484 FOUS30 KWBC 221926 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 326 PM EDT Tue Sep 22 2026 Day 1 Valid 16Z Tue Sep 22 2026 - 12Z Wed Sep 23 2026 ..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN NEW MEXICO... 16Z Update: A potentially significant and high impact flooding event is expected over the next few days across New Mexico and far southwest Texas. The risk of heavy rainfall will increase later today, ramping up considerably later this evening and overnight through Wednesday. This afternoon, expect scattered thunderstorms capable of producing intense rain rates of 1-2"/hr (locally higher). By tonight, most of the guidance shows the activity focusing into south to north oriented bands, leading to the potential for training / repeating rounds of thunderstorms and heavy rainfall. The 12Z HREF and other hi-res guidance followed previous cycles showing potential for several inches through early Wednesday. HREF neighborhood probabilities are moderate for at least 3 inches (40-60 percent) with at least a low chance (10-20 percent chance) of at least 5 inches. Given the sensitivity and potential vulnerability of the area, potential significant and higher end impacts are possible and this likely leans toward the higher end of the MDT probabilistic range. Elsewhere, the Slight Risk was adjusted to the latest radar trends and recent hi-res runs. The 12Z guidance shows the greatest concern focusing on portions of central to southeast VA where low- topped tropical showers will be capable of producing localized/isolated 2-4"+ totals. See MPD 1354 for more details. Taylor ...New Mexico and West Texas... A potentially high impact multi-day heavy rainfall event is set to begin across NM and far southwest TX today into tonight. An upper level trough approaching from the west will help strengthen an upper level jet, persistently placing the region in the favorable right entrance region. Deep southerly flow will transport tropical moisture northward, driving PW values toward mid to late September record levels by later today into Wednesday. Lift will be further augmented by low level easterly upslope flow and well defined mid level shortwave energy lifting north out of Mexico by later tonight into Wednesday. Daytime hours today will see scattered thunderstorm activity and at least some flash flood potential. Large scale forcing intensifies overnight allowing for a more concentrated rain shield with embedded heavier convective cores to impact southern NM. Neighborhood probabilities from both the 00z HREF and REFS show a 40-70% chance of rainfall exceeding 3" across NM today, though 5" probabilities drop off significantly. This suggests a reasonable max rainfall footprint of 2-4" through early Wednesday. Minimal changes were made to the inherited Slight and Moderate risk areas, as they still look in good shape. Scattered to numerous instances of flash flooding are anticipated, some of which could be locally significant. This threat includes the sensitive burn scar areas within the Sacramento Mountains. ...Ohio Valley and Mid-Atlantic... A setup for heavy rainfall will unfold across the Mid-Atlantic today into tonight as an approaching mid level trough aligns with the favorable right entrance region of an upper level jet. At the surface, strong high pressure to the north will drive a backdoor front southward, with strong easterly flow providing enhanced low level convergence. The 00z HREF and REFS show generally good agreement on two primary axes of elevated FFG exceedance probabilities. The first axis is from southeast VA into SC. Positioned along a coastal convergence zone and the backdoor front, this corridor will feature greater instability and support efficient warm rain processes. High neighborhood probabilities exist in both ensemble suites for 3" of rain. While 5" exceedance probabilities in the REFS are likely inflated due to its known high convective QPF bias, the HREF still depicts low to medium probabilities, indicating a few localized 5" totals are possible. FFG neighborhood exceedance probabilities of 15-40% justify a Slight risk, though overall coverage may end up on the lower end of Slight risk criteria. The second axis is across WV into southwest VA. Focused along an inverted trough, this area should see lower overall QPF magnitudes than the farther southeast axis mentioned above. However, antecedent conditions are wetter, resulting in much lower FFG thresholds. Strong convergence along the inverted trough combined with sufficient instability will allow for convective development, with FFG neighborhood exceedance probabilities over 25% in both the HREF and REFS. A Slight risk is warranted to cover this threat, with at least a few instances of flash flooding anticipated. Farther north into the Mid-Atlantic, insufficient instability will keep rainfall predominately stratiform, keeping rain rates below flash flood thresholds. Although strong low level forcing over top the backdoor front will still support a broad area of rainfall, with some areas receiving 1-2" of rain. ...South Florida... A Marginal Risk has been maintained for portions of South Florida. PWs remain elevated and well above average, supporting heavy rainfall rates and a localized urban flash flood risk today. Neighborhood probabilities of exceeding 5" of rain in the HREF and REFS are around 20-40%. Chenard Day 2 Valid 12Z Wed Sep 23 2026 - 12Z Thu Sep 24 2026 ..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF CENTRAL AND EASTERN NEW MEXICO... ...New Mexico and West Texas... The heavy rainfall threat established on day 1 will be ongoing and continue and peak over NM on day 2 as large scale forcing gets even stronger. A well defined mid level shortwave is forecast to lift northward across the state, accompanied by robust upper level divergence and the likely development of a surface low. PW values will remain near record levels for this time of year, with an anomalously deep moisture profile. With such strong forcing and widespread moisture in place, the primary limiting factor for heavy convective rates will be the extent of cloud cover and its impact on destabilization. While widespread clouds are a concern, daytime heating should allow at least the eastern edge of the rainfall shield to sufficiently destabilize, aided by broad easterly upslope flow. Thus while some areas may see predominately stratiform rain, a concentrated swath of intense convective rainfall remains likely. The most recent guidance still points toward totals of 2 to 4 inches during the 24-hr period, potentially higher up to 5 inches. This is likely to result in scattered to numerous instances of flash flooding, some of which could be life-threatening and significant. This would be most likely across sensitive terrain, urban areas, and burn scars. The inherited ERO risk is in good shape given the most recent guidance. ...Mid-Atlantic... A complex synoptic pattern will be present over the eastern U.S. as a mid to upper level low slowly