FOUS30 KWBC 251559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1059 AM EST Thu Dec 25 2025 Day 1 Valid 16Z Thu Dec 25 2025 - 12Z Fri Dec 26 2025 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN CALIFORNIA... 1600Z Update... Based on the latest 12Z HREF suite of guidance along with recent HRRR and RRFS solutions, the Slight Risk area over the Central Valley has been adjusted a bit to reflect a bit more shadowing of rainfall down across the central and southern portions of the San Joaquin Valley in particular. Some tightening of the Slight and Moderate Risk areas were accommodated down across southern CA and especially near the Peninsular Range to reflect the guidance showing lesser rainfall totals down across this region, but the Moderate Risk remains in place for the Transverse Range including portions of the Los Angeles Basin. Elsewhere, given the exiting of the earlier shortwave energy and heavier shower activity that was impacting portions of southwest UT and northwest AZ, and with much of this region including southern NV not likely to see much additional heavy rainfall this period, the Marginal Risk area was removed from these locations. Orrison Previous discussion... A Moderate Risk remains in effect for a large portion of the Central CA coast through much of the Transverse Ranges north of L.A. While the main AR has pushed south and weakened, the amplifying upper trough offshore and strengthening lee-side jet streak will reinvigorate deep-layer forcing downstream across Southern CA. Meanwhile, the colder air aloft will help provide some deep-layer instability (MUCAPES 250-500 J/Kg), thus supportive of additional rounds of 0.50-1.00 inch/hr rainfall rates as a secondary axis of elevated PWATs (0.80-1.10") and IVTs (500-600 Kg/m/s) traverses the Moderate Risk area. Additional rainfall amounts of 2 to 4+ inches are expected within the Moderate Risk area, with the guidance (especially high-res CAMs) indicating isolated additional totals between 5 and 7+ inches across the southern slopes of the Transverse Ranges. As such, we continued to outlook a "high-end" Moderate Risk -- denoting a more enhanced or >50% neighborhood probability of rainfall exceeding flash flood guidance -- across the San Rafael and southern Sierra Madre Ranges, where the 00Z HREF indicated 80%+ probabilities of additional rainfall exceeding 3" through 12Z Fri, along with 30-50% probabilities of rainfall totals exceeding 5". Elsewhere, the Slight Risk area was expanded across parts of the Central Valley based on Wednesday's rainfall along with the deterministic and probabilistic QPF Christmas Day through 12Z Fri. No changes were made to the broader Marginal Risk area based on the latest (00Z) guidance/trends. Hurley Day 2 Valid 12Z Fri Dec 26 2025 - 12Z Sat Dec 27 2025 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS SOUTHERN CALIFORNIA... Minor changes were made to the Slight and Marginal Risk areas from yesterday's Day 3 ERO. The secondary (weaker) Atmospheric River will be waning, however given the significant accumulations leading up to this period, soils will 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. Hurley Day 3 Valid 12Z Sat Dec 27 2025 - 12Z Sun Dec 28 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley 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