Area Forecast Discussion
Issued by NWS Eureka, CA

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458
FXUS66 KEKA 212126
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
226 PM PDT Sat Apr 21 2018

.SYNOPSIS...Above normal high temperatures are expected for the
interior Sunday through Tuesday. Occasional stratus and breezy
afternoon winds will keep temperatures near normal for coastal
areas this weekend. Mainly dry weather is expected to prevail
through most of next week. The potential for isolated showers
will enter the picture mid to late next week.

&&

.DISCUSSION...Clear skies prevailed across the region today. The
exception has been low clouds banking up along the coastline from
Capetown to the Eel Delta. Similar conditions are expected for
Sunday with perhaps less low cloud cover in the morning for the
north coast. Brisk northerly winds will resume on Sunday and any
stratus that does form will mix out with the daytime heating.

The warming trend for the interior will continue on Sunday with
highs expected to top out in the mid 70s to mid 80s for the
warmest inland valleys of Northwest California. Above normal high
temperatures along with bountiful sunshine will continue on Mon
and Tue, before the ridge aloft begins to buckle and shift east.
Brisk northerly winds will also subside on Mon and Tue for coastal
areas. Warming is expected for coastal areas on Mon. The unknown
for Tuesday is coastal status. GFS and NAM12 indicate developing
onshore flow and a strengthening marine inversion. Stratus will
be on the increase for Tue, putting a damper on the warming and
sunshine for the coast.

An upper level trough/low will develop west of 130W by Wed and
temperatures for interior locales will start to trend downward
for the remainder of the week. Marine stratus should also become
more entrenched along the coast as the upper low edges closer to
the coast toward the end of the week. The greatest uncertainty
will be the potential for showers and convection Wed through Sat.
The GFS indicates formidable instability and CAPE on Wed as a
spoke of energy pin-wheels northeastward around the offshore low
by Wed evening. The other models, primarily the ECMWF, has the
upper low farther to our west with much less energy to promote
large scale upward motion. The heating of the day will be
sufficient if the moisture advection from the GFS is correct.
Considering the disparity between models that far out, will hold
off on adding thunderstorms to the forecast at this time. Also,
the models typically handle these cut-off lows poorly and are
almost always too fast with the eastward progression. At this
point, the main impact looks to be cooling for the interior and
more cloud cover for the coast.

The chance for showers will increase Fri and Sat as the low
eventually ejects eastward across the area. The models were by no
means in great agreement on how fast this will occur and where the
low will go. The GFS indicates the low heading south into the SFO
Bay area, then wrap around moisture, showers and tstms for next
weekend. The ECMWF has the closed low plowing right into northern
California Friday night and Sat, then a ridge rapidly popping up
by Sunday.  Overall, it is not a pattern that would result in
prolonged wet weather for NW California. The potential for TSTMS
will need to be watched closely as we head into next weekend.

&&

.AVIATION...Clear skies are currently being observed over northwest
California this afternoon due to high pressure sitting over the
region. This has allowed for VFR conditions today which will likely
continue into tomorrow. Model guidance tries to indicate that some
low cloud and/or fog could form along the Del Norte and Humboldt
County coasts, but my confidence is not high enough to put that in
the forecast at this time.

&&

.MARINE...The forecast remains on track this afternoon as northerly
winds continue to increase. Buoys are currently reporting sustained
northerly winds of 20 to 25 kt with gust up to 30kt. The of these
winds are being reported near Pt. St. George, Cape Mendocino and
Point Arena. These conditions will continue through tomorrow with
the winds starting to weaken tomorrow evening. The strongest winds
for this stretch of time will be found beyond 10nm, where sustained
gale force winds are expected. Large wind waves will continue to
build in response to these winds, which combined with a
northwesterly swell, will lead to 11 to 14 ft waves in the outer
waters while the in waters wave heights range from 8 to 10 ft.

On Monday, winds will continue to decrease which will allow seas to
subside to 5 to 7 feet by Wednesday.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 9 PM PDT Sunday for PZZ450-455.
Gale Warning until midnight PDT Sunday night for PZZ470-475.

&&

$$

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