FOUS30 KWBC 102000 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Sat Oct 10 2026 Day 1 Valid 16Z Sat Oct 10 2026 - 12Z Sun Oct 11 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS THE SOUTHERN APPALACHIANS AND OVER FOR PORTIONS OF SOUTHERN CALIFORNIA... 16Z Update... Given the latest few runs of the HRRR, expanded the Slight risk area a bit northward into southwest Virginia...although the footprint of the expansion is fairly limited although the terrain. The main focus for heavy rainfall will remain in the warm sector of the system...especially along and east of a cold front from Georgia into northern Florida as well as in portions of the Carolinas where rainfall amounts look to be enhanced in the upslope region of the terrain and along the immediate coastal regions. The expectation is that there will be an uptick in the rainfall rates later today as instability increases. The previous outlook had these areas well covered and changes were minor. Across the Southwest...moisture streaming ahead of Rachel will lead to increasing coverage of rainfall across the Southwest US during the day..with an increasing potential for significant flash and urban flooding. This has remained consistent despite some small variations in the forecast track. Changes were minor. Bann Previous Excessive Rainfall Discussion... Widespread heavy rains are likely day 1 across much of the Southeast, Southern Appalachians, into the Tennessee Valley with the extra-tropical remnants of Isaias. Heaviest rains likely into the upslope regions of the Southern Appalachians from northeast Georgia into the Upstate of South Carolina and western North Carolina. Strong upslope flow will support heavy precip totals in the 3-5"+ range across these areas, with maximum totals in the 6-10 inch range across far western NC into the Upstate of SC. The HREF and RRFS neighborhood probabilities are in good agreement and show high probabilities for 2, 3, 5"+ amounts in the upslope regions of the Southern Appalachians where a moderate risk is maintained from the previous outlook. Both the HREF and RRFS means also show a defined region of 8"+ probabilities, albeit smaller than the 1, 3 and 5"+ amounts in the upslope regions of the Southern Appalachians. To the south of the maximum upslope precip area...there continues to be potential for organized convection in the developing cold frontal band southeast of the surface center across northwestern FL. Training of cells parallel to this developing front will be possible day 1, supporting 2-3"+ precip totals and isolated 5"+ totals where max training occurs. In the comma head/deformation precip band on the northwest side of the circulation, the slight risk area from the previous issuance was removed across northern MS,Northern AL into central to western TN. While there may be heavy precip totals day 1 in this comma head region, hourly rates will likely be less than 1" and remain below FFG values, with only isolated runoff issues possible. HREF and RRFS probabilities of 3 hour precip totals exceeding FFG values are zero in this comma head/deformation band region. No changes made to the risk area along the coastal Carolinas. Strong coastal convergence will favor potential for very heavy totals along the immediate upper SC and lower NC coastal regions. Both the HREF and RRFS neighborhood probabilities are high for 2 and 3"+ totals, with isolated maximum values in excess of 5" possible. ...Southwest... PW values will be increasing to very anomalous levels day 1, 2 to 5+ standard deviations above the mean, from Southern CA, into the Great Basin and portions of the Southwest as moisture associated with Rachel is drawn northeastward. Initially day 1, convection should be widely scattered across the Southwest into the Great Basin. More concentrated precip areas likely after 0300 UTC as Rachel approaches the northern Baja/Southern CA coast and a more favorable right entrance jet region develops northeastward into the Great Basin. Both the HREF and RRFS probabilities of 3 hour precip exceeding FFG values increase after 0300 UTC, with the greatest values over Southern CA into far southern NV and far northwest AZ. Overall, not a lot of changes from the previous issuance. The slight risk was extended farther northeast into southern UT to cover the slot canyon regions. Otherwise, no changes made to the moderate risk area over Southern CA. Oravec Day 2 Valid 12Z Sun Oct 11 2026 - 12Z Mon Oct 12 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN THE SOUTHWEST... 2030Z Update... Widespread coverage of heavy rainfall still on track from California into the Great Basin and Southwest US as anamolous deep moisture streams across the region. With comparable QPF amounts with previous amounts...only minor nudges were needed to the boundaries of the outlook areas. Elswhere there may still be flooding concerns with the remnants of Isaias before it heads off- shore. Bann Previous Excessive Rainfall Discussion.,. A widespread heavy rainfall threat will continue across a large region from Southern California, into the Great Basin and portions of the Southwest on day 2. The combination of the remnants of Rachel and the continued very favorable right entrance region jet dynamics over the Great Basin will keep PW anomalies very high day 2, 2 to 4+ standard deviations above the mean. Model consensus is for widespread heavy precip totals across these areas, with a moderate risk maintained from Southern CA into southern NV, including the Las Vegas region, far northwest AZ and far southwest UT. A broad slight risk area continues northeastward into the Great Basin, with a northeastward extension of this slight risk area made from the previous issuance into far northeast NV, northern UT and far southeast ID to match the model consensus heavy qpf axis. The remnants of Isaias will produce widespread moderate to heavy precipitation from the Upper OH Valley, Central Appalachians, Mid- Atlantic, Northeast and coastal NC day 2. Aside from isolated urban runoff issues, believe there will not be any excessive rainfall issues across these areas. There may be some convection along the immediate NC coast Sunday, with isolated runoff issues possible. Oravec Day 3 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... Few