Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 272246
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
246 PM PST Mon Feb 27 2017

.SYNOPSIS...An unsettled weather pattern will persist through
Tuesday, with rain showers and higher elevation snow showers
persisting through then. Drier conditions will return for the
middle of the week, as a ridge aloft builds across the region.
This will come to an end by Friday though, as widespread
precipitation develops ahead of another approaching storm system.

&&

.DISCUSSION...An upper-level trough and moist nw flow will
continue to produce periodic showers tonight through Tuesday
morning, primarily across Del Norte and Humboldt counties. The
shower activity should start to wind down Tuesday afternoon and
evening as a surface ridge builds across the region and an
offshore flow develops. Snow levels will fluctuate around from
1500 to 2500 feet tonight through Tuesday morning. Scattered
amounts of an inch or less are expected above 2500 feet.
Temperatures aloft will be sufficiently cold tonight for isolated
hail showers, especially as another vort max moves across the
area in the northwest flow aloft. Significant hail accumulations
are unlikely. Also, anyone planning travel over Berry Summit or
South Fork Mountain Summit should use extra caution tonight.
Melting snow today will refreeze tonight and may create patches of
ice on the pavement.

Another concern for tonight and tomorrow night will be overnight
low temperatures falling below freezing across Mendocino county.
We are entering the month of March when we start to issue frost
advisories and freeze warnings for the entire coast and for all
of Mendocino county. With temperatures running 10-15F below
normal, we are going to start issuing frost advisories and freeze
warnings one day early, Feb 28th. A freeze warning has been issued
for interior Mendocino county for tonight. A frost advisory has
been hoisted for coastal sections of Mendocino county. Clouds,
showers and moist air will limit the potential for frost along the
coasts of Del Norte and Humboldt counties. Frost advisories and
freeze warnings are expected again tomorrow night.


PREVIOUS LONG TERM DISCUSSION...
(Wednesday through Sunday)

The middle of the week looks to be a great time to get out and enjoy
the sunshine. Short-wave ridging aloft will build across the region
from the southwest, with 500mb heights increasing from near ~540dkm
now, to near 570dkm. A similar response is seen in the lower-level
temperature fields, with 850mb temps going from negative single
digits to positive single digits.

What this means for us is temperatures will warm several degrees
during the afternoon for the middle of the week, compared to what
has been recently observed with these cooler, cloudier, and at times
wet days. The real tricky part of the forecast though will be the
low temperatures, as light winds and mainly clear skies offer ideal
radiational cooling conditions. Typically, lows are often lower
than what the majority of the short-range models indicate. This has
particular importance along the coast and across all of Mendocino
County, where the growing season starts Wednesday. Current
indications are for lows in the mid to upper 30s along the coast,
and lower to mid 30s across the Mendocino valleys, and this may be
be a little too high for reasons stated above. Thus, there`s a good
chance frost advisories may be need in the coming days.

All good things must come to an end, especially with this brief dry
spell, as another short-wave trough will move into our area from the
west just in time for your weekend. As the ridge flattens due to the
approaching trough, widespread precipitation will develop as
moisture and lift increases admist a cooling thermal profile aloft.
Get the galoshes back out folks, as we`re not quite done with the
rain just yet. /PD

&&

.AVIATION...Post-cold front, unstable air continued to advect
into Northwest California today. This resulted in numerous
showers rolling across the region...especially north of Mendocino
County. Therefore ACV and CEC airports and local surrounding
airfields were the recipient of these showers, some with small
hail. Conditions were also up and down MVFR through the afternoon.
Although showers may taper somewhat tonight, widely scattered
light showers are expected to persist through at least early
Tuesday morning. For much of Mendocino...a slight chance of
showers are still a threat this evening, mainly along the coast
and Northern Mendocino. The UKI airport and surrounding areas were
impacted this morning by LIFR/IFR cigs/vis but mainly cigs.
Drying and slight warming is expected at UKI, but IFR conditions
may develop briefly again Tuesday morning. TA

&&

.MARINE...Light to moderate winds will persist through the week as
a ridge of high pressure shifts over the western United States. This
will keep the gradient relaxed thus winds gusts are not expected to
surpass 20 kt, at least through midweek. Meanwhile, the marine
environment will be dominated by multiple northwesterly wave
systems. Mariners can expect waves around 6 to 8 feet around 13
seconds through the week. The pressure gradient will flex late in
the work week bringing some fresh wind gusts before a quick hitting
low pressure system causes south winds to increase for the weekend.
Until then, the existing small craft advisories were extended to 9
PM this evening as nearshore buoys reported marginal seas around 10
ft late this afternoon. Seas should diminish further tonight with
no advisories expected for the next few days. /KML

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Frost Advisory from 3 AM to 8 AM PST Tuesday for CAZ109-112.

     Freeze Watch from late Tuesday night through Wednesday morning
     for CAZ110>113.

     Freeze Warning from 3 AM to 8 AM PST Tuesday for CAZ110-111-113.

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until
9 PM PST this evening for PZZ450-470-475.

&&

$$

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