Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 09 2024 00:27:09 FOUS30 KWBC 090026 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 826 PM EDT Mon Jul 8 2024 Day 1 Valid 01Z Tue Jul 09 2024 - 12Z Tue Jul 09 2024 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF NORTHEAST TEXAS INTO ARKANSAS... ....01Z Update... Beryl continues to move north/northeast through far northeastern Texas this evening and will track through Arkansas overnight. The=20 heaviest rain, generally north of the low center, will spread=20 through much of Arkansas and into southern Missouri through 12Z=20 Tuesday where the latest guidance is in reasonably good agreement=20 for the heaviest axis to be in the 3-5" range. The most recent=20 HREF and the past few runs of the HRRR show some embedded higher=20 totals, 6-8", through southwest to central Arkansas. Hourly totals=20 between 1-2" will be common, with some isolated threat of 3" hourly totals through tonight.=20 This type of rainfall and intensity is likely to bring considerable urban and flash flooding to parts of Arkansas overnight and perhaps extending into far southern Missouri. The Slight and Moderate Risk areas were adjusted northward based on the latest speed/timing of the heaviest rainfall (a bit faster) and also trimmed on the southern/southwestern edge as the low center continues to move out of eastern Texas and the threat of heaviest rainfall begins to subside.=20 Elsewhere, lingering inflow bands of heavy rain will persist=20 across portions of Louisiana where a very narrow but perhaps still very intense swath of heavy rain will occur through tonight.=20 Further to the north, moisture from Beryl interacting with a=20 stationary boundary over southwest MO through IL will be the focus=20 for some heavy rainfall and risk of flash flooding.=20 ....Southeast... Another day/evening of mainly diurnally driven slower moving thunderstorms in the very warm and moist environment will bring an isolated threat of flash flooding to parts of Alabama, Georgia, the Carolinas, and Florida until later this evening. Isolated hourly totals between 1-2" will be possible, and the activity should diminish toward 06Z with the loss of daytime heating.=20 ....New Mexico and southwest Texas... Convection firing up across the terrain areas of north-central and eastern NM will drift southeasterly through this evening before waning over the next several hours. There remains an isolated risk of flash flooding with some potential for localized 1-1.5" totals.=20 Taylor Day 2 Valid 12Z Tue Jul 09 2024 - 12Z Wed Jul 10 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST AS WELL AS FOR THE CENTRAL GULF COAST... ....2030Z Update... ....Midwest... Several notable changes were made with this afternoon's update. As regards the Slight Risk area associated with Beryl...guidance is notably faster with spreading the rain shield associated with Beryl northeastward into the Midwest. Note this isn't an increase in forward speed of Beryl's circulation...but rather an expansion of the precipitation shield. This is largely due to better interaction with a 90 kt jet streak's right entrance region, as well as frontogenesis as southeasterly flow ahead of Beryl runs into the front. Thus, the Slight was expanded. There's a bifurcation in the Slight across Indiana. The precipitation to the north from St. Louis northeast to Lake Michigan is expected to be in the form of a persistent deformation zone associated with the aforementioned front. Instability will be very limited in this area. Thus, much of the precipitation will either be elevated convection or a stationary band of light to moderate rain resulting in a swath of 3-5 inch rainfall totals. Meanwhile further south along the Ohio River, there will be much more instability resulting in stronger storms capable of much heavier rain...but less distinct forcings more directly driven by chaotic outflow boundaries will mean the storms will be much more scattered, with breaks in the rain at times in between storms. It's probable somewhere within the Slight Risk area will see Moderate Risk level impacts, especially with the tropical moisture moving in with Beryl...but given consistent track changes...generally south and east...and significant uncertainty as to the nature of the heavy rain in any one area, no Moderate Risk upgrades are included with this update, but could very well be considered with future updates. ....Gulf Coast... The inherited Slight for the southwestern Louisiana Gulf Coast was shifted and expanded well to the east with this update...to include New Orleans, Gulfport, Mobile and Pensacola. This is in line with the latest shifts in the track of Beryl...bringing its associated cold front (as it undergoes extratropical transition) further east along the Gulf Coast. Storms in this area will still have access to the entirety of the Gulf as far as moisture influx...and with the front stalling in the Slight Risk area, training convection is likely. There's significant uncertainty both with storm track and the speed of cell movement, but the abundant moisture should allow any stronger storms to overcome the otherwise very high FFGs along the Gulf Coast, with the front likely supporting training. Thus in coordination with LIX/New Orleans, LA and MOB/Mobile, AL forecast offices, the Slight risk upgrade was introduced. Meanwhile further west, drier air is now expected to reach the Gulf Coast in southwest Louisiana, prompting the downgrade in that region. ....Marginal Risks... New Mexico: Isolated to widely scattered convection is likely to form along the mountains once again Tuesday afternoon, which could very well move over flood-sensitive areas. 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. Florida: Daily diurnal storms are likely once again due to collisions of sea breezes as well as any outliers associated with the stalled front along the north Gulf Coast. 