FOUS30 KWBC 240043 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 843 PM EDT Wed Sep 23 2026 Day 1 Valid 01Z Thu Sep 24 2026 - 12Z Thu Sep 24 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE TEXAS AND OKLAHOMA PANHANDLES, CENTRAL AND EASTERN NEW MEXICO, AS WELL AS THE CENTRAL AND SOUTHERN APPALACHIANS... ...New Mexico and West Texas... Prevailing southerly flow aloft will maintain itself for the overnight period with a continued threat of flash flooding for the eastern half of NM up into portions of the TX and OK Panhandles as the remnant mid-level shortwave lifts north-northeast with increasing convergent flow in-of a surface trough positioned across the NM High Plains. PWAT anomalies remain on the order of +2 deviations across much of the region that has been plagued by heavy rainfall the last 36 hrs with one last round forecast tonight. One of the positives for this setup is the heaviest precipitation is likely away from the areas impacted last evening with the best signal for 2+ inches of rain located further northeast into northeastern NM into those adjacent Southern High Plains areas of TX/OK. 18z HREF probabilities signaled a more prominent threat within that particular zone as convergence is maximized within that zone as the mid-level energy over central NM drifts northeast and becomes a bigger factor away from the terrain for the first time in a while. Further southeast into far west TX and southeastern NM, there is some discrepancy in guidance for a secondary shortwave to lift across the Rio Grande and traverse the area with another localized convergence signature materializing across the Guadalupe Mountains up through the Upper Trans Pecos. Some of the earlier CAMs were quite bullish in the signature with less of an extent from the latest HRRR/RRFS outputs this evening that are less robust with the threat. The shortwave perturbation is noted via WV satellite across Chihuahua, so it will come down to its general evolution and whether the models that lift the disturbance northeastward have the most merit, or if the disturbance gets sheared and doesn't have a significant role in the forecast. As of now, the trends are for this setup to yield less of a threat for those aforementioned areas, but will bear watching as this could spur up some significant rainfall prospects in areas that are more flash flood prone in the terrain and Pecos River Valley. Given the current setup this evening, had enough confidence to drop the previous MDT risk back down to a SLGT, but maintained a broad high-end SLGT in its place considering the sensitivities at play, as well as some questions handling the shortwave ejection from MX. Highest confidence in heavy precip is over that area of eastern to northeast NM up through the northwest TX Panhandle, through the OK Panhandle, with a northern inflection into southwestern KS. Scattered flash flood potential within this zone with the best threat overlapping any areas that were impacted greatly last evening, and urban footprints that are prone to run off. ...Central to Southern Appalachians... A stubborn upper level low continues to churn over the Ohio Valley with a persistent convective threat situated within the terrain of WV, eastern KY, down through the Southern Appalachian front. Surface trough analyzed along and west of the Piedmont maintains a suitable convergent axis caused by the the overall synoptic setup pushing a deep CAD wedge all the way down east of the Appalachian front. Localized convergent pattern in-of the mountain chain and points west where instability remains prevalent outside the CAD wedge will continue to impact the terrain for at least the next few hours before conditions improve and we finally see a return of nocturnal stabilization with the development of a boundary layer cap that will finally put an end to the convective threat. Several flash flood warnings remain in effect over southwestern WV into eastern KY and TN which led to a continuation of the SLGT risk for those areas while they are still being impacted. Look for less of a threat after 06z for basically everywhere east of the Mississippi as the surface ridge and nocturnal stabilization will finally put the threat to rest with just some lingering light rain/showers across the region. Kleebauer Day 2 Valid 12Z Thu Sep 24 2026 - 12Z Fri Sep 25 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF NEW MEXICO INTO SOUTHWEST KANSAS... 20Z Update... Much of the previous forecast rationale remains on track after evaluating the latest WPC QPF and 12Z guidance. There is slightly greater concerns for flash flooding in southeast NM, which includes the Sacramento Mountains, given their soils will continue to saturate in wake of Wednesday's heavy rainfall. Otherwise, the Slight Risk that stretches from southwest NM to as far north and east as southern KS remains in good standing. Mullinax ---Previous Discussion--- ...Southwest and Southern Plains... Heading into Thursday the strongest mid level forcing and highest PW anomalies will shift northward out of NM and into Colorado and the Central Plains. However, in the wake of this exiting system, daytime instability is actually forecast to increase over NM compared to previous days. While PW values decrease some, they will remain above the climatological 75th percentile. Additionally, broad troughing will remain overhead, with embedded shortwave energy continuing to traverse the region. With less concentrated forcing and somewhat reduced moisture, the overall areal coverage of heavy rainfall across NM should diminish relative to prior days. However, the combination of stronger instability and sufficient moisture will still support intense localized convective rainfall rates capable of producing significant rainfall totals. Given the hydrologic sensitivity built up from preceding days of heavy rain, an additional flash flood threat appears likely. While the threat may not be as widespread as previous days, a Slight risk is maintained, as locally significant and impactful flash flooding will still be possible. The Slight risk also extends eastward across the TX and OK Panhandles and into southwest KS. Convection may be ongoing across this corridor at the start of the period. Later in the day, in the wake of the lifting shortwave and surface low, a corridor of enhanced low level convergence and instability may develop, which could result in additional rounds of locally heavy convection. Further west, isolated flash flooding will also be possible across portions of AZ, southern UT and CO as the trough moves across these areas. ...Central Plains... The highest PW anomalies and strongest synoptic forcing will overlap across KS and NE. This forcing aligns well withe a 1-3" consensus QPF swath depicted by a majority of the model guidance. The primary limiting factor for a greater flash flood threat will be the degree of available instability. Thus rainfall may take the form of a broad stratiform rain shield with only embedded heavier convective elements. Therefore, the risk level will be maintained at Marginal for now, with trends continuing to be closely monitored for any needed upgrades in subsequent forecast cycles. Chenard Day 3 Valid 12Z Fri Sep 25 2026 - 12Z Sat Sep 26 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM NEW MEXICO INTO THE PLAINS, AND OVER SOUTHEAST NEW ENGLAND... 