Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 151041
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
341 AM PDT Tue Apr 15 2014

.Synopsis...
Dry weather with well above normal high temperatures continuing
through Thursday with a slight chance of showers over the northern
mountains on Friday into the weekend. Breezy northerly winds possible
Tuesday night and Wednesday.

&&

.Short Term Discussion...
A more progressive upper air pattern is forecast over the Ern
Pacific and West Coast this week with a series of trofs/ridges
affecting Norcal wx. However...the impacts on Norcal wx will be
relatively slight with mostly dry wx and above normal max temps
continuing for the rest of the work week.

Yesterday`s mention of an Ern Pac trof and associated front eroding
the highly amplified West Coast ridge is currently underway with a
positively tilted (weak) trof moving through the region during the
morning hours. As expected...a band of cirrus gummed-up the skies
over Norcal during the Lunar (Blood Moon) eclipse. But the clouds
were not dense/thick enough to impair viewing over many areas during
the eclipse period and we did receive some awesome photos from
our FB followers during the night. If interested...check them out
at facebook.com/NWSSacramento. The back edge of the cirrus is
progged by NWS speed tracker to mainly be along and S of the I-80
corridor by sunrise. The band of colder/enhanced clouds over the
Pac NW is expected to stay N of our CWA this morning...but some
more high clouds may spread across the Nrn zones this afternoon
and tonite from short wave energy within the NWly flow aloft.

A little cooling is expected in our CWA today behind the short
wave and front...mainly across the Nrn zones as indicated by the
850 mbs and thickness progs. Still max temps will run about 5-10
degrees above normal most locations.

It is mainly the secondary energy embedded in the NWly flow aloft
from the rebuilding Ern Pac ridge in the wake of the short wave
currently moving through the CWA that will give us some gusty/breezy
Nly winds as that energy digs into the Great Basin later tonight and
Wed. The forecast Nly pressure gradients are just a little shy of
our rule-of-thumb for wind advisory criteria. The NAM 925 mbs winds
(~2 kft) peak out in the 30-33 kt range from 12z-18z Wed. This is
a little premature for the time of max heating to optimize
downward momentum transfer which is also problematic for wind
advisory criteria...and this is something we will be working on
today. The peak winds may occur around midday...then decrease
during the afternoon on Wed. Little change in high temps is
expected as the CAA will be offset by downslope warming from the
northerly winds.

Ridging rebuilds over Norcal later Wed afternoon and nite...
decreasing the Nly gradients and turning them modestly NW. This
will promote warming with maxes on Thu some 10-15 degrees above
normal. Lo and behold...another progressive trof will quickly
follow bringing a change in the wx again on Fri. Initially...the
GFS forecasts some instability in the Tuolumne/Alpine County areas
Thu afternoon/evening with also the low chance of some light
showers across Nrn Shasta Co as well. This low chance of showers
will spread SEwd over the Siernev into Fri. The valley is
expected to remain dry... except for perhaps the far N end of the
Sac Vly Thu nite.

This more progressive and deeper trof will likely bring noticeably
cooler temps to Norcal as temps cool from the 80s in the valley on
Thu into the 70s on Fri...but still a few degrees above normal. The
timing of this trof is not quite in phase with the NAM 925 mbs
wind forecast and will hold off on those details for now.   JHM

.Extended Discussion (Saturday through Tuesday)

Mostly dry and benign weather is on tap for this weekend. A few
weak shortwaves could trigger a shower or two over the Sierra Crest,
but otherwise dry weather will continue. Highs looks to continue
the current above-normal stretch, with readings about 10 degrees
above normal for the Central Valley.

After several weeks of quiet weather along the West Coast, a
change may be in store next week. All extended models are now
showing a deep and cold closed low swinging into NorCal sometime
early next week. We`ll be keeping on eye on this potential pattern
change, particularly if models show consistency in future runs.
For now, have introduced a chance of showers for much of interior
NorCal, along with cooler temperatures. -DVC

&&

.Aviation...

VFR conditions continue for interior NorCal for the next 24
hours. Generally light winds of 10 kts or less expected for
Central Valley TAF sites. Meanwhile, the Delta will see some
15-25 kt southwest winds early this morning, and some 25 kt SW
winds can expected over Sierra ridges this afternoon. -DVC


&&

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

$$







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