FOUS30 KWBC 260058 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 858 PM EDT Fri Sep 25 2026 Day 1 Valid 01Z Sat Sep 26 2026 - 12Z Sat Sep 26 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN HIGH PLAINS AND CENTRAL PLAINS... 0100Z Update: Based on the latest observational trends, have split the previous ERO's Slight Risk area into 2: a more expanded area across central and eastern NM into west TX, with the other one across central KS and eastern NE. In terms of the guidance, the recent HRRR runs have not done a good job capturing the convection across NM (in particular), especially with lingering shortwave energy behind the main mid level vort/shortwave trough. The Slight Risk areas align well with the enhanced QPF exceedance probabilities per both the HREF and REFS. ...Previous Discussion... ...Southwest to the Central Rockies and Southern High Plains... Expect some of the overnight activity impacting the region to remain ongoing beyond 12Z, with some potential for additional flooding concerns across portions of eastern New Mexico and the Texas Panhandle into the mid to late morning. Additional heavy rains should be short-lived however, with the consensus of the CAMs showing storms diminishing by late morning as the associated shortwave energy and deeper plume of moisture lift out to the northeast. However, given the antecedent soil conditions and some high probabilities in both the HREF and REFS for additional amounts of 1-2 inches, maintained a Slight extending from southeastern New Mexico to the southern Panhandle Region. The Slight Risk was also extended south into parts of West Texas, where activity later in the day is expected to produce some very localized heavy amounts (1-2 inches) including areas where 3-hr FFGs are under an inch. Back to the north and west, a mid-to-upper level shortwave will lift out of the Southwest, encouraging afternoon and evening showers and thunderstorms, especially across portions of eastern Arizona, southeastern Utah, and Colorado. The HREF and REFS generally agree that the greater potential for localized heavier amounts will center from southeastern Utah into southwestern Colorado. ...Central Plains... Shortwave energy and plenty of moisture emanating from the Southwest will spread across the region later today into the evening. While instability will remain weak and soil conditions less sensitive, deep saturation though the air column will support efficient rainfall and some portions of the area may see amounts high enough to raise at least some isolated runoff concerns. Both the HREF and REFS indicate that areas near the central Kansas- Nebraska border northeast to the northern Nebraska-Iowa border could see amounts over 2 inches. Pereira Day 2 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... ...Northern Mid-Atlantic Coast into Southern New England... Guidance is trending towards a deeper cyclone which retrogrades toward the coastline on Day 2. Accordingly, QPF has trended upwards generally along the I-95 Corridor from Philadelphia to Boston. Compared with the previous forecast, the Slight Risk area was expanded southwestward into southern New Jersey where model consensus shows widespread amounts of 1-3" during the Day 2 period. ...Southern to Central Plains... A Slight Risk was introduced to portions of eastern Nebraska and central Iowa where a corridor of cell-training is possible late Day 2 along a NW-SE oriented stationary front. Both the HREF and RRFS suite are in fairly good agreement for 24 hr QPF from this activity to exceed 2", which could support scattered flash flooding as this rainfall overlaps with heavy rainfall from the previous day. The Marginal Risk was also expanded further south where CAMS signal the potential for locally heavy rainfall near sensitive soil, although coverage of storms is expected to be lower than previous days. Asherman ...Previous Discussion... ...Northern Mid-Atlantic Coast into Southern New England... As a powerful nor'easter continues to approach and then stall east of New Jersey and south of Long Island, the potential for heavy rainfall is likely to increases substantially along portions of the northern Mid-Altantic to southern New England coasts. The system will bring a generally prevailing southeast to easterly flow, supporting a substantial influx of moisture into parts of southern New England, southern New York, and New Jersey. Increasing hydrologic concerns are expected. In addition to an increasing threat for flooding in urbanized and poor drainage areas, this heavy rain may also exacerbate ongoing coastal flooding. The Slight Risk highlights the areas where the general model consensus shows widespread amounts of 1-3 inches during the period. ...Central Plains to the Upper