Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 03 2025 00:42:12 FOUS30 KWBC 030042 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 842 PM EDT Mon Jun 2 2025 Day 1 Valid 01Z Tue Jun 03 2025 - 12Z Tue Jun 03 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL PLAINS... ....Central Plains... The Slight Risk area was trimmed southeastward out of the Sand Hills and behind the line of storms currently bisecting Nebraska. As expected, the storms across Nebraska are barely moving, and are producing rain rates to 3 inches per hour in otherwise normally dry areas. Thus, the Slight remains in place for central and much of eastern Nebraska. When the storms begin to move, likely as the line interacts with a second progressive line of storms across west Kansas, they should propagate eastward, so areas west of the line should remain with relatively little rainfall. The surrounding Marginal across Minnesota was trimmed as the storms in that area are very progressive. While there may be some redevelopment of shower activity later tonight, it is not expected to result in any flooding concerns. The Marginal in west Texas and western Oklahoma remains largely intact as potential backbuilding of the line could result in localized training, which may produce an isolated flash flood or two. The Slight across south Florida has been downgraded with this update as the peak rainfall rates from storms have come way down as the storms have congealed into a larger MCS, but with relatively low embedded rainfall rates. Most areas seeing rates below an inch per hour should preclude anything other than isolated flash flooding through the evening. Wegman Day 2 Valid 12Z Tue Jun 03 2025 - 12Z Wed Jun 04 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE CENTRAL UNITED STATES AS WELL AS SOUTH FLORIDA AND THE FLORIDA KEYS... ....Texas to the Great Lakes... An active day of convection is likely on Tuesday as a cold front sags across the Heartland, providing the focus for widespread showers and thunderstorms. This front will be pushed southeast in response to an amplifying northern stream trough which will dig across the CONUS as far south as Texas. This will drive height falls across the region, with embedded shortwave impulses racing northeast, and a poleward arcing jet streak downstream of the primary trough axis combining to provide additional ascent. This deep layer lift will work into robust thermodynamics characterized by an overlap of PWs above the 99th percentile (NAEFS) and a ribbon of MUCAPE exceeding 2000 J/kg, surging northward on 30-50 kts of 850mb flow emerging on return flow from the Gulf. The CAMs continue to be in excellent agreement in the coverage of convection on Tuesday despite some temporal and spatial differences owing to timing of the front. Despite these modest differences, there is good agreement among the REFS and HREF ensembles to suggest widespread 1"/hr rain rates from the northern TX Hill Country all the way to the eastern Missouri Valley (probabilities exceeding 50% across this entire area). Although mean 0-6km winds of 20-30 kts indicate progressive storm motions, this flow aligned to the front and combined with Corfidi vectors that collapse and veer to the NE indicate a high potential for redevelopment to the SW into the more intense thermodynamics and training of cells to the northeast. Where this occurs, total rainfall exceeding 3" is likely (>60% chance in HREF/REFS) and 5" is possible (>40% chance), with even the global ensembles suggesting a 10-30% chance for 3" in this same region. The inherited SLGT risk was tailored for this new guidance, with the biggest adjustment being an extension SW into the Hill Country of TX where convection that develops along the tail of this front will likely feature slow storm motions and backbuilding to produce heavy rainfall. Although heavy rainfall is also likely in convection that develops northeast into the Upper Midwest and Great Lakes, storms should be more progressive and the Corfidi vectors suggest less opportunity for training, so only a MRGL risk is needed north of Iowa. ....South Florida and the Florida Keys... Shortwave trough over the Gulf may amplify enough to become a weak closed low Tuesday and then spin nearly in place as it gets suppressed beneath a Bermuda- type ridge to its northeast. This will maintain modest synoptic ascent across Florida, but some enhancement is likely as a jet streak over the Atlantic tails back to the SW, placing the favorably diffluent RRQ overtop the peninsula. This forcing will combine with continued, albeit weakening, low-level convergence along a decayed front/surface trough, to result in another day of widespread showers and thunderstorms. PWs in place will again be greater than 2 inches, above the 90th percentile according to NAEFS, combining with 1000 J/kg of CAPE to produce robust thermodynamics to support rainfall rates of 2"/hr at times. There continues to be some uncertainty in the coverage of convection, as well as placement, among the various CAMs, somewhat lowering the confidence into D2. However, after heavy rain anticipated D1, any additional rainfall D2 could quickly become problematic and lead to instances of runoff and flash flooding, especially in urban areas. The inherited MRGL