Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 211109
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
409 AM PDT WED SEP 21 2016

.SYNOPSIS...
A few light showers south of Sacramento this morning. A slight
chance of showers or thunderstorms across the far northern
mountains and Sierra today and Thursday. Breezy winds over the
southern Cascades today with a Red Flag warning there today for
winds and low RH. Cooler than normal temperatures through Friday
then warmer than normal over the weekend and into next week.

&&

.Discussion...
Northern California under southwest flow aloft between high
pressure over the central U.S and a low pressure system off the
Pacific Northwest coast. A shortwave disturbance moving through
this southwest flow is currently bringing some light showers south
of about Sacramento. This area of showers will slowly shift to the
east during the morning hours. Breezy onshore flow expected today
most noticeably through the delta and over the southern Cascades
where a Red Flag warning is currently in place. The upper trough
axis is forecast to move inland this afternoon and evening. Should
see enough instability and dynamics across northern Shasta county
for a slight threat of thunderstorms today. All other areas will
see a significant drop in temperatures today as cooler air
associated with the low filters into the region. The upper low
digs to the southwest tonight and Thursday. As is does, the shower
threat shifts to the southeast as well with this threat working
southward into the northern Sierra by Thursday afternoon. There is
not a great deal of instability with this system but enough to
justify the slight thunderstorm threat. As the upper trough moves
into the Great Basin northerly flow develops across the north
state. Cool airmass and this northerly flow will keep daytime
highs Thursday well below normal. As the upper trough continues
east on Friday, high pressure pushes in over the west coast
bringing mainly fair skies. Temperatures will remain below normal
one last day Friday before warming begins on Saturday as
temperatures climb back up to a few degrees above normal.

.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)

Warm and dry conditions will dominate NorCal Sunday into midweek
as high pressure strengthens over the eastern Pacific Ocean and
builds into the West Coast. High temperatures will range about 5
to 10 degrees above normal this weekend into next week. JBB


&&

.AVIATION...

VFR conditions continue the next 24 hours with winds at TAF sites
generally between 5-15 kts with local gusts up to 25 kts this
afternoon into evening.


&&

.STO Watches/Warnings/Advisories...
Red Flag Warning from 11 AM this morning to 8 PM PDT this
evening for Northern Sierra Including Lassen NP and Plumas and
Lassen NF/S West of the Sierra Crest (West of Evans Peak-Grizzly
Peak-Beckworth Peak).

&&

$$



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