Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 141642
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
930 AM PDT Tue Apr 14 2015
A fast-moving weather system exits the region this morning. Breezy
to windy conditions along with much cooler temperatures will be
left in its wake for today. Warming mid-week through Friday under
building high pressure with locally breezy conditions continuing.
Cold front and upper trof axis have already worked their way Ewd
into NV/Great Basin (SWrn end of cdfnt moving S of our CWA into Srn
half of CA) with clearing conditions in interior Norcal from large
scale subsidence in the wake of the strong vort within the trof.
Flow over Norcal on the backside of the trof will remain cyclonic
into Wed afternoon and then transition to anticyclonic as Ern Pac
ridging builds over the area late Wed and Thu.
Pressure gradients will be more aligned from NW-SE today and then
transition to NEly tonite into Thu morning due to pressure rises
over OR and the Great Basin. This would result in offshore
flow...and a strong katabatic wind regime with a developing Nly
barrier jet on the W side of the Sac Vly into Solano Co. While the
925 mbs winds decrease this afternoon...they increase tonite and
again Wed nite as colder air from the NE plateau/Wrn Great Basin
areas is forced downslope/downhill by the increasing NEly pressure
gradient and gravity. Thus...locally breezy conditions in the valley
generally relaxing this afternoon...then increasing winds again
tonite and Wed. Locally strong winds also likely along the west
facing canyons in the northern Sierra later tonite and into Thu.
Pressure gradients relax Thu afternoon ending the windy period.
A much cooler day is expected today due to the post-frontal cooling.
850 mbs temps dropped from 11-13 deg yesterday to 2-3 degrees this
afternoon. Dry adiabatic mixing from 850 mbs only yields maxes in
the 60s in the valley this afternoon.
A couple of cold nites are expected in the NE mtn valleys/basins due
to NEly flow from the cold NE plateaus. Otherwise...adiabatic
warming and mixing will bring a rapid warmup to the region as high
pressure strengthens over Norcal and the air mass modifies. JHM
.Extended Discussion (Saturday through Tuesday)...
High pressure will weaken ever-so-slightly over NorCal for the
weekend as a weak upper disturbance moves over the region. The GFS
and ECMWF still have differences in the evolution of this
disturbance, but at the very least there will be a slight chance
of showers over the mountains over the weekend. Temperatures
should remain very warm however through at least the weekend into
early next week.
Longer-range models are depicting a much colder and deeper trough
approaching the West Coast toward Tue or Wed of next week. Given
its closed low nature...don`t expect much model agreement with its
track or intensity for at least the next few model runs. Dang
VFR conditions across the Valley the next 24 hours. North winds
10-20 kts with local gusts to 30-35 kts will be possible across the
Valley during the day today...generally relaxing this afternoon. Nly
barrier jet expected to develop on the W side of the Sac Vly into
Solano Co later tonite and into Wed morning with local gusts 30-40