Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 240541
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1040 PM PDT Thu Mar 23 2017

.Synopsis...
Rain and mountain snow returns tonight and Friday. Sierra snow
impacts likely late tonight into Saturday. Another system possible
Sunday and Monday with mountain travel impacts. Brief break in
precip mid weekend but more precipitation early next week.

&&

.Discussion...
IR imagery shows a fully occluded system off the WA coast. The
vertically stacked system indicates the surface low is off the WA
coast as well. This means the low is likely too far N of our area
for the strongest of pressure gradients and the strongest of 925 mbs
winds. These winds are forecast to be in the low 40s Kts Fri morning
with the NAM forecast Bufkit soundings forecasting very limited
downward momentum transfer of these winds. There is a vast
difference (one with WAD criteria, the other without) in the MOS
guidance from the models this evening. The strongest gradients and
thickness solenoids occur during the 18z Fri time frame, so late
morning into early afternoon looks to be the period of strongest
Valley winds.  JHM

.Previous Discussion...
Pacific storm system now approaching the coast will move into NorCal
late tonight bringing a return to precipitation. The heaviest
amounts will fall during the day Friday. Valley rainfall amounts
will range from 1-2 inches Redding area to 0.25-0.50 Stockton/
Modesto. Mountain precip amounts will be 1-2 inches liquid. Snowfall
amounts 8-14 inches above 4500 feet with up to two feet highest
elevations. Expect significant travel delays over the Sierra.
Activity will turn more showery Friday afternoon with mesoscale
models showing thunderstorms over the northern Sacramento valley.
Tightening pressure gradient will bring a few 40 mph south wind
gusts up the Sacramento valley...Stockton to Redding...strongest
central valley around Red Bluff.

Models continue the trend of drier weather Saturday with weak
ridge northwest flow. Next system will drop through Norcal Sunday
afternoon through Monday and looks to be slightly drier but colder
than Friday system. Snow levels look to be 4000 feet or lower.

&&
.EXTENDED DISCUSSION (Monday THROUGH Thursday)

Showers will linger on Monday as upper level wave moves through.
Have boosted snow amounts a bit during the day with snow levels
around 5000 feet. Modest additional accumulations likely but will
probably be enough to cause a few travel delays. Have also
introduced the possibility of thunderstorms during the
afternoon/evening hours. This will hinge on the amount of clearing
in the morning but models are indicating some decent instability.
Ridging then builds in for Tuesday and Wednesday with warming
temperatures. Models continue to show another system dropping into
the area from the Gulf of Alaska on Thursday but disagree on the
details. At this time, best chances for precipitation looks to lie
across northern and eastern portions of the area.

CEO

&&

.AVIATION...

Next system moves into NorCal tonight into Friday. VFR conditions
through this evening then local MVFR/IFR conditions after 12z
Friday with precipitation. Winds will increase on Friday with
gusts to around 25 kts at TAF sites.


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 11 PM this evening to 5 AM PDT
Saturday for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

Wind Advisory from 9 AM to 7 PM PDT Friday for Carquinez Strait
and Delta-Central Sacramento Valley-Motherlode-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Southern Sacramento Valley.

Winter Storm Warning from 11 PM this evening to 5 AM PDT
Saturday for Shasta Lake Area / Northern Shasta County.

&&

$$


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