Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 282148

National Weather Service Eureka CA
248 PM PDT Wed Oct 28 2020

.SYNOPSIS...Dry weather is expected through early next week. Above
normal afternoon temperatures are expected each day, after chilly
mornings and patches of early morning frost in some of the interior
valleys. Skies will generally remain clear except for occasional
coastal clouds and possible fog through the weekend.


.DISCUSSION...Upper level ridging will dominate through Friday.
Above normal afternoon temperatures are expected in the interior
for at least one more day. The dry air mass and clear skies will
allow temperatures to fall into the mid 30`s in some of the valleys
of southern Humboldt and northern Mendocino again tonight. A frost
advisory has been issued for these colder valleys. It will be
colder in Trinity county valleys, however many sites have already
seen a season ending freeze. Frost advisories and freeze warnings
will no longer be issued for Trinity county until Spring.

A transient shortwave disturbance will move across the Pacific NW
on Friday and temporarily flatten the ridge. This shortwave will
likely induce a low level push of higher humidities for coastal
areas and adjacent river valleys as high pressure rebuilds
offshore behind the disturbance. Satellite imagery has already
been showing low clouds and possible fog forming offshore and
along the southern Mendocino coast this afternoon. The offshore
gradients tonight will likely keep the bulk of the low clouds
over the coastal waters. BUFKIT time-height sections for coastal
land sites were not showing a considerable increase in low level
humidity and low clouds tonight and Thu. Just offshore, profiles
moisten up tonight and Thu, suggesting a greater potential for low
cloud cover along the Mendocino coast through Thursday.

Otherwise, inland areas will remain quite dry through the weekend.
A few upper level stations were still reporting 5 to 10% RH`s
today. The RH`s were higher, 15-25%, at stations with stronger
winds, gusts from 20 to 30 mph. Locally critical fire weather
conditions are expected for the windier sites, due to the very low
RH`s. Widespread and long duration red flag conditions are not
expected, however. A marine push may result in higher RH`s this
weekend, however the highest mountain peaks will probably not see
any significant RH increase. The ridge aloft will spring back up
quickly this weekend, for generally warmer daytime temperatures in
the interior. Another transient shortwave will move into the
ridge early next week, around Tuesday. Rain appears unlikely,
however will leave a 15-20% chance for a few hundredths.


.AVIATION...Visible satellite imagery continues to show some
stratus developing off the Mendocino coast and more off the SF Bay
area. Winds are expected to remain light through the period. Late
tonight the HREF is showing some stratus near the coast of Humboldt
and Del Norte counties. HRRR has been progressively brining more
stratus closer to the coastal terminals in the early morning hours
with local southerly return flow in recent runs. However, the
airmass is still relatively dry with light offshore flow expected at
times. Nevertheless, the 0Z TAFs may need more stratus.


.MARINE...Winds and seas continue to relax, with the remaining Small
Craft Advisory in the Northern Outer Waters now expired. Light
northerlies will settle in for most of the remainder of the week,
with periods of coastal southerly return flow. Small mid-period NW
swells will linger in the waters until a longer period NW swell
builds in beginning early Saturday morning. Forecast data continues
to trend a little higher with it, to likely reach 7 feet at 11
seconds on Saturday. The northerlies will pick back up starting
Friday, and potentially remain elevated Saturday. Late Sunday
afternoon a long-period WNW swell will begin filling in, and will
build to around 4 to 5 feet at 16 seconds by Monday morning. This
could pose a sneaker wave threat depending on how strong the winds
and short periods waves are at this time.


CA...Frost Advisory from 3 AM to 8 AM PDT Thursday for CAZ104-106-110-

  PDT this afternoon for PZZ470.



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