Area Forecast Discussion


303 
FXUS66 KEKA 172307
AFDEKA
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
307 PM PST Sat Feb 17 2018
.SYNOPSIS...An incoming storm system will bring rain and snow 
showers to northwest California beginning late this afternoon 
through early Monday morning. Snow levels will rapidly fall from 
3000 feet early Sunday morning to near 1000 feet Sunday night.
Small hail is possible along the coast. A prolonged period of 
cold temperatures will persist into early next week. 
&&
.DISCUSSION...Light rain will continue to spread south across the
area this evening as a cold front moves through the area. Snow
levels tonight will be above 5,000 feet with this initial band of
precip. Rainfall totals tonight are expected to range from a 
tenth to a quarter of an inch in Humboldt and Del Norte county
with lower amounts farther south and east. 
Early Sunday the upper level trough will start to spread south 
bring showers to the area. Models have come into better agreement
on some very cold air moving over the area. Snow levels are 
expected to fall to around 1,000 feet in the north to 2,000 feet 
in the south by late Sunday afternoon. Sunday night into early 
Monday morning showers will start to diminish, but snow levels 
will continue to fall to around 500 to 1,000 feet across the area.
A few snowflakes are possible at the coast, but no accumulation 
of snow is expected. Small hail or ice pellets is likely with the 
convective activity along the coast Sunday afternoon and evening. 
Instability is not too high, only around 200 j/kg, and lapse rates
are modest, between 6.5C and 7C/KM. The very cold airmass still
makes it likely there will be some accumulating small hail on 
area roadways in the heavier showers. Monday morning a few 
lingering showers are expected with snow levels ranging from 500 
to 1,000 feet. Lows Sunday night will be in the 20s inland with
temperatures around freezing at times on the coast. Temperatures 
will remain chilly in the afternoon with highs remaining in the 
40s in most areas.
Monday night into Tuesday is expected to be the coldest morning
with 850 mb temps over the area are still around -5 to -8 C. With
clear skies temperatures could easily drop into the teens and 
widespread areas in the 20s are likely, even at the coast. Some 
single digit temperatures possible in the cold spots of Trinity 
county that remain clear. The main question will be cloud cover. 
The models have recently started showing a fairly small system 
passing by to the west of the area Tuesday morning. The current 
model timing shows the clouds increasing around sunrise with some 
light showers at the coast in the afternoon. Confidence is low on 
the strength and location of this system due to it's relatively 
small scale. If this moves farther onshore it could keep 
temperatures warmer overnight. There is also the potential for 
freezing fog to develop overnight, but it is not expected to be 
very widespread. If this system does move onshore some light
precip is possible during the day on Tuesday and snow levels will
likely be quite low with it. 
Tuesday night models show this system moving out fairly quickly,
although some lingering clouds could have some impact on
temperatures. In general the airmass behind this system looks
warmer so Wednesday morning is not expected to be as cold.
Late in the week and into the weekend the ECMWF is showing 
several more fairly cold weather systems bringing some additional 
rain and snow to the area. The GFS is much drier with these 
systems, although cold air will remain over the area. Trended the 
forecast slightly toward the ECMWF as it seems to have been 
handling the moisture in these systems out of the north somewhat 
better. MKK
While northwest winds will generally remain light to 
moderate throughout the waters the remainder of the day, winds are 
expected to steadily increase Sunday morning, eventually reaching 
near 30 kt sustained with gusts to 40 kt across the outer waters. 
Meanwhile, a large swell from the northwest will move through the 
waters Sunday evening through Monday morning. The combination of 
steep wind-driven seas and the arriving swell will result in very 
large and  hazardous seas, with combined wave heights reaching 20 to 
25 feet throughout much of the waters. As a result, a Gale Warning 
has been issued for the outer waters from late Sunday morning 
through Monday afternoon, and a Hazardous Seas Warning has been 
issued for the nearshore waters of Humboldt and Del Norte counties. 
Winds will steadily decrease through the day Tuesday, allowing seas 
to slowly subside.
Tuesday and Wednesday, north winds of 15 to 20 kt will maintain 
somewhat elevated seas, likely with wave heights between 7 and 9 
feet. However, north winds will increase again Thursday through the 
end of the week, resulting in the buildup of steeper seas that will 
last through at least the end of Friday. /BRC
&&
.AVIATION...Ceilings along the coast are gradually lowering along 
the coast as a cold front approaches. MVFR ceilings have already 
developed at CEC, and are expected to do so shortly at ACV as well. 
Showers are also expected to move into both terminals this afternoon 
and evening, and these showers along with periods of MVFR ceilings 
will continue to impact both coastal terminals through Sunday 
afternoon and likely beyond. Episodes of small hail and perhaps even 
a brief snow shower or two will be possible early tomorrow morning. 
At UKI, VFR conditions continue to hold, but broken MVFR ceilings 
will be possible overnight tonight through the day tomorrow. /BRC
&&
.MARINE...While northwest winds will generally remain light to 
moderate throughout the waters the remainder of the day, winds are 
expected to steadily increase Sunday morning, eventually reaching 
near 30 kt sustained with gusts to 40 kt across the outer waters. 
Meanwhile, a large swell from the northwest will move through the 
waters Sunday evening through Monday morning. The combination of 
steep wind-driven seas and the arriving swell will result in very 
large and  hazardous seas, with combined wave heights reaching 20 to 
25 feet throughout much of the waters. As a result, a Gale Warning 
has been issued for the outer waters from late Sunday morning 
through Monday afternoon, and a Hazardous Seas Warning has been 
issued for the nearshore waters of Humboldt and Del Norte counties. 
Winds will steadily decrease through the day Tuesday, allowing seas 
to slowly subside.
Tuesday and Wednesday, north winds of 15 to 20 kt will maintain 
somewhat elevated seas, likely with wave heights between 7 and 9 
feet. However, north winds will increase again Thursday through the 
end of the week, resulting in the buildup of steeper seas that will 
last through at least the end of Friday. /BRC
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 4 AM Sunday to 4 AM PST Monday for 
 CAZ102-104>108.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory from 9 PM this evening to 9 AM PST Sunday 
     for PZZ470-475.
     Gale Warning from 9 AM Sunday to 3 PM PST Monday for PZZ470-475.
     Small Craft Advisory from 3 AM Sunday to 3 PM PST Monday for 
     PZZ455.
     Small Craft Advisory from 3 AM to 3 PM PST Sunday for PZZ450.
     Hazardous Seas Warning from 3 PM Sunday to 3 PM PST Monday for 
     PZZ450.
&&
$$
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