drifts from the Ohio Valley towards the Mid-Atlantic, while a separate coastal low develops offshore. Meanwhile, surface high pressure positioned to the north will advect drier and more stable air into the corridor between these two features. Much of the deepest moisture and instability will remain offshore with the coastal low. The primary threat for heavy rainfall over land should focus closer to the cold core of the upper low from the OH Valley down through western NC and into north GA. While PW values will have lowered across this area, model guidance still indicates CAPE exceeding 1000 J/kg within a trough axis over the region. This localized axis of instability, coupled with a stationary convergence axis, will support the development of slow moving convective cells. Even with the reduction in deep moisture, locally heavy rainfall rates are likely. Given that at least some of this region will have compromised FFG and heightened hydrologic sensitivity from previous rainfall, some flash flood risk is expected to continue. Based on signals from the 00z REFS and HREF members, as well as the GFS and ECMWF, a small Slight risk has been introduced stretching from eastern TN into eastern KY and southern WV, where the focus for slow moving convection is expected to be greatest. ...Florida... A Marginal risk continues across south FL where above normal PWs and instability will continue to pose a localized flash flood risk. Chenard/Taylor Day 3 Valid 12Z Thu Sep 24 2026 - 12Z Fri Sep 25 2026 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NEW MEXICO AND THE TEXAS PANHANDLE... ...Southwest... The stronger mid level forcing and highest PW anomalies will shift northward out of NM and into Colorado and the central PLains on Thursday. Despite the loss of stronger large scale forcing, daytime destabilization over NM is actually forecast to increase in the wake of the exiting system compared to prior days. While PW values decrease some, they will remain above the climatological 75th percentile. With less concentrated forcing and somewhat reduced moisture, the overall areal coverage of heavy rainfall across NM should diminish relative to days 1 and 2. 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, a Slight risk is maintained for NM into the TX Panhandle. Locally significant flash flood impacts will remain possible. Isolated to scattered flash flooding will also be possible across portions of Arizona, southeast Utah, and Colorado as shortwave energy lifts northward across the region. ...Central Plains... The deep moisture plume will maximize over the Central Plains on Thursday, pushing PW values toward late September record levels. The mid to upper pattern coupled with a robust low level moisture transport axis supports a favorable setup for organized convection across portions of KS and NE, with backbuilding/training a possibility. There remains some uncertainty in the placement of the heaviest rainfall and eventually a Slight Risk might be needed. Chenard/Taylor Day 4 and Day 5 Valid 12Z Fri Sep 25 2026 - 12Z Sun Sep 27 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... Day 4...Multiple areas of interest for the end of the week into the weekend with a broad trough sweeping through the interior northwest with a shortwave ejection out of the Rockies, enhancing regional ascent within the Central High Plains into the Missouri River Valley and adjacent Corn Belt. Model spread continues to be relatively low with the handling of the two features leading to better than normal confidence at range for a period of heavy rain from widespread convection across the above area. Main axis of heavy rainfall will likely be over central and eastern NE into western IA and portions of northern KS and southern SD. Totals are currently between 1-2" on areal average, but signal with instability was sufficient for a broad MRGL risk placement maintained over the area with only minor adjustments from the previous forecast. Further south over the Southern High Plains, a weak shortwave over the Southern Rockies will advance east-northeast within the mean mid-level flow with enough diurnal instability to couple with the focused ascent pattern to cause a period of convective initiation across the Southern High Plains of NM into the TX Panhandle. Signals remains on the weaker side, but some of the areas anticipated to be impacted will still be in recovery from the barrage of heavy rain prospects the day prior, especially into NM. A broad MRGL remains in effect for the above area. Day 5...Main attention over the Midwest as the disturbance over the northern tier of the CONUS migrates eastward and leads to a carryover threat from the prior period. Models are less in agreement on the overall threat, so the MRGL risk in place over the Midwest into northern Missouri is of the lower end variety given some of the model discrepancy. A period to monitor as there's an equal chance of a higher risk and a removal pending the eventual convective evolution. ...Eastern New England... Day 4...Models remain consistent on the potential for a strong synoptic surface low off northern Mid Atlantic coast with heavy rain prospects in-of southeastern New England to perhaps as far south as the northern Mid Atlantic coastal areas. As of the latest ensemble probs and mean QPF distribution, the primary threat is still over southern New England with southeastern MA into RI as the areas of interest with 2+" totals plausible in the setup. The one positive in this evolution is a limited convective footprint leading to mainly heavy stratiform type precipitation coincident with a Nor'Easter that tends to offer some flash flood threat, but primarily leans more hydrological in terms of long term heavy rain leading to swollen rivers and streams with urban flooding due to poor drainage and consistent run off from prolonged rainfall. The MRGL risk inherited was only adjusted a bit from the previous issuance but maintaining the foothold over eastern MA into RI. Day 5...There's some discrepancy in the southward push of heavy rainfall (ML vs NWP outputs) as the upper pattern shows an occluding low with a drift to the west or southwest over the course of Saturday. Pending the upper level evolution, heavy rain prospects could be felt as far south as the NJ coast, perhaps leaking into portions of the Delmarva while still dealing more rainfall into LI and portions of southern New England. At this juncture, went with persistence in the forecast as higher probs remains situated over southern New England, but will have to monitor any trends backing more west to southwest with the occluding low which would bring heavier rain and perhaps a shift of the risk area further in that direction. Given the lack of relevant instability with the setup, a MRGL risk is still the most likely excessive outcome in the forecast, but positioning is where there could be some changes in the coming days, pending trends in guidance. 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 $$