Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 191005
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
305 AM PDT THU MAY 19 2016

.Synopsis...
Temperatures cooling to near normal today. A significant cool
down Friday through Sunday with scattered showers and
thunderstorms and mountain snow. Below normal temperatures and a
mountain shower threat continues through mid week.

&&

.Discussion...
Most locations seeing a little more wind this morning as an upper
trough over the Pacific digs southeastward towards the coast.
Areas near the delta are running a little cooler thanks to a
steady delta breeze which developed last evening.
Elsewhere...increased mixing is bringing a little warmer
temperatures. Overall however...forecast area will see a
significant cool down today as cooler air associated with the low
now over western Canada filters into the region. Daytime highs
today are forecast to come in between 12 and 15 degrees below what
they were on Wednesday. A shortwave pivoting across norcal could
bring a shower over the southern Cascades today but not all models
show this feature. Overall precipitation chances increase tonight
however as the main upper low drops southward. The main
precipitation threat will remain north of interstate 80 tonight
before encompassing nearly all the forecast area by Friday
afternoon as the upper low digs southward. Models in pretty good
agreement in placing the upper low center somewhere near the
northeast corner of the state by Friday afternoon. Cold air aloft
associated with the low will bring instability to the entire CWA
so have included a slight threat of thunderstorms all areas Friday
afternoon. Daytime highs will continue to fall with maximum
temperatures dropping to well below normal for this time of year.
By Friday afternoon...snow levels will drop to pass levels and
although significant snowfall is not expected there could be
enough snow to present travel difficulties over the Sierra. Upper
low center only shifts slightly to the northeast on Saturday so
not expecting much change in the forecast from Friday with cooler
than normal temperatures and showers and afternoon thunderstorms
remaining in the forecast. The upper low shifts to the northeast
on Sunday leaving weak troughing over the entire western U.S. As a
result...although warming slightly...daytime highs will remain
below normal with a threat of mountain and north state showers
continuing. Conditions look more stable for Sunday so have remove
afternoon thunderstorm threat for now.

&&

.EXTENDED DISCUSSION (Monday THROUGH Thursday)

Long wave trough remains along the West Coast through early
next week as waves rotate through Interior NorCal. This will keep
unsettled weather into at least Tuesday with below normal
temperatures. Showers and afternoon thunderstorms will be possible
with best chances over the foothills and mountains. Snow levels
will generally be around 7000 feet or above Mon/Tue. Significant
widespread snow is not expected. High temperatures in the Central
Valley will be in the 70s with 50s and 60s for the mountains and
foothills.

Models are trending towards drier weather towards the middle of
next week as progs showing short wave ridging moving over NorCal
Wednesday into Thursday. Forecast confidence decreases towards the
end of next week as models differ with timing of next Pacific
storm moving onto the West Coast.
&&

.AVIATION...

Incrsg Wly flow alf tda as upr low digs fm PacNW into NorCal tngt.
VFR conds ovr Intr NorCal tda exc lcl MVFR/IFR poss in ST vcnty of
Delta til 18z. Lcl MVFR/IFR poss in shwrs omtns aft 06z Fri. Lcl
SW-W sfc wnd gsts up to 30 kts poss thru Delta and ovr hyr mtn
trrn nxt 24 hrs.

&&

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

$$



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