BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Sat, 30 May 2026 00:48:22 +0000 ----------------------------------------------------------- FOUS30 KWBC 300048 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 848 PM EDT Fri May 29 2026 Day 1 Valid 01Z Sat May 30 2026 - 12Z Sat May 30 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST AND TENNESSEE VALLEY... 01Z Update: As has been the case, late-period changes to the Day 1 ERO were primarily to remove areas from the Slight and Marginal Risk area that have been worked over and/or have seen a diminished threat given the loss of diurnal heating. Observational trends along with the elevated 18Z HREF neighborhood probabilities of 3+=20 inches of additional rainfall through 12Z have resulted in a continuation of the Slight Risk across much of GA into eastern AL and eastern TN. Still sufficient deep-layer instability over these areas to pose a more heightened risk of excessive rainfall, with mixed-layer CAPEs between 1000-2000 J/Kg. Peak neighborhood probabilities of >3" through 12Z per the 18Z HREF are between 40-60% in this region.=20 Hurley Day 2 Valid 12Z Sat May 30 2026 - 12Z Sun May 31 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF MONTANA... 20z Update: Upgraded to a Slight risk across portions of MT where isolated to scattered flash flooding is possible. The eastern half of the Slight risk area should see the highest rainfall rates, with 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%. There should be enough coverage of higher rainfall rates to result in some flash flood risk. Instability is less the farther west you go in MT, but rainfall coverage will be greater, resulting in higher areal averaged rainfall. The flood risk should gradually transition from flash flood to areal flood/river flood as you go west across the state. Elsewhere, the Marginal risk was broadened across the Northern Plains into the MS Valley along an elongated moisture axis. Convective details are uncertain at this lead time, but that entire corridor will have above average moisture and some forcing.The most organized convective threat may end up over portions of NE and SD Saturday night as stronger forcing ejects into the area. However, there are also signals of organized convective clusters within the moisture axis anywhere from AR to IA. While convection is unlikely along this entire axis...where it does develop rainfall rate potential will be high enough for localized flash flooding. Chenard ...Previous Discussion... ...Southeast... Latest numerical guidance has shifted a majority of the rainfall eastward enough compared with previous runs to preclude an upgrade to a Slight risk. In addition...the spread of model guidance both in terms of placement and amounts precluded an upgrade. As mentioned previously...some of the region, especially western parts of South Carolina and into the Appalachians, has been very wet as of late and is well primed, so may by more vulnerable to flooding concerns. ...Northern Rockies to High Plains... The upper level low over the West during the Day 1 period will weaken and shift northeastward, moving over the Northern Rockies to High Plains region on Saturday. Moisture anomalies will continue to be in the 90-90th percentile, supporting moderate to heavy rainfall, with widespread QPF greater than 0.5-1" likely across western and central Montana. There may not be a lot of instability to work with, so any flood or flash flood threats should be mainly localized with particular attention to burn scar locations. A fairly broad marginal risk remained in place across much of western and central Montana, into parts of northern Wyoming as well. Bann Day 3 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... 20Z Update: Expanded the Marginal risk to cover most of the anomalous moisture plume that will extend from MT into the Southeast U.S. in between troughing over the West and Northeast. Large scale forcing is more subtle outside of the Northern Plains/Rockies...but there should be some weak shortwaves embedded within the weak flow. Global deterministic models, ensemble means and AI models show a broad convective threat along this entire corridor, with no clear area of higher focus. Thus at the moment a large Marginal seems to handle the localized flash flood risk that should exist. Some fine tuning of the Marginal and/or focused Slight risk upgrades will be possible as we get closer and convective mode/evolution becomes clearer. Chenard ...Previous Discussion... ...Northern Rockies and Adjacent High Plains... The upper level low which has been supporting the prolonged wet period over the Northern Rockies will continue to move northward across Montana slowly on Sunday. This results in surface low pressure and associated surface front to makes its way out over the Plains and gradually weaken while the mid and upper level circulation keeps precipitation lingering over Montana and far northern Wyoming. Moisture remains anomalously high but instability still looks to be dependent upon cloud cover. As in the Day 2 period...any flood or flash flood threats should be mainly localized with particular attention to burn scar locations. ...Southeast... Until surface high pressure builds far enough southward into the Southeast states to decrease coverage of lingering convection on Sunday evening...the antecedent conditions keep a risk of flooding concerns over the area. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7we_l73PKnUB_0qo1S853oUXeFktdonbUW7532LZT3zF= xlRciigC8ZJcAESLQZxz6VgitXrohvclL-9DYzsJzizNMSw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7we_l73PKnUB_0qo1S853oUXeFktdonbUW7532LZT3zF= xlRciigC8ZJcAESLQZxz6VgitXrohvclL-9DYzsJQwcDIPk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7we_l73PKnUB_0qo1S853oUXeFktdonbUW7532LZT3zF= xlRciigC8ZJcAESLQZxz6VgitXrohvclL-9DYzsJ_TmjDc4$=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. 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