FOUS30 KWBC 260814 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 414 AM EDT Mon Oct 26 2026 Day 1 Valid 12Z Mon Oct 26 2026 - 12Z Tue Oct 27 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL AND SOUTHERN HIGH PLAINS AND SOUTHEAST FLORIDA... ...Central and Southern High Plains... An upper low/trough will push across the north-Central U.S. today accompanied by a surface low pressure system with a trailing cold front extending back across the central Plains and a dryline extending across the southern High Plains. Scattered showers and thunderstorms are expected along this boundary, and additional storms are expected to develop this afternoon and evening as upper level dynamics come into play. A southwesterly upper level jet ahead of the system will place portions of the central and southern Plains in the favorable right entrance region, and an upper level shortwave is expected to move north into the region. A moist (PWATs 1.25-1.5 inches) and unstable (MUCAPE 500-1500 J/kg) air mass will be in place across the central and southern High Plains, which should support some strong/deep convection with heavy rainfall rates. The HREF and REFS show modest probabilities (~30%) of rainfall rates exceeding 1 inch per hour from West Texas to the Texas Panhandle, but low probabilities (less than 20%) of rainfall rates exceeding 2 inches per hour. It will be difficult for these rates to exceed hourly FFGs for much of the area, but they could exceed FFGs in areas where soils are saturated from recent heavy rainfall from eastern New Mexico into the Texas Panhandle. Fortunately, the heaviest rainfall totals (1-2 inches, locally higher up to 3-4 inches) are expected to be displaced to the east of recent heavy rains, which will help limit the threat of flash flooding. A Marginal Risk of excessive rainfall is in effect for much of the central and southern High Plains where locally heavy rainfall will be possible with storms this afternoon and evening, and isolated instances of flash flooding may be possible. Further north, widespread precipitation is expected over the northern Plains in the vicinity of the surface low pressure system, but with little instability, rainfall rates should remain moderate at best. Model guidance is showing rainfall rates and totals remaining well below current FFGs for the area, so there will be little to no flash flood risk for this area. ...Southeast Florida... A mid/upper level low will stall southeast of the Florida Peninsula, resulting in northeasterly onshore flow along the Florida East Coast. Moisture wrapping around the low circulation will surge across Southeast Florida, raising PWATs to 1.5-2 inches between Palm Beach and the Florida Keys. The best instability will also be focused along the Southeast Florida coast and over the adjacent Atlantic waters where MUCAPE will likely reach 700-1000 J/kg this afternoon and evening. This environment will support scattered showers and storms with locally heavy rainfall that will originate over the Atlantic then migrate over the Southeast Florida coast. Model guidance has been showing a southward trend with the low, which may result in the heaviest rainfall remaining south of Florida with only isolated to widely scattered showers in Southeast Florida. With any showers that do move onshore, convergence along the coast will focus the heaviest rainfall totals over the I-95 urban corridor, an area that has received several rounds of locally heavy rainfall over the past couple of days. Given recent heavy rainfall in this area and the sensitivities of the urban areas, isolated instances of flash flooding may be possible with heavier showers and storms, so there is a Marginal Risk of excessive rainfall for Southeast Florida. Dolan Day 2 Valid 12Z Tue Oct 27 2026 - 12Z Wed Oct 28 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHEAST FLORIDA... ...Southeast Florida... Low pressure will gradually shift north over the Bahamas on Tuesday, resulting on another day of northeasterly onshore flow and increasing moisture across Southeast Florida. PWATs will increase to around 2 inches by Tuesday afternoon and evening, but instability may be limited. Global models are showing MUCAPE values 500-900 J/kg along the immediate Southeast Florida Coast, with little to no instability across the rest of the peninsula. Scattered showers and storms are expected to form over the Atlantic, some of which should be able to make it onshore in Southeast Florida. With high PWATs and modest instability, locally heavy rainfall may be possible in some showers and storms. Given recent heavy rainfall in Southeast Florida and the sensitivity of urban areas, isolated instances of flash flooding may be possible along the I-95 urban corridor of Southeast Florida and there is a Marginal Risk of