BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Wed, 27 May 2026 00:17:51 +0000 ----------------------------------------------------------- FOUS30 KWBC 270017 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 817 PM EDT Tue May 26 2026 Day 1 Valid 01Z Wed May 27 2026 - 12Z Wed May 27 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF CENTRAL AND SOUTHERN TEXAS... ...Texas into Southern Oklahoma... ...0100 UTC Update... Based on the latest observational trends -- satellite, radar,=20 mesoanalysis, etc. -- have pared the back edges of the outlook=20 areas across West TX. Also nudged the southern periphery of the=20 Slight Risk area a little farther south across South TX (Brush=20 Country), based on the latest HRRR trends and elevated 18Z HREF=20 exceedance probabilities. Over this region, still quite a bit of=20 untapped deep-layer instability (mixed-layer CAPEs ~3,000 J/Kg),=20 along with PWATs between 1.9-2.1 per the latest SPC mesoanalysis.=20 Continued low-mid level shear (esp directional) will likely=20 maintain progressive linear segments/QLCS, however given the degree of instability and TPW, sub-hourly rainfall rates of 2-3 inches=20 will be possible underneath the strongest cells.=20 Hurley ...Southeast to Mid Atlantic to Ohio Valley... ...0100 UTC Update... Weak mid-level lapse rates (<6.5 C/km per SPC mesoanalysis) is leading to a increasing lower-layer stability across much of this=20 region following sunset. MUCAPEs still 1500-3000 J/Kg over much of the area is still sufficient for areas of heavy rainfall, especially considering the overall weak flow (southerly Corfidi vectors 5-10 kts) and PWATs between 1.7-2.0+ inches over most areas. However the area(s) of convective clusters within an overall diffuse Warm Conveyor Belt (WCB) are rather disorganized, and as we continue to progress farther beyond peak diurnal heating, expect any short-term runoff issues to be more localized/isolated. As a result, all Slight Risk areas were removed.=20 Hurley ...Northern Rockies... 16Z update... Convection this morning has been firing up across eastern Washington and northern Idaho, areas very similar in topography with sensitive locations as described below. The western boundary of the Marginal Risk was expanded into eastern Washington to cover this convection and more expected later in the day. Campbell Energetic disturbance ejecting out of the Pacific Northwest and British Columbia will make headway into the Northern Rockies by later this afternoon leading to a period of convective activity to spawn along the Lewis Range down into the high valleys of western MT. PWATs running over 1" across the Northern Rockies is well above climo norms, closer to the 99th percentile as noted by the latest NAEFS outputs, more than sufficient to be a problem for any more sensitive topographic features present given the complex topography. Multiple burn scars in the area will also be under threat for seeing rainfall rates between 0.5-1"/hr at times, a threshold that could cause rapid run off and debris flows if cells linger over the sensitive areas. This is not a widespread flash flood prospect, but isolated to widely scattered instances cannot be ruled out considering the above environment. A MRGL risk remains in place to account for the lower end threat. Kleebauer Day 2 Valid 12Z Wed May 27 2026 - 12Z Thu May 28 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE EASTERN HALF OF TEXAS, PORTIONS OF THE LOWER MISSISSIPPI VALLEY, AND AREAS OF THE OHIO VALLEY TO CENTRAL APPALACHIANS... 21Z update... A new Marginal Risk area was raised for eastern Washington, northern Idaho and western Montana. Deep moisture over the region maintaining above climo PW values for late May. A wave making its way through the region along with differential heating will help trigger convection capable of rain rates upwards of 0.50 to 1+ inches/hr in isolated areas. These rates, if falling over recent burn scars and other sensitive locations have the potential to cause isolated flash flooding and/or debris flows in steep terrain. However a limiting factor will be that the areal coverage of thunder will be less than that of the Day 1 period. Campbell ...Texas to Lower Mississippi Valley... The broad upper level evolution occurring upstream over the Southern Plains will continue to shift east with the large scale forcing driving into the eastern half of TX leading to heavy rain prospects over the eastern portions of Hill Country, the I-35 corridor and much of east TX, including the middle and upper TX coastal areas on Wednesday. Environmental conditions for heavy rainfall are most favorable along the TX and LA Gulf coast areas with a corridor of elevated theta_E's aligned from Corpus Christi up through the Lower Sabine to about 100 miles inland. The setup is contingent on the behavior of the convective pattern upstream into the central portion of the state and the migration of the thunderstorm complex exiting out of I-35. The general consensus is the maxima for precip will likely occur in proximity to the same areas that were hit within the past week; the area along the upper TX coast from Houston up to Lake Charles. This is very well defined within the probability fields in both the HREF and the AIFS-ENS where >3" is likely (60-90%) within the confines of that zone with the HREF even signaling modest >5" potential (40-60%) in that same zone. There's still some uncertainty in the behavior of any mesoscale complexes that end up materializing from all the convective development the previous evening and if they cause any significant shifts in the potential. In this case, this leads to a broad SLGT risk with a MRGL risk encompassing over the Southern Plains to Lower Mississippi Valley as broad upper forcing will likely spur scattered convection all across areas from western KS down through OK in the setup. Areas away from east TX and the Lower Mississippi will have more isolated heavy rain prospects, comparatively, so the threat remains elevated in the SLGT risk within these particular locations. ...Ohio Valley... 