832 FOUS30 KWBC 091550 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1150 AM EDT Mon Mar 9 2026 Day 1 Valid 12Z Mon Mar 09 2026 - 12Z Tue Mar 10 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE LOWER MISSISSIPPI VALLEY & SOUTHEAST... 16z update: A few thunderstorms have developed within the weak isentropic ascent plane along/ahead of a subtle shortwave between the base of the remarkably flat zonal flow from the Pacific Northwest across the entire northern U.S. and the flattening of the sub-tropical jet This compact shortwave along the KS/OK border will continue to shift east providing the DPVA for continued isentropic ascent through the remainder of the day 1 period. 12z Hi-Res CAMs remain on track for an enhanced swath of QPF across recently saturated grounds of MS/AL, that there was some consideration for a small Slight Risk area, but the north-south spread keeps confidence down to just maintain the broader Marginal Risk area. Gallina ~~~~Prior Discussion~~~~ Model agreement has started to increase QPF-wise and the present Marginal Risk area was adjusted to fit the broad pattern of potentially heavy rainfall advertised by the 09/00Z runs of both the HREF and REFS guidance. Precipitable water values approaching 1.75" return somewhat northward as low level flow begins to back and accelerate in the lower levels. It appears that enough moisture, instability, and effective bulk shear will be present near the lower level section of a frontal zone for hourly amounts to approach or even exceed 2 inches. Flash flood guidance has lowered due to heavy rainfall on Saturday and Saturday night/early Sunday morning to partially saturated soils. However, the mesoscale guidance signal for 3"+ is low enough at the present time to remain in the Marginal Risk category as any flash flooding impacts appear no better than isolated to widely scattered. Bann Day 2 Valid 12Z Tue Mar 10 2026 - 12Z Wed Mar 11 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL UNITED STATES FROM THE PLAINS TO THE SOUTHERN GREAT LAKES... Gulf moisture gets drawn northward over parts of the central U.S. from Texas into the Upper Mississippi Valley and southern Great Lakes region in response to circulation around an upper level low over the Southwest U.S.. This moisture will encounter a southward moving cold front from the Upper Midwest and an area of low pressure along the front over Kansas or Nebraska on Tuesday. This combination should result in convection being capable of producing some heavy rainfall rates that results in run off or flooding concern across the southern & central Plains and somewhere in the neighborhood of the Midwest and/or Ohio Valley. The better instability...and higher rainfall rates...look to be over the southern part of the outlook area given better instability and due to increasingly diffluent flow aloft as the Southwestern U.S. upper low approaches. Farther north...the concern for excessive rainfall comes from stronger synoptic scale forcing due to the approach of an amplifying trough in the northern stream. Based on increasing numerical guidance agreement from the 09/00Z runs...felt confident enough to separate the one Slight risk area from yesterday's Day 2 outlook into two Slight risk areas today. Some places within each Slight Risk received heavy to excessive rainfall in the past few days which has added to soil saturation across portions of the Midwest, the Ohio Valley and the Mid- Mississippi Valley. Not enough confidence yet to expand the area deeper into the Midwest/Ohio Valley due to the lack of any notable mid- level capping but the possibility remains. Bann Day 3 Valid 12Z Wed Mar 11 2026 - 12Z Thu Mar 12 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN MISSISSIPPI VALLEY/SOUTHEAST UNITED STATES AND PARTS OF THE COASTAL PACIFIC NORTHWEST... ...Southern US... Maintained a Marginal Risk area over portions of the southern states as an upper low propagates eastward on Wednesday. The upper level support for heavy rainfall should be waning with time as the upper low undergoes slow weakening and filling. Even so...enough low level moisture will be in place as mid-level lapse rates steepen and increases instability at the time of maximum heating. ...Pacific Northwest... Persistent on-shore flow of deep moisture into parts of coastal Washington and northern Oregon should result in occasional moderate rainfall...mainly in the west face of the coastal ranges. Amounts on the order of 2.5 inches to 3.5 inches in 24 hours is forecast which could result in isolated flooding ot run off problems in areas of poor drainage. Bann 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