Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
408 am PDT Thursday Jul 28 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...a repeat of Wednesday is in store today with
temperatures across the interior remaining very hot while coastal
areas continue to be influenced by a thin marine layer. Southerly
mid-level flow will gradually increase today, ushering in better
moisture into the region with precipitable water values near one
inch by Friday. The increased moisture in combination with a
passing weak vorticity maximum may be just enough to trigger a few
isolated storms in the higher terrain of northern Trinity County
Friday afternoon/evening. A small area of slight chances for
showers or storms have been maintained with this forecast update.
A cooling trend will begin on Saturday with thickness values
decreasing as a passing upper shortwave moves overhead. A deeper
upper trough will move into the Pacific northwest early to mid-
next week bringing further cooling with temperatures falling back
to near normal for mid-Summer on Wednesday. A gradual warming
trend will begin again late next week into next weekend.
Along the coast, conditions will more or less remain static through
the weekend, with a shallow but persistent marine layer resulting in
overnight/morning clouds and fog each morning. Temperatures will
remain near average despite the interior heat with no significant
offshore flow to weaken the marine layer inversion. /Rpa
Aviation...a shallow marine layer of stratus and fog will meander
along the coastline through the day. LIFR to IFR conditions at kcec
and kacv should break up some by late-morning in response to weak
drainage winds and ground heating. However, onshore flow in the
afternoon will probably draw stratus and perhaps fog back into the
coastal terminals. Overall, IFR flying conditions will be the rule
through tonight at the coastal terminals. The marine layer probably
will not push very far inland and VFR will continue to reign at
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
where ascat pass indicated north winds at 35kt. The Gale Warning has
been extended through the weekend for the outer waters north of the
cape. Models continue to trend upward or near steady state through
the weekend. South of the cape 10-60nm from shore, gale conditions
will be marginal and for now issued a broad brush advisory.
Seas ramped up overnight. Heights were up around 10 to 11 ft with
periods near 8-9 seconds. This was very close to our criteria for a
hazardous seas warning north of Cape Mendocino inside 10nm.
Conditions will probably remain borderline for a warning today.
Therefore, will just run a Small Craft Advisory for hazardous seas
through the weekend. Seas may approach warning level tonight and
Friday morning. Nwps model indicates worsening wave conditions over
the weekend north of the cape where seas may reach warning criteria
as north winds offshore reach full gale. This will need to be
In Stark contrast, wind and waves will probably trend downward or
remain steady for the inner waters along the Mendocino coast. Latest
model guidance has winds going southerly over the weekend. Current
indications are for the southerly winds to remain on the light side;
around 10 kt or less. At this point in the forecast, will not hit
the wind reversal very hard.
Fire weather...very hot afternoon high temperatures will persist
through Friday as strong upper-level ridging remains in place over
northwest California. Afternoon minimum relative humidity values will bottom out
in the single digits to lower teens while overnight recoveries
remain rather poor on mountain ridges overnight. However winds
will be light throughout the period resulting in no significant
fire weather threat. The one concern is a slight chance of
thunderstorms over northern Trinity County Friday and Saturday
afternoons. If storms are able to form, the best chances will be
just north of the area into central and eastern Siskiyou County
with storms firing off the higher terrain of northern Trinity
County and moving northeast.
Coastal areas will be much cooler than the interior with a
continued marine influence throughout the next week. /Rpa
Northwest California coastal waters...
Small Craft Advisory until 8 am PDT Monday for pzz450-475.
Gale Warning until 8 am PDT Monday for pzz470.
Small Craft Advisory until 9 am PDT this morning for pzz455.
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