FOUS30 KWBC 010817 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 317 AM EST Sun Nov 1 2026 Day 1 Valid 12Z Sun Nov 01 2026 - 12Z Mon Nov 02 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE FOUR CORNERS REGION... ...Southwest... Few changes were needed to the ongoing risk areas across the Southwest. An anomalously strong atmospheric river is driving a plume of moisture and heavy rain into the Southwest from the Pacific. PWATs remain 4-6 sigma above normal for this time of year, with values between 3/4 inch and 1.5 inches. Further, essentially all of the Southwest has been in a very wet period, so this highly anomalous event is at the tail end of a long stretch of wet weather that has left the soils saturated already in most areas. Thus, all of today's rains will be converting to runoff, leading to numerous instances of flash flooding. Dry washes, arroyos, slot canyons, and burn scars will remain the most susceptible areas. The Moderate Risk for portions of Arizona into southern Utah remains largely unchanged as far as the area impacted, as for much of it, the risk area is tied to the terrain. That said, the latest guidance shows rainfall amounts have a 70-90% chance of exceeding the 100 year ARI. This is generally the threshold for considering a High Risk area, which remains possible. Ultimately, the rather fast forward speed of the plume of moisture, as well as a lack of instability will be two limiting factors which for this update will keep these areas shy of the High Risk threshold. Nonetheless, with the aforementioned highly anomalous moisture and strong upper level forcing from a pair of jet streaks and a vigorous trough following behind the rain, expect a widespread 3-5 inches of rain into portions of the Mogollon Rim, particularly areas most perpendicular to the southwesterly flow and in the core of the moisture plume. A higher-end Moderate risk is in effect for these areas, mainly north and east of Phoenix. Into Utah, the threat for flash flooding turns to the typical slot canyons and steep, rocky terrain, as well as numerous large burn scars that dot the southern Utah landscape. Each of these areas could see more severe flooding, despite not being quite in the core of the heaviest rainfall. A second Moderate Risk is in effect for the San Juans of southwest Colorado. Here too, due to a very high likelihood of exceeding 100-year ARIs, a higher-end Moderate Risk was introduced. For this area, the very recent high-impact flash flooding event from last week is top of the mind. Expect essentially a repeat, albeit with slightly lower snow levels. This might nominally mitigate any flooding concerns in river basins that drain the San Juans. It's likely that spot areas will see more total rainfall here than along the Mogollon Rim, due to steeper topography more efficiently wringing out the abundant moisture. ...South Dakota... A small, low-end, and low confidence Marginal Risk was shifted north and west with this update. This will be remnant moisture from the major flooding event occurring over the Southwest, generally targeted at the post-midnight period tonight. Soils are around normal for moisture levels for this time of year, and instability will be nominal over this otherwise generally tough to flood area. Training cells are possible, which could lead to an isolated flash flooding risk. ...Southeast... A westerly wave that has been traversing the Gulf will move into the Florida Peninsula today. Abundant Gulf moisture will converge over the Peninsula as a weak upper level trough moves over the state, further increasing atmospheric lift. A widespread 1-3 inches of rain is expected over much of the Peninsula. This will be the latest in a string of days that has caused areas of heavy rainfall over the east coast. With heavier and more widespread rain expected today, areas where soils are already saturated from previous days remain in a Slight Risk, which generally covers the I-95 corridor from the Georgia line south through Miami. Some instability and an amazing history of isolated cells producing rains of 3+ inches per hour for 6+ hours have led to incredible rainfall totals in very isolated spots. This may potentially continue over the lower Mississippi Valley today. The Marginal Risk remains in place with some small expansions. Wegman Day 2 Valid 12Z Mon Nov 02 2026 - 12Z Tue Nov 03 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE EAST COAST OF FLORIDA... ...Florida... Continued easterly flow of deep tropical moisture from the Atlantic will allow for frictional convergence along the east coast of Florida Monday and into Monday night. Heavier totals are expected during the day Monday and across southeast Florida, where instability will be a bit higher, with better moisture. The highly urbanized I-95 corridor will also support widely scattered instances of flash flooding where nearly stationary storms can persist the longest. The inherited Slight Risk area was left largely unchanged. Rain should be lighter across the west coast, so the threat level will be much lower there. ...Midwest/Plains... The large Marginal Risk area in place across much of the Midwest and Plains was also left largely unchanged with this update. The greatest flooding threat within the Marginal will be for southern areas from Texas through Missouri, where greater instability and terrain concerns around the Ozarks should work to raise the flooding threat locally higher. Nonetheless the instability will remain near the lowest thresholds supporting convection. The nature and coverage of that convection will determine how high the flooding threat gets. Since those parameters remain uncertain, the Marginal remains in place. Further north across the northern Plains to the upper Lakes, there should be very little to no instability. However, steady rainfall will persist for far longer in this area, resulting in more widespread higher rainfall totals, but over a much longer period of time. Thus, the Marginal also remains in place there with few changes. A small trim on the eastern side of the risk area, to remove much of southeastern Wisconsin was made due to slower forward speed expected of the rainfall shield. Wegman Day 3 Valid 12Z Tue Nov 03 2026 - 12Z Wed Nov 04 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE LOWER AND MID-MISSISSIPPI VALLEY AS WELL AS THE EAST COAST OF FLORIDA... ...East Coast of Florida... Lingering moisture over much of Florida as well as some daytime heating will once again lead to periods of rain across the state on Tuesday. Fortunately, organization, coverage, and intensity of rain will all be lesser on Tuesday as compared with previous days. Thus, the Marginal Risk is essentially covering the hardest hit areas of Florida where renewed convection on Tuesday may cause renewed isolated flash flooding. ...Lower and Mid-Mississippi Valley... A line of storms will track east across the lower and mid- Mississippi Valley on Tuesday. The forward speed of those storms will be slow enough that isolated flash flooding could result, especially in areas where cell mergers lead to longer periods of heavy rain. Antecedent very dry soils and high FFGs should limit any flash flooding to isolated instances, but that will need to be reevaluated as Tuesday approaches for a possible Slight, especially into the Ozarks due to terrain worsening any flash flooding. Further north towards Illinois, the flash flooding threat will be much more isolated and conditional, with the Marginal Risk generally covering urban and low-lying flood-prone areas. Wegman Day 4 and Day 5 Valid 12Z Wed Nov 04 2026 - 12Z Fri Nov 06 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE TENNESSEE AND LOWER OH VALLEYS TO THE SOUTHERN APPALACHIANS (DAY 4)... While differences in the details remain, the latest model runs are showing better agreement with the evolution of an amplified upper trough and its associated frontal boundary that are expected to move east of the Mississippi Valley midweek. This system will continue to produce widespread precipitation, with the threat for areas of heavy rain and possible flash flooding continuing into early Thursday. Deep moisture (1.50-1.75+ inches) coinciding with strong southerly flow is expected to interact with an area of strong ascent, afforded in part by right-entrace region upper jet forcing, to produce widespread moderate to heavy rain (accums 1-2+ inches) across the Tennessee into the lower Ohio valleys and the southern Appalachians. While some models suggest a Slight Risk may be necessary at some point, dry soils (high FFGs) and remaining forecast uncertainty support maintaining the Marginal Risk at least for now. Pereira 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 $$