Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 192228
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
328 PM 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...
Broad upper low is over California and will only gradually shift
east into the weekend. Not as much activity as shown by short
range models thus far this afternoon over the mountains. The best
coverage is over the coastal range...not much at all over the
Sierra. HRRR model shows best activity over the coastal range and
the Sierra south of Kirkwood through the evening. WRF core model
indicates more mountain shower and thunderstorm activity Wednesday
and Thursday with possibly an isolated cell or two in valley.
Weak/moderate onshore flow will keep temperatures slightly below
normal srn sac/nrn sj valleys into the weekend.

&&

.Extended Discussion (Saturday through Tuesday)

Area will be sandwiched between ridging building over eastern
Pacific and trough departing to the east for the start of the weekend.
Models continue to differ on the track and speed of the trough as
it departs. GFS moves the trough off faster to the east with
riding across the area for the weekend into Tuesday, which would
lead to a dry forecast. ECMWF/GEM are slower with the departure
and continue the chance for mountain showers and thunderstorms
through at least Sunday. Given uncertainty, have not made major
changes to going forecast. Feel that there may be enough
instability present to continue the chance for daily showers and
thunderstorms across higher terrain through Sunday for now. May
then see a break in convection for Monday and Tuesday. Regardless,
valley should remain dry in either scenario. Temperatures will
hover within a few degrees of normal with valley highs generally
in the 80s and foothills/mountains in the 50s to 60s. CEO


&&

.Aviation...

Mainly VFR conditions for interior NorCal except during showers
and afternoon/evening thunderstorms that bring periods of MVFR.
Best chance for showers/thunderstorms is across higher terrain and far
northern portions of Sacramento valley. 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.


&&

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

$$







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