Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 190433

National Weather Service Eureka CA
933 PM PDT Wed Apr 18 2018

.SYNOPSIS...Leftover showers occurring over the interior
mountains will continue to dissipate tonight. Clearing skies will
accompany shower dissipation and aid in chilly Thursday morning
lows. Dry and mild conditions are anticipated for Thursday
afternoon through early next week.


Made a few minor adjustments to drop shower chances from all areas
outside of the Trinity Alps, otherwise forecast remains mainly on
track. Temperatures still in the mid to upper 40s and even near 50
across most of Northwest California this hour, but light winds and
clearing skies should allow temperatures to drop for frosty
conditions across most inland areas by Thursday morning. Weak
upper-low drifting southward from southern Oregon which is aiding
lingering shower activity may allow clouds to linger a bit longer
into the overnight, perhaps keeping temperatures from dropping too
far below freezing in Trinity County...outside of the coldest
valleys. Humboldt and Del Norte coast also has dewpoints still in
the low 40s, so more urban areas and places closer to the water
may have a tough time seeing frost. Otherwise, do not see enough
reason to adjust frost advisories and freeze warnings, so will
leave those as is.


.PREV DISCUSSION... /issued 201 PM PDT Wed Apr 18 2018/

DISCUSSION...A compact upper-level shortwave trough was
positioned west of the region during Wednesday afternoon. A zone
of strongly forced showers was occurring close to the wave, and
are not expected to impact NWRN CA. Additional shower activity was
also observed over the interior mountains, and will quickly
dissipate tonight with the loss of daytime heating. Otherwise,
skies are forecast to rapidly clear tonight across the area as the
upper wave exits south toward the SRN CA coast. Temperatures will
fall to or below freezing over much of Trinity County, and range
from 33-36 over the remainder of the CWA (with the exception of
the Mendocino coast). Thus, the inherited frost/freeze headlines
remain on track.

Model guidance shows an upper ridge building over the western
CONUS during Friday, which will favor mainly dry/mild conditions
for NWRN CA. One potential caveat would be the development of
marine stratus locally penetrating inland across the coast and
limiting daytime heating/afternoon highs during Friday.

Beyond Friday afternoon...a weak upper disturbance is forecast to
move southeast across the region Friday evening/night. However,
impactful weather is not anticipated with that feature. A second
trough may amplify slightly over the West Coast Saturday night,
but again, will not generate any impacts. Besides these minor
upper waves, surface high pressure is forecast to strengthen over
the northeast Pacific during the weekend. The high, combined with
thermally generated lower pressure over the Central Valley, will
likely yield gusty northerly winds along the coast.

AVIATION...VFR conditions prevailed as decreasing mid-high
clouds covered the skies today. Therefore, conditions at most
airfields, including CEC, UKI and ACV air terminals, were quite
complimentary. Even so, interior mountain zones had scattered
convective buildups which resulted in mainly isolated showers in
Eastern Del Norte, Trinity and far Northeastern Mendocino
Counties. Another Low pressure system is approaching the Central
California Coast with a few upper level clouds zipping across the
region. Any associated precipitation should slide south of the
area. /TA

MARINE...Small craft northerly winds accompanied by steep short
period seas are forecast to develop tonight and persist through
Friday. Winds will then weaken over the northern coastal waters
during Friday, while remaining slightly gusty over the southern
waters. High pressure will strengthen over the northeastern
Pacific by Saturday, which will aid in gale force northerlies
during the weekend. Otherwise, a 15 second long period swell will
spread east across the coastal waters Friday night, followed by an
18 second westerly swell Monday night.


CA...Freeze Warning from 1 AM to 9 AM PDT Thursday for CAZ107-108.

     Frost Advisory from 1 AM to 9 AM PDT Thursday for CAZ101>106-

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from noon to 11 PM PDT Thursday for PZZ450-

     Small Craft Advisory from 3 AM Thursday to 6 AM PDT Friday for

     Small Craft Advisory from 3 AM Thursday to midnight PDT Friday
     night for PZZ475.



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