FOUS30 KWBC 250106 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 906 PM EDT Thu Sep 24 2026 Day 1 Valid 01Z Fri Sep 25 2026 - 12Z Fri Sep 25 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF SOUTHEAST NEW MEXICO... Heavy rainfall threat will continue through the overnight period across Southeast New Mexico into portions of West Texas and the Texas Panhandle this evening. Large scale ascent pattern between a meandering ULL over AZ and a broad upper ridge positioned across the Southern Plains will aid in a continued deep moist advection pattern and a multitude of shortwave/mid-level perturbation ejections out of Mexico through the next 12 hours before finally ceasing as we head into tomorrow morning. Shortwave over Chihuahua will be a primary player in tonight's extended period of heavy rainfall with the disturbance forecast to eject northeast within the mean flow centered over the NM/TX border. Sufficiently buoyant environment of 1000-2000 J/kg MUCAPE along with ample ascent and PWAT anomalies between +2 to +3 deviations will lead to rainfall rates between 1-2"/hr over much of the Southeast NM and West TX domain with sights overlapping areas recently hit hard this afternoon and the prior evening. Area FFG's remain very low with several flash flood warnings already positioned across the Southern High Plains of NM back into the terrain of Southeast NM and far West TX. 18z HREF neighborhood probs are indicative of scattered threats for over 2" of additional rainfall in these areas with the latest CAMs relatively robust in the corridor between El Paso/Donna Anna County over to Eddy/Lea counties in NM and all of the West TX to the west of the Pecos River. Significant flash flooding remains plausible for this entire area with flash flooding likely to occur throughout the night. A MDT risk remains in effect for the Sacramento Mountains where significant flash flooding is ongoing and expected to continue. A broad high-end SLGT is forecast over the surrounding areas with western and eastern fringes of the coverage labeled above between El Paso/Donna Anna and points east to the NM/TX border between Eddy/Lea and neighboring counties of TX. The threat for flash flooding extends into the western TX Panhandle where the flow maintains a persistent heading for thunderstorms to rotate into the area and cause some flash flood concerns west of the line from Midland-Lubbock-Amarillo. SLGT risk encompasses these areas, as well as the Desert Southwest into AZ where lingering convection over the Mogollon Rim will allow for some flash flood concern into the first half of the evening before the threat dwindles. Kleebauer Day 2 Valid 12Z Fri Sep 25 2026 - 12Z Sat Sep 26 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS A PORTION OF SOUTHEAST NEW MEXICO... ...2030Z Update... Moisture, instability, and forcing will all be present from the southern Rockies to the southern High Plains on Friday, with hi-res guidance keying in on another round of scattered showers and thunderstorms that are capable of producing heavy rainfall. Given the upgrade to a Moderate Risk for southeast New Mexico on Day 1, and after what will likely be another day of heavy rain on top of soils that are already well saturated, a targeted Slight Risk was introduced over a portion of southeast New Mexico for the Day 2 ERO. Even though Friday's convection is expected to produce lower overall rainfall rates compared to the last several days, the sheer hydrological sensitivity alone justifies a Slight Risk upgrade. There was consideration to include parts of the Texas Panhandle and western Oklahoma with this Slight Risk as models have been showing a persistent signal for locally heavier QPF, but ground conditions aren't as sensitive in those areas compared to New Mexico so left them out for now. The other consideration for the Day 2 ERO was to possibly introduce a Slight Risk across parts of eastern Nebraska and western Iowa. The latest WPC QPF shows a swath of 1-1.5 inches which is supported by HREF neighborhood probabilities >50% for exceeding 1 inch in 24 hours. However, much of that rainfall is expected to fall well downstream of the more robust instability plume. This should result in more stratiform precipitation and lower intensity rainfall rates as a whole. As such, opted not to introduce a new Slight Risk and will instead maintain the inherited Marginal risk for now. Only minor adjustments were made to the existing Marginal Risk across coastal New England which covers the intrusion of the western flank of the impending nor'easter's precipitation shield well. Miller ...Previous Discussion... ...Southwest... A lingering mid-level disturbance, along with sufficient instability and moisture influx from the Gulf, will support another day of showers and thunderstorms across portions of the Southwest. Antecedent conditions will remain a concern following multiple rounds of rainfall, particularly across portions of New Mexico where soils remain saturated and FFGs remain low. While the overall coverage and intensity of convection may be reduced compared to previous days, locally heavy rainfall rates will remain possible where stronger convection develops. Given the increasingly sensitive hydrologic conditions, even modest additional rainfall may result in localized flash flooding. The inherited Marginal was maintained with only minor adjustments. ...Central Plains... The mid-level shortwave will continue to progress across the Central Plains, maintaining broad ascent and