Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 281700
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1000 AM PDT Thu May 28 2015

.Synopsis...
Daytime temperatures 10 to 15 degrees above normal over the next
few days as high pressure slides across the west coast.  Cooler
early next week with a slight chance of showers and thunderstorms
over the northern Sacramento valley and surrounding mountains as
the tail end of a Pacific trough brushes through.

&&

.Discussion...
High pressure building over Norcal today with the ridge axis
shifting inland Fri/Sat as an upper trof approaches the coast by
Sun. Weakening short wave moving through the ridge will be spreading
some high cloudiness over Norcal today...then clearing/thinning of
cloud cover tonite. Ft Ord Profiler and KOAK RAOB this morning
showed the marine layer had lowered to around 2200 ft from
yesterday. Some stratus briefly advected into the Srn Sac Vly this
morning...but has now dissipated. During the next couple of
mornings...increasing subsidence from high pressure is expected to
continue to suppress the marine layer and limit the potential for
intrusion into the valley. With less of a marine influence and
weaker onshore gradients a warming trend is expected for the next
couple of days. Onshore gradients increase again on Sun with the
approaching trof yielding cooler temps and a chance of showers over
our nrn zones.

Instability progs high-lite the usual spots...Lassen Park and near
the Crest of the Coastal range the next couple of days...where
topographic forcing/convergence is likely to cause cumuliform
cloudiness and possibly brief convection. Have added a small area of
convection in these general areas for the next couple of days per
the HRRR and WRF.


.Previous Discussion...

Overall airmass warms under the ridge with daytime highs today
forecast to run about 10 to 15 degrees above normal. Friday looks to
be the warmest day as upper ridge axis centers over the west coast.
On Saturday...daytime highs drop down just a bit as the upper ridge
axis shifts east of the state in response to an eastern Pacific
trough forecast to approach the coast. This system is forecast to
move onto the coast by Sunday afternoon or evening bringing a threat
of showers to the coast range...the northern mountains and possibly
the northern Sacramento valley. Stability progs show possibly
enough instability over the coast range for thunderstorms but
conditions are more stable farther east so removed afternoon/evening
thunderstorm threat there. Most locations Sunday will just see some
increased high cloud cover...increased southwest winds and about a 5
to 10 degree drop in daytime temperatures.

&&

.Extended Discussion (Monday through Thursday)

Models continue to forecast several short wave troughs through
northern portions of California Monday into Tuesday. Dynamics and
moisture look limited with main impact being synoptic cooling
with increased onshore flow. Locally gusty southwest to west winds
expected through the Delta and over higher mountain terrain. A
slight chance of showers and afternoon thunderstorms are possible
mainly over the mountains north of I-80 through this period.

Weak ridging moves through Wednesday followed by weak upper
troughing Thursday. Slight warming of the AMS depicted through
midweek by models with mid to upper 80s for highs in the Central
and mainly 60s to around 80 for the mountains and foothills.

&&

.Aviation...

Upr rdg blds ovr the fcst area nxt 24 hrs. Mnly VFR conds for Intr
NorCal exc lcl MVFR/IFR cigs in ST vcnty Carquinez Strait/Delta til
18-19z Thu and again from 08z-19z Fri. Lcl SWly sfc wnd gsts to arnd
25 kts poss thru Delta.

&&

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

$$





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