Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 241211
Area Forecast Discussion
National Weather Service Sacramento CA
411 AM PST TUE NOV 24 2015
A COLD PACIFIC STORM WILL BRING HEAVY SNOW IN THE MOUNTAINS WITH
SNOW EXTENDING DOWN INTO THE UPPER FOOTHILLS INTO WEDNESDAY. DRY
AND COLD WEATHER EXPECTED THANKSGIVING EXCEPT FOR FLURRIES ALONG
THE SIERRA CREST.
Cold front is just off the far northwest corner of California
early this morning. Radar shows heavier precipitation along the
northwest coast beginning to spread inland across the northern
Coast Range. Satellite imagery shows cloud cover ahead of the
front now extending about as far south as the Sacramento area.
The front will sweep rapidly southward today, reaching the
Sacramento area around midday and shifting into central California
by this evening. Snow levels will quickly lower from 4000-5000
feet to below 3000 feet as the front approaches and then passes.
Moderate snow will develop along I-80 by mid-morning, then periods
of heavy snow expected this afternoon as lapse rates steepen and
heavier convective bands develop (thunder-snow is possible). May
see some snowfall rates approaching 2 inches per hour late in the
day. Needless to say, significant travel impacts are expected.
After a relative lull early tonight, a secondary vort drops down
from the north late tonight and will bring another upswing in
showers, mainly to the west of I-5 and through the northern San
Joaquin Valley. It may bring a few inches of snowfall accumulation
to the higher terrain of Lake County as well as areas of the
Motherlode toward Wednesday morning.
By Wednesday, 8 to 12 inches of snow accumulation above 5000 feet
with 12 to 22 inches along the northern Sierra Crest looks like a
good bet. Lighter accumulations, though significant, will extend
into the foothill elevations. The snow should be the light fluffy
type at the higher elevations due to the amount of cold air.
The low will linger over the Great Basin through Thanksgiving
before retrograding back into NorCal late in the week. Flurries
will likely continue along the Sierra Crest, with precipitation
possibly spreading further west by Friday.
Overnight lows will be around the freezing mark in the valley
through the remainder of the week with cloud cover and wind
possibly mitigating even colder temperatures. Widespread single
digit and teens lows will be likely in the mountains. Chilly
daytime temperatures are also expected with readings below-normal.
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)
Sat/Sun: The Rex Block Ridge will remain in place Saturday with
the high pressure cell over Wrn Canada and low pressure cell over
CA/NV. This lingering low will continue a chance of light showers
over the area. The potential for freezing/near freezing
temperatures exists in the Valley and very cold temperatures in
the mountains and mountain valleys, dropping into the teens and
single digits for the weekend. A limiting factor for the cold
morning temperatures will be mixing winds and cloud cover.
Monday: The dynamic, parent upper trough extending from the Gulf
of Alaska Sunday/Monday will finally push the blocking pattern
eastward, which will bring subtle ridging or a col area to NorCal
with a break in the precip chances. Monday adds some uncertainty
with the EC and GFS showing dirty ridging (i.e. EC is sharper than
GFS). Worse case scenario would be lingering snow showers mainly
over the Sierra and colder temps.
Tue/Wed: EC and GFS both have rather large and expansive low
pressure areas over the Gulf of Alaska. Both bring in shortwaves
supporting cold fronts into NorCal sometime between Tuesday and
Wednesday. The EC brings in multiple shortwaves from Tue to Thu
with lower snow levels, while the GFS has more of a steady
southwest flow aloft with higher snow levels as seen in an
Atmospheric River scenario Tue and Wed. Either way, we bumped up
the chance of precip Tue into Wed and increased snow levels a bit
for the first days of December. JClapp
In Central Valley and adjacent lower foothills, widespread
MVFR/IFR developing around 13z with areas of southerly sfc wind
gusts to 25 kts. Widespread MVFR/IFR with local LIFR in northern
mountains after 12z, spreading to Sierra by 16-18z Tue. Sfc wind
gusts up to 45 kts over higher mountain terrain today. Snow
levels 040 to 060 this morning, lowering 020 to 025 this
Winter Storm Warning until noon PST Wednesday for Motherlode-
Northeast Foothills/Sacramento Valley-West Slope Northern Sierra
Nevada-Western Plumas County/Lassen Park.
Winter Weather Advisory until 6 PM PST this evening for Burney
Basin / Eastern Shasta County-Mountains Southwestern Shasta
County to Northern Lake County-Shasta Lake Area / Northern