Area Forecast Discussion
Issued by NWS Sacramento, CA

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575
FXUS66 KSTO 180522
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
920 PM PST Fri Feb 17 2017

.Synopsis...
Wet weather continues with several storm system passages expected
through the middle of next week. Sierra mountain travel issues at
times. Gusty winds Friday and Monday. Increased flood threat Monday.

&&

.Discussion...
Long wave trof along the W Coast with upper low near MRY Bay
forecast to move Ewd and SEwd respectively across CA on Sat. Higher
resolution QPFs suggest the broad area of rain in Norcal will remain
oriented meridionally (mainly N-S) over the region and won`t move E
of the I-5 corridor until after noon on Sat. Precip will linger over
the Sierra through the afternoon and finally taper Sat evening. So
another 12-15 hrs of mainly light rain expected for our CWA, and a
little longer in the Sierra. The N-S orientation of the precip does
not make this a favorable orographic flow pattern for the Sierra,
but it does for the Shasta drainage. This area is also in the
favorable diffluent flow of the longer wave trof.

The core of the 40+ 925 mbs winds will be over the SCK-SMF area
through 06z and then weakening the rest of the night. Eventually
these tree-toppling, power-pole-pitching winds will subside. More
strong winds are expected with the Sun nite/Mon storm. the NAEFS
wind speed anomaly indicates an 850 mbs +2-4 anomaly in the valley
Mon afternoon with a NAM MFR-SAC gradient of 11 mbs at 12z Mon and
925 mbs wind support of 60+ kts. These factors put gust potential in
the 45-55 kts range with the weaker gusts at SAC/SCK. However, due.
to the core of the 925 mbs working from S to N with the approaching
warm front, would expect stronger winds at those locations.   JHM


.Previous Discussion...
A large upper level trough continues to influence California weather
as a high amplitude trough sets up and progresses onshore.
Radar returns show rain and snow for the higher elevations.
Mountain snow above 6000 feet could result in an additional 4 to 8
inches of snow with highest peaks receiving an additional inches
of snow through Saturday morning. Surface observations continue to
show gusty winds for locations along and south of the Interstate
80 corridor for the Valley. Wind gusts up to 55 mph will continue
through the early evening hours.

Heavier rain will break for this weekend with lighter scattered
precipitation. The next bigger system will arrive Sunday evening
through early Tuesday. Heavy snow is possible at higher terrain
with snow levels starting higher between 6000 and 7000 feet, but
colder air pushes in Tuesday with snow levels dropping to 3000 to
4000 feet.

With heavy rain and moist soils throughout the area, flood
potential is heightened Sunday evening through early Tuesday as
heavy rain re-enters the region.

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Lingering showers and some breezy winds continue into Tuesday,
with decreased intensity. The main upper trough is forecast to
move inland Tuesday night into early Wednesday resulting in
increased showers across the area, with lowering snow levels and
lighter precipitation amounts. Snowfall could cause additional
travel problems across the mountains, with snow levels dropping to
4500-5000 feet Tuesday, 3500-4000 feet on Wednesday/Wednesday
night. Snow could impact travel over the mountains. Snow intensity
and amounts are expected to be tapering off as snow levels drop,
though. Additional snow amounts in the Sierra Tuesday-Wednesday
look to to be around a foot above 6000 feet to pass levels, with
maybe 2 feet on higher peaks. Light accumulations of around an
inch or 2 are possible down to around 3500-4000 feet.

There is some potential for convection Wednesday, as the core of
the trough moves through. So far confidence is too limited to
mention thunderstorms in the forecast at this point.

A period of drier weather is expected for Thursday and Friday,
with mainly just some lingering snow showers in the mountains.
Most areas aren`t expected to see any precipitation.

The models are hinting at an inside slider system on Saturday.
This could bring some light mountains precipitation, and some
gusty winds. EK


&&

.AVIATION...

Scattered showers with local MVFR/IFR conditions across the
Valley and IFR/LIFR conditions across higher terrain through this
evening. Southeasterly winds with gusts to 40 kts with gusts from
around KSMF southward through 06z-08z this evening. Precipitation
activity continuing overnite, decreasing mainly after 18z with
lingering shower activity into Saturday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Sunday evening through late Monday night for
Burney Basin / Eastern Shasta County-Carquinez Strait and Delta-
Central Sacramento Valley-Clear Lake/Southern Lake County-
Motherlode-Mountains Southwestern Shasta County to Northern Lake
County-Northeast Foothills/Sacramento Valley-Northern Sacramento
Valley-Northern San Joaquin Valley-Shasta Lake Area / Northern
Shasta County-Southern Sacramento Valley-West Slope Northern
Sierra Nevada-Western Plumas County/Lassen Park.

Winter Weather Advisory until 10 AM PST Saturday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

Winter Storm Watch from Sunday morning through late Monday night
for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

Wind Advisory until 10 PM PST this evening for Carquinez Strait
and Delta-Northern San Joaquin Valley-Southern Sacramento Valley.

&&

$$



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