FOUS30 KWBC 221558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Thu Oct 22 2026 Day 1 Valid 16Z Thu Oct 22 2026 - 12Z Fri Oct 23 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHWEST COLORADO AND SOUTHERN UTAH... ...16Z update... The biggest change with this update was the introduction of a Slight Risk across a small portion of the interior Northwest including southeastern Oregon into northwestern Nevada and far northeastern California. While it appears instability will be limited with the recent model consensus showing MLCAPE of only a few hundred J/kg and MUCAPE locally over 500 J/kg later this afternoon, 24 hour rainfall values of 1 to 2+ inches appear likely based on the 12Z HREF/REFS through 12Z Friday. Some of the 24 hr QPF will be in the form of snow toward the end of the period but most will fall as liquid. Regarding timing, the 18-06Z window will favor increasing upper level diffluence and divergence ahead of a 90-110 kt upper level jet max located ahead of an advancing closed low/trough forecast to move across California and Nevada through tonight. Slow movement of heavy rain cores could allow for hourly rainfall locally exceeding 0.5 inches at times. While 100 year recurrence intervals may not indicate the most representative values for this region of the U.S., both the HREF and REFS show fairly high probabilities of exceeding the 100 year ARI with 40-60 percent (12Z HREF) and 60-90 percent (12Z REFS). Again, the concern for flooding impacts may be more of a longer duration concern, rather than occurring on a 1 or 3 hour time scale. Elsewhere, the Marginal Risk was expanded across portions of central California given the potential for slow moving cells beneath the core of the upper low as it moves eastward this afternoon. MLCAPE is forecast to rise into the 500-1000 J/kg range across portions of the San Joaquin Valley with cell motions less than 10 kt among precipitable water values approaching 1 inch. Hourly rainfall may exceed 1 inch locally across the Great Valley through the early evening. Otto ...previous discussion follows... ...Southwest... A broad Slight risk remains in place across the Southwest as a deep mid to upper level low tracking into the West Coast provides robust large scale scent. Dynamic forcing is further enhanced by strong upper level divergence within the favorable right entrance region of an upper jet streak at the base of the trough. Ahead of the trough deep southerly flow will continue to advect anomalous tropical moisture northward, resulting in a broad footprint of near to record PW values for the time of year to go along with near record IVT values as well. Instability will be maximized from southern to central AZ into west central NM, where MUCAPE value upwards of 2000 J/kg are expected. This corridor of greater instability is where the greatest potential for intense convective rainfall rates exists, with rates locally as high as 1-2"/hr likely. Several CAMs signal the potential for brief cell training within the unidirectional southerly flow this morning across central AZ, with the corridor between Phoenix and Flagstaff favored along the nose of the low level moisture transport axis. This higher rainfall rate potential will gradually shift eastward across central AZ and into west central NM later today into this evening. Scattered instances of flash flooding are expected along his corridor, with locally significant impacts possible. Further north, the MDT risk centered over the San Juan Mountains has been expanded westward into south central and southeastern UT. Instability will be comparatively lower over this northern flank, but portions of southern UT have already received heavy rainfall yesterday, leaving hydrologic sensitivity elevated. A prolonged duration of scattered showers and thunderstorms is expected today. While quick cell motions and marginal instability will generally cap hourly rates around 0.5"/hr, the higher CAPE axis (~1000 J/kg) is forecast to nudge northward towards southern UT by later this morning and afternoon. This destabilization, combined with brief cell training, should support localized swaths of 1"/hr rain rates over sensitive terrain, slot canyons and washes, leading to scattered to numerous instances of flash flooding. The San Juan Mountains will see the heaviest rainfall accumulations from this event, with model consensus supporting around 3-4", and localized totals potentially exceeding 5". Rainfall of this magnitude generally equates ot a 10-50yr ARI for 24hr totals. Instability will struggle to reach this far northeast, keeping high res ensemble neighborhood probabilities for 1"/hr rain subdued at roughly 10-15%. However, strong orographic ascent within the deep moisture plume will generate persistent moderate to at times heavy rainfall, with rates periodically reaching 0.5"/hr. While some snowmelt is expected to enhance runoff and the flood threat, temperature at higher elevations should remain in the 30s and 40s, allowing existing snowpack to absorb some of the rain. Overall this event is a solid MDT risk, with numerous instances of flooding likely, some of which may produce significant impacts. The lack of higher convective rates and storm totals largely holding under 5 inches keep this just below High risk levels...nonetheless, this is still expected ot be a high impact hydrologic event for the region. ...CA into ID... Along the CA coast, the initial band of heavier rainfall should have weakened by 12z. However, with the main mid to upper level low still offshore, additional isolated to scattered convective cells are likely to redevelop through the day, supporting a localized flash flood risk. Further inland, modest destabilization at or below 500 J/kg is expected into portions of NV/OR/UT. This weak instability paired with quick cell motions off to the north northeast should keep any flash flood threat localized and primarily over sensitive terrain and burn scars. A localized corridor of higher rainfall (1 to 2", locally up to 3") is expected from far northwest NV into far northeast CA and portions of southeast OR. Totals of this magnitude represent a 10-25yr ARI for this region and may be sufficient to induce hydrologic concerns. A Slight risk was considered given the anomalous rainfall magnitudes for the local climatology, but limited instability