Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
323 PM PDT Wednesday Mar 12 2014
Synopsis...a weak frontal boundary will bring increased cloud
cover and a chance for rain to northwest California on Friday. Building high
pressure will result in warm and dry weather over the weekend
before a pattern change towards cooler and wetter weather arrives
early next week.
Discussion...high pressure over the West Coast and offshore flow
has made for a warm and clear day across northwest California. Coastal
temperatures warmed quite efficiently today and should quickly
drop as the flow turns onshore this evening which will allow
overnight temperatures to fall closer to normal. Mostly clear
skies tonight will make patchy frost possible across interior
areas but withheld from issuing an advisory for interior Mendocino
due to marginal temperatures. Otherwise models indicate patchy fog
to return to the coast north of Cape Mendocino with high relative
humidity around the Humboldt Bay area. Patchy valley fog is
possible late tonight however the airmass modification will
restrict it to just a few valleys, similar to this morning.
The next opportunity for precipitation will come early Friday
morning as shortwave slides over the ridge, dragging a weakening
frontal boundary across the northern periphery of the County Warning Area. The best
forcing will be farther north across Oregon so highest chances are
restricted to del Norte County. Snow levels will remain high and
rain amounts will remain light ranging from 0.03-0.10". Ridging will
return Saturday allowing high temperatures to reach the 80s across
some inland areas.
Long range models have consistently been signaling for a deeper
trough to impact the region early next week with uncertainty in the
timing of precipitation. Operational models seemed to have been
trending slower with the arrival of this trough, however, recent GFS
ensemble runs have become more progressive with precipitation for northwest
California by Monday. The main concern is whether or not the split
flow will cause the cutoff low to drift south of our forecast area.
All that said there still is a considerable amount of uncertainty as
to what will happen and vouch to stick with climatology probability of precipitation for the long
term until the long range models fall into better agreement on a
particular outcome. \Kml
Aviation...a weakening front will pass to our north later tonight
and generate a weak northerly wind surge which should bring better
chances for low cloud and perhaps light fog along the coast north of
the cape late tonight through Thursday. Except for a few patches of
shallow fog across the inland valleys...VFR conds are expected to
continue everywhere else through Thursday.
Marine...northerly winds and short period seas will increase
slightly tonight and become moderate on Thursday after a weak front
passes to our north and high pressure builds toward the area and
thermal low pressure shifts inland. Another weak front will move
toward the region on Friday.
A couple of long period swell groups will affect the region through
the weekend. The first swell should spike around 10 feet by this
evening. An advisory for seas has been issued for tonight in all
waters...even though periods were greater than 15 seconds.
A slight risk for sneaker waves will continue into this afternoon
and evening as well...but should diminish later tonight as periods
decrease. Another long period swell from a strong Pacific storm will
arrive this weekend and may hit 10 to 13 feet by sun.
Northwest California coastal waters...Small Craft Advisory until 3 am PDT Thursday pzz450-455-470-475.
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