FOUS30 KWBC 150816 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 316 AM EST Sun Nov 15 2026 Day 1 Valid 12Z Sun Nov 15 2026 - 12Z Mon Nov 16 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF COASTAL TEXAS ON SUNDAY... The overall synoptic set-up remains fairly well handled by the 15/00Z suite of numerical guidance. Even so...some questions remain concerning whether enough rain falls on land areas to result in flooding concerns. Some guidance had backed away from that idea and kept heaviest rainfall completely over the Gulf while the ensembles still suggested some flooding concerns persist. To account for the range of possibilities...the Marginal was maintained with only some trimming of inland territory. The expansion of the Slight and Marginal risk areas still looks good without much change needed. An upper trough responsible for storms over north-central Texas overnight prior to the start of the Day 1 period will continue to dig southeastward toward the Gulf Coast. Convection is expected to reignite later this afernoon as instability builds over the area. The heaviest rainfall should wrap up by midnight Monday. The 15/00Z guidance has shifted the inland axis of greatest PF axis to between Houston and Corpus Christie and nudged a bit closer to the coast. 24 hr 5" 40km RRFS exceedance probabilities are between 20-60%, while 3" EAS probabilities are between 10-25%. Bann Day 2 Valid 12Z Mon Nov 16 2026 - 12Z Tue Nov 17 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 3 Valid 12Z Tue Nov 17 2026 - 12Z Wed Nov 18 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE FLORIDA EAST COAST AND THE SOUTHWEST U.S.... West... An upper-trough and accompanying cold front will progress eastward from the West Coast into the Interior West on Tuesday. Increasing moisture along and with the frontal passage will lead to scattered showers and thunderstorms at lower elevations across the Desert Southwest given precipitable water values on the order of 1 inch in the Lower Deserts. The fact that the system being progressive is one factor against the potential for floooding. Despite that...a Marginal Risk was introduced mainly in the west facing terrain of northern Arizona...generally at or below 6500 feet (with precipitation more likely to fall as snow at elevations above 7000 ft). Present indications are that hourly rainfall rates of 1.25 inches are possible whenever/wherever cells can align or merge or mesocyclones manage to form. Rainfall this intense could lead to issues in dry washes/arroyos or burn scars. Eastern Florida... Surface high pressure parked over the central Appalachians will keep persistent eastly low-level flow in place across much of the eastern Florida peninsula on Tuesday into early Wednesday morning from the Geogia line to Lake Okeechobee (in broad geographic terms), Precipitable water values of 1.25-1.5" are forecast, and the low- level flow should bring instability off the warmer than average Gulf Stream. Effective bulk shear should be sufficient for organized convection. Hourly rain amounts as high as 1.75" would be possible wherever short, training bands manage to materialize. Maintained the Marginal Risk area introduced on Saturday for portions of Eastern Florida with few changes needed. Bann Day 4 and Day 5 Valid 12Z Wed Nov 18 2026 - 12Z Fri Nov 20 2026 ...THERE IS SLIGHT RISK OF EXCESSIVE RAINFALL FOR CENTRAL COASTAL CALIFORNIA WEDNESDAY... ...California... An upper-trough is expected to dig southward along the West Coast and move inland across the western U.S. early this week. Additional upper-energy upstream will help to reinforce the upper-trough along the West Coast by day 4/Wednesday and day 5/Thursday, with a secondary plume of Pacific moisture/Atmospheric River (AR) accompanying the associated surface system/Pacific front. The forecast strength of the AR has trended up over the last 24 hours, now rated as Moderate through central coastal California as IVT values reach and maintain values of 500-750 KG/ms through the day 4/Wednesday period. The deterministic guidance continues to maintain areal average rainfall totals in the 1-2" range and locally higher totals of 3-5", with much of this rain likely falling in a 3-6 hour period with the passage of the Pacific front. This would be more than sufficient for scattered flooding concerns, and thus have introduced a Slight Risk along the central Coastal Ranges and through the Bay Area. Additional rainfall is expected further inland through the central Valley and along the foothills of the Sierra. However, despite the influx of warmer, moist Pacific air, colder air will still be in place overall given the upper-troughing already over the western U.S., limiting snow- level rises to around 4000 feet. This should keep the flooding threat lower along the foothills as the heaviest precipitation occurs as snow into the higher elevations of the Sierra. Heavy rainfall will continue into the day 5/Thursday period through portions of central California while spreading into southern California. Uncertainty with where the heaviest rainfall will occur is a bit higher compared to Wednesday as the deterministic guidance begins to disagree more on the orientation/progression of the Pacific front/AR, particularly into southern California along the Transverse Ranges and southward through the LA basin. Therefore, have opted to only introduce a Marginal Risk along the central/southern California coast and inland along the southern extent of the Sierra for now. However, given that the deterministic guidance remains bullish into this timeframe with totals of 1-3"+ possible, another Slight Risk will likely be needed once there is greater confidence in location. ...Eastern Florida... A situation with nearly antiparallel flow (low-level easterlies and upper level westerlies) will continue through mid- to late week across eastern Florida. Precipitable water values of 1.25-1.5" are forecast, and the low-level flow should bring instability off the warmer than average Gulf Stream. Effective bulk shear should be sufficient for organized convection. Hourly rain amounts to 1.75" would be possible wherever short, training bands manage to materialize. An approaching upper level system closes off into an upper level low which will help prolong the chances for localized heavy rainfall through the period. A Marginal Risk has been maintained for day 4/Wednesday with another Risk area introduced for day 5/Thursday for portions of Eastern FL as global guidance continues to suggest heavy rain potential. Putnam/Roth 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 $$