Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 220513

1013 PM PDT Thu May 21 2015

Mild weather with mountain showers and thunderstorms will continue
through Friday. Warmer temperatures with fewer mountain showers
expected this weekend into next week.



Mountain showers and thunderstorms have all dissipated this
evening. Skies are partly cloudy over the area with a moderate
onshore flow and winds gusting to 20 mph delta to srn sac/nrn sj
valleys. Short term models indicate showers to rotate back over
the Sierra from Nevada after midnight will keep shower chances
going. Likely to see another layer of status cloudiness towards
morning srn/sac valley. Current forecast is on track no update

.Previous Discussion...
A broad upper level trough remains quasi-stationary along the
West Coast, with blocking ridge situated over the Rockies. Several
shortwaves have been rotating through this upper trough, and the
current one is moving toward the California coast today.
Widespread showers and thunderstorms have once again developed
this afternoon across the interior mountains of Northern
California once again. Lightning networks haven`t detected quite as
much lightning as yesterday, but today`s showers do seem to be
producing more in the way of precipitation. We`ve also seen a few
reports of snow above 8000 ft or so along the high Sierra. With
southeast to easterly flow aloft, some showers may try to work
their way down the hill toward the Valley this evening into Friday
morning. The ARW, NMM, and HRRR all hint at this possibility.

The aforementioned shortwave pushes south toward Southern
California on Friday, with steering flow becoming more northerly.
While we should still expect some mountain showers and
thunderstorms Friday afternoon, they shouldn`t be as widespread.

Northerly flow aloft will continue over Northern California
through the weekend. This should promote warmer weather, with
temperatures closer to normal. Isolated showers will still be
possible over the mountains, but confined to primarily Lake Tahoe
and southward.



.Extended Discussion (Monday through Thursday)

For the extended period, the ability of the general upper trough
pattern over the region to persist through the rest of May is
impressive. with no significant heat-ups in sight. Upper low
pressure systems with weak short waves will pass through at times.
Unlike the current system, most of the lows will be centered to the
north and east of the forecast area. Most of the instability will
linger over the mountains, with afternoon heating bringing some
thunderstorms. The Valley should remain generally dry.

Temperatures will gradually warm to near to slightly above normal
levels by mid week on. Daytime highs in the valley will generally
be in the low to mid 80s with 70s in Delta Breeze influenced areas
(upper 60s for the Vallejo/Benicia area). Mountain highs will
range in the 50s/60s while Foothills warm into the 70s. EK



General VFR conditions expected for tonight. Could see some
bkn020-025 cigs for the Delta and into the southern Sacramento
Valley 12-18z Friday morning. The Delta could see gusts to 30kt


.STO Watches/Warnings/Advisories...

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