Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
259 PM PDT Friday Apr 17 2015
Synopsis...high pressure over the West Coast will maintain
warm weather across the interior through the weekend. The coast
can expect low clouds and fog each night and morning through the
Discussion...afternoon visible satellite imagery shows stratus
just off the Redwood coast and along portions of the Mendocino
coast. Expect the stratus to build back in this evening and
overnight. Generally, the coast can expect stratus each night and
morning with partial clearing each afternoon through the weekend.
Otherwise, a ridge of high pressure over the West Coast will
continue to bring mostly sunny skies and warm temperatures to the
interior through the weekend. The anomaly continues to be on
Saturday as a weak upper level disturbance is expected to detach
from a passing shortwave well to our north and gradually slide
south along the West Coast. This impulse may bring a few light
showers and weak thunderstorms to southern Trinity and eastern
Mendocino counties Saturday late afternoon into early evening.
Given the marginal instability, the lack of moisture, and the
really dry profiles, it may just end up being afternoon cumulus
buildups over the ridgetops and that's it. Conditions across the
board become less favorable for showers or thunderstorms on
Sunday, so kept those out of this forecast package. Rain chances
will then gradually increase as the next system approaches during
the beginning of next week. The models are still showing
uncertainty over what exactly will happen. In a very broad sense,
a substantial shortwave will move along the base of a large and
nearly stationary upper low located in the Bering Sea and western
Alaska, and as it approaches Canada and the Continental U.S. It will elongate
and break apart into one or more cutoff lows. These systems will
then impact the California coast starting Tuesday and continuing
beyond that. How much rain we get is still highly uncertain. We
will continue to wait until the models get a better handle of the
situation. But quantitative precipitation forecast probably won't be too high. Also, with the GFS
showing better instability and deeper moisture with the trough,
expanded the thunderstorm coverage on Monday. Tuesday is a tossup,
especially considering it's four days out in an uncertain pattern.
Regardless, kept the long term probability of precipitation unchanged.
Aviation...low clouds that developed along the Redwood coast
overnight have gradually eroded through the day...both on the northwest side
with increasing north winds and on the east side with daytime mixing.
Clouds are expected to begin to thicken along the coast this
evening and spread inland with more onshore flow before winds go
light again. Have also indicated lower visibilities
overnight...although there will be more uncertainty and certainly
more variability with this part of the forecast. Kuki is expected
to remain VFR. /Sec
Marine...northwest swell peaked this morning...and heights and periods
should continue to gradually fall tonight. This should result in a
continuation of the decreasing threat of sneaker waves and set
behavior. Breakers will gradually subside as well...but breaker
heights of up to 15 feet remain possible through this evening.
North winds will begin to increase shortly...with gale force gusts
returning to the north offshore waters later this evening and
continuing through Sat afternoon. The thermal trough will be pivoting
more NE to SW...allowing conditions to improve in the S near shore
zone later this evening. As a result...Small Craft Advisory in
that area is now slated to end at 9 PM. Winds are expected to peak
Sat morning before gradually subsiding. The next surge of north winds
is anticipated to occur late Tuesday or Tuesday night next week. /Sec
Northwest California coastal waters...
Gale Warning for pzz470.
Small Craft Advisory for pzz450-455-470-475.
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