Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 041030

330 AM PDT Mon May 4 2015

Strong Delta Breeze continues to spread some cooling inland today,
otherwise warm temperatures with a slight chance of mountain
thunderstorms continue through Tuesday. Cooler and more unsettled
weather will arrive by the middle of the week.


Other than some coastal stratus beginning to impinge on the
western edge of the forecast area, and debris cloudiness left over
from Sunday afternoon`s deep convection east of the Sierra, skies
are clear early this morning over interior NorCal. With the marine
layer deepening to around 3K ft on the Fort Ord profiler, we`ll
likely see some stratus make its way into portions of the Central
Valley early this morning. Temperatures are running a little
cooler than 24 hours ago with the biggest drops occurring further
inland as onshore flow increases.

Weak cyclonic flow will continue across NorCal today as the region
lies between a deep low approaching Vancouver Island and a much
weaker closed low moving into SoCal. The pattern will support
another round of isolated late day showers and thunderstorms along
and east of the Sierra Crest. There is a slight chance that a few
storms may develop further north today into the northern mountains
and northern Coast Range. Otherwise, temperatures will continue to
gradually cool inland today as moderately strong onshore flow

Mountain convection is forecast to take a break on Tuesday as
stronger westerly flow with the trough shifts activity further to
the east for a day. Further synoptic cooling associated with the
trough will be balanced by weakening onshore flow, so temperatures
will likely be pretty similar to today`s in many areas.

Confidence is increasing that we`ll transition to a cooler and more
unsettled weather pattern across the area Wednesday and Thursday
as the west coast trough digs southward. The current track keeps
most of the showers and thunderstorms over the mountains, but a
slight deviation further to the west could bring quite a bit of
activity to the Central Valley and areas further to the west as
well. We`ll continue to monitor.


.Extended Discussion (Friday through Monday)...
Continued confidence exists that a cold Low will drop across the
area late in the week. This system will bring the potential for
afternoon/early evening convection across the area Friday,
including portions of the Valley. Instability does not appear to
be strong at this point as the low center is expected to be over
central NV. But wrap around moisture looks sufficient enough for
locally heavier showers and some thunderstorms. Some of this
convection could linger into Saturday over the Sierra, even though
ridging dominates the upper levels. Another system passes through
Oregon and NorCal on Sunday and Monday with another round of
showers and thunderstorms. JClapp


Strong Delta Breeze with marine stratus encroaching into KSUU as
of 10Z. Marine layer near 2500ft thick at Bodega Bay at 10Z.
Expect stratus into KSAC/KMHR by 12Z and possibly expanding over
KSMF by 13Z. Tougher to get stratus at KSMF on first day of
stratus intrusion, but temp/dewpoint spread was low at KSAC last
evening. A few thunderstorms may form along the Sierra crest this
afternoon and early evening. JClapp


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


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