Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 012223
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
323 PM PDT Mon Sep 1 2014
Cooling trend early this week with near normal daytime highs
Wednesday through Saturday. Dry weather continues.
Morning raobs showed a 3 to 9 degree warming trend from Sun...and at
midday that trend was mostly holding true. On this Labor Day...max
temps are expected to equal/exceed 100 over many locations in the
valley...with 80s and 90s in the mtns. With strong ridging...weak
onshore gradients and a minimal marine layer...today should be
the warmest day this week. Adiabatic warming effects from a Nly
zephyr will also account for a couple of degrees of warming today.
A positively tilted trof is forecast to move through the Pac NW
and suppress the strong ridging over Norcal leading to cooling to
near normal temps by mid week. Cyclonic flow aloft will continue
for the rest of the week as the trof expands SWwd with a possible
weak low forming over the Nrn zones by the end of the week.
Nly gradients are forecast to weaken tonight/Tue as the ridge
weakens. This will result in cooler mins most areas tonite...
especially in the areas that benefited from the downslope warming
effects of the Nly winds in the Nrn and Wrn portions of the Sac
Vly last nite for instance. The Nly gradients are then forecast to
increase again Wed/Thu with the trof moving through the Pac NW and
offshore flow prevailing in its wake. This will suppress the
marine layer and limit the Delta Breeze Thu morning. However...Wed
morning may be that transition period where the synoptic pattern
and timing of the trof moving into the Pac NW increases onshore
gradients and allows the stratus along the coast to expand
Nwd...and perhaps deepen. The NAM forecasts a stratus intrusion
into the Sac Vly...however the forecast seems more problematic due
to the relatively weak surface pressure pattern given the larger
scale upper air pattern and lack of momentum of the boundary layer
winds. Also...the stratus will likely have to advect from the
south to the north and the timing will have to be nearly perfect.
For now...will continue the current forecast of an expected
intrusion in the afternoon package.
The wind pattern will allow some smoke from the Beaver WF to affect
our Nrn zones including Shasta Co at times...but the bigger smoke
plume from the more active Happy Camp WF complex may spread more
SWwd in the short term and then Swd along the coast...per the NAM
Hysplit model run. Some smoke or particulates may reach the N SFO
Bay and then spread into the Srn Sac Vly later tonite and Tue
morning according to the model. JHM
.Extended Discussion (Friday through Monday)
Persistent weak troughing aloft into NorCal will bring minor
cooling. Another reinforcing trough should lower heights some
more on Monday. We have kept the forecast dry with near to
slightly above normal temperatures and variable cloudiness.
General VFR conditions over the next 24 hours. Northerly winds
over the northern/central Sacramento Valley weakening this
afternoon. Then Sacramento Valley turn more southerly by Tue...SE
over interior Coastal Range and SW over Sierra. JClapp