21Z update... A minor westward nudge was made across Indiana along with a south and east expansion across West Virginia to account for the latest model trends and WPC QPF. Campbell Conditions will become increasingly favorable for heavy rainfall across the Ohio Valley going into Wednesday from a multitude of features that will ultimately couple into something more formidable during peak diurnal instability. Sheared vorticity stemming from previous period convection will likely settle over the central Ohio Valley with a west to east bisecting quasi-stationary front positioned just north of the Ohio River basin. A sweeping trough exiting out of Ontario will help tighten an axis of confluence across the Midwest and Ohio Valley by Wednesday afternoon, enticing a squeeze of the thermal gradient and regional instability axis that aligns with the frontal placement. Destabilization by the afternoon hours will lead to scattered to widespread thunderstorm initiation along the boundary with convective episodes likely to spawn heavier cells capable of hourly rates between 1-2"/hr as PWAT anomalies sit firmly within +2 standard deviations above climo. Previous periods of rainfall in the last three to four days have really brought down the areal FFG markers for all 1/3/6 hour thresholds with a vast majority of places along the Ohio River basin and points north running <1"/hr in the hourly exceedance indicator. This points to any heavier convective impacts could cause issues with the remnant soil moisture and hydrologic concerns that are lingering after the last event. This is especially true for eastern OH, southwest PA, and western WV where complex topography only exacerbate the potential in these zones. 3-hour FFG exceedance probabilities from the 00z HREF are between 20-40% for a large portion of eastern IN through the southern half of OH into southwest PA with a maxima of 40-60% located across northwest WV between US50 and WV7. Considering the antecedent conditions and expected widespread convective regime along the front, a SLGT risk was added for an increasing threat for flash flooding Wednesday. Kleebauer Day 3 Valid 12Z Thu May 28 2026 - 12Z Fri May 29 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, NORTHERN ROCKIES, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST FLORIDA... 21Z update... A new Marginal Risk area was raised for eastern Washington, northern Idaho and western Montana to carry on the elevated threat potential described in the Day 1 and Day 2 periods. A minor westward expansion of the Marginal Risk was made for Palm Beach County to account for trends and the new WPC QPF, elsewhere remains in good order. Campbell ...Plains to Lower Mississippi Valley... Breakdown of the persistent pattern for areas east of the Continental Divide will lead to weaker steering flow, but still enough moisture, lingering boundaries, and remnant mid-level vorticity to spur up bouts of scattered convection all across parts of the Central and Southern Plains into the Mississippi Valley. This setup is a far cry from what we've experienced the past several days, so the prospects of widespread flash flooding are much lower comparatively. However, environmental conditions and deep moisture presence still remain favorable along the northern periphery of the trough lingering across east TX which places the best opportunity for convective episodes to be located over the aforementioned areas. Ensemble QPF footprint is most notable across the Central Gulf coast and upper TX coastal plain, likely in part to the positioning of the trough and the fact the most prevalent theta_E is situated along the immediate Gulf. It's a period to monitor for any small scale features that could enhance convective potential further, but for now, a broad MRGL exists to cover for the threat. ...Florida... Active sea breeze pattern with weakening steering flow will lead to a period of heavy rainfall across the southeast FL coast on Thursday afternoon. Consensus within guidance is for an active period between 18-00z Thu/Fri that would allow for heavy convection with slow forward propagations to impact the South Florida metro corridor from West Palm Beach down to Miami. Globals and regional guidance even have some 2+" totals already in the output, and that's before the CAM's even have a depiction. Typically, this is a sign for heavy rainfall prospects capable of flash flooding, especially when you consider the PWATs running +1 to +2 deviations across that area of the Peninsula. A MRGL risk remains for that urban corridor of southeastern FL. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!689rZTLUPfUFczU_W5h6qGAxhZIWFLPXrlwueQ7mE7W8= EIbf8F-HOPSijYEt0DnX-Kyx5k8mme5MaMm3ghvd-0tHE3s$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!689rZTLUPfUFczU_W5h6qGAxhZIWFLPXrlwueQ7mE7W8= EIbf8F-HOPSijYEt0DnX-Kyx5k8mme5MaMm3ghvdsriwC_U$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!689rZTLUPfUFczU_W5h6qGAxhZIWFLPXrlwueQ7mE7W8= EIbf8F-HOPSijYEt0DnX-Kyx5k8mme5MaMm3ghvdAREg5OQ$=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]