Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 190438
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
938 PM PDT Mon Aug 18 2014
Near normal temperatures expected this week with a slight chance
of mountain thunderstorms next few days.
Upper low is near the Bay Area. Mostly clear skies overnight over
NorCal. A moderate onshore flow is keeping temperatures cool over
the southern Sacramento valley...where evening temperatures are
3-6 degrees cooler versus 24 hours ago. Current forecast is on
track and no evening update will be needed.
Water vapor satellite imagery shows a closed upper low centered
over the Northwest California coast this afternoon, and dropping
southward. Thunderstorms have developed along the Siskiyou,
Trinity, and Mendocino Ranges, but as of this writing have
remained outside of our forecast area. Skies have remained mostly
clear across the bulk of interior NorCal. The onshore gradient is
a fair bit stronger than the last few days and is resulting in
temperatures up to 6 degrees cooler than at this time yesterday.
The upper low will continue to drop southward over the next 24
hours. The best instability should remain just outside of our
forecast area, but can`t rule out an isolated thunderstorm along
the Shasta-Trinity or Mendocino crest this afternoon. The
instability spreads toward Lassen Peak and Northern Sierra
tomorrow, bringing a slight chance of convection there as well. By
Wednesday, instability should remain confined primarily to the
Sierra south of Lake Tahoe.
Seasonal temperatures are expected the next several days as lower
heights and thicknesses and a moderate onshore flow help to
regulate temperatures. We may see a bit of marine stratus advect
into the Sacramento metro area early Tuesday morning.
.Extended Discussion (Friday through Monday)
By late this week, the upper low will have shifted to southern
California and into Arizona. Dry northwesterly flow will be
present over Northern California. Expect benign weather and near
normal temperatures to continue this weekend and into early next
VFR conditions the next 24 hours, except local IFR conditions west
of KSUU tonight into early Tuesday. Patchy MVFR stratus may make
it to Sacramento TAF sites early Tue. Winds will remain below 12
kt across Valley TAF sites, except southwest winds 15-25 kt near
the Delta and over higher elevations.