Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 251615

Area Forecast Discussion
National Weather Service Sacramento CA
915 AM PDT Tue Jul 25 2017

Slight chance of afternoon showers or thunderstorms across
portions of the mountains into Wednesday. Near normal
temperatures today then dry and warmer Thursday through the


580 DM upper low centered near Fort Bragg this morning will be
main weather feature influencing Interior NorCal over the next 36
hours. Marine layer has continued to deepen overnight in response
to low and currently is around 2600 ft deep per Ft. Ord profiler.
Moderate flow through the Delta is providing low level CAA into
the Central Valley. This and synoptic cooling with low will result
in near normal high temperatures across Interior NorCal today. WV
imagery continuing to show a lot of drier air wrapping into the
low at lower and mid levels. NAM/GFS elevated instability progs
again suggest only a slight chance of deep moist convection over
outer fringes of the CWA today. Most likely place for any
development is over the mountains of Eastern Shasta county and the
Lassen Park area this afternoon.

Models have trended slower with progression of the upper low and
keep it nearly stationary overnight. Low then progged to move
slowly to the ENE Wednesday as it begins to fill. NAM elevated
instability progs keeps some increased 700-500 MU CAPE and TT
above 30 over Eastern Shasta and Lassen Park area. Temperatures
rebound up a few degrees Wednesday as Delta influence and synoptic
cooling weaken.

Heights increase over the area Thursday as upper ridging from the
Desert SW expands NW towards NorCal. Dry weather expected
Thursday as triple digit heat returns across much of the Central
Valley. Temperatures are forecast near to a few degrees warmer
Friday as we are sandwiched between deep troughing in the EPAC and
the 4 corners high.



Temperatures are expected be about 5-10 degrees above normal
during the extended period as high pressure over the Four Corners
region rebuilds across the area. There is still some model
disagreement in terms of the position and strength of this ridge.
Regardless, daytime highs will likely reach the century mark
across the Sacramento valley. Monsoonal moisture could be advected
northward around the Four Corners ridge early next week. In
addition, elevated instability charts suggest isolated
thunderstorms could be possible near the Sierra crest Tuesday
afternoon. The GFS is the most aggressive solution, but the Euro
and the Canadian models keep the forecast area generally dry. For
now, have added a slight chance of thunderstorms mainly south of
Lake Tahoe given model differences.


VFR conditions the next 24 hours across interior NorCal. Winds up
to 15 kt in the area, except gusts to 30 kt near the Delta and
over higher terrain.



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