Weather Service Report

FXUS66 KSTO 181219

419 AM PST Thu Dec 18 2014

A few light showers over the mountains today...otherwise dry. Next
frontal system moves through NORCAL Friday bringing relatively
light rain and mountain snow. Drying south on Saturday with a few
showers north especially over the mountains. All areas dry on
Sunday except far northern Shasta county mountains. Dry
Monday/Tuesday under high pressure ridge. Slight chance of mainly
mountain showers on Wednesday. 


A weak shortwave trough which moved through NORCAL overnight has now
moved south and east or the region. Showers are diminishing to the
south and east at this time and will allow winter weather advisory
over the Sierra to expire shortly. Once these few lingering
showers clear out...Northern California should be mainly dry today
as a small scale ridge slides across the west coast. This fairly
dirty ridge will allow plenty of clouds to spill over the area
today and can not rule out a few light showers over the mountains
where orographics may squeeze out a light shower or snow flurry.
The next Pacific storm system to impact the region has now crossed
130 west and is forecast to move into northwest California early
Friday morning. The bulk of the moisture associated with this
system is forecast to drop southward into north central California
so is not expected to be a major precipitation producer over
NORCAL. Most valley locations should only see a few tenths of an
inch of rain with locations above about 5000 feet seeing a few to
several inches of snow or enough for some minor travel impacts.
Upper ridging slowly rebuilds along the west coast Saturday and
Sunday with the precip threat retreating northward. On
Saturday...areas north of about Sacramento will see a threat of
light showers but by Sunday afternoon only Shasta county is likely
to see any precipitation threat at all. Clearer skies and a
warming airmass under the ridge will allow daytime highs to warm
to near normal on Saturday and to a few to several degrees above
normal on Sunday.  

.Extended Discussion (Monday through Thursday)

Medium range models continue the transition to a drier weather
pattern into early next week. The main weather impact will be
valley and adjacent lower foothill stratus/fog nights and

Longer range models are coming more inline with the evolution of
a deepening trough over the Pacific Northwest and into the Great
Basin toward the middle of next week. The ECMWF and GFS offer a
solution that would squeeze the bubble high westward and bring in
colder air with some lower elevation snow to the Sierra. The
colder ECMWF has the deeper low farther southwest over NV, while
the GFS is farther northeast over ID/MT. The pattern doesn't look
to be a big rain/snow producer, but we have included a limited
mention of mountain precip focusing on the Sierra. Northerly winds
are likely to develop behind this front late in the week.
Depending on the winds, this pattern could bring widespread
minimum temperatures well into the 30s across the valley with some
areas of frost.     JClapp



Upper ridge moving in today with fairly light winds. Areas of
valley MVFR this morn with local IFR near valley edge and over
mountains. Next trough over area late tonight into Friday with
showers. Enough cloudiness will limit fog production.   


.STO Watches/Warnings/Advisories...


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Western Regional Climate Center,