Special Weather Statement, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
254 AM PST Mon Jan 4 2021

.SYNOPSIS...
Strong Pacific Storm will bring periods of heavy rain, possible
thunderstorms, heavy mountain snow and blustery winds to Norcal
today. Tuesday and most of Wednesday will be dry, but additional
rain and snow is possible again later in the week.

&&

.DISCUSSION...
Moderate TPW moisture plume (AR) will be moving inland with a
favorable SW trajectory and orographic effects for heavy precip
mainly N of the I-80 corridor, and especially for the Feather/Yuba
River basins. Upper trof nearing 130W at 09z will be nearing the N
Coast by 18z and moving inland thru 00z. Surface cold front and
strong LLJ will precede the trof mainly moving across our CWA from
18z-00z with the tail end of the front hanging back over the Sierra
into the evening. The HREF Probability of >40 dBZ REF shows a 100%
bulls-eye over/around the North Complex burn scar from 10am-2pm,
then a 70%+ from 2pm-4pm. The Probability of 1 hr rainfall >0.50" is
also >70% from 11am-1pm, and given these probabilities and forecast
QPF of 1.50" to 3.50" over the burn scar today, and the convective
potential for the Valley and Sierra Foothills given negative LI's
and several hundred J/kg of CAPE, there is the potential for lines
of thunderstorms and flooding/flash flooding over that burn scar.
Model QPF has generally increased slightly from yesterday with
amounts mostly ranging from up to an inch in the Northern
Sacramento Valley to 2 to 5 tenths of an inch southward into the
San Joaquin Valley and 1 to 2.5 inches in the foothills and
mountains with 3+ inches in the aforementioned Feather/Yuba River
basins. Snow totals up to a foot to a foot and a half with
localized amounts up to 2 feet are forecast over the higher
elevations/higher peaks. Light snow will be possible down to 5000
feet this evening, especially in convective showers.

The WAD (wind advisory) for mainly the Valley and coastal mtns looks
on track given the nearly 50Kts NAM 925 winds ahead/along the front
from 15z-21z. the strongest winds are expected to the in the Nrn
half of the Sac Vly. The WSW for the mountains also looks on track
with periods of heavy snow with 1-2 inch hourly rates possible
given the instability forecast over the Sierra during the
afternoon, mainly from 21z-after 00z (1pm-5pm or so).

Ridging will follow this trof as it moves across the Nrn Plains/Nrn
Rockys on Tue, followed by a another trof mainly moving into the Pac
NW, but also brushing Norcal, late Wed and Wed night. This is a
weaker TPW plume (AR) with much lighter QPF expected in Norcal, e.g.
a couple of inches of snow for the Sierra, compared with a foot to a
foot and a half with today's system. Another system is forecast to
move into our area late Thu/thu nite.    JHM

.EXTENDED DISCUSSION (Friday THROUGH Monday)...

Pacific frontal system moves through interior NorCal Friday
bringing widespread rain and mountain snow. Snow levels look to
range from 3500 to 5000 feet and thus could impact mountain
travel. Drier weather expected over the weekend under upper
ridging. Potential for some night and morning valley fog
development under moist stable conditions. Models suggest another
system moving through on Monday with some uncertainty in timing
and strength.

&&

.AVIATION...

Wdsprd MVFR with areas of IFR and lcl LIFR tda in intr NorCal as
Pac fntl sys movs thru. Sn lvls 040-060. Isold tstm poss btwn
20z-02z in Sac Vly and ern fthls. Areas Sly sfc wnd 25g35kts in
Cntrl Vly btwn 16z-23z tda. SWly sfc wnd gsts up to 50 kts poss
ovr hyr mtn trrn tda. Conds impvg tngt, but areas MVFR/IFR/LIFR
poss in Vly BR/FG Tue mrng.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 10 AM PST this morning through this
evening for Northeast Foothills/Sacramento Valley-Western Plumas
County/Lassen Park.

Winter Storm Warning until 4 AM PST Tuesday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

Wind Advisory from 6 AM this morning to 8 PM PST this evening
for Central Sacramento Valley-Mountains Southwestern Shasta
County to Western Colusa County-Northeast Foothills/Sacramento
Valley-Northern Sacramento Valley-Southern Sacramento Valley-
Western Plumas County/Lassen Park.

&&

Special Weather Statement
National Weather Service Sacramento CA
130 PM PST Mon Jan 4 2021

CAZ015-016-066-042215-
Northeast Foothills/Sacramento Valley-Northern Sacramento
Valley-Central Sacramento Valley-
130 PM PST Mon Jan 4 2021

...A STRONG THUNDERSTORM WILL AFFECT CENTRAL TEHAMA...WEST CENTRAL
BUTTE AND NORTHERN GLENN COUNTIES...

At 128 PM PST, a strong thunderstorm was located from near Red
Bluff south to near Black Butte Summit, moving northeast at 30 mph.

Winds in excess of 30 mph and pea size hail are possible with this
storm along with heavy rain.

Locations impacted include...
Red Bluff, Corning, Tehama, Henleyville, Gerber-Las Flores,
Richfield, Vina, Los Molinos, Black Butte Dam, Black Butte Summit and
Black Butte Lake.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 3977 12240 4020 12235 4035 12185 3985 12186
TIME...MOT...LOC 2128Z 245DEG 25KT 3996 12228

CM

Special Weather Statement
National Weather Service Sacramento CA
134 PM PST Mon Jan 4 2021

CAZ013>015-066-068-042215-
Northeast Foothills/Sacramento Valley-Northern Sacramento
Valley-Burney Basin / Eastern Shasta County-Western Plumas
County/Lassen Park-Shasta Lake Area / Northern Shasta County-
134 PM PST Mon Jan 4 2021

...A STRONG THUNDERSTORM WILL AFFECT NORTH CENTRAL TEHAMA AND
SOUTHEASTERN SHASTA COUNTIES...

At 132 PM PST, a strong thunderstorm was located near Anderson
north to near Montgomery Creek, moving northeast at 25 mph.

Pea size hail and gusty winds are possible with this storm along
with heavy rain.

Locations impacted include...
Redding, Palo Cedro, Shingletown, Anderson, Whitmore, Inwood, Round
Mountain, Millville, Montgomery Creek and Cottonwood.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 4030 12203 4031 12248 4084 12209 4082 12161
TIME...MOT...LOC 2132Z 237DEG 22KT 4053 12223

CM