Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 232307

National Weather Service Eureka CA
407 PM PDT Tue May 23 2017

Warm temperatures will continue on Wednesday followed by a
gradual fall back to normal values late in the work week. Coastal
areas will remain more seasonal with morning clouds and afternoon
sunshine. Pop up showers will be possible over the mountainous
interior the next few afternoons with a slight chance for
thunderstorms on Wednesday.


An upper level ridge is current centered over Northern California
leaving much of northwest California under clear skies, except for
the normal stratus along the coast. Stratus/fog has been
particularly persistent from the mouth of the Eel River and south
along the Mendocino County coast with a well defined eddy in place
south of Cape Mendocino. This eddy has weakened over the last few
hours as northerly winds increase over the coastal waters, but it
seems unlikely that the southern Humboldt and Mendocino immediate
coasts will see much clearing at all this afternoon. Stratus will
likely reform overnight along the rest of the Humboldt and Del Norte
coastlines only to dissipate more quickly on Wednesday as gales
intensify over the coastal waters.

Temperatures will decrease significantly on Wednesday as the ridge
flattens and a shortwave trough moves through the Pacific Northwest.
Some interior areas will see temperatures fall 10 to 15 degrees as
compared to today, followed by another potentially 10 degree drop on
Thursday bringing interior areas back to normal or slightly below
normal. The upper level ridge will amplify again late in the week
into this weekend bringing a gradual warmup back to around 10
degrees above normal early next week. As the shortwave moves inland
on Wednesday, the cooling aloft may be just enough to trigger a few
showers or thunderstorms during the afternoon and evening over
eastern Trinity County.

In addition to the gradual warmup, upper level shortwaves will move
over the area from the southwest on the eastern periphery of a deep
trough. This, in combination with the warm temperatures across the
interior, will support the potential for mountain convection each
afternoon beginning Saturday through mid next week. There is
potential that one or two of these days could have scattered
afternoon showers and storms depending on the timing of the
shortwaves moving overhead. /RPA


Overnight, stratus brought IFR-LIFR conditions to most of the
airports/airfields near the the immediate coast. By Noon, only
lingering pockets of stratus continued from Humboldt Bay to Point
Saint George/Crescent City. However, the entire shoreline of
Mendocino remained under a blanket of marines clouds as a south
surge moved up its coast then around Cape Mendocino and sort of
blended with the stratus north of the Cape. By mid afternoon the
stratus surge was affecting Humboldt Bay and heading to ACV. The
surge will allow for another eve/night of IFR CIGS. Inland areas
will generally remain hot and sunny through the period, with a weak
threat of convection over Trinity tomorrow. There is also the
possibility that low clouds may edge near the UKI valley from the
south on Wednesday.


Northerly winds will increase substantially tonight into Wednesday as
high pressure over the eastern Pacific interacts with a strong
thermal trough over interior California. Model guidance is unanimous
in producing sustained gale force winds beyond 10 nm north of Cape
Mendocino and gusts to gale force into the northern inner waters and
southern outer waters. The gales and potentially a few storm force
gusts will also produce very steep seas that will propagate into the
northern inner waters and extreme northern portion of the southern
waters zone near Cape Mendocino. With seas exceeding hazardous seas
criteria north of Cape Mendocino and gusts expected to reach near
gale force, opted to raise a gale warning for the northern inner
waters. Seas will likely peak between 15 and 20 feet in the outer
waters and around 10 to 15 feet in the northern inner waters beyond
5 nm Wednesday into Wednesday evening. The models continue to
indicate that the majority of the inner waters zone south of Cape
Mendocino will not experience even small craft conditions, so no
headlines have been issued.

Winds and seas will decrease through the day Thursday into Thursday
night as the thermal trough weakens. Additionally, high pressure
over the eastern Pacific will shift farther north as an upper trough
approaches. This should result in a period of very light winds late
Friday into Saturday with coastal areas experiencing light
southerlies. /RPA


    Small Craft Advisory until 3 AM PDT Wednesday for PZZ450-475.

     Gale Warning from 3 AM Wednesday to 3 AM PDT Thursday for PZZ450.

     Small Craft Advisory until 9 PM PDT this evening for PZZ470.

     Gale Warning from 9 PM this evening to 6 PM PDT Thursday for

     Gale Warning from 3 AM Wednesday to noon PDT Thursday for PZZ475.



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