Winter Weather Advisory 3, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
246 PM PST Fri Feb 8 2019

.SYNOPSIS...Light showers occurring over southern Mendocino County
will dissipate this evening. Meanwhile, a cold storm system will
move south across the region tonight through Sunday. This system
will yield heavy snow across the mountains and small hail along
the coast. Additional episodes of high elevation snow and low-
elevation rain are likely during the next work week.

&&

.DISCUSSION...A weak upper low was in the process of moving
onshore in the vicinity of the Bay Area Friday afternoon. A zone
of enhanced ascent was occurring north and east of the low, and
was aiding in trace amounts of precipitation over Sonoma and
southern Mendocino Counties. Model guidance indicates that
precipitation will come to an end this evening as the upper low
fills and departs eastward. However, a stronger and much colder
upper low (characterized by 700 mb temperatures from -14 to -22 C)
is forecast to move from coastal WA this evening south across
coastal OR by Saturday afternoon.

As that occurs, bands of showers will spread south and east
across NWRN CA. Hi-res model guidance indicates initial activity
will enter Del Norte County by 12Z Saturday, and then fill
southward across the remainder of the CWA Saturday morning and
afternoon. Precipitation rates are forecast to peak over the
mountains near 21Z Saturday...and will be collocated with freezing
levels ranging from 1000 feet over Del Norte County, to 3000 feet
over Mendocino County. Later Saturday night, a second wave of
heavier precipitation rates is forecast to occur over the coast
mountains. That round of precipitation will be occurring amidst
freezing levels ranging from 500 feet over Del Norte County to
1500 feet in Mendocino County. These trends continue to support
the inherited Winter Storm Warning valid for elevations above 2500
feet Saturday night through Sunday morning, where 5 to 15 inches
of snow (locally higher) are anticipated. Please refer to that
product for more information.

In addition, steep lapse rates will support weak CAPE that will
favor heavy showers and isolated thunderstorms, some of which may
yield accumulating graupel and hail along the coast Saturday
through Sunday due to the very cold deep-layer airmass. A winter
weather advisory may ultimately be required for coastal locations
due to the potential for hazardous driving conditions produced by
hail/graupel accumulations.

Otherwise, latest model guidance shows the upper wave moving
inland across NRN CA by midday Sunday. This should lead to rapid
shower dissipation during Sunday afternoon. Thereafter, a second
frontal system is forecast to impact the region Sunday night into
Monday...a third Monday night through Wednesday...and then a
fourth Thursday night through the weekend. All of these systems
will have the potential to produce impactful snowfall across the
mountains, locally moderate rain at low elevations, and perhaps
small hail along the coast.

JMG

&&

.AVIATION...VFR conditions have dominated today for coastal
terminals as a system moves to the south of Point Arena. Light
rain is still possible across the southern half of Mendocino
county this evening, but conditions are expected to stay mostly
VFR since a bulk of the rainfall should pass to the south of
Ukiah. Later tonight, winds should switch to northerly across the
region as another short wave tracks south along the coast. Showery
precipitation with intermittent MVFR to possibly IFR conditions
are expected starting late tonight and early tomorrow morning in
Del Norte county, then spreading southerly as the morning
progresses. /TDJ

&&

.MARINE...Fairly light wind field is being observed this
afternoon across the coastal waters...despite the presence of a
fairly strong low pressure system. Generally southeast winds
blowing toward the low over the southern waters with west and
southwest across the norther waters. Winds speeds are generally
under 30 mph across all waters. Winds will weaken a bit through
this afternoon and evening. Westerly winds will develop by
Saturday afternoon across all waters and are forecast to increase
across all coastal zones. These strong westerlies will persist
through early on Sunday. West to southwest winds are expected to
continue through early Tuesday, with southerlies then redeveloping
across the coastal waters. Southerlies will persist through
Wednesday morning. A series of west to northwest swells will
impact the coastal waters over the next week. The next mid-period
northwest swell will move through waters later today and peak
around 13 feet at 12 seconds early on Sunday. A long- period
northwest swell will move through the waters on Saturday and peak
around 7 to 8 feet at 19 seconds early on Sunday. Additionally,
short-period wind driven westerly waves are forecasted to develop
in response to the increasing westerlies late on Saturday.
Combined seas will come down through today, but will come up again
on Saturday.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning from 4 AM Saturday to 4 PM PST Sunday for
     CAZ106>108-111.

     Winter Storm Warning from 10 PM this evening to 4 PM PST Sunday
     for CAZ102-105.

NORTHWEST CALIFORNIA COASTAL WATERS...None.

&&

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see the forecast zone map online:
http://www.weather.gov/eureka/zonemap.png