Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 250441
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
940 PM PDT Sun May 24 2015

.Synopsis...
Warmer temperatures with showers and thunderstorms expected this
weekend into mid next week, mainly over mountains. High pressure
dries things out by late in the week.

&&

.Discussion (Today through Wednesday)...

In between high pressure over the Pacific and low pressure over the
Rockies is a smaller low center over SWrn B.C. A weak trof extends
from this low into Norcal and higher resolution QPF progs keep some
isolated shower activity going over the Nrn mountains and Siernev in
our CWA until about 09z-10z or so.

Strong onshore/up valley pressure gradients AOA 4 mbs will continue
until after midnight...but are forecast to substantially decrease by
sunrise Mon morning. Although the gradients decrease...the onshore
momentum has yet to cease as the SUU winds are blowing much stronger
than last night. With the marine layer about 2600 ft on the Ft Ord
Profiler and suggested by the KOAK evening RAOB...we would
anticipate a greater than 50/50 chance of a marine stratus intrusion
into the Srn Sac Vly Mon morning. Although the stratus intrusion is
implied in our SKY grids...the text wording was more generic however
so we refined it in the evening update.

On Monday...another piece of energy from the SWrn B.C. low
will move over the Pacific Northwest and into Norcal as the low
center drifts SEwd into Ern WA. This will continue the shower and
thunderstorm activity over the mountains and bring a slight chance
for some activity to the far northern end of the central valley.

The low moves very little from Tuesday into Wednesday so expect
similar chances for thunderstorms over the mountains. Temperatures
will also be warming up into the 80s to lower 90s by midweek.

&&


.Extended Discussion (Thursday through Sunday)

Ridge of high pressure over Northern California Thursday and
Friday bringing warmer temperatures and decreased threat of
showers and thunderstorms over the mountains. High temperatures are
expected to reach in the upper 80s to mid 90s in the Valley and
60s and 70s in the mountains, which is generally around 5 to 10
degrees above normal for the end of May. The ridge shifts east on
Saturday as an upper level trough approaches the west coast. The
trough will bring an increase in onshore flow and cooler
temperatures for the weekend. Temperatures are expected to cool
to near normal for this time of year on Sunday with highs in the
low to mid 80s in the Valley and mid 50s to low 70s in the
mountains.

&&

.Aviation...

General VFR conditions expected next 24 hours except areas of MVFR
across the higher elevations of the Shasta Co mtns and Nrn Sierra
Nevada. Scattered showers and isolated thunderstorms over the Coast
Range and northern Sierra Nevada expected again 22Z Mon-03Z Tue.
Local southwesterly wind gusts to 35 kts through the Delta with
possible MVFR cigs in stratus intrusion into Srn Sac Vly Mon
morning.

&&

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

$$









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