should result in an increasingly stratiform character of the rain following a period of initial convection. This may help keep the hydrologic impacts more isolated in nature. ...Southeast Florida... A Marginal risk continues for the southeast FL urban corridor. Low level coastal convergence within prevailing northeasterly flow will remain the primary focus for convection, with the potential to anchor slow moving cell either along the immediate coast or just offshore. Several CAMs highlight localized swaths of 5"+ of rain. However, uncertainty remains whether these heavy cores will make it onshore or stay just offshore. In addition, PW values are currently around 1.4", and while these values may increase some today, a significant increase is not expected. Thus some of the more aggressive high res guidance could very well be a bit overdone with peak rainfall magnitudes. A Marginal risk remains appropriate to cover the localized conditional flash flood risk. Chenard Day 2 Valid 12Z Fri Oct 23 2026 - 12Z Sat Oct 24 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE SACRAMENTO MOUNTAINS SOUTH THROUGH THE EL PASO METRO... ...NM and southern CO... Scattered convection is expected to develop across portions of NM into southern CO downstream of a mid to upper level trough tracking eastward from CA into AZ. In the broader evolution of the system, day 2 (Friday) appears to represent a relative minimum in convective coverage and overall intensity compared to more active periods expected on both Thursday and Saturday. Nonetheless, PWs will remain anomalous and collocated with 500-1500 J/kg of CAPE. This environment will support scattered convection capable of locally high rainfall rates and an isolated flash flood threat. While the latest QPF guidance remains modest and generally supportive of a Marginal risk, the presence of better instability over southern NM could yield an uptick in convective rainfall as we get more into the high res model timeframe. Considering the hydrologic vulnerability, the inherited Slight risk was maintained across the terrain and burn scars of the Sacramento Mountains into adjacent urban corridors. ...Southeast FL... A setup similar to day 1 will persist across southeast FL, where low level northeasterly flow and coastal convergence could focus slow moving cells along the immediate coast. The heavy rainfall threat remains conditional, with a possibility the heaviest cores remain just offshore. Model differences also introduce some uncertainty regarding the moisture profile, with the GFS showing notably higher PW values than the ECMWF. Given the lingering uncertainty with these details the inherited Marginal risk was left unchanged. Chenard Day 3 Valid 12Z Sat Oct 24 2026 - 12Z Sun Oct 25 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN NEW MEXICO INTO SOUTHEASTERN COLORADO, AND OVER SOUTHEAST FLORIDA... ...Eastern NM into southeast CO... An uptick in the flash flood threat compared to day 2 is anticipated across eastern NM into southeastern CO on Saturday. Synoptic scale ascent will strengthen as the mid to upper level trough and associated jet streak approach the region, which will also help amplify the low level moisture transport axis. PWs will remain anomalous, holding well above normal and near climatological max values for late October. Model guidance also indicates upwards of 500-1500 J/kg of CAPE within this moisture plume. Deep unidirectional southerly flow will favor some cell training and backbuilding potential. Given the favorable ingredients, not surprising that model QPF values are notably higher compared to day 2. The combination of strong forcing, deep and anomalous moisture, and sufficient instability, will support convective rain rates locally as high as 1-2"/hr. Overall model agreement on the axis of heaviest rainfall is above average for a day 3 forecast. Higher end Slight risk probabilities are justified across much of eastern NM with scattered flash flooding expected. ...Southeast FL... The Slight risk has been maintained across the southeast FL urban corridor. The mesoscale setup remains similar to days 1 and 2, with northeasterly low level flow promoting coastal convergence and possible slow moving convection. By this time, dynamic ascent may be aided by a distinct mid level shortwave dropping southward into the area. While model guidance is in relatively good agreement synoptically, model spread persists regarding the magnitude of moisture present. The ECMWF and AIFS remain noticeably drier overall, depicting an environment less conducive for heavy rainfall. Conversely, the GFS/AIGFS/UKMET/CMC all depict a deeper moisture profile and consistently produce a coastal heavy rain signal. Given this lingering uncertainty and the conditional probability for slow moving convection to anchor along the sensitive coastal corridor, there is no reason to deviate from the inherited Slight risk. Trends will continue to be monitored in subsequent forecast cycles. Chenard Day 4 and Day 5 Valid 12Z Sun Oct 25 2026 - 12Z Tue Oct 27 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE WESTERN/SOUTHWEST UNITED STATES ON SUNDAY,,, Once again...the deterministic and ensemble members have maintained good run to run continuity showing a deep trough over the western United States and a persistent upper ridge to the east leaving a corridor of conditions favoring locally heavy to excessive rainfall from the Southwest US to the Western US Plains on Sunday into Monday. The ridge stays nearly stationary preventing the trough to propagate much eastward as it amplifies. The previous outlook accounted for that and only minor adjustments were made on Sunday. The overall threat for excessive rainfall begins to taper as the upper low fills and begins moving out over the plains. In this instance...kept a Marginal Risk area where the PW values/anomalies were highest and instability is best (albeit modest at best). The southeast coast of Florida remains more of a continued approach to heavy rainfall potential into the coastal areas of southeast Florida which remained depicted in some of the guidance. The trend for the guidance to be less enthusiastic continued in the 22/00Z cycle...especially on Day 5...so maintained a Slight on Sunday and went with a Marginal on Monday. Bann 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 $$