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. New England: 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. Wegman ....Previous Discussion... ....Mississippi Valley and Midwest... Beryl is still expected to quickly phase with an upper trough and surface front to the north while in transition to being extra tropical. This should lead to the potential for heavy rain to blanket part of the central U.S. causing flash flooding concerns from Arkansas to Indiana during this period. Some of the highest QPF amounts of 3+ inches are likely to focus over the Ozarks region and points northeast to the Illinois/Indiana border. Areal averages are expected to be around 2 to 4 inches with local maximums upwards of 8 inches. A Slight Risk extends from central Arkansas to western Indiana. A Marginal Risk stretches from the central Gulf Coast northward to southern Michigan. Again, an future adjustments will likely be dependent on the track for Beryl. In addition, some of the CAMs hint that some type of southwest to northeast band could set up along or just inland of south-central Louisiana coast to produce a few inches of rain over some areas that could be a little more sensitive to heavy rain impacts. A Slight Risk area was raised for this stretch of the coastline north to about I-10. ....Southwest... Monsoonal moisture feeds over eastern Arizona through the southern Rockies warranting maintenance of the Marginal Risk for most of New Mexico, southeast Arizona into southern Colorado with particularly considerations for burn scars and areas that have seen ample rainfall recently. ....Southeast... Convection will persist during this period thanks to the abundant moisture hanging around and diurnal forcing. Some of the guidance continues to suggest areas of locally heavy rainfall especially along the eastern coastline of Florida. General consensus suggests 1 to 2 inches although local maximums of 3 to 4+ inches will certainly possible. A Marginal Risk remains in effect for portions of central/northern Florida and southeast Georgia. ....Northeast... Interaction of moisture ahead of Beryl and a front settling over the Mid-Atlantic/southern New England may favor heavy rainfall potential over this region; although guidance is rather light with activity mainly in New England. Some focus of the convective rain ahead of the front(s) and sufficient instability for heavy rain rates in the northern Mid-Atlantic to Northeast favor of a Marginal Risk. Campbell Day 3 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... ....2030Z Update... ....Northeast... Fewer changes were made to the Day 3 forecast given the inherent uncertainties with Beryl both today and tomorrow, and with some consistency in the guidance as well. Oddly enough the adjustment made was generally north, or left of the previous forecast, a change we will have to see if it will pan out. For most of Beryl's lifespan the forecast has nudged right of previous so that adjustment would be unusual for Beryl's remnants. The inherited Slight Risk was expanded to the Maine and New Hampshire coastline with this update. The rain shield even now has consistently outpaced the guidance, and as such the eastward/faster adjustment here is very normal...if the very small northward shift is not. 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. The Slight remains in good shape as it's very likely given the abundance of moisture that there will be embedded convection which will locally increase totals. 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. With consistency and hopefully good CAMs support...additional upgrades to a Moderate are at least possible. Elsewhere in the mid-Atlantic the Marginal risk area was brought south to include the DC-NYC I-95 corridor with this update. 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, so the Marginal was expanded considering the lower FFGs in the urban corridor. ....Marginal Risks... New Mexico/Colorado: Same rinse and repeat forecast in this area with the typical afternoon monsoonal convection likely to redevelop once again Wednesday afternoon. Central Gulf Coast: The front will remain stalled along the Gulf Coast on Wednesday but much weaker, which should spread out the threat while reducing the severity. The Marginal on Wednesday roughly follows where the Day 2/Tuesday Slight is. Wegman ....Previous Discussion... ....Midwest to Northeast... There is still a fair amount of spread in the guidance with respect to the evolution/track for post-tropical Beryl and exactly how this upper level energy ejects into the overall Great Lakes/Midwest mean trough. The flow of tropical moisture should bring the highest precipitable water anomalies into the Lower Great Lakes and Northeast during this period. Some PWAT anomalies within this region will likely exceed the 90th percentile and west- east oriented fronts north/east of post- tropical Beryl may promote training. The exact location of the heaviest rainfall will be dependent on the location of the frontal boundary but there is a growing signal for a broad area to be impacted by the heavy rains. A Slight Risk is in effect from northern Indiana to New Hampshire while a Marginal Risk area spans from Illinois to Maine. As details resolve and get closer in time, there may be the need to upgrade the risk level, but at this time there is too much uncertainty. ....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. The inherited Marginal Risk was maintained with westward modification for New Mexico. Rain in proximity to burn scars and other sensitive areas that have seen ample rainfall recently will have an elevated risk for flash flooding. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_0aGduqxrREmYAm7nzJEmCXlXYNeKewN1Mx29Zvd-A9N= lBclD_QfFC2G72Pu5UIggh9qZ_IxhEN2zXI2Hp6mCkhzB5c$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_0aGduqxrREmYAm7nzJEmCXlXYNeKewN1Mx29Zvd-A9N= lBclD_QfFC2G72Pu5UIggh9qZ_IxhEN2zXI2Hp6m0BArdKs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_0aGduqxrREmYAm7nzJEmCXlXYNeKewN1Mx29Zvd-A9N= lBclD_QfFC2G72Pu5UIggh9qZ_IxhEN2zXI2Hp6mpk-jLCs$=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) .