Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 210506
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1005 PM PDT Wed Sep 20 2017

.SYNOPSIS...
Cooler weather continues this week with a chance of showers into
Thursday. Turning warmer and drier this weekend.

&&

.DISCUSSION...
Front has pushed Swd to a Yosemite NP-MCE line with bulk of the
precip over the Sierra and S of the I-80 corridor in our CWA. Wet
snow about 6800 ft as suggested by Dual Pol data, hopefully hitting
some of the high elevation wildfires in Tuolumne/Alpine county
areas. Earlier lightning noted in the Sierra this afternoon has
dissipated, but IR/lightning data show cumuliform clouds off the N
Coast with the secondary short wave rotating Swd on the backside of
the trof. This energy is forecast to drop towards the SFO Bay area
by 12z Thu and then into the San Joaquin Vly during the morning.
Will have to watch if the showers hold together and clip our
Solano/San Joaquin/Stanislaus zones early Thu morning.

Otherwise, a broad and deep trof will develop over our region
through Fri and into Sat morning. This will keep temps below normal.
Given the cyclonic flow aloft, clouds should linger over the Sierra
into Sat and expect to see some cumulus redevelop in the Valley
during the next couple of days.     JHM

.Previous Discussion...
Current satellite imagery indicates a deepening trough along the
West Coast. In addition, weather observations and radar returns show
a frontal system making its way southward across interior NorCal
this afternoon. Precipitation amounts have ranged from a few
hundredths up to a half inch and breezy winds have developed ahead
of this system.

As the frontal band pushes across interior NorCal, moderate
precipitation will be favored over the mountains and a few
Valley/Foothills sprinkles or showers could not be ruled out.
QPF will generally be light, however half inch or more amounts
will be possible across higher terrain.

The upper trough will usher in cold air aloft, so snow levels
could be dropping to around 6500 feet. Even a few inches of
snowfall accumulation will be possible across the higher peaks.
However, this could impact high elevation travelers and outdoor
enthusiasts who might be catch off guard.

Temperatures will be well below average (10-20 degrees) across
the region the next few days with highs only in the 70s across the
Central Valley through Friday. By late this week, dry weather is
expected as the trough shifts to the east and dry northerly flow
develops.

&&

.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)
High pressure continues to build over the region through the
extended period, leading to warm and dry conditions for interior
NorCal. Temperatures continue to rise Sunday into early next week
where most valley locations will once again reach the 90s by
Monday for the Northern Sacramento Valley and Tuesday for the rest
of the valley. Breezy north winds return this weekend and
continue through early next week which, combined with the warmer
temperatures, create an elevated fire risk for the area. HEC

&&

.AVIATION...
VFR conditions for the valley terminals for the next
24 hours, though ceilings expected to lower to 5,000-10,000 ft
until 5z Wednesday. Isolated rain showers and light mountain high
elevation snow expected this afternoon through Thursday night.
Breezy winds expected with gusts up to 25 kts possible at TAF
locations through Thursday morning.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$


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