922 FOUS30 KWBC 121553 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1153 AM EDT Mon Oct 12 2026 Day 1 Valid 16Z Mon Oct 12 2026 - 12Z Tue Oct 13 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE GREAT BASIN & SOUTHWEST... 16Z Excessive Rainfall Discussion Update... The Great Basin and Southwest US will be the only focus for excessive rainfall. Even though the upper level dynamics of Rachel will be pulling away...steep low level lapse rates associated with the broad upper level trough combined with favorable upper jet dynamics will support increasing convection at the time of maximum daytime heating. The previous outlook had that scenario covered and had the support from the latest HREF/RRFS guidance so no changes needed. Bann Previous Excessive Rainfall Discussion ..Great Basin and Southwest... Potent upper low (ULL) centered over OR this evening will slowly pivot southward through the course of the D1 with a trajectory into the Great Basin by Monday afternoon. The strength of the ULL will remain fairly prolific with even some indication of modest deepening via ensemble height probabilities indicating lowering heights within the center of the upper level disturbance. No matter the case, the deep mean trough will provide significant ascent across the Great Basin and portions of the Desert Southwest for at least one more period before we finally see the setup shift eastward. A shortwave embedded within the trough base is forecast to eject northeast as it rounds the base of the trough and motions through AZ into UT allowing for ample mid-level forcing to return over the area. Forecast upper jet strength will also become more prolific in this juncture of the forecast with deterministic output from various models indicating a 250mb jet upwards of 130kts bisecting the above areas leading to enhanced RER dynamics sufficient to generate a round of scattered to widespread convective potential across the region beginning later this afternoon, carrying through the first half of the evening. HREF neighborhood probabilities this evening are indicative of local spots ~2" additional rainfall over portions of the Desert Southwest with the main core centered over the western and central Mogollon Rim up into northwest AZ. Probabilities range from 40-80% for >2" over the terrain in AZ to about 30-60% across the Wasatch and canyon areas in UT. Heights will be falling rapidly further northwest from this area, so the very end of the period might see a shift to snow in some of the higher elevations in NV that would end the flash flood risk completely, but before that, some locally heavy rainfall is certainly plausible. Rain will be the dominate hydrometeor for the rest of the state outside the highest peaks in the Uintas. This allows for a continuation of a broad SLGT risk over the Great Basin down into the terrain in central AZ. This will likely be the end of the threat for the Desert Southwest as the pattern evolves and the focus shifts downstream into the Plains after Monday night, finally putting to rest a very active 72hrs. Kleebauer Day 2 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, ALONG WITH THE CENTRAL AND SOUTHERN PLAINS... ...Great Basin... Upper low across NV will shift slowly eastward into the interior west with sights on UT and surrounds leading to an isolated flash flood threat continuing directly underneath the low itself. As of now, the probabilities for >1" are relatively benign in terms of coverage for >50%. That said, the max probability of 50-80% is centered over the valley between Provo up to Logan which is right in the population center for the state, and coincides with more urbanization factors that could promote run off potential. The area has seen several inches of rainfall with this setup leading into Tuesday, so antecedent conditions are more favorable for these isolated flash flood prospects compared to normal. Considering the setup has not really wavered in terms of its evolution, felt it was a case to maintain continuity in the forecast with a small MRGL risk placed over the western and north-central portion of the state with the centroid over the valley of northern UT. ...Central and Southern Plains... Longwave pattern across the Central and Southern U.S. will materialize in such that a broad convective evolution is increasingly favorable for late-Tuesday afternoon, carrying into Wednesday morning. The western ULL will slowly pivot eastward into UT by Tuesday with increasingly diffluent flow positioned across the Central Plains and portions of the Southern High Plains as we move into the second half of the D2. A broad upper jet alignment will arc over the the northern tier of the CONUS leading to a well placed RER jet core centered over the Central U.S. with the ascent maximized likely south of a latitude of I-80. The current progs are for lee cyclogenesis to begin the period prior, but exhibit very little forward propagation from its initiation point as the pattern evolution out west motions very slowly. Additional input of energy streaming poleward out of the Eastern Pacific, up through Mexico, and into the High Plains will occur in tandem with the overall longwave evolution as energy on the northern edge of Hurricane Simon will advance north-northeast into the region around the western periphery of a broad ridge centered over the Lower Mississippi Valley. The ample ascent provided by both mid-level vorticity advection and improving large scale jet dynamics within deep layer moisture presence over the Plains will aid in the production of convection as we step into the peak diurnal instability hours, and beyond. The setup also calls for an integration of a LLJ development around 00z Wednesday which will only act as a convergent piece of this puzzle as the addition of low- level southerly enhancement will only act to assist the convective pattern as increasing low- level