Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
714 PM EST Fri Jan 2 2026

Day 1
Valid 01Z Sat Jan 03 2026 - 12Z Sat Jan 03 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL
CALIFORNIA COAST NORTHWARD INTO NORTHERN CALIFORNIA...

01Z Update...
The 18Z HREF guidance supports the idea that few changes...if 
any...are needed to the Marginal Risk area for the central 
California coast northward. The upper trough/front...shown by 
satellite imagery to still be offshore this evening...has gotten 
close enough to bring the first showers to northern California. 
Increasing coverage of rainfall and an increase in rainfall rates 
is expcted this evening and tonight as the trough/front continues 
moving eastward. Some localized runoff issues will be possible 
overnight and early Saturday morning given moderate to locally 
heavy rainfall rates (isolated 0.50+"/hour) and the moist/wet 
antecedent conditions.

Bann

0830Z Excessive Rainfall Discussion...

No major model disagreements with the eastward push of the strong
mid to upper level low off the northern California coast day 1. The
low level southerly flow will strengthen Friday along and ahead of
the associated frontal boundary pushing toward the central to
northern California coast. While PW values are only 1 to 1.5
standard deviations above the mean, the 850-700 mb moisture flux
values are more anomalous, 2-3+ standard deviations above the mean.
Precip should increase in intensity along the northern CA coast
after 0000 UTC Sat, and spread south into coastal central CA in the
0600-1200 UTC time frame. The frontal boundary is expected to be
fairly progressive, limiting very heavy rainfall totals. HREF and
RRFS neighborhood probabilities for .50"+ hourly amounts are
generally less than 30%, with a few localized 60%+ probabilities
along the central CA coast range to the south of Monterey, and
across the northern Sierra. Areal average 1 to 1.5" amounts
expected along the central to northern CA coast and 1.5-2" in the
northern Sierra with isolated heavier totals of 2.5-3"+ possible.
No significant changes made to the previous marginal risk, with
localized runoff issues possible where soils remain fairly
saturated from recent rains, especially across northern CA.

Oravec


Day 2
Valid 12Z Sat Jan 03 2026 - 12Z Sun Jan 04 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
NORTHERN SIERRA AND SOUTHERN CALIFORNIA...

19z Update: Only minor changes made with this update. The 12z high
res models continue to depict a band of heavy rainfall moving
southward across the Transverse Range between 12z Sat and 00z Sun.
Most high res members depict localized hourly rainfall upwards of
0.5"-1", which should be enough to result in isolated to scattered
flash flooding.

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 at the end of the day 1 period will impact
the upslope areas of the northern Sierra and spread through the
Transverse Ranges of Southern California day 2. The primary change
from the previous outlook was to add a small slight risk area in
the upslope area of the Northern Sierra. HREF neighborhood
probabilities for .50"+ hourly rainfall amounts are fairly
high...50%+ at the beginning of the day 2 period and again in the
2100 UTC Sat to 0000 UTC Sun period. This will result in day 2
rainfall totals of 2-4"+ in a region of fairly saturated soils from
recent heavy rains. No changes of note made to the previous slight
risk area over Southern CA in the vicinity of the Transverse
Range. The south southwesterly low level flow will have a
significant upslope component into the Transverse Ranges during
the first half of day 2. This is reflected in both the HREF and
RRFS .50"+ hourly probabilities which are high, 50-80%+ during this
period. Localized runoff issues are possible where soils remain
fairly saturated from recent heavy rains.

Oravec


Day 3
Valid 12Z Sun Jan 04 2026 - 12Z Mon Jan 05 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE
CALIFORNIA COAST AND IN THE UPSLOPE OF THE SIERRA...

19z Update: Minimal changes needed to the inherited Marginal risk.
Gave some consideration to carrying over the the day 2 Northern
Sierra Slight risk into day 3 as periods of heavy rainfall will
continue into Sunday. However, snow levels will drop a bit and
thus at this point any Slight risk area would probably be too
narrow to depict. Either way, some flood impacts are likely to
continue into Sunday across the Marginal risk area.

Chenard


...Previous Discussion...

Additional shortwave energy expected to rotate through the mean
trof position along the West coast and inland across California day
3. 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
broad marginal risk area was maintained from the previous outlook
this period with changes mostly to better fit the latest model and
WPC qpf. The slight risk area over Southern California in the
vicinity of the Transverse Range was removed given consensus of
additional moderate totals.

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