Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 08 2025 15:47:51 FOUS30 KWBC 081547 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1147 AM EDT Sun Jun 8 2025 Day 1 Valid 16Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS...GULF COAST...AND MID-ATLANTIC... ....Mid-Atlantic and Central Appalachians... Very few changes were made to the existing Day 1 outlook over this region, with observational trends generally matching earlier forecasts fairly well. The initial round of rain has moved through much of the Slight Risk area as of 15 UTC, and has produced a fairly widespread 0.5 to 1.0 inches of rain in much of the area. As cloud cover partially clears in the wake of the area of stratiform rain, rapid destabilization is occurring, and this is already beginning to support convective initiation. Although the PWs may be slightly lower in this area of clearing, they are still relatively high (around 1.4 to 1.5 inches) around the 90th percentile for early June. The combination of the increasingly strong instability and relatively deep moisture should support hourly rain rates of 1 to 2 inches per hour in the most vigorous and organized convection. This may lead to flash flooding, particularly in situations where the rain rates can be sustained for more than an hour, and either in the mountainous areas of N WV, W MD, SW PA that have been very wet lately, or in urbanized areas in the coastal plain. ....Gulf Coast... Training and backbuilding thunderstorm activity has been far more persistent this morning in portions of E MS and C AL than models have been indicating. However, 12 UTC hi-res guidance appears to generally have a better handle on the current mesoscale environment and state of the convection. There is good agreement that the convective line itself and/or the associated gust front will make steady progress toward the coast today, and then begin to stall later this afternoon or early tonight. This may focus additional convective clusters and lines later today and tonight, with a favorable configuration for backbuilding (southwesterly inflow with an upstream reservoir of strong instability). The combination of the very high CAPE values, and anomalously high PWs around 2=20 inches, will support very heavy hourly rain rates approaching or exceeding 2 inches in the most organized convective clusters. If the gust front interacts with the coastal convergence zone and anchors convection somewhere near the coastline, heavy rain rates could persist for several hours and lead to a locally extreme rainfall event with potential for significant flash flooding. ....Southern Plains... The heavy rainfall and associated flash flooding threat in this region is more conditional, given excellent hi-res model agreement in a very organized, rapidly forward propagating bowing line late this afternoon and this evening. Although the instantaneous rain rates in the line itself would be likely to be high, the fast forward speed would likely mitigate that factor a bit. Corridors of heavy rainfall in these cases tend to occur either: 1. Near the poleward bookend vortex, which can tend to move slower and still have relatively high rain rates. In this case, that would be most likely over portions of SC OK, although the fast forward=20 motion of the line makes it uncertain how impactful this would be=20 from a rainfall perspective. 2. Or along the upshear flank of the cold pool. That seems plausible in this case, and would be most likely either in far SW OK or in western N TX. In particular, a corridor of locally heavy rainfall and flash flooding would seem more likely if convective development occurs near a lingering front in advance of the main forward propagating MCS, thereby increasing the duration of the heavy rainfall. However, it's unclear whether this antecedent development and the eventual gust front location will be co-located.=20 Therefore, the Slight Risk was maintained given these uncertainties, and was only nudged slightly to the southwest to account for latest observational data trends and hi-res guidance. Lamers Day 2 Valid 12Z Mon Jun 09 2025 - 12Z Tue Jun 10 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE UPPER OHIO VALLEY THROUGH CENTRAL NEW YORK... ....Upper Ohio Valley through Central New York... A potent upper level low over the Great Lakes on Monday will become increasingly negatively tilted through the period as a shortwave and the low itself begin the process of rejoining the jet stream. Thus, expect the upper low and any flow around it over the Northeast to become more southwesterly with time. At the surface, a strong cold front will rapidly sweep across the Midwest. That front will be slower-moving in northern areas as the upper level pattern becomes more amplified. Thus, the storms that will develop ahead of the cold front will be slower moving from Pennsylvania north into New York, supporting a higher likelihood for training. Ahead of this cold front, Gulf moisture