marginal=20 Risk in the Southeast as far north and west as south-central TN. Otherwise, some minor tweaks were made to the Marginal in the=20 Southeast and Northern and Central Plains, as well as the Slight=20 Risk in MT based on latest 12Z HREF and 12Z CAMs guidance. The=20 threat areas and rationale provided by night shift remain in good=20 shape as of this update. Mullinax ---Previous Discussion--- ...Northern Rockies to the Plains... Maintained the Slight risk across portions of Montana as a mid- and upper-level system makes its way northward slowly today. The system should foster locally intense rainfall rates...especially in the eastern portion of the Slight Risk area...given moderately steep lapse rates and some potential for enough breaks in cloud cover. The HREF neighborhood probabilities of exceeding 1"/hr in the 30-50% range, and 2"/hr around 10%. This results in HREF FFG exceedance probabilities broadly over 25 percent. The RRFS shows a similar evolution in roughly the same area but was not quite as high with its probability of exceedance or with the probability of 1 inch per hour rainfall. Farther west;..the instability is expected to be weaker but the greater coverage of rainfall looks to offset the instability shortfall. As mentioned previously...the flood risk should gradually transition from flash flood to areal flood/river flood as you go west across the state. A Marginal Risk area extending eastward from Montana and then southward from the Northern Plains and Mid-Mississippi Valley was largely left in place given the signal in the HREF for locally heavy rainfall rates within an elongated moisture plume originating from the Southeast US. It was done so despite convective details remaining uncertain. The most organized convective threat may end up over portions of NE and SD given a highly difluent flow aloft and low level convergent flow. However, there are also signals of organized convective clusters within the moisture axis anywhere from Arkansas to Iowa, While convection is unlikely along this entire axis...where it does develop rainfall rate potential will be high enough for localized flash flooding. ...Southeast... Latest numerical guidance continued to show locally heavy rainfall today and tonight along and south of a boundary moving in from the north. There was a bit of a westward expansion in the western extent shown by the HREF and RRFS of the 1-inch per hour probabilities and the probability of exceedance. As a result...the Marginal Risk was expanded westward in parts of Georgia to Alabama. Bann Day 2 Valid 12Z Sun May 31 2026 - 12Z Mon Jun 01 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL STRETCHING FROM MONTANA TO NORTHERN FLORIDA... Any heavy to excessive rainfall should be located in or near a plume of anomalous moisture plume that will extend from Montana into the Southeast United State. Large scale forcing is more subtle outside of the Northern Plains/Rockies...but there should be some weak shortwave energy embedded within the weak flow that will make them difficult or impossible to time. As this shortwave energy encounters a late day atmosphere with MUCAPE values in excess of 3000 J per kg from the Plains into the Mississippi Valley and parts of the Southeast US...storms have the potential to produce very intense rainfall rates that approach or exceed flash flood guidance along this entire corridor. A large and generally unfocused Marginal Risk area still seems to handle the localized nature of flash flood risk that should exist. The Montana portion of the Marginal Risk has the strongest synoptic forcing as a mid- and upper-level system gradually moves north of the border...keeping the western part of the state in lingering wrap-around rainfall before gradually tapering off. Bann Day 3 Valid 12Z Mon Jun 01 2026 - 12Z Tue Jun 02 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. There are some hints in the guidance that the overall risk of excessive rainfall is non-zero over the Plains from Kansas into Colorado as models show a low level axis of moisture and instability moving northward on Monday afternoon. The ensemble and deterministic QPF is fairly low...perhaps due to a component of low level flow off the moisture. In addition...lingering deep moisture may fuel some late day thunderstorms on Monday that are capable of locally heavy rainfall but the model spread limits confidence. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-mbo0MaiJ5BqRgXFgubIleaJdsnRfvdronGdFD9oOiNv= s0bTXAUXgyAms06Z25bbvrqnU2YjkO_IZAYVsSrdSTz-Bzc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-mbo0MaiJ5BqRgXFgubIleaJdsnRfvdronGdFD9oOiNv= s0bTXAUXgyAms06Z25bbvrqnU2YjkO_IZAYVsSrdrBsNpUI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-mbo0MaiJ5BqRgXFgubIleaJdsnRfvdronGdFD9oOiNv= s0bTXAUXgyAms06Z25bbvrqnU2YjkO_IZAYVsSrd79g1XEg$=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]