shear and maintenance of general buoyancy across the Plains will allow for a maturation of area convection over the Central Plains and Mid-Mississippi Valley. Model consensus indicates a blossoming of convective coverage across KS/MO/OK by nightfall on Tuesday with an expected initiation of convection over west TX thanks to the LLJ interaction with the streaming mid- level energy ejecting out of Mexico. Generally slow cell motions and potential for repeating convection are anticipated over the entire stretch from southwest TX up through the Central Plains with the latest forecast soundings across the South-Central U.S. indicative of weakening mean winds and backing of the low-level flow that would support some back-building potential of precipitation in-of OK/KS into western MO. As of this time, the relative FFG's in the area would support at least the initial threat of heavy rainfall as current QPF means hover between 1-2" over a broad area from the Permian Basin up into eastern KS and adjacent western MO. Deterministic outputs do signal some local totals >3" across portions of the aforementioned area which would place them near the 3 and 6hr FFG thresholds in place across these particular areas. We are still at the very end of the HREF output for this setup meaning we are missing the key final 12hrs of the period to see how the CAMs handle the magnitude of the convection for this time frame. At first glance, there may be enough of a signal for a SLGT risk somewhere across the High Plains extending northeast, so stay tuned over the next few forecast cycles for possible upgrades for the period. For now, the previous MRGL risk from the Big Bend up through the southern tier of the Midwest remains consistent with this evening's guidance. Kleebauer Day 3 Valid 12Z Wed Oct 14 2026 - 12Z Thu Oct 15 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS INTO THE CENTRAL PLAINS AND LOWER MISSOURI VALLEY... A generally classic setup for persistent heavy rainfall will materialize over the Central and Southern U.S. come mid-week with a vast, arcing jet situated from the Central Rockies to the Canadian Maritimes. At the surface, a slow-moving surface low with attendant frontal alignments will pivot meander over the Front Range with a cold front at the base making headway through the Southern Rockies into the Southern High Plains by the end of the forecast cycle with a press of Pacific air in wake of the front. The combination of large scale ascent situated under a broad RER of the upper jet along with ample moisture advected up out of the Gulf and from some of the remnants of now Hurricane Simon being pulled poleward will create a broad convective regime with general QPF maxima occurring during peak diurnal instability and overnight when the nocturnal LLJ initiates over the Plains. Consensus among all guidance for a prolonged heavy rain event has allowed for increased confidence in both the longevity and magnitude of potential rainfall from southwest TX up through the Mid-Mississippi Valley, arcing as far east as the Ohio Valley another cold front on the leading edge of a strong surface high moving over the northern tier of the CONUS. With PWAT anomalies running consistently between +2 to +3 standard deviations over much of the Central and Southern U.S. into the western Ohio Valley, the prospects of convection capable of rainfall rates between 1-2"/hr or greater are much more viable which will spell for flash flood potential, especially when you couple with what will fall the period prior to prime the upper layer of the soils. The previous SLGT risk was extended down through all of southwest TX with an extension of the risk a bit more north and west given the trends in ensembles and general bias to these more meridional patterns where the evolution leans slower in their progression. Higher risks in future forecasts are plausible in this particular setup, so stay tuned for the latest updates over the course of the week ahead. Kleebauer Day 4 and Day 5 Valid 12Z Thu Oct 15 2026 - 12Z Sat Oct 17 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHERN AND CENTRAL PLAINS TO THE LOWER Missouri VALLEY ON DAY 4... DAY 4... The heavy rain threat that begins day 2 across the Southern to Central Plains into the Lower Missouri Valley will persist into the day 4 time period. The amplified upper trof that is expected to push steadily eastward across the Great Basin into the Rockies Tue and Wed will slow by Thu as it begins to shear. This will allow for a continuation of favorable right entrance region jet dynamics in the axis of above average PW values, 2 to 3 standard deviations above the mean, that are expected along and ahead of the surface front oriented southwest to northeast across the Southern to Central Plains into the Lower MO Valley. Model consensus is for additional heavy precip potential along and ahead of this front. There will likely be overlap in heavy precip axes from day 3 into day 4 along and ahead of this front. No major changes made to the previous slight risk, with additional runoff issues possible. Day 5... The upper trof that begins to shear day 4 over the Central Plains will continue to do so on day 5, with a new closed low then forming over the northern Baja day 5. Heavy precip may develop to the east of this new closed low across portions of the Southwest into the Southern High Plains from eastern AZ into southern NM and far southwest TX where low level easterly flow is expected to strengthen. There is a lot of spread with respect the details of the closed low formation and the resultant qpf axis. The EC is the most emphatic about spreading potentially heavy precip farther to the northwest into AZ/NM. Given the spread, at the moment, only a marginal risk is depicted day 5 for far southeast AZ into southern NM and far southwest TX. Oravec 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 $$