815
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
314 PM PDT Wed May 1 2024

.SYNOPSIS...Warm and dry weather will be interrupted by a weak frontal
passage Thursday. Unsettled conditions will continue through the end
of the weak before a more impactful system arrives this weekend,
bringing measurable rainfall and gusty winds to the area Friday -
Saturday.


&&

.DISCUSSION...Cold morning temperatures have risen to highs in the
upper 50`s and mid-60`s this afternoon beneath clear skies and
abundant solar insolation. Some valleys approached 70 at the peak of
daytime heating. Gusty offshore northerly winds continue to expand
inland south of Cape Mendocino - current observations indicate gusts
20-30 mph along the Humboldt and Mendocino coasts and exposed ridges
within the coastal ranges. Meanwhile, the interior is still expected
to briefly warm and dry out for the next 24 hours. Hi-res models
have interior valleys reaching into the mid to upper 60`s while RH
values drop to between 30-50%.

High to mid level clouds will continue to stream into the PNW as a
weak shortwave digs into northern CA, eroding away at the meridional
pressure gradient driving northerly winds. Cloud ceilings will lower
and thicken ahead of a weak surface front, with HREF indicating
light precipitation beginning as early as 3 am Thursday morning in
far northern Del Norte county. Precip will gradually expand south
through Humboldt county during the day Thursday. Hi-res models are
trending toward heavier precip rates, with HREF forecasting between
0.20-0.30 inches/6 hours from 8 am to 12 pm. Accumulations 0.25 to
0.75 inches expected through 11 am Friday, with highest amounts in
northern Del Norte county and NW facing slopes tapering off heading
south into southern Humboldt County.

After some mid level drying with the offshore ridge axis, the
descending upper low driven along a broad upper trough complex will
usher additional moisture into the area late Thursday into Friday
ahead of a larger system arriving this weekend. Some scattered
showers are possible in northern counties as the winds turn
southerly ahead of the leading warm sector of the low. As the cold
upper low descends into the PNW, the associated surface low will
produce significant rainfall Friday night into Saturday as the cold
front pushes onshore and turns winds WNW. WPC and NBM QPF are
currently forecasting 1-2 inches of rain in the 24 hours spanning
Friday night to Saturday night for northern Mendocino, Humboldt, Del
Norte and eastern Trinity counties, with the higher totals (1.75-2)
expected on westward facing slopes. Southern Mendocino and Lake
counties are leaning closer to 0.5-0.75 inches over the same
period. Long range deterministic models are trending a bit higher
across the board due to variations in the surface low track, but
are in agreement with NBM that the bulk of precip will taper off
early Sunday morning. With snow levels around 3,000-4,000 ft,
mountain snow will be possible on the tail end of this system,
leaving behind unseasonably cold temperatures in its wake.

Late weekend into early next week, model clusters and Euro ensembles
are leaning toward a colder, more unsettled pattern at least through
Tuesday.


&&

.AVIATION...Mostly VFR conditions have and will persist during the
daylight today. Northerlies will continue to be gusty in the
afternoon at all the terminals and will diminish by sunset. An
approaching frontal system arriving later tonight will bring low
clouds and occasional precipitation to the coastal terminals
tonight, impacting conditions to IFR or MVFR.

At KCEC, ceilings have around a 75% probability of being below
1000ft with a 30% chance of being below 500ft. At KACV, these
ceiling height probabilities are 70% at 1000ft and 30% at 500ft.
Mist, drizzle, and even light rain have over 90% chance of occurring
at both coastal sites according to the National Blend of Models.
Visibilities tomorrow morning have a 50% probability of dropping
below 5SM and a 15-20% probability of being under 2SM periodically
during this front passage. Forecast confidence remains low at this
point, and these drops in visibility will be addressed in subsequent
TAF publications.

Inland, KUKI looks on track to stay mostly clear for
the next 24 hours, but a low level wind shear threat due to
significantly increased wind speeds about 1-1.5km height compared to
the light winds at the surface is forecasted for this evening as
the front crosses over the area. DS


&&

.MARINE...Gusty northerly winds have continued through most
the day. Gusts have been near or at gale force in the southern
waters, particularly south of Cape Mendocino. Winds and waves are
already beginning to diminish and are forecasted to continue to do
so into tomorrow across all the marine zones. An approaching warm
front entering our area will force westerly winds to blow tomorrow.
North of Cape Mendocino, the winds will blow towards the north while
Mendocino Co. and the southern part of Humboldt Co. will blow towards
the south. These winds will remain fairly light (>15kt) during this
period of split flow. The light winds and relatively calmer sea
state accompanied by them will continue until the beginning of this
weekend. On Friday afternoon, winds will increase and shift
northerly as a cold front approaches, increasing the wind speeds
even more on Saturday. DS


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 3 AM PDT Thursday for PZZ450-470.

     Gale Warning until 8 PM PDT this evening for PZZ455-475.

&&

$$

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