Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 191033

National Weather Service Eureka CA
333 AM PDT Fri Apr 19 2019

.SYNOPSIS...While warm interior temperatures are expected again
today, cooler and cloudier conditions are expected along the
coast. Isolated weak thunderstorms will be possible this
afternoon and Saturday across interior mountains. Warm and dry
conditions are expected Sunday through at least Tuesday, with a
gradual cooling trend to close out the week.


.DISCUSSION...An expansive shield of marine stratus continues to
grow along much of the California coastline early this morning,
gradually filling in any remaining cloudless areas as it does so.
Satellite imagery and local profiler observations indicate that
the marine layer is deepening with time, spreading stratus and
localized fog farther inland by way of coastal river valleys. This
deepening is likely in response to an approaching weak upper-
level low pressure system and the gradual cooling of temperatures
aloft. This is expected to continue through the day, likely
spreading marine stratus well inland and to elevations as high as
2500 feet by late morning. While the weakening marine inversion
and afternoon mixing will likely allow for some localized
clearing to occur by mid afternoon, some areas along the coast and
especially in the coastal hills in Humboldt and Del Norte
counties will likely stay cloudy much of the day.

Farther inland, most areas will likely remain mostly sunny
through roughly mid-day aside from some increasing high cirrus.
Meanwhile, atmospheric moisture will steadily increase ahead of
the approaching trough, and the combination of this increasing
moisture, slightly cooler temperatures aloft, and afternoon
surface heating will yield some modest instability by the mid to
late afternoon. This instability will be maximized across the
higher terrain regions of far eastern Trinity and Mendocino
counties, where some isolated showers and perhaps a few
thunderstorms may develop during the late afternoon and evening.
While just enough instability to support weak thunderstorms may
develop, poor mid level lapse rates and modest wind shear will
prevent these storms from becoming particularly strong. This
initial convective activity will wane by late evening, but a
passing weak cold front will likely bring a wave of lighter
showers and perhaps some coastal drizzle to the region overnight
Friday and early Saturday morning. A lack of instability will
preclude this nocturnal activity from becoming particularly

Late Saturday morning more substantial cold air advection aloft
will occur as the trough axis moves overhead. While instability
will be weaker overall than the previous day, another round of
renewed convection is expected to develop across the eastern
mountains as early as mid to late Saturday morning. Despite the
fact that shower coverage may actually be greater Saturday than
Friday, the more significant activity and widespread precipitation
is expected to the east of Trinity county. Showers will diminish
by late afternoon, and the remainder of the night will be dry as a
ridge of high pressure begins to build into the region.

Quiet and downright pleasant spring weather is expected Sunday
through at least Tuesday as the aforementioned ridge builds into
California. After a relatively cool day Saturday, a steady warming
trend will begin Sunday with interior valley areas likely climbing
well into the 80s by Tuesday. A gradual cooling trend will then
follow Wednesday through the end of the weak as the ridge diminishes
and a weak upper trough sinks back into the region, perhaps also
bringing more opportunities for isolated interior showers. /BRC


.AVIATION...Marine stratus continues to expand along the coast
and into coastal river valleys. Area profilers suggest the marine
layer will continue to deepen as an upper-level low approaches the
area. Stratus will continue to spread inland and to some of the
coastal hills early this morning. Widespread clearing is not
expected along the coast, coastal river valleys, and coastal hills
until this afternoon. Localized areas of clearing and localized
areas of overcast are also possible through this evening in
coastal areas. Ceilings are expected to rise at coastal terminals
late this morning, allowing for MVFR to VFR conditions to develop.
Low clouds will continue across the interior valleys through late
this morning, with VFR conditions expected to prevail by mid-


.MARINE...Moderate northerlies will continue through this
morning, with winds expected to be a little stronger south of Cape
Mendocino. Northerlies will increase by this evening and continue
to increase to Gale Force in strength on Saturday across the
outer waters. The Gale Watch has been upgraded to a Gale Warning
beginning Saturday morning and continuing through early Sunday
morning. Steep, short- period seas will develop as a result of
these increasing northerlies. Winds will remain elevated through
early Sunday and are forecast to gradually weaken through early
next week. Otherwise, a long-period northwest swell will persist
through today, before weakening this weekend.


NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 5 PM this afternoon to 8 AM PDT
     Saturday for PZZ470.

     Gale Warning from 8 AM Saturday to 5 AM PDT Sunday for PZZ470-

     Small Craft Advisory from 11 AM this morning to 8 AM PDT
     Saturday for PZZ475.



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