Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 171545
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
845 AM PDT Sun Aug 17 2014

.Synopsis...
Temperatures will be near to a little above normal today and drop
to near to a few degrees below normal temperatures through the
week. A low off the coast may bring some isolated
showers/thunderstorms Monday and Tuesday for mainly the Coastal
Range, Shasta County, and Lassen Park area, and the Sierra south
of Lake Tahoe Tuesday.

.Discussion...
Weak shortwave over the area and a low dropping along the coast
of Washington today. Low clouds made it inland to around Cordelia
this morning with onshore flow. Marine layer only around 1500 ft
deep so onshore flow will not bring much cooling today. Low clouds
should dissipate around 11 am and return again to around Cordelia
again tomorrow morning. Maximum Temperatures today are expected
to be in the 90s in the Valley and 70s and 80s in the mountains,
which is near to a little above normal for mid August. Instability
should remain north and west of our area this afternoon so should
be dry another day.

The low that is off the coast of Washington today will glide down
to the Northern California coast tomorrow afternoon. This will
bring some instability and moisture over the Coastal Range, Shasta
County and Lassen Park area for a slight chance of thunderstorms.
Although, the best instability will still be north of Shasta
County. Temperatures will cool a few degrees on Monday with
stronger onshore flow and deeper marine layer with weakening high
pressure. The low continues to drop down the California coast on
Tuesday to around Pt Conception with a broad trough over
California. A little instability and moisture over the mountains
of interior Northern California on Tuesday afternoon for a slight
chance of thunderstorms. The best instability will be to the north
and east of the area. Temperatures are expected to stay similar to
Monday on Tuesday. The low moves farther south and east on Wednesday
but there is variability in its track in the models. If the low is
farther north and inland like the NAM we could get some
instability and moisture wrapping around into the sierra South of
Highway 50 for a slight chance of thunderstorms but will hold of
mentioning for now due to uncertainty in the track of the low.


.Extended Discussion (Thursday through Sunday)

Medium-range models are still unsure how to handle the
aforementioned cut off low, but have started to become in better
agreement with each other than previous runs. EC and GEM suggest
keeping the cut off low off the southern California coast separate
from a longwave trough over the northwest US, which would also
keep the broad trough farther north and progress eastward a bit
faster. This solution would also potentially support drawing in
some moisture from the south...though latest runs have kept the
cut off low far enough off the coast to keep our area dry. The GFS
wants to inhale that little cut off low right into the longwave
trough, and allow the trough to remain over the northwest US
through at least Saturday. This solution would generally keep us
under a dry, northwest flow pattern. Minimal changes were made to
the forecast until a better model consensus comes into focus. All
major models do agree on a general troughy pattern over NorCal,
which would suggest around to below-normal temperatures
continuing. Shen


&&

.Aviation...

VFR conds will persist for TAF sites next 24 hrs exc lcl IFR cigs
W of KSUU til abt 17Z. Some gusty WSW ridge winds 15-25 kts over
higher trrn Siernev this afternoon.

&&

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

$$







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