Area Forecast Discussion
Issued by NWS Eureka, CA
FXUS66 KEKA 291036
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
336 AM PDT FRI JUL 29 2016
.SYNOPSIS...Hot and dry conditions will continue through the end
of the week across the interior. Coastal areas will likely see
little change, with nocturnal and morning clouds and near normal
temperatures. A slight cooling trend is expected this weekend
through early next week.
.DISCUSSION...Not much has changed over the region since yesterday
with high pressure dominating the current conditions.
Temperatures will once again be hot across the interior while
coastal areas fight the stratus within the marine layer. Moisture
is on the increase as southerly flow increases on the west
periphery of the upper level ridge, and there may be just enough
moisture combined with afternoon heating to trigger a thunderstorm
over the higher terrain of northern Trinity County this afternoon.
Model soundings remain rather unimpressive with a mid-level cap
likely stout enough to keep most upward motion limited. Thus,
chances for storms have been kept at 15-20% in the farthest
northern mountains of Trinity County and this percentage could be
too high. Similar conditions are expected on Saturday only with
less surface heating, so chances for any storms on Saturday in the
Trinity horn have been kept below 10 percent.
A slight cool down will occur over the weekend into early next week
as an upper trough moves through the Pacific Northwest and lowers
heights across Northwest California. High temperatures across the
interior will fall back to near normal but only for a brief period
as 850 mb temperatures quickly rebound again mid to late next week.
Coastal areas will remain stuck within the cool marine layer with
highs in the upper 50s to mid 60s. The marine layer will likely
deepen slightly as the upper trough slides by early next week.
Otherwise a continued pattern of overnight and morning clouds/fog
with partial to complete afternoon clearing will persist for at
least the next week and likely beyond. /RPA
.AVIATION...Ceilings and VSBYs have been falling through the night
at both KACV and KCEC as a shallow marine layer clings to the
shoreline of northern California. Light drainage winds have been
keeping the fog (FG) and stratus somewhat subdued around KCEC.
Stratus and fog should dissipate quickly there shortly after sunrise.
Also, VSBYs probably will not be as low as yesterday. Expect the
bulk of stratus and fog to dissipate by mid to late morning at both
airports as the land mass heats up. Light northerly flow in the
afternoon will pump cool marine air onshore through the day and
expect flying conditions to deteriorate once again this evening
after solar heating abates. The marine layer will NOT push very far
into the coastal river valleys today or tonight. VFR will continue
to reign at KUKI through the period.
.MARINE...Strong north winds and large steep seas will persist
across the outer waters through the weekend as high pressure
interacts with a thermally induced trough over the interior.
The strongest winds will continue to be in the northern outer
waters. ASCAT pass indicated a swath of northerly winds at 30kt.
There have been local maxima of 35kt just north of the area across
southern Oregon coastal waters. Models continue to trend upward
through the weekend and northerly wind are expected to reach full
GALE tonight through Saturday. South of the Cape 10-60nm from shore,
GALE conditions will be marginal, however seas will be large and
very steep. The small craft ADVISORY for winds and seas will need to
be upgraded to WARNING for seas if this upward trend continues.
Once again buoys have been reporting seas around 10 ft with periods
at 9 seconds early this morning. This is clearly within our criteria
for a WARNING for seas north of Cape Mendocino inside 10nm. Wave
heights will probably fall off later this morning and for that
reason will maintain only a small craft ADVISORY for seas. Wave
heights inside 10nm north of the Cape will most likely build and
become very steep again tonight through Saturday as north winds
crank up to 30-40kt offshore. A WARNING for hazardous seas will need
to be hoisted if the current trend continues. Thus far the NWPS
model has been very close to the observed buoy wave heights and
In stark contrast, wind and waves will probably trend downward or
remain steady for the inner waters along the Mendocino coast through
the weekend. Latest model guidance has winds going southerly this
weekend. Current indications are for the southerly winds to remain
on the light side; around 10 kt or less.
Conditions should ease up slightly offshore early next weekend,
however the NWPS model continues to indicate rough and steep
northerly waves with near GALE conditions through mid week. The
strongest winds may end up shifting south of the Cape as the
thermally induced trough retreats southward.
.FIRE WEATHER...Hot temperatures and low humidity can be expected
to last through Saturday, before a slight cool down brings
temperatures back to normal...which is to say still quite warm and
dry. Gusty offshore winds and moderate humidity recoveries can be
expected along exposed ridges across Del Norte, northern Humboldt,
and northern Trinity counties overnight tonight.
This afternoon, a weakness in the upper level ridge overhead will
develop offshore, and an area of weak vorticity will slowly move
onto the coast. As this occurs, a tongue of modest mid-level
moisture will creep northwards along the western periphery of the
ridge. As a result, the combination of increased
moisture/instability and modest upper forcing may be enough to
trigger a few mostly dry thunderstorms across mainly the mountains
of west-central Siskiyou County, and perhaps a few in extreme
northeastern Trinity County. While fuels are receptive to fire
growth in most areas, given that coverage will likely be extremely
limited in this region, this event will continue to be represented
with a headline in the Fire Weather Forecast. /BRC/RPA
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 11 AM PDT Monday for PZZ450.
Gale Warning until 8 AM PDT Monday for PZZ470.
Small Craft Advisory until 5 AM PDT Wednesday for PZZ475.
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