Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 162241

National Weather Service Eureka CA
341 PM PDT Wed Aug 16 2017

.SYNOPSIS...High pressure building over the west coast will bring
warming to the interior for the rest of the week. An upper level
trough will knock down temperatures slighlty this weekend.


.DISCUSSION...Pics from space today showing a pronounced smoke
signature from fires near Happy Camp and Orleans. Due to the
Northeast flow the smoke is making a bee line from northeast to
southwest promoting very hazy and somewhat obscured skies over
the north coast and Humboldt Bay. The current ridge of high
pressure will nose over the area on Thursday and high
temperatures across the interior valleys will warm another 5-10F.
The heat risk will be moderate across central and eastern Trinity
county as well as northeastern Mendocino county where high
temperatures are expected to peak around 100-105F. Folks are
encouraged to take necessary precautions to avoid heat related
issues...and stay as hydrated as possible. The north coast should
see warming also as an offshore wind flow pattern suppresses the
marine layer and limits the extent and duration of stratus and
fog. Lower 70`s for Eureka seems unlikely with a distinct onshore
component in the afternoon...but given the squashing of the marine
layer (2000` Tues to < 1000` today) late morning clearing at the
coast is likely over the next few days.  The Mendocino coast on
the other extreme will continue to be socked in due to a stronger
southerly push of the low clouds up against the terrain.  Marine
air may trickle into the Anderson valley and perhaps into the
Russian river valley reducing the potential for 100F heat. It is
not clear that stratus will round the Cape Thu or Fri. Diurnal
local stratus will still form north of the Cape, especially around
Humboldt bay and in the delta...but again..may clear earlier in
the day than what was seen earlier this week. The warming trend
will level off or reverse this weekend as an upper level trough
approaches the northwest California coast. The trough will weaken
and split with a cut-off low forming nearby the forecast area by
late in the weekend. We may be in store for another round of
interior showers and thunderstorms early next week. The latest GFS
continues to indicate wrap around moisture as well as instability
on Tuesday. The threat for interior showers and wet storms may
continue into Wed. However confidence still fairly low on this


.AVIATION...Marine stratus, MVFR-LIFR continued along the North Coast
today although clouds did not appear to be as expansive. This was
especially so at CEC this morning where clouds advected out of
the area early. Elsewhere clouds were slower to mix out and
continued to hug the immediate coast through afternoon...and
stayed offshore. At CEC, north winds ramped up around noon helping
to keep clouds well south of the area. Therefore, CEC may remain
mostly clear overnight. Model guidance is somewhat "IFFY" at this
time (mid-afternoon). Along the Humboldt Coast, the extent of the
low clouds were thinned out shortly after noonday, but may see
clouds push back into ACV by this evening. The Mendocino coastline
will remain saturated with stratus clouds. Inland areas will
remain VFR through the TAF period. TA


.MARINE...Strong to gale force north winds will persist through the weekend in
the outer waters as a thermal trough strengthens over interior
California and surface high pressure builds over the eastern
Pacific. The strong winds will result in very steep and high seas,
particularly in the northern outer waters and northwestern portion
of the southern outer waters. Winds and seas will be lower in the
inner waters zones but some of the steeper seas could propagate into
the western half of the near coastal zones. Have opted to not expand
or lengthen the small craft in the northern waters zone as there is
very high uncertainty as to how the pressure gradient will set up
and where the steepest seas will be situated in relation to the two
near shore zones. /RPA


.FIRE WEATHER...Weak offshore flow will return tonight and early
Thursday and magnitude of wind looks very similar to last night`s.
Have continued to headline the klamath/trinity zones to reflect
the gustiness and accompanying localized lower recoveries. The
ridge of high pressure which is contributing to the offshore flow
will continue to gain momentum and gradually move east over the
region. This will reduce the offshore flow but allow interior
temperatures to warm and lowering corresponding daytime RH`s. The
ridge will gradually shift over the area on Thu through Fri and
high temperatures will likely peak around 100-105F in the hottest
interior valleys. Min RH`s will bottom out around 10-25% each day
for the next several days...and perhaps some single digit RHs over
the usual spots like Somes Bar and Big Bar. By Friday the upper
level ridge begins to flatten and the airmass becomes a bit more
troughy allowing temperatures to fall back to near normal for this
weekend. This trough may also generate a few mountain
showers...with the first day decent instability being Friday. The
focus of attention on Friday looks to occur over extreme east
side of the CWA around the alps and yolla bolla spine. Next week
is looking much more interesting for storms. The GFS continues to
show a cut- off low forming off the coast early next week. The
track and evolution of the upper low are still very uncertain as
the GFS changes around ever so slightly from one run to the next.
The GFS does indicate wrap around moisture and southeasterly flow
on Tuesday and Wednesday for wet storms at this time. For now will
indicate only a slight chance for Tuesday based on the last
several runs of the GFS...with confidence improving once (if) the
ECMWF comes around.



NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 5 AM PDT Thursday for PZZ410-450.

     Gale Warning until 9 PM PDT Sunday for PZZ470.

     Small Craft Advisory until 9 PM PDT Sunday for PZZ475.

     Hazardous Seas Warning from 7 PM this evening to 9 AM PDT
     Thursday for PZZ475.



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