Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 301024
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
324 AM PDT FRI SEP 30 2016


.SYNOPSIS...
Continued cooling trend through the weekend with daytime highs 15
to 25 degrees below normal by Sunday. Warmer temperatures next
week. Chance of showers and isolated thunderstorms Sunday into
Tuesday. Drier mid week with another chance of showers northern
mountains by Friday.

&&

.DISCUSSION...
Temperatures are running a few degrees lower this morning most
areas and this trend will continue into today as the overall
cooling trend continues. As the early season low pressure system
from the Gulf of Alaska continues to drop southeast into the
eastern Pacific, cooler air will filter into the region bringing
a cooling effect of about 5 to 10 degrees compared to Thursday.
The delta breeze is running similar to 24 hours ago with winds at
Travis AFB sustained at around 20 knots but should see some
increase in ridgetop winds today as pressure gradients increase
ahead of the low. A shortwave disturbance passes to the north of
the forecast area on Saturday bringing a bit more cooling but any
precipitation should remain west and north of the forecast area.
Another disturbance out of the Gulf of Alaska will dig the upper
low farther southward on Saturday night and Sunday. This
disturbance and associated frontal band is now fairly consistently
progged by the models to move through northern California during
the afternoon on Sunday moving into the Sierra late afternoon or
evening. Models show enough instability for a chance of
thunderstorms but a lot will depend on timing of the front and
coincidence with daytime heating. Cloud cover and cooler airmass
will bring another big drop in temperatures Sunday with daytime
highs in the valley mainly in the 60s or about 20 degrees below
normal. The upper low moves into the Great Basin on Monday and
this should bring an end to the precipitation threat most areas
although a few lingering showers will be possible over the Sierra
in the morning hours. Building high pressure will bring warmer
temperatures. ECMWF not as robust in building the ridge however
showing a flat ridge solution Monday and this could allow some
precipitation into the coast range.
&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

On Tuesday, medium-range models are projecting a weakening wave to
approach California from the northwest. Some light precipitation
is possible, particularly along the NW portions of our forecast
area, but the current consensus keeps most of the region dry.
Drier weather is likely next Wednesday and Thursday as a weak,
transient ridge moves through. High temperatures are expected to
warm back up to near normal levels.

The ECMWF and Canadian models are hinting at another round of
precipitation late next week as an upper trough moves through the
region. The GFS is much weaker and drier with this system. For
now, we`ve opted to include "slight chance" wording across the
northern portions of our forecast area, though confidence is low.

Dang

&&

.AVIATION...

VFR conditions across Valley terminals the next 24 hours.
South to west wind continue across the Valley today, with local
gusts up to 25 kt during the afternoon. Near the Delta and over
higher terrain...higher gusts are possible.

Dang

&&

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

$$


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