Winter Storm Watch 3, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
300 PM PST Sun Jan 7 2024

.SYNOPSIS...Light showers spread over the Redwood Coast early
Monday, with more fronts expected Tuesday and Wednesday. A brief
dry period is possible late this week, then a more powerful system
possibly moves onshore early next weekend.

&&

.DISCUSSION...High pressure has quickly built aloft this morning,
quenching most shower activity...although stray showers are still
visible on radar imagery offshore, and a slight chance for these to
drift onshore still exists through this afternoon.

A weak disturbance is forecast to slip over this building ridge late
tonight and early Monday , bringing light precip to primarily Del
Norte and the mountains of Humboldt and northern Trinity. Latest
model soundings are showing an isothermal layer in the lower 5 to 6
kft of the atmosphere as this feature approaches...so precipitation
may start out as very light snow Monday morning before generally
switching to rain by the afternoon, particularly in the Trinity
River Valley, should showers reach that far inland.

This weak disturbance passing Monday will be followed by a trough
dropping into the PNW on Tuesday, which is expected to bring periods
of rain and snow from early Tuesday through late Thursday. Snow
levels steadily fall through most of Tuesday, beginning the day
around 5 to 6 kft and dropping to around 2 to 3 kft by Tuesday night
then remain steady into Wednesday. Thus travel impacts are expected
Wednesday morning, primarily affecting the passes on highways 299
and 3...and possibly 199 at Collier Tunnel...similar to yesterday
morning. The main bands of precip associated with this trough are
forecast to leave the area by late Wednesday, although scattered
post-frontal showers will likely continue into Thursday. A brief
dry period is expected behind this trough sometime late this week,
although the timing on this is uncertain.

Ensemble and deterministic guidance continue to depict a more
powerful system dropping over the region sometime between Friday and
Sunday. The compact low itself has been depicted generally as
splitting from the main flow over the NEPAC, dropping south then
west to move onshore somewhere along the West Coast. Meanwhile,
moisture from the remnants of a Kona Low (developing Mon/Tues near
the Hawaiian Islands) is forecast to track northward  and west
around a subtropical high off the central coast of CA, then
intersect with this compact low's track toward the West Coast on
Friday. Should this occur, it would significantly increase the PWAT
values within this low, compared to yesterday's and Tuesday's
system, and significantly strengthen the baroclinic zone present
along the northern portion of the West coast...with frigid, dry
arctic air to the NE over British Columbia and the mountains of the
PNW while warm, tropical air sits just offshore over much of the
NEPAC...right as the compact low nears the coast. As a result, this
system has the potential to intensify as it moves onshore...although
with the wild variations in depth, track, and intensity that exist
in the model spread with this system...confidence remains low on
really any forecast details this weekend beyond "expect some sort of
precipitation". /TDJ

&&

.AVIATION...VFR conditions to start out with this afternoon. Sky
cover will gradually increase and lower as a warm front approaches
from the west northwest. Some gusts in UKI today may hit near 18-
20KTS from the west northwest as low-level lapse rates help mix down
some wind, but should decrease as the sun sets. MVFR conditions will
eventually take hold late tonight into Monday morning as chances of
rain increase Tuesday morning with the approach of the
aforementioned warm front.

&&

.MARINE...The prominent northwest swell continues to diminish as
expected and the small craft advisory is still on track to expire
for all waters at 11Z Monday. The next weather system in a
forecast series of systems will approach Monday. South wind and
waves may increase enough for small craft advisory conditions for
northern outer waters Monday night ahead of an approaching cold
front.

A new northwest swell starts to build in late Monday night into
Tuesday with likely small craft advisory conditions for all waters
by Tuesday night, with combined seas in the 17-19 feet range
forecast for Wednesday for much of the waters, especially northern
outer waters.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 3 AM PST Monday for PZZ450-455-
     470-475.

&&

Visit us at https://www.weather.gov/eureka

Follow us on Facebook and Twitter at:
https://www.facebook.com/NWSEureka
https://www.twitter.com/NWSEureka

For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png