Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 010419
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
919 PM PDT Fri Oct 31 2014

.Synopsis...
A cold front will bring rain and mountain snow to interior northern
California overnight. Lingering showers are expected behind the
front on Saturday...ending Sunday. Drier and milder weather next
week.

&&

.Discussion...
Backedge of the rain is mainly E of line from Fall River Mills...
Oroville...just E of the SAC area...to Galt...and Morgan Hill. This
is on the east side of the neutrally tilted trof that has moved
inside 130W and is now along the W Coast. Energy has reached the
bottom of the trof near 33M/125W with more energy upstream. Models
phase this energy or vort maxes together as the trof moves inland
later tonight. This phased energy should keep precip going over the
Ern portion of our CWA overnite...including the Nrn San Joaquin
Valley.

As the trof swings across the CWA on Sat...the main vort max will
sweep east of our CWA with additional energy on the backside of the
trof remaining along the coast. Thus dynamics will be weak...but
the 5H cold pocket will move overhead destabilizing the
atmosphere...especially if there are some breaks in the clouds...
and convective showers will occur. Upslope flow over the Siernev
will generate numerous showers there during the day while cross mtn
flow over the coastal range will likely preclude most of the shower
activity. However...the energy on the backside of the trof should
lead to showers W of the coastal range and near our Wrn CWA
border.

Temperature analysis and CA web cams suggests the snow level has
dipped to near/below the trans-Sierra passes this evening...around 7
kft. As the 5H cold pocket moves overhead on Sat the snow should dip
to 4500 to 5000 feet or near or below BLU level where the SREF
plumes show a mean of less than a half inch with only two of the 24
members above an inch.

QPFs thus far show .75 to 1.25 inches over Shasta...3 to 6 tenths of
an inch over the Sierra...to a few hundredths up to 5 or 6 tenths in
the Valley. With the vort max (energy) near the base of the trof
rotating inland tonite...another broad area of moderate to heavy
rain should affect the Nrn SJV...southern Motherlode and Sierra
overnite especially Stanislaus...Tuolumne...Amador...Calaveras
counties in our CWA overnight. An additional inch is likely in the
mtns...with several tenths on the E side of the Nrn SJV valley and
Srn Motherlode areas.

Thunder chances look to be limited to areas SW and S of our CWA as
the vort max (energy) in the base of the offshore trof rotates
inland.    JHM


.Previous Discussion...

Showery conditions will linger into Saturday after the main
frontal band passes east with some mountain showers persisting
into early Sunday morning. With all this moisture and cold morning
temperatures, there could be some patchy fog development during
the very early morning hours on Sunday. It`s tricky to say how
widespread the fog could be or how long it will last because
northerly winds will also develop Sunday morning. Even light
northerly winds (around 5 mph or higher) can inhibit fog.

Daytime highs over the weekend will be cool with valley highs only
warming into the mid 60s for much of our CWA. By Monday, dry
weather with a warming trend will settle in for the rest of the week.
JBB


.Extended Discussion (Tuesday through Friday)

High pressure ridging along the west coast will be the dominant
weather feature through the extended period. Daytime highs will
climb Tuesday and Wednesday before stabilizing Thursday and
Friday. In any case, max temperature will be around 5 degrees
above normal. Extended models do move a weak system over the north
end of the ridge and into the Pacific Northwest on Thursday
according to the ECMWF. On the other hand, the GFS and GEM are a
bit slower (12-18 hrs) and weaker with this wave. We compromised
with the models and meshed with our neighboring coastal offices on
introduced and slight chance of precip over the Coastal Mountains
Wed night into Thu night.    JClapp

&&

.Aviation...

Deep upr trof movs into CA Sat. For Cstl rnge and Cntrl Vly, lcl
MVFR/IFR conds poss ovngt in shwrs. Isold LIFR poss in vly ST/Fog
btwn 08z-16z. Ovr Shasta, Wrn Plumas, and Siernev mtns sct
MVFR/IFR with isold LIFR conds poss ovngt into Sat in shwrs with
snow shwrs poss abv 055. Conds impvg Sat eve.

&&

.STO Watches/Warnings/Advisories...
winter weather advisory until 2 pm pdt saturday above 6000 feet
in the western plumas county/lassen park.

winter storm warning until 2 pm pdt saturday above 6000 feet in
the west slope northern sierra nevada.

&&

$$







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