Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 051325

625 AM PDT Tue May 5 2015

Dry weather will continue through early Wednesday before a cooler
and more unsettled pattern begins later Wednesday into the end of
the work week, bringing a chance for showers and thunderstorms,
mainly to the mountains.


.Discussion (Today through Friday)...
Clear skies across the interior of NorCal early this morning. The
marine layer has mixed-out somewhat, but still remains between
2500-3000 ft deep and a moderately strong onshore breeze continues
through the Delta into the Central Valley. Temperature/dew point
spreads in the Sacramento area are only down just a bit compared
to Monday morning, so cannot completely rule out seeing some
stratus again early this morning - but likely not as extensive as
yesterday. Temperatures are similar to 24 hours ago and range from
the 30s and 40s in the mountains to the 50s and lower 60s in the
Central Valley.

Large slow moving closed low tracks onshore to our distant north
across southern BC and Washington today. This should limit deeper
convection to east of the Sierra crest today as westerly flow is
progged to be a little stronger. Temperatures today expected to be
pretty similar to Monday across the Central Valley while a little
synoptic cooling is forecast to bring temperatures down a little
further today in the mountains.

More significant changes forecast to develop across the region
Wednesday and Thursday as the trough deepens along the west coast
with the southern portion forecast to dig southward into NorCal
from the PacNW. Appears there is sufficient moisture along with
dynamics and instability with the system for scattered showers.
Models appear to be tracking the system a little further to the
west, so have bumped up shower chances for the valley a bit.

The system will be convective in nature, so precipitation amounts
will vary considerably depending on location of shower
development, but cannot rule out some decent precip amounts even
for portions of the valley as the low tracks southward.
Accumulating snowfall of 2-6 inches will be possible along the
crest of the northern Sierra as snow levels drop to around 5500 to
6000 feet.

System is forecast to move into SoCal Friday with decreasing
precipitation chances across NorCal.


.Extended Discussion (Saturday through Tuesday)
Precipitation is expected to wind down on Saturday with just some
lingering showers in the Sierra southward of Lake Tahoe. A weak
wave brushing through to the north on Sunday will bring just a
slight chance of some showers over Shasta county. The overall
extended period has a trough near 130W latitude. The GFS has a
deeper trough with a less progressive flow that deepens into a
closed low just offshore, while the EC and GEM have a flatter,
more progressive flow. By Monday/Tuesday, the GFS solution looks
wetter, but we have put more weight in the EC/GEM due to the GFS
still having quite a bit of run to run spread. Therefore, the area
looks precip-free except for chances over the Shasta/Plumas county
region next week. Temperatures looks near to slightly above
normal. JClapp


.Aviation Update...
No marine stratus this morning with continued VFR
conditions today. SW winds 15-20 kts with gusts to 25 kts around
the Delta today and weakening tonight. Showers and thunderstorms
over Sierra Wed. JClapp


.STO Watches/Warnings/Advisories...

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