BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Thu, 28 May 2026 00:54:48 +0000 ----------------------------------------------------------- FOUS30 KWBC 280054 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 854 PM EDT Wed May 27 2026 Day 1 Valid 01Z Thu May 28 2026 - 12Z Thu May 28 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF WEST VIRGINIA AND ACROSS SOUTHWEST LOUISIANA... ...0100 UTC Update... Have trimmed quite a bit of real estate with both the Slight and Marginal areas, based on the latest observational trends, including mesoanalysis (dCAPE/dt), along with the recent HRRRs and 18Z HREF QPF exceedance probabilities. The remaining Slight Risk area over central WV (and a small sliver of northeast KY/southeast OH) is essentially for the near term...through 03-04Z...given the current radar trends and lingering deep-layer instability (MUCAPEs ~1000 J/Kg). The other remaining Slight Risk area (southwest LA) was supported by the latest HREF and RRFS exceedance probabilities, along with the recent HRRR output. Hurley Elsewhere (Northern Rockies), the Marginal Risk area remains (previous discussion below)... Relatively buoyant environment within a deep, anomalous moisture=20 presence across the Northern Rockies along with regional ascent=20 provided by sheared vorticity maxima maneuvering through the area=20 will allow for another round of widely scattered convection to=20 materialize across the Lewis Range in northwest MT. Instability and regional forcing will be a bit less than the previous period,=20 however sensitivities remain from remnant burn scars present within the mountainous terrain in the aforementioned area which is a=20 cause for concern for any cells that happen to occur over the burn=20 scars themselves. Hourly rates between 0.5-1"/hr in the stronger=20 cell cores would be capable of providing localized flash flood=20 impacts over those more sensitive grounds and this setup will=20 maintain the prospects given the anomalous moisture presence as=20 PWATs remain above the 90th percentile over the entire stretch of=20 the Northern Rockies. The previous MRGL risk inherited was=20 maintained given the relative continuity. Kleebauer Day 2 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, PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST FLORIDA... ...Plains to Lower Mississippi Valley... 21z update... The region with a highlighted threat for excessive rainfall and isolated flash flooding remain in good order, requiring no adjustments at this time. Campbell A bit of an omega block pattern is shaping up across the CONUS with a broad upper trough axis fixated over the Central and Southern Plains with with ridging in place over the top. This will cause a rather chaotic flow under the mean trough with deep moisture and several smaller mid-level perturbations basically "stuck" under the the overall trough axis. Ample instability with deep moisture presence will certain be a cause for continuing at least a scattered heavy rain footprint across areas under the influence of the trough. Scattered elevated probabilities between 30-60% exists for localized amounts >2" from KS all the way into the Southeast U.S. with the maxima split between KS and the Central Gulf coast. The two areas are different in the reasoning as the primary center of the trough will be fixed over KS leading to the best upper forcing pattern and stagnant flow remaining parked over the area as we move through D2. Pending the amount of rain that falls over the course of D1, a targeted upgrade is possible, but maintained the MRGL and will reassess as we move forward in future updates to see if an upgrade is warranted. The Central Gulf coast will remain in a favorable instability maxima with weak flow likely a component that could lead to isolated heavy totals stemming from slow-moving convection. The area from the Upper TX coast over through southern GA has been leaning wet over the past week, so antecedent conditions are a little more unforgiving for these types of setups. In any case, the threat remains modest, at best, so the MRGL risk was sufficient for the pattern with any upgrades likely to stem from more near term sampling of the radar trends. ...Florida... 21Z update... No changes were made for this period. Campbell 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. Latest 00z HREF is modestly robust with the signature for at least 3" off the neighborhood probabilities with a steady 60-90% output along the southeastern coast of FL with the maxima generally confined to the Miami Metro up to West Palm Beach. This correlates strongly with what has been advertised via regional and global guidance the past few days with the deterministic CAMs even indicating some 4-6" bullseye's within the main QPF footprint. This is a relatively classic pattern capable of locally significant rainfall within a deep moisture presence as PWAT anomalies sit between +1 to +2 standard deviations within the various ensemble packages. A MRGL risk remains in effect for the period across the South Florida metro corridor. ...Washington/Oregon into the Northern Rockies... 21Z update... A substantial expansion of the Northern Rockies Marginal Risk was made to include most of eastern Washington up to the Continental Divide and south into the Oregon Cascades and surrounding areas on both sides of the Divide. Anomalous PW values have been observed across the region, with some nearing the climatology max for late May. Should thunderstorms hold together, especially west of the Cascades, there will be an elevated threat for local flash flooding. Campbell Maturing ULL over the west coast will allow for a broad axis of diffluent flow across the interior northwest with the highlight of scattered convection likely to pivot further west into eastern WA, northern ID, and the western slopes of the Northern Rockies. Signals are not as prevalent compared to previous periods, however the environmental conditions are still favorable, especially when it comes to PWAT anomalies still generally running between the 90-95th percentile across northeast WA into northern ID. Burn scar remnants will likely be the most susceptible to seeing impacts, so the threat remains low-end and generally localized. Maintained continuity from the previous forecast with a MRGL risk in place across the aforementioned areas. Kleebauer Day 3 Valid 12Z Fri May 29 2026 - 12Z Sat May 30 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST U.S. AND FOR EASTERN WASHINGTON INTO THE NORTHERN ROCKIES... 21z update... A Marginal Risk was raised for portions of eastern Washington, northern Idaho and northwest Montana where there has been an elevated threat for localized excessive rainfall and isolated flash flooding as described in the Day 1 and Day 2 sections. Guidance is signaling a notable increase in QPF amounts and coverage for parts of northern Idaho and into Montana, thus continuing the flooding threat for this time period. Further south, guidance still varied on where the highest QPF was placed; however there was consensus for an increase in amounts across southern Missouri, central/eastern Tennessee and western South Carolina. This trend supported an adjustment of the northern boundary of the Marginal Risk area. Campbell Strong Canadian high pressure pressing in from the north will lead to a persistent quasi-stationary turned cold front to press south over the course of Thursday into Friday with convection likely to spawn along and ahead of the front with dry air advecting behind the front leading to a cutoff of activity. Jury is still out on specifics with the placement of the front generally over the Carolina's by Friday morning with slow push south as the day wears on. Frontal alignment is more of a arcing back into the Tennessee Valley as the persistent troughing in the South-Central Plains will likely maintain some southerly flow for areas along and west of the Mississippi. Anywhere within proximity to this front will be subject to various convective outputs with some heavier cells likely intertwined in over the pattern. No discernible areas of interest are present at this juncture, however the environmental favorability likely points to the best chances occurring across the Southeast into the lower Tennessee Valley. A broad MRGL is forecast for the above areas through the Lower Mississippi Valley. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7tUfWqqUeqFMBccGFZelwSR1F32kIUZycXlDz4scVJYG= OB7encO21_oSFocdLVZhLhcKbxwcq5Wj5JUfV7IrZE2tarw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7tUfWqqUeqFMBccGFZelwSR1F32kIUZycXlDz4scVJYG= OB7encO21_oSFocdLVZhLhcKbxwcq5Wj5JUfV7Ir-CiWWcQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7tUfWqqUeqFMBccGFZelwSR1F32kIUZycXlDz4scVJYG= OB7encO21_oSFocdLVZhLhcKbxwcq5Wj5JUfV7IrqXGPscE$=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]