Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 191020
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
320 AM PDT Tue Aug 19 2014

.Synopsis...
A low pressure system will move southward off the coast today
reaching SoCal on Wednesday. Temperatures will cool to near or
slightly below normal. There will be a slight chance of mountain
thunderstorms today and Wednesday.

&&

.Discussion...
Closed mid/upper low now centered just offshore to the WSW of the
Bay Area. This system is forecast to move southeastward and be
over SoCal on Wednesday. Stronger short-wave in the northern
stream presently over Vancouver Island will move through the PacNW
today and the tail end may be a factor in NorCal thunderstorm
development later today.

Skies are mostly clear across the interior of NorCal early this
morning except for high clouds which are beginning to increase
south of I-80 and over the far northern Sierra as lift increases
ahead of a upper jet max rounding the base of the low. The marine
layer has deepened dramatically overnight and is now approaching
3k ft in depth. Satellite imagery shows extensive marine stratus
throughout the Bay Area now extending into the Sacramento area.
Temperatures are running pretty similar to readings of 24 hours
ago, though 5-10 degrees of cooling is occurring along the leading
edge of the Delta Breeze which now extends up into the Oroville
and Chico areas in the Sacramento Valley and into the Modesto area
in the San Joaquin Valley.

After a quiet Monday thunderstorm-wise for the interior NorCal
mountains, prospects for a few storms look better today. The
blended TPW satellite product indicates 0.60 to around 0.75 inches
TPW overhead while the area with the lowest TPW (<1/2 inch) and
strongest subsidence has shifted further south and east into
western NV and central CA. Mid-level COL will be over the northern
portion of the forecast area as the low drifts further south. The
tail end of the previously mentioned short-wave will move into the
far north later today and may assist with initiating deeper
convection later this afternoon over the northern Coast Range and
around Mt Lassen. The Sierra south of Lake Tahoe may see a few
storms late today as well.

By Wednesday, the whole pattern shifts further south and appears
the best prospects for deep convection will be limited to late in
the day across the Sierra to the south of Lake Tahoe.

Seasonal temperatures are expected the next several days as lower
heights and thicknesses and a moderate onshore flow continues
helping to regulate temperatures. We may see a bit of marine
stratus advect into the Sacramento metro area again early
Wednesday morning.

Not much change is expected through the weekend as a weak trough
is forecast to linger across NorCal.

&&

.Aviation...
Stronger delta breeze overnight has allowed marine stratus to move
inland. Much of the delta region is under low ceilings and the
onshore flow has moved stratus into the Sacramento Metro region
early this morning. KSAC is reporting ceilings at SCT to BKN009
which is expected to continue through about 16z this morning for
Sac Metro vcty. Otherwise, the rest of interior NorCal will have
VFR conds. Surface winds today will be onshore flow ranging 5 to
15 kts with the stronger winds in the southern Sacramento Valley
(closer to the delta breeze). Winds over ridge tops and in the
delta will range 15-25 kts today with locally higher gusts. JBB

&&

.STO Watches/Warnings/Advisories...None.

&&

$$




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