743 FOUS30 KWBC 110048 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 848 PM EDT Fri Jul 10 2026 Day 1 Valid 01Z Sat Jul 11 2026 - 12Z Sat Jul 11 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID MISSISSIPPI VALLEY... ...Mid Mississippi Valley to the Central Appalachians... 01Z Update... Few changes made to the most higher-end categories in the Mid- Mississippi Calley that remain hydrologically sensitive following the excessive rainfall during the past 24 hours. Trends in radar and satellite imagery allowed the eastern boundary of the Marginal risk area to be trimmed from the Mid-Atlantic region south of the Mason Dixon Line and east of the Appalachians. Those same trends...combined with the latest HRRR/HREF...also allowed trimming the Slight Risk area out of parts of the Ohio and Tennessee Valley overnight. No change made in the Southwest US...previous forecast reasoning remained valid. Bann 16Z Update... Guidance still in general agreement that heavy rainfall will overspread much of the Mid-Mississippi Valley into the Tennessee Valley and parts of the Ohio Valley/Central Appalachians today. Evaluation of 12Z guidance suggests that the potential remains for locally very heavy rainfall (HREF 24-hr probabilities for 5" over 20%) which is depicted via most high- res CAMs. However, the placement remains quite uncertain as there is virtually no overlap in the footprint between the available high-res models. After coordination with the local WFOs, a targeted MDT risk was added basically to overlap the area that had significant rainfall overnight leading to extremely vulnerable soils with 3-hr FFG less than 1". Elevated PWs above +1.5 sigma combined with 1000-3000 J/kg will support heavy rain producing convection anywhere across this region today, with the wavering front and any weak mid-level impulses providing the locally enhanced ascent for stronger convection. This will likely cause at least scattered instances of flash flooding due to compromised FFG from recent rainfall. The focus for the heaviest rainfall (and accompanying flash flooding) should be downstream of a potent (especially for July) shortwave dropping across MO which will additionally interact with the stationary front and the relatively higher moisture along and to its south. A potent LLJ progged to reach 30-35 kts will draw impressive thermodynamics into the boundary as well, supporting a situation with impressive training (weak and anti-parallel Corfidi vectors) with rainfall rates of 2-3"/hr thanks to more than 4000m of warm cloud depth. Training of these intense rain rates will likely produce stripes of heavy rainfall for which nearly all high-res CAMs indicate will reach 5-7+" in localized areas. Despite that, the probabilities are only marginally supportive of a higher ERO category, but at least locally significant impacts are becoming more likely from near southeast MO through western KY and central TN where the 0-10cm RSM from NASA SPoRT is above 70% due to recent heavy rainfall, creating enhanced vulnerability across the region. Previous Discussion: The Slight risk has been expanded northward across portions of MO, IL, IN and OH to account for multiple evolving convective threats. Otherwise the broad Slight risk remains similar to the previous forecast. Convection will be ongoing at 12z this morning across southern MO into portions of KY and TN, with areas of flash flooding already underway across portions of this region. While the activity across KY and TN today is forecast to become primarily forward propagating, which should limit the overall magnitude of the flash flood risk, strong low level westerly moisture transport will help maintain weak Corfidi vectors. Thus, upwind propagation and periods of backbuilding/training are possible as the convection tracks across KY and TN today. This introduces the potential that localized rainfall totals will exceed high res model guidance, a trend that will be monitored closely. A Slight risk area also covers slow moving convection that should develop near a frontal boundary across portions of IN/OH and southwest PA. PWs are slightly lower here than past days events, but still remain well above climatological averages. When combined with upwards of 2000 J/kg of CAPE, this environment supports intense rainfall rates locally around 2" per hour. Slow cell motions and periodic mergers should result in isolated to scattered instances of flash flooding. The 00z HREF FFG exceedance probabilities exceed 25%, with REFS values over 40% (noting a typical high bias for the REFS in this type of regime). The northward expansion of the Slight risk across portions of MO/IL/IN covers the convective threat associated with a shortwave/MCV ejecting eastward from the ongoing Plains convection. Thunderstorms should become increasingly organized by this afternoon and evening across this region. While the storm mode may lean forward propagating, some cell mergers appear likely and should drive a flash flood threat. Both the 00z HREF and REFS highlight this corridor with FFG exceedance probabilities of 15-30% and depict a 10-30% chance of hourly rainfall exceeding 3". Heading into tonight, convection from the aforementioned shortwave/MCV is forecast to dive southeastward from IL/IN into KY and TN. High res model simulated reflectivity suggest a forward propagating convective line. However, persistent low level westerly moisture transport will keep Corfidi vectors weak, offering further opportunities