Area Forecast Discussion
Issued by NWS Eureka, CA

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754
FXUS66 KEKA 262139
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
239 PM PDT Thu Apr 26 2018

.SYNOPSIS...An upper-level low will bring cooler weather and a
chance for showers Friday through Sunday. The potential for
isolated thunderstorms will also increase on Friday as the upper
low approaches the north coast.

&&

.DISCUSSION...Marine layer cloudiness has been covering most
coastal areas today. Clouds have cleared along the Mendocino
coast south of Ft Bragg, however expect a quick redevelopment
this evening as the flow remains onshore. The marine layer will
remain fairly deep tonight and expect low clouds to push well into
the interior valleys again tonight into early Friday morning.
Cooling aloft and southeasterly low level flow will most likely
eradicate or lift the marine layer up on Friday.

Cumulus clouds have been building over the higher terrain of
Trinity, Mendocino and Humboldt counties today. BUFKIT and NAM
profiles continue to indicate a slight potential for late day
convection and isolated storms, mainly over South Fork Mountain
and the Yolla Bolly wilderness area. Confidence we are going to
see storms is low, so have scaled back thunder chances and LAL`s
for this evening.

An upper level low west of 130W will slowly edge east-northeast
toward the west coast tonight through Friday. The latest GFS, NAM
and ECMWF handle the slow eastward progression about the same,
but continue to differ on smaller scale perturbations pin-wheeling
around the low center. The potential for showers will increase
everywhere on Friday. The threat for showers will continue through
the weekend. There is a slight chance for thunderstorms as well
starting as early as late Friday afternoon, mainly over the
coastal waters. In fact, a dozen or so lightning strikes have been
detected well offshore under the cold core aloft. NAM guidance
does indicate instability and low CAPE developing over the waters
Fri afternoon as a spoke of energy pin-wheels toward Cape
Mendocino by late afternoon. The instability should spread over
land areas by early evening. Another shortwave will swing toward
the coast late Fri night into early Saturday morning and may spark
up another bout of isolated storms for land areas and over the
coastal waters. The sounding from BUFKIT were not looking all that
impressive for thundertorms, however. It is a pattern favorable
for storms out toward the coast and over the waters. The main
threat will be cloud-to-ground strikes, however we will need to
keep an eye out for some small hail, heavy showers and gusty winds.

Model guidance remains in good agreement with another shortwave
trough dropping in from the northwest on Sunday. This will result
in another uptick in showers for Sunday. Overall, rainfall amounts
each day will be fairly low, with some areas dodging showers
completely, especially far southern Mendocino County.

Medium-range model guidance continues to be in good agreement with
a building ridge early to mid next week. Expect dry weather,
plenty of sunshine and warmer temperatures for the interior. Coastal
areas may be quite breezy initially Mon and Tue. Also, night and
morning coastal stratus will become a forecast problem by mid week.

&&

.AVIATION...Widespread stratus enveloped the North Coast today...as
well as local interior valleys and the coastal range. By 12 noon,
clouds remained quite entrenched with CIGS lifting into MVFR and
VIS 7+. IFR Cigs also expanded into the Mendocino Interior...and
surged north into UKI until shortly before noon. Through the
remainder of the 24hr 00Z TAF package: Clouds will persist along
the North Coast. Model guidances are somewhat conflicted whether
or not clouds will continue into MVFR or lower back into IFR
overnight. With an approaching "showery" weather disturbance
expected Friday, the solution for MVFR Cigs seems more probable.
/TA


&&

.MARINE...A low pressure center is moving towards the coast
however in the mean time ocean conditions will be relatively
tranquil with low winds and combined sea heights of 5-8 feet. The
seas are from a NW swell that is moving through the waters
currently. With the low pressure system there is a slight chance
of thunderstorms over the waters on Friday afternoon with
localized gusty winds and cloud to ocean lightning strikes being
the main hazard. Winds and seas will begin to build Sunday as
northerly winds and seas begin to ramp up. Winds will approach
gale force by late Sunday and persist through early next week
which will generate steep and hazardous seas. /WCI

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...None.
&&

$$

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