Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 161130
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
430 AM PDT Tue Sep 16 2014
Temperatures cooling to below normal later this week with a chance
of showers and thunderstorms returning to the region later
Wednesday into Thursday.
Clear skies across interior NorCal early this morning under dry
southwest flow aloft ahead of deepening upstream trough west of
130W. Temperatures are mostly cooler compared to 24 hours ago and
range from the upper 40s in the colder mountain valleys to the mid
50s to mid 60s in the Central Valley.
Temperatures will be down by about 5 degrees across the region
today compared to Monday. The strong upper ridge will continue to
shift slowly eastward allowing minor synoptic cooling. While
onshore gradients have weakened compared to 24 hours ago and the
marine layer has been disrupted, some Delta influence will
continue into the southern Sacramento Valley today.
The cool down will accelerate Wednesday as the upper trough and
frontal system approach and onshore flow increases. Appears there
will be enough moisture with this system (TPW around 1.5 inches)
that despite relatively weak forcing, many areas will see
potential for showers. Looks like the best timing for any
precipitation will be later Wednesday into early Thursday as the
front moves inland, and then again later Thursday as deep
convection increases as the upper trough moves overhead. Overall
QPF will be light with most areas likely lucky to see a tenth of
an inch of rain.
Still looks like a good bet that the region will see warmer and
drier conditions return for the weekend as the trough forms a
closed low that drifts south to off the SoCal coast. Still a lot
of model uncertainty by early next week as the GFS, GEM and EC
differ in the timing and evolution of how the low moves off to the
east, but appears main impacts would be south of our area.
VFR conditions over interior Northern California through early
Wednesday with an upper level trough in the the Eastern Pacific
approaching the California coast. Local SW surface wind gusts to
30 kts over mountains and in the Delta.