Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 271144

444 AM PDT Sun Jul 27 2014

Above normal temperatures through the coming week but a slight
cooling trend after Tuesday. Daytime highs in the central valley
topping 100 through mid week. The Sierra crest will see a threat
of thunderstorms through much of the week with a chance of
thunderstorms over the northern mountains Wednesday.


Water vapor imagery loop shows mid level sub tropical moisture
being pull northward into northern California over the last 24
hours. Most areas will see variable high clouds today with a
slight increase in higher elevation humidity but over all this
moisture will have little impact today. Upper level high pressure
ridge over the western U.S. will continue to bring in daytime
highs several degrees above normal for the next several days. Most
valley locations will see high temperatures topping 100 through at
least Tuesday. Main forecast issue, other than tracking smoke
from NORCAL Fires, will be afternoon mountain thunderstorm threat
now that monsoon moisture has made it into the region. Stability
progs indicate enough instability for a slight threat of Sierra
crest thunderstorms mainly south of Tahoe today. This threat will
shift northward up the Sierra a bit on Monday as southerly flow
aloft continues but again mainly near the crest with southeast
flow aloft bringing better orographics on the east side of the
range. The Sierra Cascade thunderstorm threat will continue on
Tuesday slipping just a bit farther north. GFS and GEM models
hint at a weak ripple moving up the back side of the ridge and
through NORCAL sometime Tuesday or Wednesday and with this very
slight decrease in stability the afternoon thunderstorm threat
could spread to the mountains of Shasta county. Will need to watch
for the development and timing of this feature with timing likely
to change in subsequent runs having impact on Thunderstorm

.Extended Discussion (Thursday through Sunday)

Mid range models show a slight shift in the Western U.S. ridge to
the east by Thursday. This should bring the beginning of a very
minor cooling trend. The resultant southwest flow aloft will bring
more stable conditions for a decreased thunderstorm threat most
mountain locations. Have kept a slight threat of thunderstorms
over the northern mountains Thursday and Friday as models
continue to indicate the passage of minor ripples as they move
through upper southwest flow. A more pronounced southwest flow
aloft should bring drier air aloft and more stable conditions by
next Saturday removing the last of the mountain thunderstorms next



Mainly VFR conditions the next 24 hours, except areas of smoke
near the Sand Fire. Winds will remain below 10-15 kt across Valley
TAF sites. Near the Delta, SW winds 15-25 kt continue.



.STO Watches/Warnings/Advisories...

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