632 FOUS30 KWBC 120056 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 856 PM EDT Sun Oct 11 2026 Day 1 Valid 01Z Mon Oct 12 2026 - 12Z Mon Oct 12 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE GREAT BASIN & SOUTHWEST... ..Great Basin and Southwest... Post-T.C. Rachel was quite findable in the surface observations, moving through southwest WY near Big Piney at 00z, headed towards Jackson Hole and Dubois. Continued very favorable right entrance region jet dynamics over the Great Basin combined with the moisture Rachel has left behind and a couple possible zones of frontogenesis is expected to keep some convection percolating overnight. CIN has yet to develop, and may not for a while considering how much moisture exists regionally (precipitable water values of 0.75-1" across the Great Basin and southern AZ). Due to the reduction in expected convective coverage, the Moderate Risk was dropped. The highest risk going forward appears to be across western AZ where both the 18z HREF and 12z REFS keep heavy rainfall most persistent overnight -- penciled the area in as an enhanced Slight Risk. Kept a broad Slight Risk from northwest AZ across portions of the Great Basin as a course of least regret, to account for any recent saturation. The usual spots -- burn scars, box/slot canyons, dry washes/arroyos, and urban areas -- would see the greatest impact wherever heavy rainfall persisted for an hour or more. ...Mid-Atlantic... Isaias' surface low is no more; it could not escape WV. It elongated into a surface trough, absorbed by a downstream cyclone formation on the other side of the CAD/wedge which at 00z lies across southern VA. The new cyclone is forecast to move east and could produce some moderate to heavy precipitation overnight where precipitable water values remains 1.5"+ and MU CAPE remains in the 500-1000 J/kg range. It may take until 12z Monday for the heavy rainfall to depart the Eastern/Jersey Shores, though the heavy rain threat is expected to steadily reduce from here on out. Removed the Slight Risk but kept a Marginal Risk for what appears to be a more localized heavy rain threat. Roth Day 2 Valid 12Z Mon Oct 12 2026 - 12Z Tue Oct 13 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE GREAT BASIN AND THE SOUTHWEST... 2030Z Update... The 12Z suite of guidance still shows the remnants of Rachel moving away in the Day 1 period with closed low settling into the region from the north. Given that consistency and similar QPF solutions with other guidance...only minor changes were needed. Bann Previous Excessive Rainfall Discussion... ...Great Basin into the Southwest... While the remnants of Rachel will have accelerated rapidly northeast day 1 away from the Southwest and Great Basin, a closed low will settle southeastward day 2 across the Great Basin. This will help maintain above average PW values to the east and southeast of this closed low from Southern California into the Southwest and Great Basin, although values will be lower than the day 1 period. Model consensus is for additional moderate to heavy precip totals from northwest Arizona into eastern Nevada and much of Utah. While precip totals are much lower than the day 1 period, a slight risk was maintained from northwest Arizona into much of Utah along the Wasatch as there will likely be overlap of heavy rain areas on day 1 with the potential day 2 moderate to heavy totals. Oravec Day 3 Valid 12Z Tue Oct 13 2026 - 12Z Wed Oct 14 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE GREAT BASIN AND FROM THE SOUTHERN HIGH PLAINS INTO THE CENTRAL PLAINS AND LOWER MISSOURI VALLEY... 2030Z Update... Focus for excessive rainfall shifts with time from the Great Basin into the Plains on Tuesday. Only minor changes were needed given the 12Z deterministic models as well as spaghetti plots from the ensembles. Bann Previous Excessive Rainfall Discussion... ...Great Basin... The closed low over the Great Basin day 2 will be pushing east toward the four corners region by the end of day 3. Additional moderate to isolated heavy precip totals possible in the comma head/deformation band to the north of the closed low center across the Great Basin into the Central Rockies. Snow level will be dropping day 3 in the Wasatch/Uinta with rain primarily over northwestern Utah. A marginal risk is depicted here where isolated runoff issues may occur, especially after heavy rain totals days 1 and 2. ...Southern High Plains, Central Plains, Lower Missouri Valley... Across the Southern High Plains into the Central Plains/Lower Missouri Valley region, PW values expected to rise to 2-4+ standard deviations above the mean in the broad southwesterly mid to upper level flow on the east side of the Great Basin closed low. Some moisture, likely mid to upper level, from the remnants of Simon moving into the west coast of Mexico late Monday into Tuesday may push northeastward in this broad mid to upper level southwesterly flow. This should support increasing coverage of precip across these areas, especially Tuesday night into early Wednesday when overall favorable right entrance region jet dynamics will be present in this above average PW axis. There still is a lot of spread in the latest guidance with details of where the heaviest precip will fall, keeping the threat level, at the moment. to marginal. Oravec Day 4 and Day 5 Valid 12Z Wed Oct 14 2026 - 12Z Fri Oct 16 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHERN AND CENTRAL PLAINS TO MID-MISSISSIPPI VALLEY ON DAY 4 AND DAY 5... 