Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 091555

Area Forecast Discussion
National Weather Service Sacramento CA
855 AM PDT Wed Aug 9 2017

.SYNOPSIS... Showers and thunderstorms are possible over the next
several days mainly over the mountains. Temperatures will remain
near to slightly above normal through the weekend.


Upper low continues to exist off the NW California coast helping
to moderate temperatures and keeping a threat of showers and
thunderstorms, mainly over the mountains. KOAK sounding showing
marine layer this morning is around 2000 ft deep with strong flow
through the Delta. Some patches of stratus were evident around the
office earlier this morning but were short lived. Temperatures are
currently running close to what they were 24 hours ago and thus
max temps this afternoon also should be similar. Elevated
instability progs showing increased 700-500 MB MU CAPE and TT
values over the coastal, northern, and eastern mountains this
afternoon to support deep moist convection.

Water vapor imagery reveals a strong vort max rotating around
base of upper low at this time and is forecast to track across
Interior NorCal tonight. This could help keep some nocturnal
activity going, mainly over the mountains. However hi res models
are currently not supporting this, probably because of the lack
of available moisture. Flow through the Delta looks to continue
strong tonight and with depth of marine layer, may see a little
more stratus into the Southern Sac Valley tomorrow morning.

Models similar in tracking the low inland across Interior NorCal
Thursday. Little change expected in max temps and showers and
thunderstorms will again be possible, mainly over the mountains
in the afternoon.

Low lifts NE into SE Oregon Friday with weak height rises over
Interior NorCal. Temperatures likely to warm a couple degrees and
drier SW flow should suppress deep moist convection. Little change
expected into the weekend with weak upper troughing continuing off
the West Coast.



Forecast models continue to indicate an upper trough digging into
the Pacific Northwest early next week. However, model uncertainty
remains regarding the evolution of this system. The ECMWF
indicates a deeper and farther south solution compared to the GFS.
Despite model discrepancies, latest guidance is in fair agreement
to cooler temperatures across interior NorCal as the upper trough
settles in and onshore flow increases. Main dynamics associated
with this system should stay north of the forecast area so have
kept the forecast dry.


VFR conditions at the TAF sites the next 24 hours. Isolated to
scattered thunderstorms possible over the mountains between 21z
Wednesday and 06z Thursday. Activity could continue this evening
over the Sierra mainly north of I-80. Generally light winds across
TAF sites. Gusts to 30 kts possible through the Delta and in the
vicinity of any thunderstorms.



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