Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 09 2024 15:58:14 FOUS30 KWBC 091557 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1157 AM EDT Tue Jul 9 2024 Day 1 Valid 16Z Tue Jul 09 2024 - 12Z Wed Jul 10 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST, MID MISSISSIPPI AND OHIO VALLEYS, AS WELL AS FOR THE=20 SOUTHEASTERN LOUISIANA... ....16z Update Summary... Two primary updates to the previous D1 to reflect changes in guidance and to update on the recent radar reflection going forward. The SLGT risk across the center of the country into MI was expanded to the east over southern IN and further northeast across much of southern MI. The second update was across the Central Gulf Coast where the previous SLGT risk was scaled back in size to mainly encompass the New Orleans metro and surrounding locales given the recent radar trends and CAMs output through the period. More details were added to the respective sub-headings below.... Elsewhere over the CONUS, the other notable change exists across FL where the MRGL was cut over much of the western coast and over far southern FL due to the setup for flash flood potential being primarily confined to the FL Panhandle, FL Big Bend, and the eastern coast given the flow pattern conducive for localized enhancement from the Atlantic sea breeze. Spotty max totals over 3" are forecast within CAMs, but the placement is very variable, so wanted to maintain some coverage to account for the threat, but local uncertainty. The setup across New England, Southern Appalachians, and portions of the Southwestern US are all fairly similar with regards to the threat being localized for flash flooding within the respective terrain. The best threat remains over the burn scars in NM where any convective impact over the affected areas will be susceptible to flashy returns. The other areas within New England and the Southern Appalachians lie within the lower-end of MRGL, but non-zero considering the environment and terrain focus.=20 Kleebauer ....Mississippi Valley and Midwest... ...16Z Update.. Increasing signals for heavy rainfall from the remnants of Beryl=20 will impact some of the urbanized areas extending through the=20 Detroit Metro with a greater convective concern located over southern IN. Southern IN will be within the best instability axis=20 in the Ohio Valley with several small mid-level perturbations=20 advecting overhead this morning through the evening around the broad periphery of Beryl's circulation. Recent HREF mean QPF across the area has really ramped up with storms already impacting the southern fringe of the state with locally heavy rain as rates top 1.5-2"/hr in the recent radar QPE output. A second round is expected this evening in wake of better instability leading to a multi-wave threat of convection within portions of the area. Considering the priming this morning and eventual impact later, the threat for flash flooding has increased enough to warrant the SLGT expansion. Across southern MI, the forward speed of Beryl's remnants will allow for a solid 925-700mb moisture flux through the region with sights on the Detroit metro by the end of the period. HREF neighborhood probabilities for at least 3" have shot up to 40-60% across portions of Southeast MI, including Detroit with signals over Southwest MI growing to 80-90% for at least 3" and 25-40% for potential of 5". This was a significant enough signal to warrant the SLGT expansion across Southern MI through the Detroit Metro with agreement from the local Detroit WFO.=20 Kleebauer ...Previous Discussion.. Tropical moisture associated with Beryl will spread a swath of heavy rain across the Mississippi Valley and into the Midwest as a cold front advances east through the region. The last few runs of guidance have trended toward a more narrow axis setting up right along the front and QPF values increasing further northeast across Illinois/Indiana and southern Michigan. A sizable swath of 3+ inches continues to span from the Missouri Ozarks to northwest Indiana with local maximums upwards of 8 inches. A Slight Risk extends from central Arkansas to southern Michigan. A Marginal Risk stretches from the central Arkansas northward to southern Michigan and central Ohio. Campbell ....Central Gulf Coast and Southeast... ...16Z Update.. Recent trends in the enhanced QPF focus across the Central Gulf coast have led to the New Orleans metro and surrounding locales over Southeast LA as the focal point for heavy rainfall today into the evening. Considering very high FFGs located over the coastal portions of LA/MS/AL, the threat will be mainly an urban flood threat with the New Orleans metro easily being the target for the current setup. HREF probabilities for at least 2"/3-hrs is highest across Southeast LA with values mainly between 25-40% over a span of several hrs beginning now through 06z with the spatial coverage centered right over NoLA and surrounding Parishes. This allowed the previous SLGT to shrink in size to mainly encompass the New Orleans metro and Parishes just off to the south and southwest.