Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 222235 CCA

National Weather Service Eureka CA
335 PM PDT Tue Aug 22 2017

.SYNOPSIS...An upper trough will moderate interior temperatures
through most of the week. Warmer weather conditions are expected
for the weekend as high pressure builds over the area. Coastal
locations will continue to see the usual dose of low clouds and
fog through the week before the marine layer decreases.


.DISCUSSION...The primary concern tonight is the potential for
thunderstorms and lightning activity in Trinity county. An upper
level low offshore the southern CA coast has been steering mid
level moisture from the Great Basin northwestward into the NW
California today. The GFS and NAM as well as mesoscale analysis
indicates the best chance for storms across the Trinity mountains
north and northeast of Weaverville this evening. The storms appear
to be driven by the heating of the day and for the most part
should die down by mid to late evening. A shortwave pin-wheeling
around the upper level low may trigger a few overnight storms
past midnight, mainly across northern Trinity county.

Drier mid level southwesterly flow will spread into the area
through the day on Wednesday as an upper level trough approaches
the west coast. Thus, expect the thunderstorm threat to shift off
to the northeast and east. There does appear to be some lingering
instability in NE trinity county early Wednesday morning, so left
a slight chance of showers in the forecast for that area.

The offshore trough will moderate temperatures across the
interior through the week. The marine layer should remain
moderately deep with onshore flow dominating through the week. A
dry cold front will move across the region on Thursday and the
layer may lift up and push into the coastal mountains while
coastal areas clear out. The BUFKIT profiles support the idea of
a deeper marine through Thursday. The increase in northerly winds
offshore should help to erode the stratus clouds late in the week,
especially south of the Cape. For now, the stratus forecast has
been based largely on persistence and climatology due to the weak
offshore flow signal from the models and small amount of cooling
aloft from the front.

Going into this weekend, an upper level ridge will build over the
area resulting in warming for the interior. Interior valleys will
once again flirt with 100F degree heat as 850mb temperatures hit
25-30C in response to strong adiabatic warming. The marine layer
should compress with the potential for dense fog at sea level. The
offshore flow does not look very pronounced at this point, thus
patches of low clouds and fog may linger near or at the shoreline
through the day. The hot weather will most likely continue into
the early portion of next week as strong ridging aloft dominates
the weather across the region.


.AVIATION...The marine layer stratus has persistently and
consistently kept coastal conditions below VFR through several
day`s TAF cycles.... remaining quite entrenched and showed little
possibility of breakup. However, middle upper level clouds
advecting west to east into Humboldt today "may" be the catalyst
to briefly allow for some dispersal of stratus from EKA-
ACV...therefore briefly raising CIGS at ACV. The 20Z (1PM)
Satellite Visual Picture gave weak indication of this scenario.
Still plenty of skepticism since the stratus has been quite
prevalent and has been a little tough to see under all the mid-
high level clouds. Also models not really optimistic. For now
will hang on to model solutions. Inland mountains/valleys:
Plethora of mid-upper level clouds being driven across the region
will continue to produce Thunderstorm threats to flight
operations. However, VFR skies and visibilities should prevail. ta


.MARINE...Relatively low marine conditions prevailed today with
predominately light winds and seas ranging from 3 to 5 feet.
Conditions will change starting tonight as high pressure offshore
brings increasing northerlies. Moderate to fresh winds will develop
on Wednesday, with the strongest winds across the southern waters.
Then strong winds will become more widespread Thursday and Friday as
the pressure gradient tightens further. Gale force wind gusts will
be possible, primarily across the outer waters, later in the work
week. The existing advisories will continue but we will have to take
a look at the possibility for a potential gale warning. As of now,
gale gusts look marginal but there may be a quick shot of gusts near
40 kt Thursday night. Stay tuned. In addition, small craft
advisories will likely be needed across the inner waters but it is a
bit too early issue. Steep seas will build through the week with a
few moderate northwesterly wave systems forecast to propagate the
waters. It looks like some relief will come late this weekend into
next week as the ridge of high pressure weakens offshore. This will
subsequently allow winds to diminish and seas to subside but there
is some uncertainty this far in advance. /kml


.FIRE WEATHER...A red flag warning remains in effect for zone 283
through this evening for abundant lightning. Thus far, the only
lightning activity has been in-cloud just north of the Trinity
Alps. The models continue indicate favorable convective
parameters for isolated storms over the Trinity mountains this
evening, though confidence is not high we are going to see a
major outbreak of lightning activity in zone 283 this evening.
The storms should be slow moving resulting in the potential for
locally heavy rain. An isolated dry strike may still occur outside
of these wet cores. Warmer and drier weather conditions are
expected to return this weekend. This may allow holdover fires to
intensify and spread. An offshore flow is expected for the
weekend, however current indications are for east winds to be
lighter than the offshore flow event last weekend.


CA...Red Flag Warning until midnight PDT tonight for CAZ283.

Small Craft Advisory from 3 AM Wednesday to 9 PM PDT Thursday
for PZZ470-475.



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