Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
831 am PDT Thursday Jul 31 2014
Synopsis...another weak disturbance will couple with atmospheric
instability to produce another round of isolated thunderstorms
over the Trinity horn this afternoon. Low clouds and patchy fog
along the coast will give way to partial clearing during the
afternoon. Daytime temperatures will remain hot over the interior.
Update...did a quick update this morning to adjust sky cover to
current trends and to add patchy smoke to northern Mendocino...southern
Humboldt...and southern Trinity counties. Ongoing fires in
northwest Mendocino County have resulted in smoke...as seen on the
latest visible satellite imagery. Also nudged high temperatures today up
slightly across the interior given the lack of cloud cover.
Otherwise...the forecast remains on track with thunderstorms
expected to form later this afternoon over the Trinity Alps. Stp
Previous discussion......issued at 431 am PDT...
Discussion...a well-defined shortwave near 40n/132w is currently
shearing out as it moves NE...ejected from the base of a
persistent upper trough over the North Pacific. A vorticity maximum is moving
toward north California early this morning. Right now...this feature is
producing thickening middle and high clouds over the local area...
but no sign of any lower cloudiness or precipitation. This vorticity maximum
will weaken as it moves slowly NE...with some weak negative
vorticity advection behind it. However...another piece of energy
is forecast to follow the same track this afternoon during peak
daytime heating. Yesterday's layer of lower lapse rates near 500
mb remains across the area and will provide a weak cap to
convection. Models continue to indicate this cap will weaken
toward 00z from the north. All-in-all...thunderstorm coverage should be
similar to yesterday with the Trinity horn being the most favored
area. Current thinking is that thunderstorm initiation may be a bit later
Shortwave energy ejecting beneath the North Pacific low and the high
pressure ridge over the desert SW will lead to above normal inland
temperature through the weekend along with enough instability for
isolated thunderstorms over the north interior sections of the County Warning
As expected...the bank of coastal low clouds has shrunk with a
more narrow strip covering the near shore coastal waters. Partial
clearing should occur by afternoon. Coastal clouds are expected to
expand once again this weekend. /Sec
Aviation...LIFR conditions will continue at kcec through the
early morning with light winds to calm conditions occurring.
Ceilings and visibilities will increase at kcec late this morning to
MVFR conditions with light to moderate winds occurring. MVFR to LIFR
conditions will occur at kacv through the early morning due to
ceilings and visibilities decreasing. Winds will be light to calm
through this morning at kacv. Ceilings and visibilities will improve
later this morning and MVFR to VFR conditions will occur at kacv
this afternoon. VFR conditions and light winds to calm conditions
will continue at kuki the next few days.
Marine...a persistent high pressure system offshore combined with a
persistent thermal low pressure trough across California will
maintain a tight pressure gradient over the outer waters through the
middle of next week. The winds and short period seas will remain
elevated across the outer waters through the middle of next week.
Therefore small craft advisories will continue in effect across the
outer waters through this weekend and it will be necessary to
continue extending the small craft advisories through the middle of
next week. Short period seas will increase across the near shore
waters late this week to near small craft criteria.
Fire weather...will include another headline for isolated
thunderstorms in north portion of zone 283...but no warnings are
Northwest California coastal waters...Small Craft Advisory until 3 am PDT Monday pzz470-475.
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