Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
228 FOUS30 KWBC 021540 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1040 AM EST Tue Dec 2 2025 Day 1 Valid 16Z Tue Dec 02 2025 - 12Z Wed Dec 03 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Otto Day 2 Valid 12Z Wed Dec 03 2025 - 12Z Thu Dec 04 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Thu Dec 04 2025 - 12Z Fri Dec 05 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE MISSISSIPPI DELTA AND THE CENTRAL GULF COAST... A strong warm advection regime of deep Gulf moisture will have developed along the central Gulf Coast on Thursday morning. A polar high over the Midwest will suppress the northward extent of the precipitation. A unidirectional WSW flow regime will set up over all of the Southeastern U.S. with a 170 kt jet streak aligned roughly along the Ohio Valley, with a longwave positively tilted trough over the Southwest. Weak impulses of shortwave energy will eject out of the trough and along the jet streak, locally enhancing any convection. The primary forcing for precipitation however will be overrunning, as warm Gulf air tries to lift over the much colder air mass over much of the eastern U.S. The combination of unidirectional flow at all levels out of the WSW, overrunning of anomalously moist air, and some, albeit far from impressive instability will support training thunderstorms capable of 2 inch per hour rates. These storms will align in lines parallel to one another. Those lines will be slow moving, supporting multiple rounds of training storms over much of southern/southeastern Louisiana and into coastal Mississippi. NASA Sport imagery shows soils in much of southern Louisiana to be bone dry, with moisture levels at single digit percentages as compared with climatology. Thus, much of the rainfall, especially in areas where it remains light, will be beneficial for these areas. The Drought Monitor also shows this area to be in D2/Moderate Drought. Thus, it will take some time for enough rain to fall to support flash flooding. However, guidance suggests the New Orleans metro to be in the bullseye with the greatest chances for prolonged heavy rain. Given all of the above, the area remains in a Marginal Risk, but the area in and around New Orleans to the urbanized Mississippi Gulf Coast will be evaluated for the need for a Slight Risk upgrade with future updates. 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