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fxus66 keka 222245 
afdeka

Area forecast discussion
National Weather Service Eureka California
345 PM PDT Sat Jul 22 2017

Synopsis...
isolated thunderstorms are possible for portions of Trinity, del
norte, and Humboldt counties tomorrow through early next week.
Otherwise, hot and dry conditions will continue to persist across
the interior for a few more days before more seasonal temperatures
return early next week. Coastal low clouds and patchy fog will
also be possible each night however sunshine should return each
afternoon.

&&

Discussion...
the marine layer has been shrinking throughout the day and most of
the coastal stratus has disappeared this afternoon. Tonight,
offshore flow in combination with a compressed marine layer should
keep the stratus confined to areas just along the coast. This
coastal stratus should dissipate again tomorrow by early
afternoon.

Inland hot temperatures will persist for at least one more day with
more seasonal temperatures (granted still warm) returning early next
week. The main forecast issue for this cycle is the chance for
thunderstorms across the interior tomorrow through mid-week. Water
vapor analysis currently shows a mid-level low located across the
Pacific slowly moving towards the California coast which will be the main
player for the week. While the GFS has been consistent for the past
few runs of developing isolated thunderstorms across the interior
mountains, other models do not present the same scenario. Therefore
quite a few questions still remain as to what will actually happen.

Most models are consistent with slowly bringing the mid-level low
just south of Cape Mendocino and then leaving it there to spin lobes
of energy across our area. Models have been slowing the progression
of this low onto land with subsequent runs which is why isolated
thunderstorms now appear possible through Wednesday. Timing of this
passage will dictate when the thunderstorm chances across the
interior will come to an end. Precipitable water values are
expected to increase to around an inch by tomorrow afternoon by
several models however the exact source of this moisture is still
a bit questionable. GOES-16 derived total precipitable water still
shows around 0.4 inches across our region with no indication of
higher precipitable waters streaming in however the stratus is preventing
retrieval of values across the Pacific but bears watching tonight
into tomorrow. Other convective parameters do appear favorable
for thunderstorms with CAPES near 1000 j/kg, Li near
-3, and lapse rates near 8.0 c/km. Modest 0-6km shear values are
also present with an upper level jet streak off to our south and
west which would help to organize any thunderstorms that do form.
As this system approaches the coast it will be better analyzed
which should help models come to a more uniform solution.

The second half of the week the mid level low should push inland
leaving US in zonal southwest flow. This will lead to the
termination of thunderstorm chances and a return to more seasonal
temperatures. /Wci

&&

Aviation...
a bank of low clouds developed and lowered late last
night, with a period of low visibilities at kcec this morning. This
cloudiness dispersed early this afternoon, with just a few clouds
lingering in the Eel River valley. Looking at the model low-level
moisture flux convergence product, it appears likely that clouds
will reform near the coast north of Cape Mendocino later this evening,
and have generally indicated a similar forecast at Redwood coast taf
sites to what happened this morning. High resolution guidance does
indicate some low-level offshore flow tonight in del Norte County,
so uncertainty is moderate to high at kcec. In addition, smoke from
a fire in east Curry County in SW Oregon may periodically produce a
smoke layer near kcec. Kuki is expected to remain VFR. /Sec



&&

Marine...
a thermal trough over the interior and east Pacific high
pressure will maintain a tight pressure gradient over the coastal
waters into the middle of the coming week. As a result, winds will
continue to gradually increase tonight with sustained gales possible
over the north outer waters. Have hoisted a hazardous seas watch for the
S outer waters for Sunday afternoon through Monday afternoon. Gale
force gusts will affect the northwest portion of the S outer zone, but the
areal extent isn't forecast to necessitate a gale watch. However,
building seas will continue to be directed into the zone from the
stronger winds to the north. Have also extended the Small Craft Advisory
for the north inner and S outer waters into midday Tuesday. /Sec



&&

Fire weather...
gusty northeast and easterly winds will continue over
the exposed ridges of Humboldt and del norte counties tonight with
poorer relative humidity recoveries. The offshore flow pattern coupled with
strong warming aloft will continue to bring hot daytime
temperatures as well as lower daytime humidities on Sunday. In
addition, an upper-level low will bring the possibility for
thunderstorms Sunday through early next week especially across
the interior mountains.




&&

Eka watches/warnings/advisories...
California...none.
Northwest California coastal waters...Small Craft Advisory until noon PDT Tuesday for pzz450-475.

Gale Warning until 5 PM PDT Monday for pzz470.

Small Craft Advisory until 11 am PDT Sunday for pzz455.

Hazardous seas watch from Sunday afternoon through Monday
afternoon for pzz475.

&&

$$

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