Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 012217

317 PM PDT Wed Apr 1 2015

An upper trough will bring a slight chance of showers to the
northern mountains this evening, then breezy north winds tonight
into Thursday. A stronger trough will bring better chances of
rain and snow Saturday night into early next week.


Partly cloudy skies are prevalent this afternoon as a weak upper
trough makes its way across Northern California. This upper
trough has already brought a considerable amount of synoptic
cooling, as temperatures at this hour are running up to 7 degrees
cooler than 24 hours ago. Much of the showery activity associated
with this system has been confined to Siskiyou County, but a few
showers have now been spilling into Shasta and Plumas Counties.

As this system moves through, pressure gradients will rapidly
tighten and result in breezy north winds across much of the
forecast area. It currently looks like pressure gradients will be
tightest tonight, then rapidly weaken during the day on Thursday.
As such, while we may see some 15-20 mph winds with gusts to 35
mph in the Sacramento Valley, they will likely be short-lived and
locally confined.

A modest warmup is expected Thursday and Friday as high pressure
builds across California. This will be short-lived however, as a
2nd stronger trough approaches the West Coast Saturday.



.Extended Discussion (Sunday through Wednesday)

A large low pressure system progged to drop southeast from the Gulf
of Alaska will approach the region by Saturday night. As system
rotates inland, two waves will impact the local area. Models in
decent agreement with general details but still differ a bit in
timing and precip amounts. Regardless, two rounds of precipitation
look likely, first from late Saturday night into Sunday and second
on Tuesday. Early estimates of precip amounts range from 0.25 to
an inch in the valley/foothills and upwards of an inch in the
mountains. Could see locally higher amounts if any thunderstorms
do materialize. Model fields suggest this is possible with a bit of
instability accompanying each wave.

Given the origins of the system, cooler air will accompany each
wave. This will drop snow levels below major pass levels with
accumulations likely above 4000 feet. A few inches possible with
first wave Sunday with higher snowfall rates expected on Tuesday.
Total accumulations could be around a foot at higher elevations.
Will be a system to watch as snow will likely impact Sierra
travel. Heightened concern due to lack of recent storms and
complacency of trans-Sierra travelers this late in the season. Details
will be further refined as we head toward the weekend. Cooler
temperatures (more near normal) will accompany this system as

Ridging will build back in behind this system with a return to dry
weather for mid week.




VFR conditions thru the forecast period. Skies will generally
remain mostly clear. Breezy northerly winds will continue with
some gusts AOA 20 kts possible.


.STO Watches/Warnings/Advisories...

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