Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 241146

446 AM PDT Fri Oct 24 2014

Dry and warmer conditions today as a ridge of high pressure builds
over the western U.S. A weather system will bring rain, mountain
snow and windy conditions Saturday with showers Sunday. A brief
break Monday will be followed by a chance of rain over areas north
of Sacramento Tuesday and Wednesday. This precip threat will drop
southward bringing rain or mountain snow over much of NORCAL for
the end of the next week.


The high pressure ridge over the southwest U.S has continued to
build northward in response to a low pressure trough digging into
the eastern Pacific. Radar has shown the rain line over Shasta
county pushing northward overnight and at this time, only the far
northern most CWA is seeing any shower activity. This activity is
likely to clear by later today with mainly fair skies expected
over the entire CWA by afternoon. Clearer skies and a warmer
airmass will result in higher daytime temperatures today with many
locations hitting highs a little above normal. The offshore trough
will move coastward over night with the associated frontal system
moving onshore by morning. The main frontal passage impacts will
be during the afternoon on Saturday. Light to moderate amounts of
precipitation are expected with this system with perhaps the main
impact being a period of fairly strong winds. 9 or 10 mb surface
gradients are predicted between MFR and SAC between about 18z
Saturday and 00z Sunday with good upper level support from the
upper trough. Would expect the central and northern Sacramento
valley to hit wind advisory criteria during this time. Shear in
the central SAC valley is quite high and stability proggs showing
enough instability over the northern half of the CWA for a threat
of thunderstorms as well. Instability is somewhat weak however so
at this time would not expect to see much in the way of
significant thunderstorm activity. Main front passes east of the
CWA by Saturday evening and surface gradients drop off quickly.
Upper trough passes through Saturday night and early Sunday for a
continued threat of showers on Sunday mainly over the mountains.
Snow levels are expected to remain quite high especially during
the main precip event, not dropping until after frontal passage
Saturday. Therefore not expecting much snow at the higher
elevations with only an inch or two at pass levels. High pressure
ridging slides temporarily over over west coast on Monday for a
brief clearing and warming trend.
This weekend, the main weather system will move inland and bring
widespread rain and some breezy to locally windy conditions to
the region. Saturday looks to be the day with the most activity.
Winds, widespread showers and potential for afternoon/evening
isolated thunderstorms. At this time, the winds look like they`ll
be a nuisance for outdoor events and may blow holiday decorations
around. However, the slower progression of this system may result
in slightly higher winds. We will continue to monitor later runs
and see if any wind headlines are necessary. Also, the snow levels
are expected to lower to around 7000 feet Saturday night, so there
could be some light accumulations over the higher passes. Showers
will linger on Sunday, but should see decreasing showers from
south to north through the day. Precipitation amounts this weekend
should be a couple tenths in the San Joaquin Valley to up to half
an inch in the northern Sacramento Valley. The mountains could see
1-1.5 inches of liquid.

Monday will once again see a drying trend as a weak ridge builds
in behind the exiting system with temperatures rebounding to near

.Extended Discussion (Tuesday through Friday)

Flat high pressure over the southwest U.S will keep at least the
southern half of the forecast area dry Tuesday and Wednesday. The
northern portions of the forecast area will see a continued threat
of light rain. Daytime high temperatures under mainly cloudy skies
are expected to come in a few to several degrees below normal.
Another cool low pressure system dropping out of the Gulf of
Alaska will bring precipitation chances southward on Thursday and
Friday. Models still not showing real good consistency during this
7 to 8 day time frame however both run to run and model to model so
forecast confidence not high during this time frame.



Lingering rainfall this morning is associated with a frontal
boundary currently located along the northern coastal range and
northern mountains. This is shifting north, with dry conditions to
the south. VFR conditions for the Valley today except for lcl
MVFR/IFR possible in patchy BR/FG for the northern and central
Sacramento Valley through 16z this morning. High thin clouds with
winds from the south between 10-15 mph in the afternoon. A system
spreads in tonight late tonight bringing chances of rain and
increasing winds. EK


.STO Watches/Warnings/Advisories...

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