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   FOUS30 KWBC 031952   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   252 PM EST Sat Jan 3 2026   
      
   Day 1   
   Valid 16Z Sat Jan 03 2026 - 12Z Sun Jan 04 2026   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF   
   SOUTHERN CALIFORNIA AND IN THE UPSLOPE REGIONS OF THE SIERRA AND   
   THE SHASTA OF NORTHERN CALIFORNIA...   
      
   16z Update: Only minor changes needed to the inherited risk areas.   
   Rainfall rates over portions of Santa Barbara and Ventura Counties   
   are expected to increase this morning resulting in an isolated to   
   scattered flash flood risk. Mudslides and debris flows will also   
   be a possibility. Recent satellite imagery depicts cooling cloud   
   tops moving into this portion of southern CA. Rainfall as high as   
   0.75" in an hour is already occurring on a localized basis, with   
   recent HRRR runs supporting amounts locally exceeding 1" in an hour   
   between now and 22z as this axis of heavier rain gradually shifts   
   southward. Given observational and model trends it seems probable   
   that rates will continue to increase as embedded convective   
   elements develop just onshore. Current indications are that this   
   area of heavier rainfall rates will weaken as it moves into Las   
   Angeles County, although 0.5"/hr rainfall will still be possible   
   here.   
      
   Convective elements may also increase across portions of central   
   and northern CA as we head into the afternoon resulting in a   
   localized flash flood risk. The coverage of these higher rates   
   should be pretty low, so not looking at a widespread flash flood   
   risk. But if/where heavier convective cells do develop then urban   
   and small stream flooding will be possible.   
      
   Chenard   
      
   ...Previous Discussion...   
      
   The axis of anomalous 850-700 mb moisture flux values...2 to 4+   
   standard deviations above the mean...along and ahead of the inland   
   moving frontal boundary early Saturday will impact the upslope   
   areas of the Sierra, northward into the Shasta of northern   
   California and spread through the Transverse Ranges of Southern   
   California. The primary change from the previous outlook was to   
   expand the slight risk area along all of the upslope regions of the   
   Sierra and expand it northward into the upslope of the northern CA   
   Shasta Range. HREF and RRFS neighborhood probabilities are high in   
   the slight risk area along the Sierra into the Shasta for 1, 2 and   
   3"+ totals and high along the Transverse Range for 1 and 2"+   
   totals day 1. In the slight risk area along the Sierra and Shasta,   
   hourly rainfall totals of .25-.50"+ are possible through the day 1   
   period and along the Transverse Range primarily during the first   
   half of day 1. This is resulting in HREF and RRFS probabilities of 3   
   hour precip exceeding 3 hour FFG values being well defined in the   
   upslope area of the Sierra and Shasta through day 1 and over the   
   Transverse Range during the fist half of day 1. Soils remain fairly   
   saturated in the slight risk areas from recent heavy rains at the   
   end of 2025 with runoff issues possible as additional heavy   
   rainfall occurs over these saturated soils.   
      
      
   Oravec   
      
   Day 2   
   Valid 12Z Sun Jan 04 2026 - 12Z Mon Jan 05 2026   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE   
   NORTHERN SIERRA...   
      
   19z Update: Forecast generally looks on track. Higher rainfall   
   rates will be possible Sunday morning from Santa Cruz into=20   
   Monterey counties as a cold front drops southward supporting some=20   
   embedded convection. Hourly rainfall should exceed 0.5", and=20   
   possibly approach 1" on a localized basis...which should be enough=20   
   for an isolated flash flood/mudslide risk.   
      
   Rainfall will continue into the central/northern Sierra as well,=20   
   with briefly heavier rates also possible here during the morning as   
   the front drops south. This risk combined with the saturated soil=20   
   conditions continues to warrant the Slight risk over this region.   
      
   Chenard   
      
   ...Previous Discussion...=20   
      
   Additional shortwave energy expected to rotate through the mean   
   trof position along the West coast and inland across California day   
   2. This will support a continued wet showery pattern with   
   additional moderate to locally heavy precip totals along much of   
   the California coast Ranges and into the upslope of the Sierra. A   
   small slight risk area was introduced in the upslope of the northern   
   Sierra where model consensus is for potential of additional 1 to 2"   
   of rain. While rainfall rates are expected to be less than day 1,   
   generally .10-.25, there will be overlap with the day 1 qpf axis in   
   places with 48 hour totals of 3-6" in the slight risk area. Much   
   of the day 2 precip will occur during the first half of day 2. HREF   
   and RRFS 12 hour precip ending 0000 UTC Mon are high for 1 and 2"+   
   totals. Otherwise, no changes made to the broad marginal risk area   
   for much of coastal and northern California.   
      
   Oravec   
      
      
   Day 3   
   Valid 12Z Mon Jan 05 2026 - 12Z Tue Jan 06 2026   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE CENTRAL   
   TO NORTHERN CALIFORNIA COAST AND NORTHERN CALIFORNIA...   
      
   19z Update: Model QPF is trending up across portions of central   
   and/or northern CA this period as a closed low develops off the=20   
   coast. As these closed low develop you often see the=20   
   front/convergence axis briefly stall, which could allow for a=20   
   period of more persistent moderate to heavy rainfall. Still some=20   
   uncertainty on these details, and so we will stick with a Marginal   
   risk for now. But will need to continue to monitor trends, as=20   
   given saturated soil conditions over some of this region, a future   
   Slight risk upgrade can not be ruled out.   
      
   Chenard   
      
   ...Previous Discussion...   
      
   The mean trof position is maintained day 3 off the West coast with   
   model consensus for amplification of a new closed low in the base   
   of the mean trof off the Central to Southern CA coast. The low   
   level southerly flow on the east side of this developing closed low   
   will not be as strong as the day 1 and 2 low level south   
   southwesterly flow, resulting in 850-700 mb moisture flux values   
   only 1 to 1.5 standard deviations above the mean. PW values also   
   expected to be lower than day 1 and 2, with anomalies only 1 to   
   1.5 standard deviations above the mean. Model consensus is for   
   additional .50-1"+ rainfall amounts along the Central to Northern   
   CA coast and into the upslope of the Northern Sierra. At the   
   moment, these amounts warrant keeping the Excessive Rainfall   
   Outlook threat level at marginal for the day 3 period, with no   
   significant changes made to the previous outlook.   
      
   Oravec   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!95hKGCblOpLV8Dlwhp7s4j6ZgHogdryf8cRonjxRT-Hw=   
   fQkouqpNWbeFJpQTf0WsdYcaRc2WgA-FHZZ-bmMABQMUNIs$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!95hKGCblOpLV8Dlwhp7s4j6ZgHogdryf8cRonjxRT-Hw=   
   fQkouqpNWbeFJpQTf0WsdYcaRc2WgA-FHZZ-bmMA4JA714U$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!95hKGCblOpLV8Dlwhp7s4j6ZgHogdryf8cRonjxRT-Hw=   
   fQkouqpNWbeFJpQTf0WsdYcaRc2WgA-FHZZ-bmMANoJ6Oew$=20   
      
   =3D =3D =3D   
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