precipitation from portions of Kansas northeastward through Nebraska and Iowa. Locally appreciable rainfall total remain possible, though limited instability may again favor a substantial stratiform component and temper rainfall rates. A Slight Risk was considered across portions of Nebraska into Iowa. However, uncertainty regarding the coverage and magnitude of heavier rainfall precludes an upgrade at this time, and the Marginal Risk was maintained. An upgrade may become necessary in later forecast cycles as a consensus hopefully becomes more clear, and confidence in mesoscale details increase. ...Northeast... A Marginal Risk has been maintained for parts of the Northeast as the details of a potent coastal low continue to be ironed out. There is still uncertainty pertaining to the time and location of the low track, but there is a consensus forming in heavy rainfall occurring along coastal Massachusetts, Rhode Island, and Connecticut. However, placement of the low along with its central pressure vary. With global guidance remaining in disagreement, enough uncertainty was raised to preclude any upgrade at this time, with continuity of the previous forecast being favored. Blanco-Alcala Day 3 Valid 12Z Sat Sep 26 2026 - 12Z Sun Sep 27 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE NORTHEAST... ...2030Z Update... The latest 12Z guidance continues to trend this weekend's nor'easter a bit farther south and west compared to previous runs, with the low center now tracking closer to the northern Mid- Atlantic coastline by 12Z Sunday. Unsurprisingly, the resulting precipitation shield has also ticked to the south and west, though the heaviest rain is still confined to a swath from Cape Cod to Long Island to the Jersey Shore. Given the latest QPF, both the Marginal and Slight Risks were adjusted westward by a county or two to account for these trends, but otherwise no major changes were necessary. The inherited Marginal Risk centered mostly over western Iowa and northern Missouri was expanded south and west to include eastern Kansas and northern Oklahoma with this update, mainly due to a sufficient QPF signal anchored by a plume of 1000+ j/kg of MUCAPE draped across the central and southern Plains. The QPF signal becomes more pronounced across Iowa and Missouri and follows a fair amount of rain that is expected to fall on Day 2/Friday. With the potential for Day 3 QPF to fall on soils that are now more saturated, a Slight Risk was considered. However, the best instability still remains displaced to the west, so opted to hold off on an upgrade for now. Miller ...Previous Discussion... ...Northern Mid-Atlantic Coast into Southern New England... The potential for heavy rainfall increases substantially in the Northeast in the Day 3 period. The coastal low will bring a generally prevailing southeast to easterly flow around a low centered around Long Island, aiding in a substantial influx of moisture onshore into the Northeast and parts of the Mid-Atlantic. Current QPF guidance suggest widespread totals of 2-4" with isolated totals as high as 5" in the 24-hour period. The significant amount of expected rainfall over the long period into the urban corridor of eastern MA will likely cause widespread hydrologic concerns, including flooding in urban areas including Boston, and poor drainage locations. Additionally, given increased confidence regarding the heavy rain area, the now "higher-end" Slight Risk area was maintained as inherited. ...Central Plains... Further west the focus of the possible heavy to excessive rainfall remains over the Midwest/Central Plains on Saturday as a shortwave energy ejects northeastward from the Rockies. The envelope of solutions span the EC on the north side and the GFS favoring a more southerly solution corresponding to Iowa and Missouri/Kansas respectively. A few of the globals remain rather bullish on the amount of expected rainfall, particularly the ECMWF, while ensembles continue to focus on this area as well. As such, the Marginal Risk in Iowa was maintained where flash flood guidance is lowest after the recent rainfall. Blanco-Alcala Day 4 and Day 5 Valid 12Z Sun Sep 27 2026 - 12Z Tue Sep 29 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF NEW ENGLAND ON SATURDAY... New England... 20Z Update: Little change necessary for the D4 and D5 forecasts across New England with eastern MA continuing to be the focal point for heaviest rainfall in the D4 with a degrading rainfall outlook for D5 as our system finally begins drifting away from the region, but not before one last hit of moderate to locally heavy rainfall from southeastern ME into southern New England the first part of Monday. SLGT risk for D4 remains in effect with the risk encompassing areas where PQPF for >1" remains 40% or greater from the latest forecast. It will be imperative to keep tabs on the forecast as we move closer as the behavior of these broad closed upper level disturbances can be tricky in their final evolution leading to some short term shifts in the risk areas forecast. For now, went with a multi-model consensus of heavy rain into eastern New England, backed by ML outputs and ensemble mean QPF being heaviest in this corridor. Kleebauer ..Previous Discussion.. There is a Slight risk of excessive rainfall in proximity to a deep coastal low that slows its forward speed near southeast New England. Heavy rainfall will begin to taper off during the period in terms of areal coverage, rainfall rates and daily rainfall amounts as the upper