Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 061724
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
924 AM PST Thu Mar 6 2014
Lingering showers are possible today, along with a few
thunderstorms in the afternoon and early evening. Dry and mild
conditions expected for Friday and Saturday. A disturbance late
Sunday into Monday will bring another chance of precipitation to
Disturbance will drop southeast over Norcal this afternoon
increasing shower and isolated thunderstorm coverage. The best
coverage will be over the northern valley and mountains along with
the Sierra. Hrrr model pinpoints Butte county and Lassen area with
best convective coverage this afternoon and have updated forecast
to shift threat into these areas. Small hail will be possible in
some of the stronger storms. Models not showing much precip in the
valleys...but will keep isolated showers in the forecast with
disturbance nearby. Otherwise...forecast is on track.
A convective band which pushed through Norcal this evening
brought some excitement in the form of heavy rain and lightning.
450+ cloud-to-ground strikes were recorded between 9pm and 2am.
Conditions have quieted down now, with area radars showing
lingering showers mostly confined to the mountains and no
lightning activity. Interestingly, this convection was
accomplished without much upper-level dynamics. The NAM suggests
the main trigger was strong cold air advection aloft combined
with a favorable moisture tap near the surface.
Better upper-level dynamics can be expected today as a shortwave
trough and associated vortmax push through NorCal. Convective
parameters such as MUCAPE look much more impressive than
yesterday evening in fact. Lapse rates remain fairly steep with
CAA aloft. The only component less favorable than yesterday is
less low-level moisture to work with. Drier conditions may limit
convection to cumulus development as opposed to showers and
thunderstorms, as hinted at by the NAM12 in buffkit. If anything
does get going, there will be plenty of shear aloft with trough
passage. Have gone with a chance of showers and slight chance
thunder from Sacramento northward. Snow levels will lower to
around 6000 feet by the afternoon, although it appears light
precip amounts will limit accumulations to only a few inches over
the passes. Breezy conditions can be expected for the higher
Showers decrease quickly Thursday evening as ridging builds into
the West Coast. Temperatures will be warm but not record-
breaking, rising into the 70s in the Central Valley 50s/60s in
The ridge begins to break down Sunday allowing a 1.25"+ PWAT tap
to approach the NorCal coast, while A trough moving into the
Pacific NW provides some weak dynamics. Models are in fair
agreement in pushing a resulting precipitation band across our
area by late Sunday. The best chances look to be initially north
of I-80, then eventually spreading to the whole area by Monday.
.Extended Discussion (Monday through Thursday)
Pacific frontal system still on track to drop across NORCAL early
Monday with only slight timing differences across models. Dynamics
with this system are not overly impressive. The subtropical
moisture plume feeding into this system is fairly impressive
however with GFS still showing 1.35 inches TPW just offshore.
Still...with relatively weak dynamics...Models showing this storm
will be a low to moderate precipitation producer and with snow
levels mainly above 7000 feet impacts should be minimal. With warm
airmass and some afternoon clearing possible...looking for daytime
highs on Monday at a few degrees above normal.
Extended models in good agreement in building a high amplitude
ridge over the west coast so after a few possible lingering
showers Tuesday morning...precipitation threat disappears for at
least the remainder of the week. Daytime highs under the ridge
will remain well above normal under mainly fair skies Wednesday
through Thursday. Surface high pressure pushing into the Pacific
Northwest will bring a transition to northerly winds Tuesday. GFS
model shows a fairly tight northeast surface gradient developing
Wednesday morning as an upper shortwave drops into the great
basin. Therefore...a period of breezy to gusty north winds will be
possible around the middle of next week. Current extended models
are indicating that there will be no return of a wet pattern for
Northern California through at least next weekend.
A second Pacific front will be moving across interior Norcal
roughly from late morning into the afternoon. Line of showers and
isolated thunderstorms expected to affect TAF sites mainly central
and Nrn SAC vly from KMYV...Nwd to KRBL and KRDD. MVFR cigs/vsbys
expected with showers and isolated TRWS in proximity of
front...otherwise mostly VFR conditions. VFR all areas tonight.
South to Southwest winds with gusts to 30 knots higher Sierra
elevations today. Sly winds up to 10 knots in the valley.