Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 01 2024 00:23:12 FOUS30 KWBC 010022 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 822 PM EDT Sat Aug 31 2024 Day 1 Valid 01Z Sun Sep 01 2024 - 12Z Sun Sep 01 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER TEXAS COAST AND SOUTHERN LOUISIANA AS WELL AS THE CENTRAL=20 APPALACHIANS... ....01Z Update... ....Central and Southern Appalachians... Repeating/training storms ahead of a slow moving cold front and interacting with the terrain with antecedent wet soil conditions will continue to support a flash flooding threat into the overnight for mainly southwest Pennsylvania and north-central West Virginia. The Slight Risk was refocused over this area. Further info can be found in MPD 0958 which is in effect until 05Z.=20 Earlier activity east of the Appalachian Crest into the central=20 Mid- Atlantic has worked over that area, so the Slight Risk was=20 withdrawn from areas like the eastern WV Panhandle. Scattered activity over the southern Appalachians/Cumberland Plateau will continue into the overnight with additional isolated flash flood threats. The Marginal Risk is maintained there. ....West-Central Gulf Coast... Slow low persisting off the Upper TX Coast continues to feed=20 plentiful Gulf moisture over the coast with renewed overnight expected again along and ahead of the low. Saturated soil=20 conditions are present near the coast which will promote more runoff that normal. The Slight Risk is maintained for the rest of the night. ....Mid-South to North Texas... Limited the Marginal Risk to these areas for widely scattered diurnally initiated activity that should generally wane rest of=20 this evening. The presence of the slow moving cold front will continue to allow a localized flash flood threat. ....Arizona... High pressure centered over the southern Rockies will continue to=20=20 support enough southerly flow over the Mogollon Rim to warrant keeping the Marginal Risk overnight for the threat of additional 1"/hr rain rates over central AZ terrain. ....Florida... Outflow from Cuban activity should allow heavy rain in the Keys overnight, but not enough to warrant a flash flood threat, so the Marginal has been pulled. Jackson Day 2 Valid 12Z Sun Sep 01 2024 - 12Z Mon Sep 02 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NEW MEXICO/TEXAS, THE NORTHERN GULF COAST, AND THE MID-ATLANTIC... ....2030Z Update... No major changes were made to the risk areas on Sunday. For the mid-Atlantic, the signal into eastern West Virginia decreased in favor of an increased signal into the Delmarva. Thus, the portion of the Marginal in West Virginia was trimmed in favor of an expanded Marginal east of I-95. Along the Gulf Coast, guidance continues to keep heavy rain associated with the tropical low just off the Texas and Louisiana coasts. Given most of the heavy rain the past few days have only resulted in flash flooding into urban areas such as New Orleans, the consistent nature of the heaviest rain staying offshore has precluded another day with a Slight risk upgrade for now. That said, given that soils there are saturated, any northward shift in the guidance could mean a Slight may be needed. No major changes were needed in west Texas and New Mexico. Any rainfall that occurs Sunday will saturate soils as a precursor to Monday/Labor Day's rain. Wegman ....Previous Discussion... ....Southeastern New Mexico and West Texas... 250 mb upper trough moving out of northern Mexico and southern AZ/NM and mid-level vort max (perhaps weakly closed low) will creep close to far western Texas day 2. Sufficient moisture (through near normal) will be in place over the region to sustain some isolated excessive rainfall via afternoon convection. ....Gulf Coast... Meandering weakness in the mid-lower levels will again help drive some heavier rainfall along the Upper TX Coast into southern Louisiana. Maintained a Marginal Risk for now given the uncertainty in the day 1 period with respect to heavy rain placement (on or offshore) and amounts. Again, the highest rainfall may linger just off the coast but potential is certainly there to nudge inland. ....Eastern Tennessee Valley and Mid-Atlantic Region... Cold front will continue to push through the area to the east and south, squeezing the best forcing into southern Virginia and into North Carolina where afternoon convection may yield 1-2 inch amounts and a localized threat of flash flooding. There and to the west over western VA into WV, FFG guidance is lower and some lingering rain may eclipse those values as the front works through. Fracasso Day 3 Valid 12Z Mon Sep 02 2024 - 12Z Tue Sep 03 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE HILL COUNTRY OF TEXAS... ....2030Z Update... ....Texas... Increasing rainfall forecasts and CSU first guess field input both have increased confidence in a Slight Risk upgrade across much of the Hill Country of Texas. Expected widespread rainfall totals Monday of 1-3 inches with locally higher amounts will likely result in widely scattered instances of flash flooding. Despite recent dry conditions, any rain from Sunday will prime some of the soils, but elsewhere, the expectation of heavy rain will likely cause localized flash flooding in the usually flashy areas. In coordination with SJT/San Angelo, TX; EWX/San Antonio, TX; LUB/Lubbock, TX; and OUN/Norman, OK forecast offices, the Slight Risk upgrade was introduced with this update. ....Carolinas... Signals for heavy rain have been both shifting south and decreasing. The Marginal Risk has been shifted more towards the coast due to these changes in the forecast. Wegman ....Previous Discussion... ....Texas... Mid-level vort and upper trough will move into West Texas on Monday atop increased moisture from the southeast. Guidance continues to show modest QPF of 1-5 inches in various locations but the spread is quite large -- nearly covering the whole state in their QPF max region among the deterministic, ensemble, and AI guidance. The CSU machine learning first guess fields suggest a broad Slight Risk over the Hill Country, which is, perhaps, a best consensus placement, but prefer to hold off an upgrade to a Slight Risk for now until at least the ensembles come into better agreement. ....Carolinas... Cold front will sink into the Carolinas which will nudge the excessive rainfall threat south from day 2/Sunday. Best dynamics move offshore with the trough axis but the Marginal Risk should cover any isolated flooding threat due to the afternoon convection. Fracasso Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_iU-Fs7gik48-QY5kxoBOeMaBRGe5JorBpp7oZGcnQq2= KtTeLtADozvm7mdi8Gx-DDnqaG5jgYpEufZZ5q4N8h9w6KY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_iU-Fs7gik48-QY5kxoBOeMaBRGe5JorBpp7oZGcnQq2= KtTeLtADozvm7mdi8Gx-DDnqaG5jgYpEufZZ5q4NdqjtUUI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_iU-Fs7gik48-QY5kxoBOeMaBRGe5JorBpp7oZGcnQq2= KtTeLtADozvm7mdi8Gx-DDnqaG5jgYpEufZZ5q4Nyite1Qs$=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) .