Gale Watch 12, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
304 PM PDT Sun Mar 24 2024

.SYNOPSIS...Calmer, cooler weather will build in early this week
with widespread valley fog and frost early this week. Another rain
system with gusty wind will arrive Wednesday.

&&

.DISCUSSION...The last few showers have slowly diminished today as
the upper level trough continues to push east and dry, cold air
builds across the area. Clearing skies and lingering surface
moisture will mos likely aid in widespread fog formation in stable
valleys tonight, where dewpoints are low enough, areas of frost are
also expected. This could prove impactful in Mendocino and Lake
COunties where the growing season has already begun, Closer to
shore, onshore flow and marine influence will limit any frost
formation.

Generally cool, drier and clear weather will bring a brief respite
to rain through Tuesday. More widespread clouds and moisture will
return by late Tuesday as another low pressure system approaches
the area. In contrast to this last system, there is good ensemble
agreement that this next system will produce stronger south winds.
NBM shows a 70 to 90% chance of peak gusts over 45 mph Wednesday on
high ridges in Humboldt and Del Norte and along the rim of the
Sacramento Valley. There is a lower chance (40 to 60%) of gusts to
55 mph, mostly on near coastal ridges. Such winds will bring an
increased risk of debris and power outages, especially given recent
rain.

In terms of rain, the GEFS ensemble shows a 90% chance of a moisture
plume with IVT values in excess of 250 Kg/ms on Wednesday. A plume
of this magnitude represents a minor to moderate atmospheric river.
It shows essentially 0% chance of IVTs reaching 500 Kg/ms indicating
a confident "cap" on the total amount of rainfall. That said,
rainfall seems reactively concentrated on Wednesday with NBM showing
most likely rainfall along coastal ridges of 2 to 3.5 inches over 24
hours, mostly in Humboldt and Del Norte. Such concentrated rainfall
will bring a minor risk of urban and small stream flooding. That
said, southerly wind during the peak rainfall will decrease rainfall
efficiency at lower elevations as is typical for these events.

Cold air will build as the cutoff low pressure traverses the area.
Cold air will be inconsistent and mild at best, especially
considering the time of year, but could still drop snow levels as
low as 3000 feet. That said, only meager QPF will lead to light and
inconsistent snow. NBM currently shows most likely snowfall of only
1 to 4 inches capable on the high pass of Highways 36 and 299,
mostly early Thursday and Friday mornings. Even with the meager
climatology, these amounts are too low to flag as unusual int he
ECMWF EFI. These amounts could increase, however, if convective
models suggest showers will linger longer.

Unsettled weather is most likely to continue into the first week of
April with 60 to 80% of ensemble members showing yet another minor
atmospheric river next weekend. /JHW

&&

.AVIATION...MVFR ceilings are lifting and scattering this afternoon as
a surface low over OR weakens and moves inland. Gusty NW winds will
continue at coastal terminals until late this afternoon, with 10-20
mph gusts lingering at UKI into the late evening hours. A broad
shield of warm frontal stratus riding over an offshore ridge will
descend into the region overnight, bringing ceilings back to mostly
MVFR for all terminals. Winds are expected to gradually turn SE
early Monday as the high pressure ridge builds into the area. High-
res models indicate an additional weak boundary traversing the
northern CA coast late Monday morning. Scattered rain showers are
possible at CEC and ACV during this period, after which only
scattered high cirrus ceilings and scattered low stratus will
prevail. Widespread clearing and subsequent fog are likely Monday
night.

&&

.MARINE...Northerly winds will continue to subside as an area of low
pressure over OR moves inland and weakens. Wind waves will rapidly
diminish from northern to southern zones while a long period NW
swell fills into the waters tonight into Monday. This will moderate
the sea state, keeping sig wave heights below 10 feet Monday and
Tuesday. Another system is expected to arrive early Wednesday and
produce robust southerly winds, especially in the northern waters.
Gale gusts and responsive wind waves will likely generate another
round of small craft conditions Wednesday into Thursday. Even as
winds diminish slightly, another large NW swell is expected to fill
into the waters Thursday into Friday. Wave heights with this swell
have the potential to exceed 16 feet, producing dangerous seas
through the end of this week.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Frost Advisory from 3 AM to 9 AM PDT Monday for CAZ110-111-
     114.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 PM PDT this evening for PZZ450-
     470.

     Small Craft Advisory until 3 AM PDT Monday for PZZ455-475.

&&

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