=20 Kleebauer ...Previous Discussion.. Deep, onshore flow will continue to drive convection to form along the Gulf Coast, with the potential for heavy down pours. Areal average rainfall is expected to be in the 1 to 2 inch range however the CAM guidance suggests very localized maximums of 3 to 5 inches possible. A Slight Risk is in effect for portions of the Gulf Coast from eastern Louisiana to the Florida Panhandle. Campbell ....Previous Discussions... ....Southwest... Isolated to widely scattered convection is likely to form along the mountains once during the afternoon and evening, which could very well move over flood-sensitive areas. A Marginal Risk remains in effect for portions of Arizona, New Mexico, southern Colorado and extreme western Texas. ....Rio Grande of Texas... Convection that forms along the mountains of Mexico will have enough of an eastward push that some may cross into the Del Rio and Eagle Pass areas. Isolated instances of flash flooding may develop, therefore a Marginal Risk remains in effect. ....Southern Appalachians... Storms are likely to form in the deep tropical moisture indirectly associated with Beryl with the mountains acting as the primary forcing. Numerous flood sensitive areas in western NC may support flash flooding with any slow moving or stationary storms. A Marginal Risk area remains in effect. ....Northeast... Deep tropical moisture pumping north well ahead of Beryl will make for anomalous PWATs across New England. The Appalachians of this region may also act as forcing for widely scattered thunderstorms capable of heavy rainfall. A Marginal Risk area is in effect for across this region. Campbell Day 2 Valid 12Z Wed Jul 10 2024 - 12Z Thu Jul 11 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE GREAT LAKES REGION INTO THE NORTHEAST AND FOR CENTRAL NEW MEXICO... ....Northeast... Training of storms will likely develop along the west-east orientated front across New York, Vermont and New Hampshire. The heaviest rains are expected into the Adirondacks primarily...where the mountains will provide the greatest additional lift being oriented largely orthogonal to the WSW flow. PWATs will be more than 3 sigma above the mean, which compared with GFS climatology would break the daily record. Thus...there will be unusual amounts of moisture available for Beryl's remnants to convert to rainfall. A Slight Risk is in effect from northern Indiana to Maine while a Marginal Risk area spans from Illinois to Maine. Currently, much of northern New York and Vermont will be a higher end Slight Risk. As details resolve and get closer in time, there may be the need to upgrade to a Moderate Risk. There will be similarly abundant atmospheric moisture all along the Eastern Seaboard Wednesday and Wednesday night, but the forcing further south will be much more limited, resulting in less widespread convection. However, given the amount of moisture in place...even local forcings should be enough to result in some storms. ....Central Rockies and portions of the Southwest... Continuation of the monsoonal moisture and diurnal heating will keep convection possible across portions of the Central and Southern Rockies and southwest New Mexico during this period. Higher QPF is expected to concentrate in the vicinity of the Sacramento Mountains where there have been a few recent wildfires. The burn scar complex (Blue-2, South FOrk, Salt and McBride) is very sensitive to anything more than a gentle, light rain. QPF is forecast to range from 0.25 to 1 inch across portions of central New Mexico which elevates the threat for flash flooding and debris flows. A Slight Risk was raised for this part of the state given the aforementioned sensitivity. ....Central Gulf Coast... A stalled frontal boundary along the Gulf Coast may continue to provide focus for convection capable or producing heavy rainfall. A Marginal Risk area remains in effect. Campbell Day 3 Valid 12Z Thu Jul 11 2024 - 12Z Fri Jul 12 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE NEW ENGLAND... ....East Coast... The low pressure system and associated tropical moisture will progress through New England during this period with its trailing cold front sweeping through the Mid-Atlantic. Lingering showers and thunderstorms will persist over New England while maintaining an elevated threat for excessive rainfall and flash flooding. A Slight Risk remains in effect for much of Vermont, New Hampshire and central Maine. There will be a better concentration of convection producing higher QPF across southeast Virginia and eastern North Carolina. Model consensus had areal averages of 1 to 2 inches for this area although local maximums up to 5 inches may be possible. A Marginal Risk spans from South Carolina northward to Maine for this period. ....Southwest... The monsoonal pattern of diurnal convection will persist thus maintaining an elevated threat for localized flash flooding. A Marginal Risk remains in effect for portions of eastern Arizona and much of New Mexico.m Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!80G_ZFBwwDiNLGX8rrCglp64wFtf3l-LwS6NjcaPpPil= buVeI5Bh53G6UZlVUCK3CnPlz-4SMNo8jv_qBVQEdi36FZM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!80G_ZFBwwDiNLGX8rrCglp64wFtf3l-LwS6NjcaPpPil= buVeI5Bh53G6UZlVUCK3CnPlz-4SMNo8jv_qBVQEg79YLHY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!80G_ZFBwwDiNLGX8rrCglp64wFtf3l-LwS6NjcaPpPil= buVeI5Bh53G6UZlVUCK3CnPlz-4SMNo8jv_qBVQEp4sp2BE$=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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