Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
345 PM PST Thursday Dec 5 2013
Synopsis...a cold storm will drop down from the north on
Friday bringing rain and snow to the region. Dry but cold
weather will return on Saturday and continue through Sunday.
Discussion...clear skies prevailed across the region again
today. Temperatures were running a tad lower but the north winds
were not as strong today so it felt warmer. Overnight temperatures
should increase slightly tonight due mainly to an increase in cloud
cover later tonight. It will still be cold with readings similar
to last night. With low dew points and mostly clear skies...it
will cool off quickly after sunset.
Main story for tomorrow is the potential for low elevation snow.
This is first one of the season and we decided to go forward with
a Winter Storm Warning for all interior zones. A short-wave will
dive southward offshore the Pacific northwest coast Friday morning...then
into northwest cal Friday afternoon. The over water trajectory will
allow this system to acquire moisture as a cold front develops
offshore the coast. GFS and European model (ecmwf) were similar to yesterday with
precipitation initially spreading into del Norte County Friday
morning...then into the rest of the area Friday afternoon. With
cold temperatures expected tonight...snow level will be quite low
Friday morning. Southerly winds and slight warming in the boundary
layer near shore should inhibit significant snow accumulations at
the coast. However it is possible for folks on the Redwood coast to
see some heavy wet snow or a mix of rain and snow in the morning.
Inland areas away from the immediate coast stand a better chance
of seeing accumulations with perhaps an inch or so on the valley
floors in del Norte County Friday morning. Snow levels should
increase through the day as westerly flow spreads warmer air
inland. GFS and ecwmf were in good agreement showing the bulk of
the precipitation spreading into the area from northwest to southeast Friday afternoon and
evening. Most the precipitation will be over the coastal ranges of del
norte and Humboldt counties with lesser amounts in eastern Trinity
and southern Mendocino. The watch has been upgraded to the Winter
Storm Warning for all interior zones even though amounts do not look
all that impressive...with a couple inches or so over the passes.
However snow levels will be fairly low and will affect travel.
Also...this is the first low elevation snow event of the season
and the snowy weather may catch folks off-guard.
Models were in good agreement with the cold front exiting the
region...and high pressure with brisk northerly flow building
into the area on Saturday. Drying condition and clearing skies
Saturday night will lead to another record cold morning Sunday.
Hard frost warnings will need to be considered for the Redwood
and Mendocino coast zones. Inland zones should see mostly teens
and lower 20s with a few sites in the single digits as the north-northeast
winds die down overnight.
Models indicate gradual warming next week as a ridge builds offshore
and the air mass slowly modifies. Dry weather appears to be the
rule Monday and Tuesday. GFS and European model (ecmwf) continue to hint at potentially
wetter weather around middle to late next week as the high amplitude
flow pattern breaks down some. I am not too confident on the
details as the model waver around from one run to the next. Thus I
will go with a broad-brush chance of rain middle to late next week.
Aviation...high pressure will bring VFR and light winds to
northwest California tonight. Clouds will increase overnight as a
storm approaches the region.
Marine...conditions will continue to improve this evening as the
pressure gradient weakens. The 1830z ascat pass was over parts of
our outer waters, but it did show winds of about 20 knots. This matches
our forecast. Winds closer to shore are slightly lower than forecast
as indicated by the nearshore buoys, so bumped down the winds there
over the next few hours to reflect this. With conditions improving
the Small Craft Advisory for zone 475 was dropped. Expect light winds and low seas
this evening into Friday morning. A storm will generate northerly
near gale conditions for the outer waters and a fresh to strong
breeze with steep short period seas for the inner waters late Friday
into Saturday. Sca's will probably be needed, but held off on
issuing them with this forecast package because there's still some
uncertainty with the start time and it's near the outer edge of our
Small Craft Advisory issuance window.
California...Winter Storm Warning from 10 am Friday to midnight PST Friday
night above 1500 feet for the caz003-004-076.
Northwest California coastal waters...none.
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