FOUS30 KWBC 221950 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 350 PM EDT Wed Apr 22 2026 Day 1 Valid 16Z Wed Apr 22 2026 - 12Z Thu Apr 23 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST TEXAS AND SOUTHWESTERN LOUISIANA... 16Z update...There continues to be a modest western trend with the convection across eastern Texas toward east-central Texas. The latest CAMs depicted hourly rates up to 1.25 inches/hr near and outside of the inherited Northwest periphery of the Marginal for several hours along with rates up to 3-4 inches/hrs between Victoria and Corpus Christi metros beyond the southwest periphery. As such the western and southern portion of the Marginal Risk boundary was modestly expanded to cover these locations. Campbell Steady southerly flow off the Gulf will continue to advect a plume of Gulf moisture northward across the Marginal Risk area. The flow will not be much to write home about, generally between 5-15 kts at 850 mb. In addition to the rather weak advection the upper levels will become decidedly less favorable for widespread rain across the region as ridging and associated subsidence build in. Thus, there is good agreement that any heavy rains will be disorganized and widely scattered in nature, as compared with the rains further west across Texas the past couple days. Urban concerns remain a driving factor for maintaining the Marginal. Guidance has shifted a bit to the south and west with the threat for a few cells capable of heavy rains. This resulted in the Marginal being shifted west along I-10, over an area that has been hard-hit with heavy rains in recent days. Meanwhile portions of the Piney Woods of far eastern Texas were removed as guidance has suggested any more organized cells will be confined to around the I-10 corridor. The westward shift resulted in small trimming in south-central Louisiana as well. Should there be greater than expected organization from Houston west along I-10, a targeted Slight Risk may need to be considered due to the saturated soils from yesterday's and prior days' rainfall. Wegman Day 2 Valid 12Z Thu Apr 23 2026 - 12Z Fri Apr 24 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM NORTHEASTERN OKLAHOMA THROUGH THE ARROWHEAD OF MINNESOTA... 21Z update... General setup described below still expected with the QPF footprint primarily focusing from eastern Oklahoma to the Minnesota Arrowhead. Consensus trended a bit drier across central Minnesota down to eastern Nebraska which will reduce the risk for reaching/exceeding flash flood guidance. The back edge of the Marginal Risk was adjusted to the east about 1-2 tiers of counties. Campbell A strong but slow-moving low will lurk north of North Dakota in southern Manitoba Thursday and Thursday night. The leading cold front associated with this low has consequently also slowed down its forward speed in much of the guidance. The result has been an increase in forecasted rainfall that will occur ahead of that cold front as it uplifts a moist and unstable air mass with a 30-50 kt LLJ. Since the front has slowed down, there's more time for moisture to advect north with the LLJ into Iowa, Minnesota, and Wisconsin. While portions of Minnesota and Wisconsin were hard hit with heavy rains last week, there has been sufficient time for the soils to dry out some and for the rivers to drain that rainfall. Thus, conditions are at or even a bit below normal for soil moisture. Despite that, potential for fast-moving but training storms could still result in some "stripes" of heavier rainfall that could cause isolated flash flooding, especially if urban centers such as the Twin Cities are included. The inherited Marginal was shifted west but expanded well to the north to include some of these more vulnerable areas of Minnesota and Wisconsin with this update. The good news is further south across Kansas and Missouri, the forcing now doesn't look like it will be quite as strong as the forecast looked 24 hours ago. Thus, while a Slight Risk upgrade was considered for along the KS/MO border south of Kansas City yesterday, confidence has increased that the current Marginal Risk for that area will suffice. Wegman Day 3 Valid 12Z Fri Apr 24 2026 - 12Z Sat Apr 25 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDDLE AND LOWER MISSISSIPPI VALLEY... 21Z update... Minor adjustments were made to the northern boundary of the Marginal Risk, reducing the placement by 1-2 tiers of counties. This reflects consensus for the QPF footprint and the modest southward trend across portions of Missouri, Illinois and Indiana. The highest amounts are expected to focus along the Mississippi River Valley of southeast Missouri, western Kentucky, western Tennessee and northeast Arkansas. Campbell A slow-moving cold front will run into increasing Gulf moisture and instability across the Middle and Lower Mississippi Valley on Friday. Clusters of showers and thunderstorms will develop along the front in northwestern portions of the Marginal across Arkansas and southeastern Missouri with peak heating Friday afternoon. Those storms will gradually progress south and east, with the potential for localized training of stronger cells embedded within these clusters of storms. Almost all of the Marginal Risk area is in an area with extremely dry soils. Depending on the soil type, this could make some of the soils (clays) start out the rainfall event in a very hydrophobic state, which would support rapid runoff. However, for most, all but the heaviest rains will be very beneficial for this parched area of the country. Urban areas, areas with hydrophobic soils, and poor-drainage areas will be at the greatest risk for isolated instances of flash flooding. Smaller drainage basins and the portions of Arkansas with the Ozarks topographically confining any potential runoff to steep valleys will also be at a locally higher risk for flash flooding. Wegman 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