changes were needed to the previously-issued Excessive Rainfall Outlook. Bann Previously Issued Excessive Rainfall Discussion... While the remnants of Rachel will have accelerated rapidly northeast day 2 away from the Southwest and Great Basin, a strong amplified mid to upper level trof will continue across the Great Basin into central to southern California. This will maintain above average PW values to the east of this upper trof from Southern California into the Southwest and Great Basin, although values will be lower than the day 1 and 2 time 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 2 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 day 2 with the potential day 3 moderate to heavy totals. Oravec Day 4 and Day 5 Valid 12Z Tue Oct 13 2026 - 12Z Thu Oct 15 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF ARIZONA INTO UTAH MONDAY INTO EARLY WEDNESDAY... ...Western U.S... The previous discussion remains in good shape. Only adjustments were to expand the Marginal Risk into southern Arizona where anomalous moisture coupled with saturated soils could support a very localized flash flood threat. The rest of the western U.S. Day 4 threat areas remain on track. Mullinax ---Previous Discussion--- Remnants from Rachel plus the influence of a mature upper level low centered over the Great Basin will maintain another active period with convection centered over the Mogollon Rim in AZ up through UT where the model consensus continues to depict scattered heavy convective prospects in-of the terrain and the valley areas to the north. The good news compared to previous periods is the remaining energy from Rachel will be diffuse by this juncture of the forecast, however the upper level progression just to the east will be plentiful in providing a continued ascent regime capable of maintaining a broad convective threat with locally heavy rainfall thanks to PWATs lingering between 1-2 standard deviations above normal. Considering the environment prior, this is progress to waining the worst of the flash flood threat that will ensue over the weekend. That said, antecedent soils may be pretty well- saturated by this point leading to perhaps a bit of an easier chance for flash flooding despite rates and expected rainfall accumulations being lower than previous periods. A broad MRGL risk remains over the interior west with an embedded SLGT still lingering over northwest AZ up through much of UT where the best mid and upper level forcing is progged for much of Tuesday before the threat finally ends heading into mid-week. Kleebauer ...Southern High Plains into the Central Plains... Day 4... The rationale for the Day 4 ERO remains on track, so other than a minor expansion of the Marginal Risk, no additional risk upgrades were made this cycle. Some heavier QPF could occur towards the end of the period, but confidence in the timing as to where the heaviest QPF would occur in late Day 3 or early Day 4 was low to consider an upgrade as of this forecast cycle. Mullinax ---Previous Discussion--- An increasing threat of heavy rainfall will be brought into the Central and Southern Plains by D4 thanks to the introduction of remnant energy and moisture advection from now Hurricane Simon in the Eastern Pacific off Mexico. The current upper pattern depicts Simon taking a turn and moving due north through Mexico with its primary energy becoming sheared as it migrates poleward across northern Mexico and eventually makes headway into the CONUS. Current ensembles are in agreement for the energy of Simon to maneuver through Coahuila and up through southwest TX before pivoting north-northeast around a broad ridge centered over the Southeast U.S. This will bring the main energy, albeit sheared and weaker than the prior 72 hrs, across the Central and Southern Plains leading to a focused area of ascent to couple with elevated PWATs bring brought into the area. A surface ridge to the north will only act to increase low-level convergence in tandem with the primary energy ejection leading to an area of convection spawning after 00z with the introduction of a budding nocturnal LLJ. Models are consistent with a signal for 1-3" of rainfall in areas where convection develops with a few pockets with higher totals. Ensemble mean QPF is much lower overall, so the maxima is more in line with the deterministic output from the global suite. In any case, this signal is reputable for a broad MRGL risk with the alignment of the risk basically right within the expected path of the mid-level energy as it moves north-northeast into the CONUS. The best potential will likely be over OK/KS into MO thanks to the added benefit of the low-level convergence regime being introduced with the combination LLJ and surface ridge to the north. Kleebauer Day 5... Latest 06Z and 12Z ensemble guidance have trended wetter in parts of the Southern Plains, spear-headed by the EC-AIFS guidance. EC- AIFS members show hints of Simon maintaining a surface circulation by 12Z Wednesday just off the Mexico coast and its moisture being directed into the South Central U.S.. This is thanks to the interaction between the anomalous trough in the West and the impressive upper-level ridge over the Southeast. The newest 12Z EC-AIFS ensembles show a stronger 500mb low than subsequent cycles over the Intermountain West, with pockets of 30-50% for >1" of rainfall from the Permian Basin to as far north as eastern KS and western MO for Day 5. Individual deterministic model members show some of the higher-end potential from this setup with 2-4" totals showing up across various global models. Where some of these higher amounts come to fruition remains unclear, but the ECMWF does shows PWs approaching monthly record levels in the Ozarks and eastern OK. This implies that with sufficient instability and excellent upper-level forcing via right-entrance region jet streak dynamics aloft, that excessive rainfall rates are a growing concern from the Southern Plains to the Middle MS Valley. With increased QPF becoming focused farther south, the Slight Risk was extended into West Texas, and the Marginal Risk in the Northern Plains was dropped given drier trends. Mullinax 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 $$