will be drawn northeastward, supported by the increasing upper level forcing as the trough becomes more negatively tilted by Monday evening. Longer-range CAMs guidance shows multiple rounds of storms tracking across Pennsylvania and New York through the period, being driven by different impulses of upper level energy as those shortwave troughs track more south to north with time. While duration of the heavier rains will be lesser on Monday across WV, MD, and VA, expected heavy rainfall from the Day 1/Sunday period in this area should lower the FFGs in the area by the Day 2/Monday period. Thus, the Slight Risk includes areas expecting less rainfall on Monday afternoon. Meanwhile in PA and NY, sensitive soils will still be present, as well as topographic concerns, so the higher threat for flash flooding will be into western and central NY. ....Southeast... Across the Southeast, expect multiple rounds of storms to cross Mississippi, Alabama, and Georgia through the period. The storms will be supported by periodic passages of shortwave disturbances in the upper levels, but they will be much further in between disturbances as compared with areas further north, as the Southeast will be further from the greatest forcing associated with the low over the Great Lakes. Partially offsetting this will be the proximity to the Gulf, which will allow for there to be far more moisture available for the storms as compared with areas further north. Soils in this area are around average for moisture content as there has been some time for the soils to dry out from past rainfall events. This has allowed FFGs to recover quite a bit, and the high FFGs will play a big role at tampering the severity and frequency of instances of flash flooding due to the heavy rains. Thus, for now, the area remains in a Marginal risk, but will be evaluated with future updates for upgrade potential. ....Texas... Significant uncertainty remains in the potential for flash flooding across Texas on Monday. The cold front impacting much of north Texas on Sunday will push further south, turning the predominant flow out of the north across the northern half of the state. This should allow for advection of drier air. Ample solar heating will still promote the development of instability, as well as any evapotranspiration in the area. Thus, expect at least some shower and thunderstorm activity again on Monday, albeit more likely on Monday night. Given the sensitivities from heavy rains in this area, the lesser coverage and duration of storms may still be enough to eventually need a targeted Slight Risk upgrade between now and Monday afternoon, but the confidence is not quite there yet. Wegman Day 3 Valid 12Z Tue Jun 10 2025 - 12Z Wed Jun 11 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WEST TEXAS AND SOUTHEASTERN NEW MEXICO... ....West Texas and New Mexico... After potentially leftover convection in the early morning hours of Tuesday from Monday night's convection, much of the day across the Slight Risk area will be mostly dry. With peak solar heating in the late afternoon, however, a strengthening subtropical shortwave ejecting out of the Southwest will interact with the plentiful Gulf moisture already in place across west Texas. This will result in widespread convective development Tuesday evening. There is significant uncertainty however with the nature, coverage, and strength of the thunderstorms, as well as where and when they will impact any one area. Given that, and the spread in the guidance, the Slight Risk was expanded westward into New Mexico to account for potential development off the Sacramento Mountains, and any dry line convection. Regardless, there remains enough agreement that given plentiful recent rainfall and convective activity across West Texas, this new round of rain should result in widely scattered instances of flash flooding. This may be start of another period of daily thunderstorms in this area through the mid-range. ....New England... Convective activity in this region will be ongoing at the start of the period and continue through the day as Atlantic moisture is drawn northward ahead of a NNE moving upper level trough that will be rejoining the jet stream. The rainfall should be largely over in New England by Tuesday evening. Given most of the day the rainfall will be in the cooler, more stable part of the day, expect lesser rainfall rates. Thus, the inherited Marginal Risk was left unchanged with this update. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5aUQslzEGp0yufBV5f61uEajX4JmCcVZJeTGj2qIqjs1= IIR283Rwl-sOrHTj7V3FADeVzkRxjCPkMrh2aMwqukkT6Nw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5aUQslzEGp0yufBV5f61uEajX4JmCcVZJeTGj2qIqjs1= IIR283Rwl-sOrHTj7V3FADeVzkRxjCPkMrh2aMwqyC-zuyI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5aUQslzEGp0yufBV5f61uEajX4JmCcVZJeTGj2qIqjs1= IIR283Rwl-sOrHTj7V3FADeVzkRxjCPkMrh2aMwqzt6p5tY$=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) .