Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 231118

National Weather Service Eureka CA
318 AM PST Thu Feb 23 2017

.SYNOPSIS...A cold upper disturbance is forecast to move south
across northern California Friday and Saturday. Accumulating
snowfall will be likely as a result for elevations above 1500


.DISCUSSION...Lapse rates and ascent are forecast to diminish over
NWRN CA today as a cold upper wave shifts slightly eastward. This
will result in dissipating shower coverage/intensity going into
Thursday afternoon. Latest model guidance then shows skies
partially clearing by late tonight as weak post-trough subsidence
develops across the region. This, combined with generally weak
winds and recent ground wetting precipitation will favor fog
development...mainly over interior valleys.

Attention quickly turns toward an upper disturbance dropping south
out of western Canada during Friday. Multi-model consensus shows
a positively tilted upper trough moving south along the OR coast
Friday afternoon/night, and then continuing south across northern
CA during Saturday. As this occurs, 500 mb temperatures near -36 C
will spread across the CWA, which will aid in very steep lapse
rates and snow levels around 1000-1500 feet. In addition, a
persistent zone of ascent will occur along the southern periphery
of the trough, which is forecast to be focused over NWRN CA from
Friday afternoon through Saturday. As a result, training shower
development is expected, which could be vigorous given the steep
lapse rate environment. These showers are expected to yield
locally heavy snow (5 to 9 inches in a 24 hour period) above 1500
feet over Del Norte and Humboldt Counties.

After trough passage late Saturday afternoon, showers will once
again dissipate, but are then forecast to redevelop during Sunday
as a second cold upper disturbance slides southeast across the
region. High elevation snow accumulation is likely with this
wave...though the duration of snowfall may be shorter compared to
the Friday/Saturday event. After Sunday, a period of milder and
drier weather may be in store for the region as broad upper
ridging develops over a large portion of the NERN PAC.


.AVIATION...VFR to MVFR conditions and light winds to calm
conditions will continue at KCEC and KACV through the early
afternoon. The lower conditions will be due to reduced ceilings
and/or visibilities at times as showers move across the region.
VFR to MVFR conditions and light to moderate winds will prevail at
KCEC and KACV this afternoon and evening. VFR conditions and
light winds to calm conditions will continue at KUKI today.


.MARINE...The winds and seas will continue to gradually diminish
today and Friday as an offshore high pressure ridge builds across
the waters. An offshore low pressure system and associated frontal
boundary will increase the winds and seas across the waters
Sunday and Monday.


CA...Winter Weather Advisory until 10 AM PST this morning for CAZ108.

     Winter Storm Watch from Friday afternoon through Saturday
     morning for CAZ102-105-106.



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