system fills. Model consensus has been building around the idea that the surface system heads inland compared with pivoting and heading back out to sea. The cumulative effect of rainfall over the long period into the urban corridor of eastern Massachusetts will cause hydrologic concerns, including some flooding in poor drainage locations. For that reason, opted to keep the Slight risk on Day 4. Opted for a Marginal risk given the additional amounts shown by the models on Monday...but that may ultimately depend on the hydrologic state by then. Bann ...Southwest US... Sunday will begin to see influence of moisture advection being pulled off the Eastern Pacific from two different disturbances (Odalys and Polo) with increasing IVT/PWATs being pulled poleward into the Desert Southwest. Models initially for D4 are less bullish in their depictions when it comes to a convective threat over the region, however there are inferences of some convective development later Sunday given the continued moisture pull coupling with the afternoon diurnal instability max. The ECMWF is the most aggressive with its signature of convection into the region with the deterministic output suggesting some of the energy from Odalys being pulled into the Southwestern CONUS as it moves in ahead of a broad upper trough sliding down the Pacific coast come Sunday afternoon. Pending the evolution of the vorticity and PWAT advection, there could be an instance of scattered convection as far north as southern and central UT for D4 which has led to an expansion of the MRGL risk into this region to go along with much of AZ and western NM. D5, and beyond, is the period to watch as the setup becomes increasingly favorable for another round of widespread heavy convection as we begin to see an interaction between the eventual closed upper reflection (ULL) over CA and what will be Polo as it begins moving northward towards Baja over the course of the weekend into early next week. The current model trends at 12z are murky when it comes to the finer details of exactly when the interaction between the two features takes place with the ECMWF and GFS deterministic relaying very different evolutions that will play a significant role in the final outcome for the period. The ensemble means for Monday into early Tuesday note a broad expanse of heavier rainfall increasingly likely for the Southwest CONUS into the Four Corners area due to the ascent pattern downstream of the ULL swinging into the region. Regardless of any interaction with Polo, enough moisture (PWAT anomalies between +2 to +3.5 standard deviations forecast across AZ/NM into southern UT/CO) and strong diffluent flow aloft into the region will allow for widespread heavy convection to occur for Monday afternoon into Tuesday leading to enough consensus in the means to upgrade a large portion of the Southwest to a SLGT risk for D5. If there is further indication of more interaction with Polo with the progressing ULL on Monday and beyond, a much more significant excessive rainfall threat is plausible, one that would likely yield a higher risk over a broader area. This is forecast currently with some of the ensemble members on both the GEFS/ECENS, as well as the EC-AIFS ENS which is already quite bullish in its presentation of the QPF at 5-day leads. Stay tuned for the latest as this setup has the potential for more substantial impacts pending the aforementioned interaction. ...Northern Plains/Upper Midwest... Progressive northern stream trough coupled with prevalent moisture advection from the southwest will lead to a period of convective concerns and isolated flash flood potential on Sunday into early Monday as model outputs target the Northern Plains into portions of the Upper Midwest for the D4 time frame. The current setup looks to remain progressive enough to limit flash flood concerns at this time, so a risk was not added, but wanted to make mention for the non-zero threat. A broad MRGL risk remains forecast for the area across the Dakotas down into the Central Plains as a continued advection of elevated PWATs streams poleward ahead of a broad upper trough/ULL reflection out west. Remnant energy from what is currently Odalys will get pulled northeastward out of the Pacific on D4 with sights on the Southwest for Sunday into Monday, eventually progressive steadily northeast into the Northern and Central Plains by Monday into early Tuesday leading to quite a larger coverage of convection over the above area. Latest ensemble means are more indicative to widespread heavier convective potential, especially when you factor in the stronger PWAT/IVT advection scheme that comes with the remnant energy from Odalys. A previous case with a similar evolution occurred a few weeks prior with heavy rain focused over the Northern Plains that led to some flash flood concerns where impacted. Mean QPF is currently between 1-2" with locally higher at 5-day leads, a testament to the threat in question as there will likely be more significant rainfall potential with this setup. As of now, there is enough consensus to maintain the broad MRGL risk inherited, but did expand a bit further south and east to account for the latest trends in ensembles. This setup will likely see some higher risk potential due to the tropical influence as is historically the case with these evolutions, so this will be yet another area to maintain situational awareness for future updates and potential upgrades. 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 $$