From Dumas Walker@21:1/175 to All on Sat Dec 20 09:56:40 2025
FOUS30 KWBC 200809
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
309 AM EST Sat Dec 20 2025
Day 1
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...
Still expecting areas within the northern Sierra Nevada to receive
the most appreciable precipitation given the trajectory of the IVT
pulse and persistent 850-600mb moisture feed with added upslope
components near the terrain. Greatest flood concerns likely in the
adjacent foothills on the windward side of the Sierra Nevada.
Highest probs for >5" are across the I-80 corridor at the
California/Nevada border with the highest terrain still likely to
be snow, limiting the threat for flash flooding for the period to
that of a Marginal.
Campbell/Kleebauer
Day 2 Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025
...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...
A significant uptick in moisture will be surging into northern
California during this period within the reinforced atmospheric
river and will lead to widespread heavy rainfall and greater
threat for flash flooding, particularly for portions of the Sierra
Nevada foothills where multi-day totals of 5-10" are forecast. A
Moderate Risk area was raised for this period given more locations
will be at risk for rapid runoff and potential debris flows. The
areal extent of the Moderate will continue to be monitored and may
be adjusted with future updates.
Campbell
Day 3
Valid 12Z Mon Dec 22 2025 - 12Z Tue Dec 23 2025
...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...
The ongoing atmospheric river will persist while sinking a bit southward
toward central California, spreading rainfall further down the
Sierra Nevada Range and along the coastline. With the reduction of
rain on the northern periphery the threat for excessive rainfall
will remain at a Marginal level. A Moderate Risk was raised again
for much of the area identified during the day 2 period and for
locations a touch to the south. This part of the state is expected
to pick up another 3+ inches which will tip the 3 day accumulations
over 12 inches for some areas. Any additional rainfall will lead to
runoff and increase the potential for sloughing and debris flow
along the foothills/adjacent locations.
From Dumas Walker@21:1/175 to All on Sun Dec 21 08:58:16 2025
FOUS30 KWBC 210820
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 AM EST Sun Dec 21 2025
Day 1
Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025
...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...
A significant surge in Pacific moisture will overspread much of
northern California during this period within the reinforced
atmospheric river and will lead to widespread heavy rainfall.
Within the Moderate Risk area over the portions of the Sierra
Nevada range there are several hours of >50% HREF probabilities of
at least 0.50"/hr rates between 12Z Sun and 03Z Mon, while HREF
probabilities of >8" within the 24 hour Day 2 period are >60% for
much of the area. There will likely be many areas where flash
flooding may arise, along with sloughing and debris flows. For
additional details please refer to WPC MPD #1267.
Campbell/Hurley
Day 2
Valid 12Z Mon Dec 22 2025 - 12Z Tue Dec 23 2025
...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...
The atmospheric river will move southward during this period as
will the heavy rainfall footprint spread further down the Sierra
Nevada Range and along the coastline. Much of the same area of the
Sierra Nevada is projected to receive additional 2-3 inches over
the water logged area from Day 1. A Moderate Risk was maintained
along with expanding a touch to the south. Multi-day accumulations
will likely be well into the double digits by this time and leading
to several instances of rapid runoff, sloughing and debris flows
along the foothills/adjacent locations.
Campbell
Day 3
Valid 12Z Tue Dec 23 2025 - 12Z Wed Dec 24 2025
...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA, ALONG THE
COASTLINE OF CENTRAL CALIFORNIA AND FOR SOUTHERN CALIFORNIA....
Another reinforcing surge of Pacific moisture will be moving
onshore northern California while the southward moving impulse will
lead to a rapid uptick in rainfall in southern California. The
latest guidance is depicting another 1 to 4 inches for northern and
central California and 2 to 4+ for the higher terrain of southern
California. A Slight Risk covers much of the coastline from central
to northern California and into the northern part of the Sierra
Nevada. Additionally, another Slight Risk is in place for the
favored terrain of southern California.