Winter Storm and Flooding in California, February 24 to 28, 2019

Area Forecast Discussion
National Weather Service Sacramento CA
228 PM PST Sun Feb 24 2019

.SYNOPSIS...
An active weather pattern will continue to set up over northern
California this week. Heavy snow is forecast for the higher
elevations of the mountains while increasing flooding potential
remains the threat for the valley and foothills.

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.DISCUSSION...
Low pressure area near British Columbia will drift southward to
off the Oregon/Washington coast in the next day then will remain
in a semi-permanent position through the middle of this week. This
will allow for an abundant amount of moisture to stream into the
region from the southwest to west. The models are in general good
agreement into Monday with light amounts of precipitation moving
over the interior...mainly for areas north of I-80. Snow levels
will rise slightly this evening to near 4000 feet but some local
snow down to 3500 feet may continue into the evening. General snow
advisory conditions are expected into Monday ahead of the main
band of precipitation over the northern mountain areas with some
increased snowfall expected overnight for those areas.

Monday through Wednesday there are still some differences in the
models on where the heavy precipitation will set up. The European
has the heaviest from the Feather River Basin northward while the
GFS brings heavier precipitation further south in addition to the
heavier totals to the north. The European did increase its
precipitation output a little today. The models are indicating
anywhere from 8 to 12 inches of rainfall for the Feather River
Basin over three days. Snow levels will be rising next week into
the 5000 to 6500 foot range for the event as we get into Tuesday
and Wednesday. Heavy snow is expected over the higher elevations
and depending on where the focus of precipitation is flooding
concerns will be on the rise. Rising rivers and the potential for
major ponding of water throughout the interior from the lower
mountain elevations into the valley will materialize. Some snow
melt mainly below 4000 to 5000 feet will likely add to the water
flowing into the rivers and streams as well as onto the roadways.
Most rivers in the foothills continue to likely be
cresting/peaking on Wednesday based on the latest forecast.

Currently forecasting 6 to 10 inches of rain over Western Shasta
County...8 to 12 inches through the feather river basin...5 to 8
over the mountains in Lake County...3 to 6 inches in the
motherlode with local amounts up to 8 inches over the higher
foothill elevations. The valley is forecast to have 2 to 5 inches
with local higher amounts possible. Flash Flood watch issued for
areas below 4000 feet and into the Redding area due to the amount
of water expected on top of the already nearly saturated soils
with a Flood Watch for the valley where the terrain is flatter.

Abundant snowfall accumulation will likely close major pass
levels over the crest for an extended period of time so motorist
might want to consider alternate routes if possible or avoid
travel. 6 to 8 feet of new snow is expected near pass levels and
above.

In addition breezy to windy conditions Monday into Wednesday will
add to the problems with downed trees and limbs likely along with
possible power outages. Heavy snow in the higher elevations of the
mountains will replace the lower elevation rain related issues
with trees and power outages.

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.EXTENDED DISCUSSION (Thursday THROUGH Sunday)

A cold front will be making its way through the region to start
off the extended period. This will bring diminishing valley rain
chances with lingering mountain showers. Snow levels will be
lowering to 2000 to 3500 feet by late Thursday but overall
additional accumulation should remain light. Chilly overnight lows
are expected Thursday night as cold air builds in behind the
front. Short wave ridging will bring quiet weather on Friday.

Our next system will start to move into the region on Saturday as
a short wave trough approaches NorCal from the west. Precip
chances are expected to continue throughout the weekend. The
higher moisture does look to stay to our south but we will still
likely see a steady rain at some point throughout the weekend.
Given the expected rain this week this system would likely bring
enough rain to bring some flooding concerns. Snow levels will
start out between 3000 and 4500 feet Friday night but will raise
to above 6000 feet by Saturday night.

-CJM
&&

.AVIATION...

VFR conditions expected for the southern terminals the next 24
hours. Rain chances and low cigs will bring MVFR conditions to
the northern terminals by this evening continuing into Monday.
Southernly winds increase overnight and become breezy on Monday
10-20 knots gusting to 30 knots.
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.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 10 AM PST Monday for Burney Basin
/ Eastern Shasta County-Mountains Southwestern Shasta County to
Northern Lake County-Shasta Lake Area / Northern Shasta County-
Western Plumas County/Lassen Park.

Winter Storm Warning from 10 AM Monday to 4 AM PST Thursday for
West Slope Northern Sierra Nevada-Western Plumas County/Lassen
Park.

Flash Flood Watch from Monday afternoon through Thursday morning
for Clear Lake/Southern Lake County-Motherlode-Mountains
Southwestern Shasta County to Northern Lake County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Shasta
Lake Area / Northern Shasta County-West Slope Northern Sierra
Nevada-Western Plumas County/Lassen Park.

Wind Advisory from 7 AM Monday to 10 AM PST Tuesday for Central
Sacramento Valley-Motherlode-Northeast Foothills/Sacramento
Valley-Northern Sacramento Valley-Southern Sacramento Valley.

Flood Watch from Monday evening through Thursday morning for
Carquinez Strait and Delta-Central Sacramento Valley-Northern
San Joaquin Valley-Southern Sacramento Valley.

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