BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Fri, 29 May 2026 00:56:25 +0000 ----------------------------------------------------------- FOUS30 KWBC 290056 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 856 PM EDT Thu May 28 2026 Day 1 Valid 01Z Fri May 29 2026 - 12Z Fri May 29 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE MID-SOUTH AND OZARKS... 01Z Update... Have dropped the Marginal Risk across much of the Southeast (outside of SE FL), given the lack of deep layer forcing, decaying diurnal heating and sea breezes, and weak mid level lapse rates. Despite better forcing (along mid level deformation axis/TROWAL zone), diminishing deep-layer instability has also allowed for the Slight Risk over KS to drop to a Marginal. Otherwise, the Slight over central-northern AR into southwest and south-central MO continues, based on the latest observational trends (radar, satellite, mesoanalysis), along with recent HRRR trends and elevated QPF exceedance probabilities from the 18Z HREF.=20 Have also expanded the Marginal Risk over the northern Rockies and Intermountain West areas, based largely on current observational trends.=20 Hurley ---Previous Discussion--- ...Florida... An active sea breeze pattern with weakening steering flow will lead to periods of heavy rainfall across southeast Florida this afternoon. Greatest concern remains over the South Florida metro corridor from West Palm Beach to Miami. Latest HREF is robust with showing greater than 50% probabilities for 3" in 24-hours, with even some modest, albeit localized, probabilities for 5". This correlates well with CAM guidance, with some indicating bullseyes of greater than 3" within the larger QPF footprint. Locally significant rainfall is likely in this relatively classic pattern with ample moisture and instability present. A marginal risk remains in effect across Southeast Florida. ...Washington/Oregon... A deep upper level low over the West will allow for a broad axis of diffluent flow across the interior Northwest. Precipitable water values 1-1.5" are in the 90-90th percentile, and with sufficient instability, should support convection capable of producing heavy rainfall. Flooding and flash flooding are a concern for mainly the more vulnerable areas - urban, small stream, and low lying areas. HREF 24-hr probabilities for greater than 3" are between 40-70% for especially the Oregon cascades. Given the favorable environment though, a marginal risk extends all the way from far northern California northward to the eastern half of Washington state. A previous marginal risk for parts of the northern Rockies was trimmed out for this update given the lack of QPF signal. Santorelli Day 2 Valid 12Z Fri May 29 2026 - 12Z Sat May 30 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST... 20Z Update... In collaboration with several Southeast WFOs, a Slight Risk was introduced from eastern AL to the GA/SC border. The region is caught out ahead of a sheared 500mb vorticity maximum approaching from the west. This feature is caught between a closed low traversing the Great Basin, an upper level ridge in the Midwest, and a strong trough in the Northeast. At lower levels, weak high pressure over the FL Straits and troughing in the western Gulf is producing a lengthy moisture fetch with origins in the Caribbean Sea. By 00Z Sat, ECMWF SATs shows a >90th climatological percentile IVT oriented N-S and directed at the Southeast. This culminates in a tropical air-mass sporting 2.0-2.2" PWs that is directed at a stationary front in draped from the TN Valley to the SC coast. Instability will be highest over AL on east into central and southern GA with MUCAPE between 1,000-2,000 J/kg most often. MUCAPE up to 1,000 J/kg will be available Friday night from the Savannah River to coastal SC. Area-averaged soundings show warm cloud layers as deep as 13,000ft over eastern GA at the same time as a weak, yet negatively-tilted 250mb trough fosters synoptic-scale ascent aloft. Guidance shows a cluster of heavy thunderstorms forming that will slowly make their way east. The Slight Risk area resides just south of the stalled front where greater instability will reside and atop some of the more saturated soils in the region. The strongest storms will have the capability to produce max rates up to 3"/hr rainfall rates from eastern AL on east to the Savannah River Friday afternoon and through Friday night. With increased confidence in locally considerable rainfall rates over sensitive soils, a Slight Risk was introduced. Otherwise, some minor tweaks to the inherited Marginal Risk areas were made in the Central Plains and Northern Rockies to account for the latest WPC QPF. Mullinax ---Previous Discussion--- ...Eastern Washington to Northern Rockies... A marginal risk is in place across far northeast Washington to northwest Montana due to an increase in the heavy rainfall signal for this period as the upper low over the West on Day 1, pivots slightly northeastward, placing this region in an area with better upper forcing and advection of moisture. The presence of anomalous moisture and some instability may present a threat for localized heavy rainfall and flash flooding, especially for burn scar locations within this region. ...Middle Mississippi Valley to the Southeast... Strong Canadian high pressure pressing in from the north will allow for a slow moving cold front to press south over the course of Thursday into Friday with convection likely to spawn along and ahead of the front and dry air advecting behind the front leading to a quick cutoff of activity. The front will arc back into the Tennessee Valley to Middle Mississippi Valley, supported by the persistent troughing over the south-central Plains. A moist and unstable environment near and south of this front will support scattered convection, with some heavier cells likely within the pattern. It is still too hard to pick out any discernible areas of interest, so maintained a very broad marginal risk over this area which is quite wet and will continue to be in the Day 1 period. Santorelli Day 3 Valid 12Z Sat May 30 2026 - 12Z Sun May 31 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE NORTHERN ROCKIES TO HIGH PLAINS AND THE SOUTHEAST... 20Z Update... There was consideration given to a Slight Risk over eastern GA on east though much of coastal SC given the same setup supporting a Slight Risk farther west on Friday should move east Saturday morning. However, lingering model spread in both amounts and the axis of heavier rainfall (as far north as northern SC, as far south as the FL Panhandle) made it difficult to pinpoint a more "at- risk" area. The coastal areas of the Southeast will be monitored closely in the coming forecast cycles, but opted to maintain a Marginal Risk given the lingering uncertainty. Meanwhile, in the Northern Rockies, plenty of precipitation is likely coming to the region on Saturday. The primary reason for no Slight Risk is due to the potential for large sums of clouds possibly reducing the instability available. This should be a beneficial soaking rain event for drought-stricken central MT, but localized areas of flash flooding are possible in poor drainage areas and along complex terrain. Mullinax ---Previous Discussion--- ...Northern Rockies to High Plains... The upper level low over the West during the Day 1 and 2 periods will weaken and shift northeastward, moving over the Northern Rockies to High Plains region on Day 3/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 is in place across much of western and central Montana, into parts of northern Wyoming as well. ...Southeast... Same story as Days 1 and 2, with ample moisture and instability present near and south of a cold front that may stall over the region on Saturday supporting convection, across much of the Southeast. Some of this region, especially western parts of South Carolina and into the Appalachians has been very wet as of late and is well primed, so may be more favorable for flooding concerns. The marginal risk though continues towards the coast due to the presence of a weak frontal wave in the region. The Marginal Risk extends from the Southeast coast, westward into northeast Alabama and southeast Tennessee. Santorelli Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!902C38snp3pXPRtfz4A7rnbHIikqtOm0XpqTP14K8Nsg= Bnuw6ZPa_lURLpQ-OZwotaY6YscB2EwW1OAb1kCjLiu7AOE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!902C38snp3pXPRtfz4A7rnbHIikqtOm0XpqTP14K8Nsg= Bnuw6ZPa_lURLpQ-OZwotaY6YscB2EwW1OAb1kCj0sgGPBE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!902C38snp3pXPRtfz4A7rnbHIikqtOm0XpqTP14K8Nsg= Bnuw6ZPa_lURLpQ-OZwotaY6YscB2EwW1OAb1kCjzdjNcCU$=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]