Mississippi Valley... Rainfall developing late in the Day 1 period, may continue into late Saturday morning across parts of Iowa and southern Minnesota. Expect a diminishing threat for heavy to excessive rain by late morning, followed a potential return later in the day centered farther to the southwest. While confidence is limited, there remains some signal in the guidance for storms developing back across across parts of the central Plains along a strengthening low level jet and axis of increasing instability and moisture. ...West Texas... Weak mid-level energy interacting with an uptick in low level moisture may produce some additional localized heavy amounts, impacting the more sensitive areas of West Texas around the Davis Mountains and Stockton Plateau. Therefore, a small Marginal Risk was added. Pereira Day 3 Valid 12Z Sun Sep 27 2026 - 12Z Mon Sep 28 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE NORTHEAST... ...2030 Update... As highlighted on Day 2, the nor'easter is trending towards a slower track overall. Thus, heavy rainfall is expected to linger overhead, leading to an additional 1-2" of rainfall over much of the same area. As this overlaps with much of the rain from Day 2, the Slight Risk was adjusted southwestward to encompass a similar area. Asherman ...Previous Discussion... ...Northeast... The general consensus of the models shows a powerful nor'easter beginning to weaken as it lingers in the vicinity of the northern Mid-Atlantic coast. How far inland, if at all, the storm drifts will help dictate how far beyond the coastal regions its associated heavy rains will reach. For now, maintained a Slight Risk over eastern Massachusetts, where confidence in additional heavy amounts is greater regardless of the track. ...Southwest... Increasing southwesterly flow ahead of an amplifying trough digging south across California will begin to tap moisture and mid- to-upper level energy, supporting an increase in shower and thunderstorm activity and the potential for localized areas of flash flooding from Southern California into the Southwest. Pereira Day 4 and Day 5 Valid 12Z Mon Sep 28 2026 - 12Z Wed Sep 30 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF THE SOUTHWEST AND FOUR CORNERS REGION THAT EXPANDS INTO THE SOUTHERN AND CENTRAL PLAINS ON TUESDAY... 2000Z Update: The biggest change from this morning's ERO was made to the Day 5 Slight Risk. Given the guidance trends, led by several AI members, the eventual absorption of POLO's remnants into an amplifying Southwest U.S. upper trough have led to a slower and wetter trend across the Southwest-Four Corners and into the High PLains Tuesday into Wednesday. The global ensemble guidance, particularly the ECMWF (ECENS), all show a notable uptick in QPF exceedance probabilities from the 00Z guidance suite. Hurley Previous discussion below.. ...Southwest US... Tropical moisture from Odalys and Polo will be pulled northward into the Desert Southwest and when coupled with the afternoon diurnal instability max will trigger scattered to widespread convection across the region. An interaction between the eventual closed upper reflection (ULL) over California and what will be Polo as it begins moving northward towards Baja over the course of the weekend into early next week. The ensemble means for Monday into early Tuesday continue to 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 upper low swinging into the region. PW anomalies during this period will be between 2-3.5 standard deviations above seasonal normal for late September. A Slight Risk for excessive rainfall and flash flooding has been maintained. ...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 Monday. A broad Marginal Risk remains in effect for the Dakotas/Minnesota down into the Central Plains as a continued advection of elevated PWs streams poleward ahead of a broad upper trough/low reflection out west. Remnant energy from what is currently Odalys will get pulled northeastward out of the Pacific prior to the period reaching the Northern and Central Plains Monday into early Tuesday leading to quite a larger coverage of convection over the above area. Areal coverage of convection will increase Tuesday as there will be a stronger PW surge with the remnant energy from Odalys. 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. A broad Marginal is in effect for Monday and then a Slight Risk for Tuesday from Texas to southern Iowa. New England... Eastern Massachuesetts continues to be the focus for the highest QPF on Monday as the coastal low begins to drift away from the region. 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. 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. Campbell 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 $$