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 
Monterey counties as a cold front drops southward supporting some 
embedded convection. Hourly rainfall should exceed 0.5", and 
possibly approach 1" on a localized basis...which should be enough 
for an isolated flash flood/mudslide risk.

Rainfall will continue into the central/northern Sierra as well, 
with briefly heavier rates also possible here during the morning as
the front drops south. This risk combined with the saturated soil 
conditions continues to warrant the Slight risk over this region.

Chenard

...Previous Discussion... 

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 
coast. As these closed low develop you often see the 
front/convergence axis briefly stall, which could allow for a 
period of more persistent moderate to heavy rainfall. Still some 
uncertainty on these details, and so we will stick with a Marginal
risk for now. But will need to continue to monitor trends, as 
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://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