Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 090616
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1016 PM PST Sat Mar 8 2014
A stream of Pacific moisture will bring precipitation to the
region tomorrow and Monday, especially for areas north of I-80.
Breezy winds are possible Tuesday. Dry and mild conditions return
for the remainder of the week.
Initial moisture plume is moving into Norcal this evening with
light rain reported at Redding and Red Bluff over the past few
hours. Radar is showing returns just offshore the bay area. These
are not being shown by models and have added slight shower
chances tomorrow morning over the southern Sacramento
valley...have also added sprinkle chances after midnight for these
areas. Any precip that falls overnight will be light due to the
dry low levels. More significant precip will spread over the area
tomorrow afternoon and evening. The rest of the forecast looks on
Warm day today with temps running within a couple of degrees of
yesterday. A few sites were a little cooler due to the limiting
factor of thickening high clouds spreading inland ahead of the
offshore system...which is forecast to move into our CWA later Sun
and Mon. Satellite Blended Total PW shows a maximum PWs in excess of
1.6" near 135W or about 600 miles offshore...fairly well illustrated
by the 08/12z GFS.
Upper trof nearing 140W is forecast to progress Ewd to near 130W by
00z Mon...pushing the associated frontal band onto the N Coast.
However...WAA precip should begin later tonite...and spreading over
the Nrn portion of our CWA mainly N of I-80 Sun afternoon.
Convection looks very problematic on Sun as lapse rates/instability
appear too stable due to WAA. Have removed thunder from Sun forecast
in this afternoon package...but continued the chances with Fropa Sun
nite and Mon morning.
The upper trof is forecast to move across our CWA between 12z Mon
and 21z Mon preceded by the cold front that is forecast to move
across our CWA from 03z Mon to 18z Mon. A higher probability of
convection is expected with the frontal band...with the possibility
of post-frontal convection into early Mon afternoon given albeit
shallow elevated convective instability where theta-e decreases
with height. Jet dynamics could also be a factor as the timing of
the frontal band is also forecast to be nearly coincidental with
the timing of the upper jet over our CWA. The initial surge of
drier air behind the upper trof axis will augment instability in
the forenoon hrs...but will gradually increase stability from west
to east during the afternoon. We left a chance of thunder over the
Siernev foothills into Mon afternoon where cyclonic upper-level
flow and low-level upslope flow and heating on the back edge of
the cloud deck will increase convective potential.
Cyclonic flow lingers into Tue morning...and transitions to
anticyclonic during the day. Pressure/height rises will tighten the
Nly and NEly pressure gradients on the backside of the trough Mon
nite into Tue creating gusty north winds for the N and W sides of
the Sac Valley.
Due to the subtropical origin of the TPW plume...snow levels will be
high above the Sierra passes and then lower behind the cold front to
around 5500 to 6000 ft...but by then the plume will be shunted
Swd. 2-6 inches snow expected over the high Sierra with up to 10
inches over the higher peaks. QPFS from 1 to over 2.5 inches are
expected over the mtns...with amounts near an inch in the Nrn Sac
vly tapering to .10 to .25 over the Srn Sac/Nrn San Joaquin vly.
.Extended Discussion (Wednesday through Saturday)
High pressure will remain in control over northern California
through the extended period, bringing dry and mild conditions to
the region. Breezy winds may linger into Wednesday but should
diminish by the end of the week as pressure gradients weaken. Look
for Central Valley highs to remain generally in the 70s for much
of next week, with the mountains in the 50s to lower 70s.
Increasing high clouds are spreading into the region this
afternoon ahead of an approaching system. Light rain will move
inland later this evening through the coastal mountains and into
the northern Sacramento Valley, with gradually lowering ceilings
and local MVFR conditions. More widespread MVFR after 12z Sunday,
north of KMYV. KSMF southward should remain generally dry until
late Sunday afternoon. Snow levels 7500-8500 feet. Generally light
and variable Valley winds tonight into Sunday. EK