000
FXUS66 KSTO 261204
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
404 AM PST Tue Jan 26 2021

.SYNOPSIS...
Freezing temperatures are expected across much the area this
morning. A long duration, high impact winter storm this evening
into Friday bringing periods of gusty winds and moderate to heavy
rain and mountain snow. Potential for significant low elevation
snow and damaging winds tonight and Wednesday as well as burn
scar impacts to the LNU Complex and SCU Complex burn scars.

&&

.DISCUSSION...
We are in the calm before the storm early this morning as a short
wave ridge builds in. This is bringing clear skies and with a cold
air mass in place we are seeing cold temps this morning and the
Hard Freeze Warning looks to be on track. Quiet weather is
expected for much of the day today with increasing clouds.

The forecast will become very active starting in the evening as a
trough drops out of the Gulf of Alaska. This will bring a high
impact winter storm to NorCal. As the tough drops south we will
see warm air advection increase over the region this afternoon
into the evening with light precip developing over the Coastal
Range after 1 pm. Precip will continue to overspread the area
during the late afternoon into the evening. Precip will become
heavier during the evening and will be the heaviest overnight as
the cold front moves through. A NCFR (narrow cold frontal
rainband) is likely to develop along the cold front and this will
bring us the most intense rain and snow. This can be expected
between 8 pm Tuesday and 8 am Wednesday and we could see rain
rates exceed 0.50" per hour and snow rates exceed 2" per hour
during this time. The best chances for the rain rain rates
greater than 0.50" per hour will be over western Yolo County into
Solano County and south into western San Joaquin and Stanislaus
County. This does include the LNU and SCU Lightning Complexes and
a Flash Flood Watch has been issued for both of those burn scars.

The other big concern with this system will be the low snow
levels. Snow levels will be 500 to 2000 feet this evening and will
fall to the Valley floor over the northern Sacramento Valley
overnight tonight into Wednesday morning. This will result in snow
in Redding and Red Bluff with several inches expected. Snow levels
will rise throughout the day Wednesday and we should see them rise
above 3000 feet during the afternoon but they will remain locally
down to 2000 feet over Shasta County.

Southerly winds increase rapidly overnight tonight as this storm
moves in with 925mb NAM winds maxing out around 75 knots. This may
translate to winds across the Valley of 35 to 45 mph with gusts
of up to 50-65 mph. A High Wind Warning has been issued for these
anticipated damaging winds. With widespread rain and heavy snow
also anticipated during these overnight hours, expect extremely
poor visibilities and hazardous travel conditions.

The back side of the trough will continue to dig down the CA
Coast and that will help to stall the cold front over the region.
This will keep rain and snow in the forecast for Wednesday and
Thursday with the heaviest rain and snow expected from I-80 south.
Snow levels into Wednesday night will generally be between 3000
and 4000 feet locally lower over Shasta County. Snow levels on
Thursday will continue to come up and we should see them rise to
around 4000 feet by the afternoon. Light showers will linger into
Thursday night especially over the higher elevations.

-CJM

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...
Active storm pattern continues into early next week as an upper
trough remains off the coast bringing persistent moist southwest
flow into NorCal. Precipitation amounts likely to be significantly
less than earlier in the week on Saturday giving a relative break
to mountain travelers, but another round of impactful mountain
snow looks likely Sunday into Monday. &&

.AVIATION...
VFR conditions predominate thru 00Z Wednesday, except
local MVFR visibilities south of KSAC 13Z-17Z. Southerly surface
wind gusts 10-20 kts 18Z-00Z Wednesday.

Widespread MVFR conditions develop across the Central Valley
between 22Z-02Z Wednesday, with IFR/LIFR developing over the
mountains, as frontal system moves into NorCal. Low snow levels
with accumulating snow likely at KRDD and KRBL beginning this
evening. Increasing southerly surface wind gusts 35-50 kts after
03Z Wednesday.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 4 PM this afternoon to 2 AM PST Friday
for Burney Basin / Eastern Shasta County-Central Sacramento
Valley-Motherlode-Mountains Southwestern Shasta County to
Western Colusa County-Northeast Foothills/Sacramento Valley-
Northern Sacramento Valley-Shasta Lake Area / Northern Shasta
County-West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

High Wind Warning from 8 PM this evening to noon PST Wednesday
for Carquinez Strait and Delta-Central Sacramento Valley-
Motherlode-Mountains Southwestern Shasta County to Western
Colusa County-Northeast Foothills/Sacramento Valley-Northern
Sacramento Valley-Northern San Joaquin Valley-Southern
Sacramento Valley.

Flash Flood Watch from 4 PM PST this afternoon through Thursday
afternoon for Northern San Joaquin Valley-Southern Sacramento
Valley.

&&

$$