FXUS66 KEKA 232153
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
253 PM PDT Fri Mar 23 2018
.SYNOPSIS...A round of heavy showers and isolated coastal
thunderstorms will move across the region Friday evening, and a
second round will impact the area during Saturday. This will
result in locally heavy mountain snow and possible small hail
along the coast. The unsettled weekend weather will be followed
by mild and dry conditions next week.
.DISCUSSION...A cold upper-level low was positioned offshore from
WA Friday afternoon. Numerous showers and isolated thunderstorms
were occurring along the southern periphery of the low, and were
impacting the coastal waters of NWRN CA and adjacent inland areas.
Small hail has occurred with some of the stronger showers and
storms near Crescent City and SWRN Humboldt County during Friday,
with hail remaining possible along the coast into the evening as
convection continues to train NE across the area. In addition, a
strong upper impulse will approach the region during the late
evening hours, and should aid in increasing precipitation rates
over the interior. As that takes place, snow levels are forecast
to fall to around 2000 feet. Thus, 2 to 5 inches of snow appears
probable tonight for elevations above 2000 feet in Trinity County,
as well as interior Del Norte and Humboldt Counties. Refer to the
latest winter weather advisory for more details.
A short-lived 6-9 hour lull in precipitation is expected during
part of Saturday morning. Thereafter, showers are forecast to
increase in coverage and intensity from midday Saturday into the
evening as the previously mentioned upper-low approaches NWRN CA.
In addition, 500 mb temperatures will quickly cool to around -32
to -35 C. The cold airmass will yield steep lapse rates, modest
CAPE, and snow levels from 1500-2500 feet. Heavy mountain snow
will be probable, especially as strengthening low-level
southwesterlies contribute toward favorable upslope ascent during
the afternoon. These ingredients support potential warning level
snowfall...refer to the latest winter storm watch for more
information. Isolated thunderstorms will also be possible in the
vicinity of the coast, and accumulating hail on area roadways may
occur, resulting in hazardous travel conditions.
The upper low will move east of the area during Sunday, and
lingering showers will progressively weaken as a result. An upper
ridge will then build over the northeastern Pacific during early
to mid next week. This will yield a dry weather regime, with
afternoon temperatures moderating into the 60s and 70s by
Wednesday. In addition, warming and subsidence aloft combined
with northerly surface winds promoting upwelling within the
coastal waters will lead to an increasingly favorable environment
for marine stratus by the middle of next week.
.AVIATION...Flight weather hazards continued to precede an
approaching cold front today. Activity ahead of the front seemed
to become more energetic in the afternoon at coastal
airports/airfields, especially around Cape Mendocino and other
North Coast locales. Through late afternoon into evening, isolated
thunderstorms & lightning with small hail will continue to be
embedded in showers. Southerly gusty winds will persist. Cigs/Vis
will generally stay VFR except in periods of moderate-heavy
showers...and occasional LLWS outside of convection possible at
least through early evening. Interior airfields...including UKI
will continue to host mostly showers, local breezy winds and
periodic reduced Cigs/VIS into evening. Higher terrain airfields
may be impacted by snowfall.
.MARINE...SW winds will drop off a bit tonight before picking
back up again early Saturday ahead of the next frontal system.
Winds will veer to NW behind the front late Saturday night and
early Sunday and diminish. Have kept the existing Small Craft
Advisory in place with no change to end time. N winds are forecast
to increase by Monday night as high pressure builds offshore and
a thermal trough develops over the land.
NW swell at a period of around 12 seconds will decay through
early next week. Another, much smaller NW swell at a period of
around 12 seconds will arrive by next Tuesday. /SEC
CA...Winter Weather Advisory until 5 AM PDT Saturday for CAZ102-
Winter Storm Watch from Saturday morning through late Saturday
night for CAZ102-105>108-110-111.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until
9 AM PDT Sunday for PZZ450-455-470- 475.
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