036 FOUS30 KWBC 100826 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 426 AM EDT Sat Oct 10 2026 Day 1 Valid 12Z 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... 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... 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... 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... 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. ...Southern High Plains into the Central Plains... 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. As we move into D5, the threat blossoms into some more appreciable with sights on the Central and Southern Plains, perhaps expanding as far north as the Northern Plains as the upstream pattern evolves further with a strong ULL disturbance migrating through the Inter- Mountain West leading to lee cyclogenesis over the Front Range. The addition of the low and upper low into the pattern will only benefit a more pronounced convergence pattern and favorable upper support to maintain a broader, more intense precipitation shield over the Central U.S. come Wednesday afternoon and beyond. This is fairly classic in the evolution the surface ridge to the north and now maturing lee cyclone will only set the stage for a more prototypical synoptic evolution that typically correlates to more widespread convection within a budding warm sector and the migration of a cold front that materializes along the base of the surface low. Ample moisture noted via widespread PWAT anomalies between 2-3 standard deviations above normal coupled with increasingly favorable jet and kinematic ascent will lead to quite a resurgence of convection over the Central Plains into the Mid- Mississippi Valley by Wednesday night creating a broad area of potentially heavy rainfall and flash flood concerns. The greatest threat based on recent NBM and global ensemble probabilities, as well as the latest First Guess Fields center the risk over eastern KS into MO with an already robust 2+ inch forecast being depicted within the means. At this lead time, that's fairly impressive, but makes sense synoptically. Another broad MRGL risk was added for the new D5 period, but a SLGT is also forecast within that aforementioned area where probabilities for >2" are highest across the Central Plain into the Mid-Mississippi Valley. 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 $$