for upwind propagation and backbuilding into the westerly flow. Should this occur, rainfall totals and the flash flood risk could end up higher than currently forecast by the models. Thus while FFG exceedance probabilities from both the HREF and REFS are generally under 15% across this area, the Slight risk remains fully warranted due to the potential for multiple convective rounds and backbuilding. However, we will hold off any any MDT risk upgrade due to the modest model QPF blends and lower confidence on the exact convective mode. ...Arizona... A similar mesoscale setup to Thursday is expected, though potentially with slightly higher instability. Convection is forecast to develop over the higher terrain during the afternoon before propagating southwest into the desert valleys. Just like yesterday, localized cell mergers could enhance rainfall and result in a localized flash flood risk. While models suggest overall storm coverage may be slightly greater today, the threat remains isolated enough to maintain a Marginal risk, and the risk area was cosmetically adjusted slightly to account for new probabilities and the plume of highest instability. ...High Plains... Additional shortwave energy ejecting out of the Rockies will lead to convective development this afternoon from CO into KS and south to the TX Panhandle. This activity is expected to be less robust than yesterday due to generally weaker low level inflow, lower instability, and weaker large scale forcing. Nonetheless, one or two organized convective clusters should develop and push eastward, posing a localized flash flood threat. Chenard/Weiss Day 2 Valid 12Z Sat Jul 11 2026 - 12Z Sun Jul 12 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MS VALLEY TO THE CENTRAL APPALACHIANS... ...MS/OH/TN Valleys... Concerning excessive rainfall forecast continues for portions of the MS/TN/OH Valleys on Saturday as the pattern evolves very little from Friday into Saturday. A cold front will shift slowly southward through the Mid-Mississippi Valley and Tennessee Valley, but will become stalled in a west-east orientation by Sunday morning in response to flattening mid-level flow. This evolution will be driven primarily by the downstream evolution to a pronounced ridge blossoming over the Four Corners, with an extension of that ridge pushing over the Gulf Coast to slow troughing digging from the Great Lakes. Within this trough, several shortwaves, including those convectively reinforced my prior thunderstorms, will try to dig southeast along the front, but will generally be squashed to move west to east. However, each of these could spawn waves of low pressure along the boundary to enhance local ascent. This will result in an elongated area of enhanced ascent from generally the Southern Plains eastward along the boundary through the Mid-Atlantic states, leading to areas of heavy rainfall. The concern for Saturday will be that this ascent is acting upon robust thermodynamics characterized by PWs exceeding 2 inches in many areas (above the 90th percentile and more than +1.5 sigma from the climatological mean) overlapped with plentiful CAPE of 2000-3000 J/kg. Together, these will drive scattered to numerous thunderstorms capable of producing hourly rainfall exceeding 2" (20-40% chance from the HREF) which by itself could be sufficient to cause excessive rainfall in some areas. However, more concerning is the focused convective threat and training potential leading to prolonged duration of these heavy rain rates. While the exact placement of these focused areas remains uncertain due to tracking of any mid-level impulses and accompanying MCVs/boundaries leftover from remnant convection, there is strong agreement in the CAMs that axes of intense rainfall will occur associated with these features, with some of this rainfall occurring atop extremely vulnerable soils from recent rains and flash flooding. While the exact placement of the heaviest rainfall is uncertain, there have been some trends slightly west and even north as reflected by the AIGFS/ECMWF-AIFS/high-res, likely related to a stronger (and anomalous) shortwave diving out of Missouri. With convection blossoming downstream of this feature and within a warm (warm cloud depths above 4000m) and highly sheared (25-40 kts of bulk shear) environment, clusters of storms are likely, with slow and chaotic motion reflected by Corfidi vectors falling to around 5 kts Saturday evening as the LLJ ramps up and draws impressive thermodynamics northward. The inherited ERO was cosmetically adjusted, but a higher risk area to MDT was not added at this time due to uncertainty. In fact, there has been an increasing divergence between the HREF and REFS neighborhood probabilities, with the HREF leaning a bit north (which aligns with some of the AI guidance actually) while the REFS remains south. The farther south solutions usually verify in these scenarios, so have hedged the elevated slight risk area a bit SW to match better both the REFS guidance but also the EAS probabilities from both the HREF and REFS. However, the SLGT was expanded north and east into the Ohio Valley and Mid-Atlantic to account for the potential of the farther north heavy rainfall footprint. At this time there was not enough confidence for a MDT risk area, but a targeted MDT risk may be needed with later updates where D2 rainfall overlaps D1 rainfall, especially from southeast MO through central TN. ...Southwest... The monsoonal pattern begins to