and SLGT risks were tailored slightly to encompass the highest probabilities of 1+" and 3+" on D2. Although not included in a risk area at this time, some of the guidance has become a bit more aggressive with a wave of low pressure developing along an inverted trough aligned to the east coast of Florida. If this low were to develop a bit more rapidly or track farther west, some heavy rain could move onshore the northeast Florida coast before 12Z Wednesday. ....Four Corners... A MRGL risk was expanded westward from the Central Plains to the UT/NV/AZ borders with this update. The guidance has become more aggressive with showers and thunderstorms blossoming during the aftn/evening as forcing intensifies from broad divergence downstream of a closed low filling and moving into the Desert Southwest, producing ascent atop a wavering frontal boundary positioned over the region. This lift will impinge into favorable thermodynamics with PWs reaching above 0.75 inches into a bubble of MUCAPE of 750-1000 J/kg. Mean storm motions will be weak, generally around 5 kts, so with rainfall rates which have a 5-15% chance of exceeding 1"/hr, these slow motions could result in locally as much as 1" of rainfall in a short period of time. If this occurs over sensitive soils, urban areas, or terrain features, instances of flash flooding could result. Weiss Day 3 Valid 12Z Wed Jun 04 2025 - 12Z Thu Jun 05 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER MIDWEST, THE FOUR CORNERS, AND THE SOUTHEAST COAST... ....Four Corners... Another active day of showers and thunderstorms expected as the upper low over northern Baja fills and ejects northeast atop the Four Corners. The accompanying ascent will move into continued anomalous PWs which will exceed the 99th percentile according to NAEFS. This will fuel widespread convection with rainfall rates of 0.5"/hr, or at times higher, likely., and storms will likely move slowly beneath the upper trough, leading to a longer duration of heavy rain. Although total rainfall will be modest in most areas (24-hr probability from the ECENS/GEFS for 1" peaks around 25%), where the heavy rain impacts sensitive terrain features or urban areas, or should heavier rain impact the wetter soils in the CO/NM high plains, instances of flash flooding could result. ....Mid-Mississippi Valley to Great Lakes... The cold front from D2 will continue its trek eastward on Wednesday, but will start to slow and become aligned more west to east as its tail gets pulled northward by an approaching shortwave over the Four Corners region. Shortwaves embedded within the flow will continue to race northeast, especially from Missouri to Michigan, which is where the greatest concentration of thunderstorms is expected on D3. Storm motions along the front are likely to be progressive, lifting off to the northeast on 0-6km mean winds of 20-30 kts, but weaker Corfidi vectors aligned both to this mean wind and the front suggests a potential for training. As rainfall rates peak above 1"/hr within favorable thermodynamics, this could result in stripes of heavy rainfall for which the SREF/ECENS/GEFS ensembles indicate have a 20-30% chance of exceeding 1", with some low-end probabilities (5% or less) of exceeding 3". The MRGL risk was split, with the Central Plains removed from the risk on D3 due to a more progressive front and some NVA behind impulses, but also extended a bit northeast to reach the Canadian border for isolated flash flood potential. ....Southeast Coast... Guidance has become more aggressive with a wave of low pressure potentially developing along an inverted trough shifting northeast along the FL/GA/SC coasts. While NHC has placed a 10% probability of tropical or sub-tropical development on this feature, regardless of whether a circulation forms or not, there is increasing confidence that heavy rain will spread across the FL Peninsula and then rotate onshore the GA/SC coasts on Wednesday. With PWs in the vicinity progged to exceed 2", above the 90th percentile, supported by warm cloud depths that may exceed 15,000 ft, efficient rainfall rates of 1-2"/hr will be likely in any showers/thunderstorms. It is possible that the heaviest rainfall will remain just offshore, but impressive moisture convergence from Jacksonville, FL to Charleston, SC should support waves of heavy rainfall regardless of development of this system, and although EFI is modest, it does capture the region of greatest potential at this time range. Additionally, plentiful tropical moisture across the rest of the FL Peninsula and a shortwave continuing to pivot across the Gulf could enhance rainfall over much of Florida Wednesday, and the MRGL risk was expanded from Winyah Bay, along the coastal plain of GA/SC, and across much of the FL Peninsula. Weiss Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_Nv0_imDNZUpR-fgoC7KaxWLsiGHz0fGfAujLDhVF5F-= GQRFMEOrcDE8k5uj-kokUnZZgZm_KV_r5ZS0A2SWORYKua0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_Nv0_imDNZUpR-fgoC7KaxWLsiGHz0fGfAujLDhVF5F-= GQRFMEOrcDE8k5uj-kokUnZZgZm_KV_r5ZS0A2SWkmo6sNs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_Nv0_imDNZUpR-fgoC7KaxWLsiGHz0fGfAujLDhVF5F-= GQRFMEOrcDE8k5uj-kokUnZZgZm_KV_r5ZS0A2SWab-ONNo$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .