Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 191526
AFDSTO

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

.Synopsis...
Slightly cooler than normal temperatures next few days. A slight
chance of an afternoon or evening thunderstorm mountains today and
tomorrow. A slight warming trend into weekend and dry.

.Discussion...
Upper low is sliding southward today...in a nutshell should result
in slight chance of showers and thunderstorms in higher terrain and
continued mild temperatures. HiRes short term models in good
agreement today that instability will be limited today and will be
limited to far north (highest elevations of Shasta County) and
also Sierra south of Highway 50 in our forecast area. This
scenario covered well. Did tweak the areal coverage of pops a bit
as well. Some moisture and instability does linger in Sierra south
of Highway tomorrow and even into Thursday which current forecast
covers as well. Update to ZFP on the way but very minimal changes
to forecast. Rasch

.Previous 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 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 today for a few storms look better. 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.

&&

.Extended Discussion (Saturday through Tuesday)

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
week.

Dang


&&

.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 vicinity. Otherwise, the rest of interior NorCal will
have VFR conditions. 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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