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Area forecast discussion 
National Weather Service Eureka California
429 am PDT Monday Jul 6 2015

Synopsis...low clouds and fog will again hug the coastal regions
today. Meanwhile...a disturbance off the California coast will
bring a chance of showers and thunderstorms to portions of
interior northwest California. This disturbance will maintain a threat of
unsettled weather through the week.

&&

Discussion...low clouds and fog are repeating their performance
again this morning along the coastal regions of northwest California due
to persistent moist onshore flow. An upper low off the coast has
been acting to deepen the marine layer and should continue to do
over the next few days. This will help to bring low clouds deeper
through interior valleys, especially those that have coastal
influence.

The main story of the week with be the threat of thunderstorms
across northwest California as a result of the passing upper low. This
upper low will bring sufficient instability in moist southerly
flow. Models continue to waver on placement of the best convective
forcing, which is typical for the West Coast due to lacking
observations over the eastern Pacific Ocean. As this low crosses
more data rich regions to our south, we should get a better
snapshot on its structure. Regardless, models have been fairly
consistent that this upper low will provide the needed forcing to
generate thunderstorms, some of which may be strong. Today,
Monday, will only see a slight chance of thunderstorms over the
interior mountains today. The main threat of any storms that form
will be from heavy rain and possible cloud to ground lightning.

Tuesday and Wednesday look to be the most active days with regards
to convective activity. At this point the low will be sliding by
to our south and will be feeding in plenty of moisture, along with
cooler air aloft. Depending where this low actually tracks, it
could line up interior portions of northwest California for strong
thunderstorms. Models continue to be in agreement with cape in the
2000 j/kg range, steepening lapse rates, plenty of moisture, lifted
index around negative 3c, and sufficient shear. Conditions look
to be coming together to bring strong thunderstorms Tuesday and
Wednesday with gusty winds, heavy rain, and small hail. One item
to watch will be how high the freezing levels will be. Too high
and hail will be very limited, but rain will very heavy. Freezing
levels down around 12 to 13 kft, we could see hail in the one
inch range, possibly larger, along with frequent lightning. With
everything looking like it is coming together for strong
thunderstorms, went ahead and added in wording of gusty winds,
small hail, and heavy rain for Tuesday afternoon. It may be needed
to add similar wording in for Wednesday if Tuesday pans out. The
wild card will be what happens overnight Tuesday into Wednesday.
Models are showing convective cells continuing overnight. With all
the instability parameters in place, do not see why, at minimum,
showers would not continue overnight. So have expanded coverage
for the overnight hours. The other challenge is storm motion. As
the low slips by to the south, storm motions should be from east
to west across northwest California. This would bring the chance of some
showers moving out over the coast and then offshore. Went ahead
and added this into the forecast with showers over the coastal
plains and coastal waters. Kept these as showers instead of
thunderstorms thinking that once these cells move over cooler
surface temperatures and waters the strong instability should not
be there.

For the rest of the week, weak instability remains in place. Have
maintained a slight chance of thunderstorms each afternoon through
the week. Temperatures will reflect the cooling air mass, both
highs and lows. Overall, should be an interesting week as we look
at the potentially for strong thunderstorms. Bfg

&&

Aviation...10z satellite imagery shows stratus/fog along most of
the coast and mostly clear skies inland. Along the
coast...stratus/fog will bring IFR/LIFR. Conditions should improve
a little by this afternoon as the stratus/fog Burns off. Tempo VFR
is possible, but confidence in this occurring is low.
Inland...moisture and instability may generate some showers and
thunderstorms this afternoon. Tempo reductions are possible in
some of the stronger showers/storms.

&&

Marine...the buoys this morning are reporting a light to gentle
breeze and mixed seas ranging from 4-6 feet. The 0555z ascat pass
showed southerly winds of about 5-10 kt, which was up to 5 knots
lower than the forecast. Bumped up the short term winds a few knots
to reflect this. The models are in great agreement showing an
upper level low (which was located near 37n 129w at 930z) very
slowly moving towards the coast and then over central California
by Thursday. This will result in light wind and low seas for our
waters this week.

&&

Fire weather...will continue to headline the fire weather
forecast for thunderstorms through the week. Any convection that
occurs this week is expected to be very wet, under the main cores.
Strong relative humidity is expected much of the week, accompanied by cooling
temperatures. Will continue to assess the potential for warning
criteria, but at this point do not see a need for any warnings
this week. Bfg

&&

Eka watches/warnings/advisories...
California...none.
Northwest California coastal waters...none.
&&

$$

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