Area Forecast Discussion
Issued by NWS Sacramento, CA

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717
FXUS66 KSTO 191717
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1017 AM PDT Tue May 19 2015

.Synopsis...
Variable clouds and mainly mountain showers and afternoon
thunderstorms through the week as a series of weak low pressure
systems move across California. Daytime highs forecast to remain
below normal.

&&

.Discussion...
Scattered patches of valley low clouds beginning to clear. Showers
and thunderstorms will again develop over the mountains isolated ones
which might drift into the valley...especially the west side.
Overall...expecting a more active convective day. The current
forecast handles this well and no update will be needed.

.Previous Discussion (Today through Thursday)...
Mostly clear skies cover much of the interior of NorCal early this
morning while partly to mostly cloudy skies continue over the far
northern portion of the state and the Sierra Nevada. The weak
upper low has drifted into Nevada and north to northeast flow on
its backside has carried a few showers to the crest of the
northern Sierra around Donner Pass. Onshore gradients have
increased overnight and it`s possible some low clouds will develop
in the Sacramento area by sunrise. Temperatures through the valley
are in the 50s to lower 60s.

Little change to the overall pattern is expected through the end
of the week as the long-wave trough remains along the west coast.
Systems embedded within the pattern will continue to result in
daily showers and thunderstorms over the mountains and keep
daytime temperatures below normal. Best chance for seeing more
widespread showers over the valley will arrive later Thursday into
Friday as a stronger low moves into SoCal.

&&

.Extended Discussion (Saturday through Tuesday)

On Saturday, interior NorCal will be between the back side of the
trough to our east while high pressure ridging builds over the
eastern Pacific. Extended models depict another low pressure system from
the Pacific NW moving southward and meandering towards the Great
Basin over the weekend into early next week. Details in the
position of this low are still uncertain, but there is fair
confidence that instability over the Sierra will maintain a slight
chance of showers and afternoon thunderstorms through the extended
forecast. Daytime highs should be within a few degrees above/below
normal depending on the position of the low.  JBB


&&

.Aviation...

Mainly VFR conditions for interior NorCal today except during showers
and afternoon/evening thunderstorms that bring periods of MVFR.
The onshore flow will bring light winds to TAF sites around 5-12
kts. Delta breeze will be 10-20 kts with gusts up to 25 kts. JBB


&&

.STO Watches/Warnings/Advisories...
None.
&&

$$







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