Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 08 2025 08:09:53 FOUS30 KWBC 080808 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 408 AM EDT Sun Jun 8 2025 Day 1 Valid 12Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AND MID-ATLANTIC... ....Southern Plains... A southward moving upper level shortwave rounding the western periphery of a potent upper level low will support a strong cold front tracking south across the central Plains this afternoon and evening. Meanwhile, ample Gulf moisture in place across Texas and along the Gulf moisture will advect northward ahead of the cold front, drawn to the front my the pressure differential. The result of these clashing air masses will be widespread convective=20 development, partially aided further by the dry line, across the=20 Panhandles and western Oklahoma mid-to-late afternoon. In addition=20 to significant severe potential with the abundant shear in the area from these clashing boundaries, the storms will be moving over a=20 very sensitive area for soil moisture due to numerous rounds of=20 recent rainfall across the Panhandles and the Red River Valley.=20 This supports the continuance of the Slight Risk across much of the region, including a higher-end Slight in and around the Wichita=20 Falls, TX area. The higher-end risk is due in part to some CAMs=20 agreement for additional training and cell mergers in the early=20 evening. As is fairly typical of areas of strong thunderstorms and supercells, their merger into a single area of storms should accompany a faster forward speed, which should gradually decrease the flash flooding potential across the region into the overnight hours tonight. There is much greater disagreement as to whether additional shower and thunderstorm activity will develop behind the area of storms, which are very likely to set up along a preexisting cold-pool boundary. The coverage and intensity of the storms is highly uncertain, but a preponderance of the guidance suggesting the storms will develop and track southeastward over many of the same areas, particularly on the Texas side of the state line, could support a higher flash flooding threat. While the issuance of an upgraded Moderate Risk for these areas is not out of the question, it will likely take seeing the whites of the storms' eyes to have the confidence for such an upgrade. This will also be highly dependent on how the storms behave with the initial MCS development over these areas. ....Mid-Atlantic... A developing upper level shortwave will team up with a surface low and associated showers and a few storms early this morning across the Mid-Atlantic. With daytime heating and advection of additional moisture and instability, expect the rainfall across the area to become increasingly convective across the Slight Risk area. These storms will be capable of heavy rainfall with potential for widely scattered flash flooding. This portion of the Mid-Atlantic is also very sensitive to heavy rainfall due to recent heavy rains over the past week or so. Topographic concerns will also be present as the mountains funnel any heavy rain quickly into the adjacent river valleys. Expect the heaviest rainfall to occur south and west of the warm front associated with the surface low. There is considerable uncertainty as to how far north and east the warm front will get, as the surface low will be weakening due to interactions with the mountains. Thus, by this afternoon the instability and moisture supporting the storms will be the primary forcing supporting their capability of producing heavy rain.=20 Given these aforementioned uncertainties, the inherited Slight Risk area is largely the same. The biggest change with this update was to expand the Slight Risk northwestward to include the Pittsburgh metro area. The heaviest rains are likely to fall along a northwest to southeast oriented line from Pittsburgh to the Hampton Roads area of southeast Virginia. There is significant uncertainty around the DC metro area due to distance from the greatest forcing and how far north and east the warm front can get, with the most likely scenario for the DMV area to be missed by the heaviest rains, which stay south and west. However, given the sensitivities and urban concerns requiring less rain to produce flash flooding, the Slight Risk was left in effect for this update in the DC area. Once again the Virginia suburbs will have the greatest chance of seeing the most consistent heavy rains. Wegman 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.=20 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!8Uqyf66T_Hoo_n9Adt4ahkNOmWiDS7-rkn_tFPjj7XEV= y-blHOaTfTB7jNaByrdbQ7zynaOqUefo9xyS2ZoRdJ57aHE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8Uqyf66T_Hoo_n9Adt4ahkNOmWiDS7-rkn_tFPjj7XEV= y-blHOaTfTB7jNaByrdbQ7zynaOqUefo9xyS2ZoR3u-Tb4w$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8Uqyf66T_Hoo_n9Adt4ahkNOmWiDS7-rkn_tFPjj7XEV= y-blHOaTfTB7jNaByrdbQ7zynaOqUefo9xyS2ZoRtWz4ij4$=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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