Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 251225

National Weather Service Eureka CA
425 AM PST Sat Feb 25 2017

.SYNOPSIS...Shower activity spreading inland early Saturday
morning is forecast to dissipate by Saturday afternoon. Another
storm system will then enter the region during Sunday, resulting
in additional shower development and high elevation snowfall.
Showers will persist going into early next week, followed by a
period of warmer and drier weather.


.DISCUSSION...A zone of enhanced ascent associated with a
southward moving trough, as well as increased low-level
convergence occurring with an offshore low pressure center, are
aiding in the development of locally heavy training showers. The
most vigorous shower activity is spreading inland near Cape
Mendocino, with one band of showers producing an intracloud
lightning strike (per recent lightning data). The lightning
confirms the convective environment these showers are embedded
within...which is mainly a result of cold midlevel temperatures
(near -34 C at 500 mb) and lapse rates from 7-8 C/km in the low
to midlevels. These trends suggest that locally heavy snow is
probably occurring above 2000 feet over southwestern and interior
portions of Humboldt County. Thus, the ongoing winter weather
advisory has been maintained, though the expiration time is now
18Z based on short term model consensus showing an increasingly
marginal environment for inland shower development by midday.

Meanwhile, WV imagery shows a vigorous midlevel impulse moving
south across the NRN AK panhandle this morning. This impulse is
forecast to reach coastal WA by 12Z Sunday, and then move across
far NRN CA by 00Z Monday. Several waves of ascent are forecast to
move across Del Norte and Humboldt Counties as this takes
place...and with lapse rates steepening once again in response to
cold midlevel temperatures, heavy shower development will be
possible. These showers will spread onshore by midday Sunday, and
then taper off in intensity during Sunday night. In addition,
current model guidance indicates the heaviest QPF with this
activity will occur over the northern half of the CWA. The
relatively heavy precipitation combined with subfreezing
mountain/ridge-top temperatures will support 12-hour snowfall
accumulations from 4-6 inches between 18Z Sunday and 06Z
Monday...which has prompted a winter storm watch issuance for
locations above 1500 feet in Humboldt and Del Norte Counties.
Lighter high elevation snow amounts are forecast to occur

Cold deep-layer northerlies are forecast to persist into early
next week, which will aid in sufficiently steep lapse rates for
occasional shower development. Midlevel ridging is then forecast
to occur over the NERN PAC by midweek, which will shunt cold air
aloft to the east. Large-scale subsidence will also develop over
the region...the end result being an extended period of dry
weather occurring during mid to late next week, and also
potentially warmer surface temperatures.


.AVIATION...Overnight, showers were impacting all terminals as
the low pressure dropped south along the coast and brought in
cooler and more unstable airmass into the area. The showers can
potentially lower conditions down to MVFR. Do expect the shower
activities to taper off by mid morning, as the low continues to
drift south of the area. Clearing skies will take place in the
late morning hours, should turn out to be a nice afternoon. For
overnight tonight, don`t expect much clouds to form, as the
northerlies should be strong enough to bring in enough dry air to
keep the sky cover to a minimum. /RCL


.MARINE...A compact low, currently off the NW California coast,
is making its southward trek. Early this morning, light to
moderate southerlies were found on the coastal waters. As the low
moved south of the area, the winds will shift to the north later
this afternoon and evening. The northerly winds will stick around
through Sunday morning, then shifting to the west with the advance
of the next low pressure system.

On Sunday morning, the next system will be over the Olympic
Peninsula. The main low will remain north of our area. For us, we
will be seeing mostly west to northwest winds in our coastal
waters for Sunday. After that, winds will shift to the north, and
persist through end of the work week.

Seas will remain fairly low, around 7 to 8 feet. There will be
time periods when the seas will go up to 9 to 10 feet at times
with the occasional increase in northerly winds.

No marine hazards are in effect at this time. /RCL

.SNEAKER WAVE POTENTIAL...Models are indicating there is a
moderate possibility for sneaker waves to occur along coastal
beaches from early Sunday morning through Sunday afternoon.
However, the models are still working on fine tuning the timing
of this event. Have issued a beach hazard statement to highlight
this potential hazard. /RCL


CA...Beach Hazards Statement from late tonight through Sunday
     afternoon for CAZ101-103-104-109.

     Winter Weather Advisory until 10 AM PST this morning for CAZ102-

     Winter Storm Watch from Sunday morning through Sunday evening
     for CAZ102-105.

NORTHWEST CALIFORNIA COASTAL WATERS...Beach Hazards Statement from late
     tonight through Sunday afternoon for PZZ410.



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