20Z Update... Not much change with regards to the Marginal Risk area in the Central U.S.. The Marginal was adjusted a little farther east in the MO River Valley, but otherwise, the Marginal's Central and Southern Plains areas were kept that same from overnight. There remains a fair amount of model spread on the potential placement of the developing coastal storm Friday night. The ECMWF/EC- AIFS suite remains slower and farther west, while GEFS/CMCE ensembles are a little more progressive and farther east. The 12Z GEFS has been continuing a trend over the last 24 hours of its members gradually coming west by 06Z Saturday, which suggests a move towards the ECMWF suite. When accounting for all ensemble members, there has generally been an increase in QPF across southern New England and as far south and west and Long Island. With that being the case on the latest WPC QPF, I did decide to expand the Marginal Risk into eastern CT and eastern LI this cycle. No Slight Risk was proposed for the time being, given the heaviest rainfall arrives late Friday night and any longer duration heavy rainfall would be more likely to unfold by Day 4 (Saturday). Mullinax ---Previous Discussion--- ...NM into the Central Plains... A broad axis of anomalous PWs, low level moisture transport, and CAPE will persist from portions of eastern NM northeastward through NE and IA on Friday. The strongest and most persistent mid to upper level forcing, coupled with the primary moisture transport axis, is forecast to focus across the northern extent of this corridor. Conversely, the most robust instability is expected to pool further south, stretching from eastern NM into southern KS. The spatial offset between the best large scale forcing and greatest instability introduces uncertainty regarding exactly how the flash flood threat will evolve. While it will undoubtedly be a wet period across this corridor, the magnitude and extent of the flash flood threat will depend on whether sufficient rainfall rates can materialize further north, or if convection can organize and become widespread enough further south where the instability is more firmly established. Given these lingering questions, a broad Marginal risk has been maintained across the region. However, the available environmental ingredients certainly support the potential for an embedded Slight risk. Upgrades may be necessary in subsequent forecast cycles as the event draws closer and confidence in mesoscale details increase. ...Northeast... A Marginal risk has been maintained from RI into eastern MA as uncertainty lingers regarding the exact track and evolution of a developing coastal low. While the better chance for more widespread heavy rainfall is likely to hold of until day 4, the northern edge of the rain shield could push into coastal areas by later Friday. Current indications suggest that the best instability and any convective elements should remain offshore through the day 3 period, keeping rainfall rates predominately stratiform over land. Consequently, the overall flash flood threat is expected to remain relatively low. However, with 1-3 inches of rain possible and ongoing uncertainty regarding the precise behavior of the coastal low, continuity with the previous forecast is preferred for now, and the Marginal risk remains in place. Chenard Day 4 and Day 5 Valid 12Z Sat Sep 26 2026 - 12Z Mon Sep 28 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN US/WESTERN PLAINS AS WELL AS EASTERN NEW ENGLAND... ...Southern Rockies to Central and High Plains... 20Z Update: Little change in the previous forecast. The ECMWF remains the more aggressive of the solutions with widespread convective potential from northwest IA down through northern MO. The EC-AIFS continues to pinpoint the area of central IA down into northern and western MO as a target, a bit south of the deterministic ECMWF, and closer to the deterministic GFS solution. In any case, overall magnitude is closer to a higher risk, but with some variations in where the heaviest will occur, went with general continuity and nudged the risk area a touch south to account for ML trends. Kleebauer ..Previous Discussion.. The main focus of attention for 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. Maintained the Marginal in Iowa where flash flood guidance is lowest after the recent rainfall although confidence is waning about the need for one based on the latest QPF. If the ECMWF verifies...the flash flood numbers are higher with a correspondingly reduced threat of excessive rainfall. A broadening mid/upper level trough to the east shunts deepest moisture out of the Midwest by Sunday. ...New England... General consensus is for heavy rainfall to plague much of southern New England with the maxima centered right over eastern MA, including the Boston metro for both D4 and D5 periods. Multi-day heavy rain threat is due to a slow-moving coastal low as the mid and upper height fields note a stacked 850-300mb low presentation as we move into Sunday with a weakening expectation occurring the back half of D4 into the D5 time frame. The prevailing southeast to easterly flow around the low center positioned near LI will aid in copious amounts of moisture being thrown back into the northern Mid Atlantic into southern New England as the main axis of heaviest precip will likely promote widespread 2-4" with locally as high as 5" with the current forecast over the 48-60 time frame of impact. Limited instability over the region will limit the upper threshold of flash flood capabilities, however, the significant amount of rainfall over the long period into the urban corridor of eastern MA will likely cause widespread hydrologic concerns, including some flooding in poor drainage locations. The previous SLGT risks were maintained as a result. 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 $$