Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 232315
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
415 PM PDT Fri Jun 23 2017

.SYNOPSIS...Hot conditions will continue through Saturday, with a
gradual cooling to near normal temperatures beginning Sunday.
Isolated thunderstorms will be possible Sunday and Monday across
the interior.

&&

.DISCUSSION...The heat continues throughout northwest California
as a persistent ridge of high pressure maintains it`s grip on the
west coast. Temperatures across the interior valleys have
generally reached near or slightly above 100 degrees across a
broad area...and while final highs may end up being 2 to 5 degrees
cooler than yesterday, it may not be noticeable to most. This is
expected to continue tomorrow, with very similar readings
throughout the interior. No changes were made to the ongoing heat
advisory, and it will continue into tomorrow. Trinity county may
see this advisory extended into Sunday, as these hot temperatures
may linger a bit longer here. Meanwhile along the coast, a
weakening offshore pressure gradient has resulted in a southerly
flow reversal along the coast, allowing a shallow stratus deck
to move northward through the day. While some very low elevation
areas have seen periods of stratus on land, the bulk of this cloud
cover has remained offshore. Overnight tonight this stratus will
likely surge inland, although the shallow depth of the marine
layer will limit its inland extent. This stratus will continue to
linger along the coast through at least Monday morning, inundating
low elevation areas in the evening and overnight and slowly
dissipating on land during the afternoons.

The next item of interest will be the potential for thunderstorms
over the weekend, as an upper level low pressure system is set to
develop off the coast and move onshore. As this low develops
Saturday and into Sunday, southerly flow will begin to advect
midlevel moisture into the region. The best chance for
thunderstorms will occur Sunday afternoon and evening when
instability and upper forcing is maximized, and storms will likely
be widely scattered and closely tied to the higher terrain in
Siskiyou, northern Trinity, and northeastern Mendocino counties.
The primary concerns with this activity will be lightning and the
potential for fire starts, although fuels in the higher elevations
remain relatively wet for this time of year. This is not the case
in the lower elevations, and the potential for fire starts does
exist. While Sunday will present the best chances for storms, a
stray storm or two will be possible late Saturday night or early
Sunday morning as modest midlevel instability advects into the
region. While likely very isolated in nature, should any nocturnal
storms develop during this period they would likely feature
little rainfall, and any lightning strikes would be mostly dry.
Isolated storms will again be possible Monday afternoon, but will
likely be focused from the Trinity Horn northward.

A notable cooling trend can be expected Monday and beyond as the
upper level ridge weakens, with temperatures generally near
normal. Chances for thunderstorms will also decrease Monday and
beyond. /BRC

&&

.AVIATION...Along the North Coast, skies remained clear (SKC)
overnight even as a stratus surged rounded Cape Mendocino...and
then advected more quickly than expected north to ACV. By 9:00 am,
the marine clouds had pushed across Humboldt Bay and up to
Trinidad. However, mixing caused the stratus to pull back to the
coast and out of much of THE Bay. ACV Airport and the nearby
immediate coast, including the coves of Westhaven/Trinidad, were
nevertheless breached by the stratus advection. With very little
mixing early on at that coast location, IFR/LIFR cigs became a
potential flight threat at ACV. By 1 PM, the stratus surged had
reached the Oregon border but mostly stayed well offshore. Expect
Cig and Vis to seriously deteriorate through the evening as the
marine influence shifts onshore. VFR skies will keep fair and hot
conditions over the Inland areas. TA

&&

.MARINE...Light winds and low seas this weekend. A trough of low
pressure is set up off the coast of NW California. This allows the
pressure gradient to relaxes. Do expect light winds through this
weekend. With light winds, seas will be lowering to 5 feet or less
for this weekend. However, we are still dealing with some steep
seas along the coastal waters at least through this evening.


We will return to a strong northerly wind regime starting next
Tuesday as the thermal trough moves back inland and the East
Pacific High re-establishes itself. With the tight northerly
pressure gradient, the strong northerly wind regime will persist
through most of next week.

Forecast is still on track. Little changes were made to the
previous forecast package. Extend the small craft advisory through
this evening as the steep seas is taking a little bit longer to
subside. GFS is used to update the forecast package.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Saturday for CAZ102-105>108-110-111-
     113.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 9 PM PDT this evening for PZZ450-470-
     475.

&&

$$

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