FOUS30 KWBC 241600 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1100 AM EST Wed Dec 24 2025 Day 1 Valid 16Z Wed Dec 24 2025 - 12Z Thu Dec 25 2025 ...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL ACROSS SOUTHERN CALIFORNIA... 1600Z Update... A strong atmospheric river event continues to impact California as a full-latitude trough offshore of the West Coast advances gradually east and sends a cold front inland across the coastal ranges and the Central Valley. Changes to the previous outlook include trimming especially the Slight Risk area across portions of central and northern CA where the heaviest rains have now shifted off to the south and east. Some minor and generally cosmetic adjustments were made to the Marginal Risk area. Additional shower activity will impact much of northern California going into the overnight hours as additional shortwave energy embedded within the larger scale trough impacts the region. Farther south for southern California, no changes have been made to the High Risk. Heavy and persistent rainfall rates into the 0.50" to 1"/hour range, and some spotty peak rates perhaps to near 1.5"/hour will continue to be a threat which is advertised by the 12Z HREF guidance along with the recent HRRR and WoFS guidance. Please consult WPC's MPDs for additional short-term information on the evolution of this strong atmospheric river which will continue to bring dangerous and locally life-threatening flooding and flash flooding impacts. Orrison Previous discussion... Highly anomalous 850-700 mb moisture flux on the order of 5+ standard deviations above the mean will yield extremely heavy rainfall ahead of the amplifying mid/upper trough located offshore of the California coast. The heavy rainfall totals for Southern CA will likely occur over an 18 hour period, with widespread 4-7 inch totals, with isolated max amounts of 9"+. Expect a well defined south to north precip band in this anomalous moisture flux axis with hourly rainfall rates of 0.50-1.5"+ likely. The potential for high hourly rainfall totals will accentuate runoff over soil that is relatively dry and or over recent burn scar areas. This will pose a significant threat of flash flooding, landslides, rock falls and mud slides. The greater than normal travel during the Christmas Holiday will likely expose a potentially larger number of people to these lift threatening hazards and was taken into consideration with the upgrade to high risk. Although snow levels will be lowering across the Sierra Nevada and adjacent locations and much of the highest elevations will have significant snow, some of the lower elevations could receive additional rainfall of 1 to 4 inches. The Slight Risk areas were combined to cover heavy rain tracking eastward across eastern California, southern Nevada and into southern Utah and western Arizona where areal averages up to 1 to 2+ are forecast. Campbell Day 2 Valid 12Z Thu Dec 25 2025 - 12Z Fri Dec 26 2025 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN CALIFORNIA... A Moderate Risk remains in effect for a large portion of the coast from San Luis Obispo through much of the Transverse Ranges north of L.A. Expect much of the heaviest rain to occur on D2/Wednesday, but by Christmas Day, there will still be one more front that will cross the area from west to east, which will result in another round of heavy rainfall in southern California. Since this next front will arrive soon after the heaviest rains from Wednesday, expect there will be outsized impacts from the heavy rainfall associated therewith. Showers and maybe even a few thunderstorms will impact much of coastal southern California and the adjacent mountains. While each one will be fast moving, the rivers and streams all across southern California will likely already be flooding, so any additional rainfall, especially where heavy, will make ongoing flooding worse. Campbell/Wegman Day 3 Valid 12Z Fri Dec 26 2025 - 12Z Sat Dec 27 2025 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS SOUTHERN CALIFORNIA... The atmospheric river will be waning however given the significant accumulations leading up to this period soils remain hyper sensitive to any additional precipitation, particularly across the Transverse Range and surrounding locations. As such, a Slight Risk area was maintained for this part of the state along with a Marginal Risk that extends up the coast toward San Francisco and along the foothills of the Sierra Nevada Range. Campbell 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