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Area forecast discussion 
National Weather Service Sacramento California
948 am PDT Monday Aug 3 2015

Synopsis...
cooler weather this week with temperatures around average for
early August. Slight chance of mainly mountain thunderstorms
Tuesday and Friday.

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Discussion...
no updates this morning to the forecast package. Primary concern
for our area continues to be the threat of mountain thunderstorms
for tomorrow and on Friday. Latest NAM model is showing weaker
instability over our region for Tuesday. If thunderstorms do
develop, the best possibility will be over the coastal range in
western Shasta & Tehama counties as well as near the Lassen park
area in eastern Shasta County. Jbb

Previous discussion...
clearing skies returning to most of the interior of norcal early
this morning as the weak short-wave moving up from the southwest
shifts deeper moisture farther to the north and east. Marine layer
is deepening along the coast, and with robust onshore flow
continuing through the Delta, we may see some low clouds spread
into the Sacramento region around sunrise. May even see a little
drizzle around the Carquinez Strait. Temperatures are running a
little cooler than 24 hours ago and generally range from the upper
40s to middle 50s in the mountain valleys to the 60s to lower 70s
elsewhere.

A little drier and more stable airmass returns to the region today
with southwest flow, so the thunderstorm threat is expected to
remain to the north and east of the region. Temperatures will
continue to moderate, and will be a little below average in many
areas.

Another stronger short-wave is forecast to move across the region
later on Tuesday and may bring a return of thunderstorms to the
northern mountains. We may also begin to see increasing high
clouds ushered up from the southwest by the subtropical jet, some
of it high-level moisture from Hurricane Guillermo to the east
southeast of Hawaii. Temperatures will cool a bit further.

Following Tuesday/S wave, short-wave ridging develops across
norcal Wednesday and Thursday ahead of another closed low
developing off the coast. This will result in a brief warmup for a
couple of days as onshore flow drops off, and we/ll likely be too
dry and stable for deep convection over the mountains.

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Extended discussion (friday through monday)

A Pacific upper level low pressure area is expected to move
eastward into northern California on Friday. Models are in fairly
good agreement with this system...with the European model (ecmwf) a little slower
than the GFS to exit it to the east by Saturday. Instability with
this low is expected to generate some mountain showers and
thunderstorms Friday afternoon/evening and potentially some
lingering into Saturday. A limiting factor will be moisture which
will be less than seen with recent systems. Any storms that
develop are not expected to be very wet. A weak disturbance may
just brush the area as it passes to the north on Sunday with the
possibility of convection limited to northern Shasta County.

Temperatures through the extended period are expected to be below
normal levels. Some warming is expected to near normal levels by
early next week. Ek

&&

Aviation...

Southwest flow aloft continues today with general VFR conditions
and dry weather. SW winds gusting to 35 kts through the Delta
expected to redevelop this evening. Marine layer thickened to
around 3000 feet and stratus clouds spread into the Delta this
morning but they are now dissipating. Ek/jbb

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Sto watches/warnings/advisories...
none.
&&

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