478 FOUS30 KWBC 070830 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 330 AM EST Sat Mar 7 2026 Day 1 Valid 12Z Sat Mar 07 2026 - 12Z Sun Mar 08 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY... Maintained the Slight risk area from the Southern Plains into the Lower Mississippi Valley and the Upper Texas coast...with an expansion that effectively brought the Slight Risk area to the Upper Texas coast and nearby Louisiana given the 07/00Z HREF and RRFS probabilities for 24 hour rainfall 2-inch and 3-inch thresholds. There were even a few neighborhood probabilities exceeding 10 percent at the 5 inch threshold. Of course the actual extent and magnitude of the flash flood risk remains a bit uncertain relating to how quickly activity propagates off to the south and east. Some guidance supports a rather quick southward propagation of convection, which could keep the flash flood risk more isolated in nature. The HREF guidance tended to side with the faster solution and the RRFS was slower and was more aggressive with its probabilities for 1- and 2-inch per hour rates. At this point...tended to favor the HREF guidance and associated models although can not entirely rule out the faster solutions. A Marginal risk surrounding the Slight Risk area extended north and east as far as western New York. There should be plenty of moisture advectiving northward along this corridor, with as much as 500-1000 j/kg. Thus while areal averaged rainfall is not that impressive, there will be an opportunity for locally heavy rates. With saturated conditions over portions of the Ohio Valley, and some snow pack and frozen ground over New York...any enhanced rainfall rates could be enough to result in isolated/locally excess runoff and minor flood concerns. Bann Day 2 Valid 12Z Sun Mar 08 2026 - 12Z Mon Mar 09 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE GULF COAST REGION... Deep moisture...instability and the risk of excessive rainfall should be confined to a shrinking area south of an approaching cold front on Sunday. Model guidance showed a corresponding decrease in QPF and spaghetti plots from the SREF and the GEFS maintaining a few members kept neighborhood probabilities of 1 inch or greater confined from Louisiana into Georgia with greatest clustering from southern Mississippi into central and southern Alabama with QPF spaghetti plots showing few members at 2 inch amounts in 24 hours from either the SREF ir GEFS. In this portion of the Marginal risk...there was good agreement between WPC and the CSU machine learning first-guess ERO. The WPC Marginal Risk area extended west along the Louisiana and Upper Texas coast if deference to the HREF and RRFS runs which lingered some 1+ in per hour rainfall along the coast and even some 2 inch per 6 hour lingering through at least 08/18Z. In addition...Gulf moisture starts to return northward over southwestern Texas later in the period...also supporting a westward expansion. Bann Day 3 Valid 12Z Mon Mar 09 2026 - 12Z Tue Mar 10 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHEAST UNITED STATES... The front which had been moving from west to east in the Day 1 and Day 2 period will slow its forward motion and become oriented along a west to east axis on Monday and the start to inch northward Monday afternoon and Monday night. There is a wide range of solutions in where convection could fire along that boundary which limits confidence. However...confidence is higher in the occurrence of showers and thunderstorms occurring rather than details of where that could happen given precipitable water values approaching 1.75 inches ready to to be lifted isentropically above the front as low level flow becomes southerly. The area should become better focused in subsequent outlooks. 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