Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 011030
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
330 AM PDT SUN MAY 1 2016

.Synopsis...
Locally breezy North to East wind today then lighter wind into
early next week. Threat of afternoon showers and thunderstorms
continues over the mountains into Tuesday then a more widespread
chance Wednesday into Friday. Cooling to near normal midweek.

&&

.Discussion...
Low level pressure gradient over Interior NorCal still remains
fairly strong this morning at 10 MB between KMFR and KSAC.
Gradient is also becoming more NE-SW oriented and partial
decoupling has occurred overnight. Winds in the Central Valley are
currently below 10 kts. Speeds expected to increase this morning
as momentum aloft mixes down, but then trend down during the
afternoon. Upper meso low currently crossing ORCA border will
drop into NorCal today. Associated synoptic lift combines with
differential heating instability for possible afternoon showers
and thunderstorms over the eastern mountains from about Lassen
Park south. Remainder of Interior NorCal remains dry today as
airmass warms. High temps increase into the mid 80s in the Central
Valley this afternoon.

Meso low weakens over NorCal Monday as deep upper trough in EPAC
approaches into Tuesday. Threat of afternoon mountains showers
and thunderstorms continues Mon/Tue. High temps slowly trend down
into Tuesday as synoptic cooling and onshore flow gradually increase
over Interior NorCal.

Models similar in closing off upper trough into low Wednesday
along the CA coast then gradually dig feature through Friday.
Unsettled weather pattern results due to increased synoptic lift,
moisture, and instability...leading to a more widespread threat
of showers and thunderstorms over Interior NorCal. High temps cool
to near or slightly below normal through midweek.

PCH

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)

Extended models consistent in moving a Pacific low through central
California at the end of the week for a shower and thunderstorm
threat across the CWA. Models then keep the upper low over the
Great Basin bringing continued impacts for the forecast area for
the remainder of the extended period. Forecast models in good
agreement in bringing upper low center onshore somewhere over
Socal late next Thursday. Lift and instability and sufficient
moisture should allow for scattered showers across the area. Upper
level divergence should also aid in isolated thunderstorms just
about anywhere over Norcal. Cloud cover and cooler airmass will
continue to bring down daytime high temperatures with highs
Thursday possibly a little below normal. Upper low moves eastward
very slowly Friday so not all that much change is expected in the
forecast with showers and thunderstorms remaining a possibility.

By next weekend...upper low center should have moved into the
Great Basin but model timing varies some. Upper low remains well
within influence of Norcal however with enough instability and
moisture to warrant a continued threat of showers and afternoon
thunderstorms through next weekend. Once upper low shifts east of
the state...there should be at least some warm up in airmass with
highs next weekend expected to climb back above normal.

&&

.AVIATION...

VFR conditions are expected at the terminals for the next 24
hours. A slight chance of thunderstorms over the Sierra Cascade
range this afternoon and evening. Breezy north winds gusting to 20
mph over the Sacramento valley and foothills decreasing after 20z
today.

&&

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

$$


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