Area Forecast Discussion
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FXUS66 KSTO 251244

444 AM PST Thu Dec 25 2014

Dry weather and breezy winds are expected for Christmas Day.
There is a slight chance of light showers across the northern
mountains Saturday night and early Sunday...otherwise dry Friday
through the middle of next week. Cold morning temperatures with
many temperatures below freezing for the valley Saturday morning
and by the middle of next week. Patchy morning valley fog is
possible Saturday and Sunday.


Upper trough now over the Great Basin with high pressure now
pushing in off the eastern Pacific. A minor shortwave disturbance
dripping southward in northerly flow is bringing a few showers off
the north coast at this time but it is unlikely that these low
level showers will make it over the coast range. Most of the
forecast area is under fair skies this morning with breezy
northerly winds keeping any fog from developing in the valley. MFR
to SAC surface gradient is about 5 mb this morning and it may
tighten slightly during the day. Guidance shows strongest winds
will hit around late morning but at this time expect winds to
remain well below advisory criteria. Surface gradient is expected
to decrease during the night but should be tight enough to keep
light northerly breezes going most locations through the night. As
a result...should see minimal fog development again tonight and
Friday morning. Fair skies and light northerly winds expected
again on Friday as high pressure aloft continues to push inland
over the west coast. Daytime highs should push up to a few degrees
above normal for the end of December.

Another dry day is expected on Saturday under stable high
pressure with daytime highs remaining near or a little above
normal. A low pressure system dropping out of the Gulf of Alaska
and into the Pacific Northwest late Saturday afternoon and night
will bring increasing clouds and a slight threat of showers over
the northern part of Shasta county. The remainder of the forecast
area will remain dry Sunday.


.Extended Discussion (Monday through Thursday)

The most significant weather events in the extended will be
breezy to strong northerly to northeasterly winds Monday and
Tuesday followed by cold overnight temperatures.

Models are still in agreement that a very high amplitude ridge is
just inside 140W on Monday with a broad upper low over the
northern Great Basin (southern Idaho). A shortwave and associated
cold front slides down the eastern side of the ridge, which may
brush the higher Sierra with a minimal chance of light snow
showers due to very little moisture associated with this system.
What this dry cold front doesn`t bring is moisture, it brings in
post-frontal cold air and breezy to strong offshore surface winds
Monday and Tuesday. By Wednesday/Thursday, the ridge axis moves
closer to the coast which will begin to weaken winds. As a result,
much colder temperatures will likely occur. The best chance for
frost and freezing valley temperatures will likely be
Wednesday/Thursday when winds subside, especially on the less
windy eastern side of the valley. JClapp



VFR conditions with breezy north surface winds today in Central
Valley after 17z with sun mixing boundary layer (sfc-030). Gusts
20 to 30 kts by afternoon and toward sunset. Sustained winds 20
to 30 kts at 2-3K MSL continue today.    JClapp


.STO Watches/Warnings/Advisories...

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