Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
504 FOUS30 KWBC 021849 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 149 PM 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 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA... Mid-level flow will amplify dramatically across much of Texas ahead of an approaching mid-level wave near the Four Corners. Meanwhile at the surface, 850mb flow will increase dramatically into a small part of southeast Texas and adjacent areas of the northwestern Gulf and southwestern Louisiana. Ascent on the nose of this low-level flow will combined with modest increases in low- and mid-level instability to force mostly elevated deep convection initially across southeastern Texas around 03-06Z Thursday. These cells will will form in an environment favoring appreciable storm motions, although the development of convection relative to an east-west oriented warm frontal zone across the region will likely support areas of training. CAMs are depicting local 3+ inch rainfall totals in areas southwest of Houston that could be realized especially if storms can become rooted in the boundary layer and/or training becomes focused along a local corridor in the region. A Marginal Risk/5% area was added to the outlook to account for these model trends. This risk is likely to begin after 03Z Thursday and persist through 12Z and into the D3 forecast period. Cook Day 3 Valid 12Z Thu Dec 04 2025 - 12Z Fri Dec 05 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL GULF COAST... ...21Z Outlook Update... The previous discussion and forecast philosophy is still on track, with an extensive overrunning event expected to produce widespread areas of 2-4 inch rainfall totals especially across southern Louisiana. Urban/flood prone areas will be most susceptible to flash flooding in this regime. The notion that most convection will be elevated atop a cool stable layer precludes any introduction of Slight Risk probabilities for this outlook. Marginal Risk areas have been trimmed/confined southward to locations expected to experience the highest rainfall totals. Cook ...Previous Discussion... 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