excessive rainfall. Dolan Day 3 Valid 12Z Wed Oct 28 2026 - 12Z Thu Oct 29 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR EAST-CENTRAL AND SOUTHEAST FLORIDA... A mid/upper low will continue moving north of the Bahamas off the Florida East Coast. The stream of moisture on the northern side of the low circulation will shift north along the Florida coast, with the highest PWATs (around 2 inches) focused between Cape Canaveral and Fort Lauderdale. Instability will increase as shortwave energy moves across Central and South Florida, which could support increased precipitation coverage, but there is some uncertainty in how much instability will increase. The ECMWF and EC-AIFS are much more aggressive, increasing MUCAPE to 1000-1500 J/kg, while the GFS and AI-GFS only increase MUCAPE to 500-700 J/kg. If showers and storms can tap into the elevated instability, there will be sufficient moisture to support locally heavy rainfall rates. The heaviest rainfall totals will once again focus along the coast, impacting the I-95 urban corridor. Given recent heavy rainfall along the Florida East Coast and the sensitivities of the urban areas, isolated instances of flash flooding may be possible and there is a Marginal Risk of excessive rainfall for portions of east-Central and Southeast Florida. Dolan Day 4 and Day 5 Valid 12Z Thu Oct 29 2026 - 12Z Sat Oct 31 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTH-CENTRAL TEXAS ON THURSDAY AND CENTRAL ARIZONA ON FRIDAY... ..Texas into New Mexico... A Slight risk has been maintained on day 4 (Thu) across portions of TX, stretching from the Stockton Plateau through parts of the western Hill Country and into south-central TX. Overall, not much change was needed to the inherited risk area. Large scale forcing for ascent will be driven in part by a strong southern stream upper jet providing divergence aloft. Embedded shortwave energy will also eject out of the East Pacific within the deep southwesterly flow aloft, with some potential moisture and mid level vorticity contribution from what is currently tropical cyclone Vance. Mid to upper level moisture sourced from the East Pacific will combine with a strong southeasterly low level jet bringing moisture out of the Gulf. This combination will drive PW values well above the climatological 90th percentile for late October. The environmental ingredients in place will support an organized heavy rainfall event. As expected at a day 4 lead time, exact spatial and temporal details will change some as the event nears. However, models continue to converge on a solution, and confidence in a flash flood event continues to increase. The last few runs of the ECMWF, AIFS, AIGFS and GFS are all clustered fairly well with a max rainfall axis over south-central TX. The latest model consensus is for 2-4" of rain, but with some backbuilding/training probable the potential for at least localized swaths of 6"+ seems in play. We will continue to closely monitor trends, as locally significant flood impacts are possible with this event. Will just carry a marginal risk into day 5. The risk of flash flooding over TX will persist as the features responsible for the day 4 risk shift northward. However the signal becomes a bit more muted by day 5 and uncertainty on the details become higher. So will stick with a Marginal for now, but could eventually need an embedded Slight risk. ...Arizona... Synoptic scale model agreement is above average for a day 5 forecast with broad troughing progressing into the western United States. While some timing uncertainty persists regarding individual embedded shortwaves, the overall environmental ingredients are coming together to support a robust convective and heavy rainfall threat centered over AZ on Friday. Dynamic forcing will be impressive, featuring a very strong southern stream upper level jet that will place AZ within its favored left exit region, promoting strong upper level divergence. Mid level shortwave energy ejecting east will interact with a rather strong southerly low level jet resulting in impressive low level moisture transport and PWs across the region. This strong low level flow should help organize and sustain some training/backbuilding convective cells. While thermodynamic details carry inherent uncertainty at this lead time, current model guidance suggests that corridors of 1000+ J/kg of CAPE are probable. Much of the region has been anomalously west of late, which has notably increased the hydrologic sensitivity across the area. While the exact placement and magnitude of the heaviest rainfall axis remains subject to adjustments as we get closer, confidence is high enough in an isolated to scattered flash flood threat to warrant a Slight risk. Chenard 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 $$