19z Update: The Slight risk areas still look in pretty good shape, with models remaining in agreement on a heavy rainfall and flood risk from portions of Texas into Missouri. Given the favorable forcing/moisture/instability forecast, the potential is there for an embedded corridor of higher end impacts on both days, so we will need to continue to monitor trends going forward. Chenard ...Previous Discussion... ...Southern & Central Plains... Day 4... Longwave pattern across the west begins to shift eastward with an increasingly diffluent pattern downstream of the mean trough over the Central and Southern Plains. The current progs are textbook synoptic evolutions for lee cyclogenesis within the Front Range of CO which will help translate into quite an active setup for both the D4 and D5 time frames. Remnant moisture from now Hurricane Simon is expected to pull northward the beginning of the week as the moisture flux and energy from what is left of Simon pivots around the western periphery of a ridge positioned across the Southeast CONUS. PWAT anomalies across the Southern High Plains all the way up into portions of the Midwest will run between +2 to +3 sigma according to both the ECENS and NAEFS anomaly outputs for PWATs. This will place a large area of PWAT outputs between 1.75-2.3" from the Big Bend of TX up through at least the southern half of the Midwest (IL/IA/WI) leading to a primed environment capable for heavy rainfall in any convective environments. Synoptic evolution will yield a surface low over the Front Range of CO with a cold front extension down through the Southern Rockies with an advancement eastward expected as the upstream upper level setup continues its forward propagation into the Central U.S. A broad warm sector regime will materialize on Wednesday afternoon and evening with a crescendo of convective development expected Wednesday evening with the addition of a stronger low-level jet (LLJ) initiating around 00z Thu, lasting through the evening. Model outputs have been increasingly favorable for widespread 2-3" totals across portions of the Central and Southern Plains into the Mid- Mississippi Valley with the maxima focused over OK into MO with a southwest inflection back into north TX across the Red River. Heavy rain is likely in any convective cores that develop thanks to the environment in place with such a prolific deep moisture plume in place thanks to the remnants of Simon. Given such a prominent QPF signature and expected synoptic evolution for mid to late week, a broad SLGT risk is in place over the aforementioned areas with only some minor adjustments over the region from the previous forecast. Further assessment in the coming days may lead to a higher risk, or at least wording of a higher end SLGT with perhaps some adjustment in the areal coverage of the risk. Until then, this will be the start of an active period of heavy rainfall potential across a large part of the Plains. Day 5... The D5 time frame is almost a repeat of the previous period with an ongoing heavy rain threat from widespread convection along and ahead of a slow-moving cold front out of the Rockies into the Central and Southern High Plains. There will be quite a bit of resistance against the front over the Southern Plains thanks to the stout ridge axis flexing its muscle over the Southeast U.S extending back into the Southern High Plains. This will likely infer a slow propagation of the front and continued onslaught of convection during the afternoon and evening portions of Thursday into early Friday morning. Surface ridge over the Northern U.S. will act to press the front southward from the standpoint for areas north of I-70. Despite the assistance from the ridge to the north, it will be difficult for the cold front trailing back into the High Plains to make much progress until the upper pattern over the Rockies finally opens up and kicks northeast out of the region. This is the current indication with the most likely outcome leading to yet another period of heavy rainfall extending from southwestern TX back into the at least the southern half of MO. Models are less consistent with the placement of the heaviest rainfall in this period, but there is still enough of a consensus in the ensembles to warrant another broad SLGT risk encompassing the Southern High Plains into the Mid-Mississippi Valley. The SLGT risk outline is fairly identical to the D4 period which notes just how slow the evolution of the upcoming pattern will be before we finally see progress by the end of the weekend and following weekend. As was noted in the D4, this time frame will need to be monitored for a potentially higher risk over anywhere within the current SLGT forecast, so stay tuned over the next several forecast cycles for continued updates on the threat. 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 $$