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   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   740 PM EST Thu Dec 25 2025   
      
   Day 1   
   Valid 01Z Fri Dec 26 2025 - 12Z Fri Dec 26 2025   
      
   ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF   
   SOUTHERN CALIFORNIA...   
      
   0100Z Update...   
      
   Needed to make only minor adjustments to the on-going Excessive   
   Rainfall Outlook based on the 25/18Z HREF and most recent runs of   
   the WoFS and NSSL/MPAS. At least one more atmospheric river surge   
   will impact portions of central and southern and southern   
   California through early Friday morning. The area is extremely   
   sensitive hydrologically and further rainfall with only promote   
   additional areas of flash flooding with locally dangerous and   
   life-threatening impacts possible. Farther north in   
   California...rainfall rates and amounts are not expected to be as   
   high as areas to the south but still soils are saturated (or nearly   
   so) with high streamflows and additional areas of flooding and   
   flash flooding are likely. Overall, the 12Z GFS/ECMWF as well as the   
   WoFS and MPAS seemed to have a handle on the overall pattern of   
   moisture transport.   
      
   Bann   
      
      
   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...   
      
   20z Update...   
      
   Maintained the inherited ERO areas for this update, as additional   
   localized rainfall totals of 2"+ will be possible over areas that   
   received significant rainfall earlier in the week. These amounts   
   should be spread out over a relatively long period of the day and   
   largely confined to where upslope flow is most ideal (with the best   
   signal for 2" and 3" exceedance from 12z CAMs concentrated near the   
   San Bernardino Mountains).   
      
   Churchill   
      
      
   Previous Discussion...   
      
   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.   
      
   Churchill/Hurley   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!7b0dEIjpJGiH8RV6-oC7CFVrtlwqNRoHVfs42gfIPbAh=   
   1UuYFWRojAHp5t_fUp3UwPyYFHs8_KRBeVd3ReKFNljerxQ$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!7b0dEIjpJGiH8RV6-oC7CFVrtlwqNRoHVfs42gfIPbAh=   
   1UuYFWRojAHp5t_fUp3UwPyYFHs8_KRBeVd3ReKF7igNr8g$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!7b0dEIjpJGiH8RV6-oC7CFVrtlwqNRoHVfs42gfIPbAh=   
   1UuYFWRojAHp5t_fUp3UwPyYFHs8_KRBeVd3ReKFpegEvSQ$=20   
      
   =3D =3D =3D   
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