FOUS30 KWBC 100828 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 428 AM EDT Fri Jul 10 2026 Day 1 Valid 12Z Fri Jul 10 2026 - 12Z Sat Jul 11 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE MID MISSISSIPPI VALLEY INTO THE CENTRAL APPALACHIANS... ...Mid MS Valley to the Central Appalachians... 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. ...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 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... A shortwave trough is progged to extend from MO to OH by 12z Saturday, likely featuring one or more embedded MCVs. Uncertainty remains with the exact rack and strength of these mesoscale features, which will play a large role in where the flash flood threat is maximized. Some high res guidance indicates an MCV moving towards WV Saturday, which could interact with a southward dropping frontal boundary and produce an area of enhanced convective coverage. Slow moving convection near these features could maintain a flash flood threat for portions of WV/OH/PA/MD/VA. Confidence is highest over WV, where the Slight risk remains, with a Marginal risk maintained further north and east. Model consensus is trending towards a stronger shortwave/MCV hanging back over IL/IN/KY, although guidance diverges on how convection evolves around this feature. This evolution is dependent on Friday's convective outcomes and the ultimate strength/position of the shortwave. The RRFS/REFS/FV3/Gem reg focus heavy convection over central/eastern TN and KY to the southeast of the shortwave, a solution also generally supported by the AIFS and AIGFS. Conversely, the GFS and ECMWF are displaced further southwest, placing maximum rainfall over AR, MS and western TN and showing lower values to the northeast. At the moment, higher confidence is placed in the high res/AI consensus favoring a maximum over central/eastern TN and KY. Given that portions of this region will have seen heavy rainfall on day 1, a higher end Slight risk remains warranted due to the possibility of increased hydrologic sensitivity. If models converge on a repeatable heavy rainfall footprint over these areas, a MDT risk upgrade may eventually be needed. Additionally, heavy rainfall is also expected to extend westward across western TN, AR and portions of MS and AL. The Slight risk has been expanded westward into more of AR with this update, where the RRFS/REFS/FV3/3km NAM all support heavier convection...with northern AR potentially favored for training and backbuilding along the southwestern flank of the broader convective regime. ...Southwest... The terrain driven convective pattern continues as storms roll off the higher elevations of AZ and into a pooling instability axis across the southern portion of the state. Instability and PW values are forecast to be higher than on day 1. The 00z REFS neighborhood probabilities show a 40-60% chance of locally exceeding 3" of rain, with the 3km NAM and FV3 also depicting locally high totals. Given the favorable environmental ingredients and a growing model QPF signal, southern AZ has been upgraded to a Slight risk with this update. Chenard Day 3 Valid 12Z Sun Jul 12 2026 - 12Z Mon Jul 13 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF ARIZONA 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. An embedded shortwave/MCV is forecast to become blocked downstream of an expanding upper level ridge centered over the Rockies. This feature will interact with a southward dropping front and an upper level jet streak, providing ample synoptic forcing to focus convective development. Across much of the region, PW values will exceed 2" alongside CAPE values of 2000-3000 J/kg where daytime heating is maximized. While this environment is favorable for high rainfall rates and some organized convective clusters, significant uncertainty exists regarding the finer details, including the strength/position of the shortwave and exact positioning of the frontal boundary. Given the high PW and instability profiles, an embedded Slight risk or two will almost certainly be needed on future updates. However, because FFG is climatologically higher across this portion of the country (particularly from the lower MS Valley into the Southeast), avoided placing a large Slight risk with this update. Current model guidance hints at two potential heavy rainfall maxima...one over the carolinas where an MCV may interact with a backdoor front, and another in the vicinity of AR to the central Gulf Coast. Not confident enough at the moment for a Slight risk across either area...but will continue to closely monitor trends. ...Southwest... Moisture and instability will continue to expand northwestward on Sunday, warranting a larger Marginal risk across AZ. While an embedded Slight risk may eventually be required, lingering questions regarding the overall coverage and organizational structure of convection justify keeping the risk at Marginal for this update. Chenard 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 as we move into early next week. Broad ridging over the center of the country will maintain prevalence on Mon/Tue with a prevailing easterly flow situated around the southern periphery of the ridge. At the surface, a cold front will eventually hit a road block along the Gulf coast, extending westward into TX leading to a transition to a quasi-stationary front situated from the Southeastern U.S. back into central TX. Deep moisture layer will be present within the southern confines of the ridge with a well-defined theta_E alignment positioned within proximity of the front. Diurnal destabilization on Monday will allow for enhanced convective potential with cell motions liable to anchor and/or train over the same areas as they become fixated to the stationary front. This is a generally classic pattern for heavy rainfall across the Southern U.S. this time of year as high CAPE, low shear environments provide conditionally favorable patterns for multi-day heavy rainfall potential. This setup is no different with the multi-model consensus and global ensemble means indicating heavy convective episodes possible from the SC/GA area, on west through the Southeast, eventually making headway back into the Southern Plains of TX. The area of greatest focus currently is over the Central Gulf coast extending into east TX 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 component that would provide targeted low-level convergence where the disturbance moves nearby. 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... Further west, 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 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 $$