take shape more robustly on Saturday as a mid-level ridge re-centers and expands across the Four Corners with weak impulses rotating westward beneath it. A subtle weakness in the building ridge should allow for greater coverage of convection as it taps into elevated PWs (1.25 to 1.5 inches) and MUCAPE (~1000 J/kg) than prior days. Storms should develop initially across higher elevations and then drop slowly westward with some organization possible through 20-30 kts of shear. Rainfall rates as much as 0.75"+/hr are progged via the UA WRF, leading to a 20-40% chance of at least 3" of rainfall and 40-70% chance of exceeding hourly FFG. For this reason the inherited SLGT risk was maintained, and just slightly adjusted cosmetically. Weiss Day 3 Valid 12Z Sun Jul 12 2026 - 12Z Mon Jul 13 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHWEST, AND FROM TEXAS INTO THE SOUTHEAST... ...Southeast Quarter of the Country... A broad Marginal risk extends from eastern TX stretching northeastward into portions of the TN/OH Valley, the southern Mid- Atlantic and much of the Southeast. A cold front will drop slowly through the Southeast and towards the Gulf Coast states on Sunday, providing convergence for ascent within broad mid-level trough and beneath the diffluent tail of a departing jet streak. This will produce widespread deep layer ascent across the region, tapping into PWs above 2 inches overlapping MUCAPE of 2000-3000 J/kg. This will likely lead to scattered to numerous thunderstorms, especially during peak heating, with additional development later D3 with the onset of the LLJ and its accompanying moisture convergence. While the environment will support heavy rainfall rates within any of this convection, the location of any focused areas of heavy rainfall leading to a higher risk category remains uncertain. The greatest threat for higher rainfall totals should be in the vicinity of dual mid-level impulses: one over the Carolinas and one near the ArkLaMiss where focused and more prolonged ascent could lead to stronger and more organized convection to support training. However, these areas have a climatologically naturally higher FFG, and 0-40cm soil moisture from NASA SPoRT is generally below the 20th percentile reflecting the recent hot and dry conditions. A slight risk upgrade may be needed eventually (more likely in the Carolinas than elsewhere) but at this time, and after coordination with the WFOs, the MRGL risk was maintained until higher confidence in placement can be established. ...Southwest... Expanding mid-level ridge centered over the Northern High Plains will extend into the Four Corners, but leave a subtle weakness along the Mexico/Arizona/New Mexico border. Within this weakness, a shortwave may rotate cyclonically to the west to cause locally enhanced lift into expanding favorable thermodynamics lifting beneath the ridge. At this time there appears to be a relative lack of overlap between the most anomalous PWs and the greatest CAPE, leading to some uncertainty into how convection will evolve on Sunday. For this reason the MRGL risk was maintained, but with the shortwave aloft, any better match of the higher thermodynamics could necessitate a SLGT risk upgrade across parts of southern AZ. Weiss Day 4 and Day 5 Valid 12Z Mon Jul 13 2026 - 12Z Wed Jul 15 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG PARTS OF THE CENTRAL GULF COAST ON MONDAY... ...Southeast U.S. into Texas... A generally stable upper pattern will lead to relative persistence in the convective setup across the CONUS into early next week which keeps the risk of excessive rainfall in a broad corridor on the southern side if a sprawling upper ridge. Deep moisture will be present in that corridor with enough embedded shortwave energy within the larger scale flow pattern to trigger and support thunderstorms capable of producing heavy to excessive rainfall given the high CAPE/low shear environment. Greatest focus currently is over the Central Gulf coast extending into eastern Texas and Louisiana where the adage of a organized mid-level disturbance rotating out of the Tennessee Valley will enter the picture allowing for enhanced forcing and perhaps a surface wave. A SLGT risk was maintained from the previous forecast across the Central Gulf coast area for the D4 period with a broad MRGL encompassing on D4, followed by a general MRGL D5 over similar areas on the southern periphery of the ridge. ...Southwest U.S... The Southwestern U.S. will lie within the western flank of the broad ridge pattern over the Central and Eastern U.S which will provide a dominant southerly flow over the region allowing for continued moisture advection and enhanced surface troughing over AZ up through the Great Basin. This pattern is a continuation of the Monsoonal presence out west with a potential for increasing flash flood prospects as multi-day impacts could spur targeted opportunities for repetition of areas getting hit by convection in consecutive periods. For now, maintained a MRGL risk throughout the Southwestern CONUS for both the D4 and D5 time frames, however will need to monitor the periods closely as move forward in time for possible upgrades with the greatest potential likely over southeastern AZ up through the Mogollon Rim where several days of consecutive impacts are forecast beginning this weekend, carrying forward into next week as the pattern remains stable. Kleebauer/Bann Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt $$