Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
346 PM PST Friday Dec 6 2013
Synopsis...a cold storm system will bring rain and snow to the
region through tonight. Drier weather will return on Saturday and
continue through Sunday. Cold weather conditions will persist
through the weekend.
Discussion...several reports of low elevation snow today...with
rain mixed with snow as low as sea level this morning. Levels have
been slowly rising out near the coast as warmer air gradually
spreads into the area from the west. Many inland sites have not
warmed up very much today...with all sites in zone 4 less than 32f
and most sites below 2500ft in zones 3 and 76 ranging from 27-35f
as of 2pm. Snow has been reported on the valley floors in most all
interior zones today. So far the accumulations have ranged from a
trace to a couple of inches around 500 feet. In addition...all
the web cams over the mountain passes have been showing periodic
snow through the day. The instability parameters are weak tonight
and the chance for low top convection and bursts of heavy snow and
hail seems fairly low. We will continue with the Winter Storm
Warning for all interior zones through this evening as periodic
snow continues to occur at very low elevations in all interior
zones. This first snow event of the season will continue to create
travel hazardous on all the roads this evening. Even after the
snow showers end...roadways will likely continue to be hazardous
due to local pockets of ice and slush.
Models were in good agreement with precipitation winding down after midnight
tonight as the front moves south of the region. Snow levels may
start to increase later tonight as the front takes the lid off and
allows warmer air aloft to mix down to the valley floors. The
strong cold air advection expected later tonight and through the
day on Saturday may offset this and snow levels will continue to
be very low. Models continue to show linger showers...mostly over
the higher terrain... Saturday morning. However...high pressure
is expected to build in from the north on Saturday ushering in
dry northerly flow and subsidence. A cold and dry air mass will
settle over the region Saturday night...bringing extremely cold
conditions to northwest California again. Once again we are expecting record cold
temperatures in all zones Sunday. It may be the coldest morning so
far this season if the NE winds decouple. Hard freeze warnings
will be needed for zones 1 and 2 as temperatures dip into the
lower to middle 20s by early Sunday morning. Inland zones will dip
into the teens and lower 20s with pockets of ice on roadways and
patches of freezing fog Sunday morning.
Dry weather looks to continue into Monday as a ridge builds up
offshore. Even though the air mass warms up aloft...many lower
elevations sites will still be quite cold Monday morning. I am
not sure if we will need another hard freeze warning for the coast.
It may take longer for the air mass to moderate on Monday.
Long-range...(tuesday through saturday)...high pressure over
northwest California will give way to a trough approaching the
West Coast for the middle to latter half of the week. Models forecast the
trough to begin to break down the meridional flow that has been in
place over the eastern Pacific for quite some time...bringing a
possible pattern change. An associated frontal system may approach
the coast bringing the next chance of rain to the area later
Wednesday into Friday. Raised probability of precipitation on Thursday into Friday to
account for the increasing model confidence. Temperatures will
gradually warm through the early part of the week and remain
fairly steady the latter half of the week. Stp
Aviation...storm system pushing across northwest California this afternoon
resulting in MVFR conditions in -shra along the coast with IFR
conditions in -shsn across the interior this afternoon. Gusty southerly
winds ahead of and along the boundary will shift to northerly in the wake
of the boundary. Current conditions will persist through this
evening with tempo lower in stronger showers. Skies will clear from
north to S overnight...although MVFR ceilings will persist across the
interior into Sat afternoon.
Marine...southerly winds rising quickly ahead of an approaching boundary
with buoy observation reporting 20g30kt over pzz450. Winds will shift to the
north and rise slightly in the wake of the front resulting in building
short period seas. Given that winds are stronger than models...and
marginal gales and steep hazard seas forecast overnight into Sat over the
offshore zones...elected to hoist a Gale Warning for the outer
waters through Sat afternoon. High pressure will settle over the
region sun with improving conditions early next week.
California...Winter Storm Warning until midnight PST tonight above 1500 feet
for the caz003-004-076.
Northwest California coastal waters...Small Craft Advisory until 8
PM PST Saturday pzz450.
Small Craft Advisory until 2 am PST Saturday pzz470.
Gale Warning from 2 am to 9 am PST Saturday pzz470.
Small Craft Advisory from 6 PM this evening to 2 am PST Saturday
Gale Warning from 2 am to 3 PM PST Saturday pzz475.
Small Craft Advisory from 6 PM this evening to 2 am PST Sunday
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