Tornado and Winter Storm in California, April 20 to 22, 2022

Area Forecast Discussion
National Weather Service Sacramento CA
339 PM PDT Wed Apr 20 2022

.SYNOPSIS...
Widespread rain, heavy mountain snow and periods of gusty winds
today through Friday. Drier and milder conditions return this
weekend.

&&

.DISCUSSION...
A deep trough is digging out of the Gulf of Alaska over the
Pacific and this trough is going to bring active weather to NorCal
over the next 24-48 hours. Southerly flow has increased ahead of
this approaching trough and we are seeing breezy winds this
afternoon with gusts 20-35 mph from Sacramento north. These winds
will increase some as the afternoon goes on and are going to
remain breezy into the overnight. Ridge top winds over the Sierra
will also increase with gusts 50+ mph possible. We are also seeing
weak warm air advection over the northern portions of the area and
this is leading to light showers. Activity will continue to
increase in coverage later this evening into the overnight as a
cold front pushes south through the area. The cold front will push
into the far southern part of the area by daybreak tomorrow but
widespread showers are going to continue as the trough axis
approaches.

Some weak instability will start to build into northern areas
after 9 this evening and we could see an isolated thunderstorms
over Shasta County or the northern foothills overnight.
Instability will continue to build into NorCal during the morning
hours and this is looking like a good set up for thunderstorms for
us by the afternoon. The best chances for scattered thunderstorms
will be from around Sacramento north to the Redding area east into
the foothills, this is an area that could see some clearing in the
morning. Sounding profiles will support small hail along with
gusty winds. We do see some low level veering which could lead to
a few funnel clouds but 0-1 km shear is a bit low around 5-10
knots. 0-1 km shear is a bit higher in the Red Bluff to Willow to
Chico area, this would be the greatest area to see isolated funnel
clouds. PWATs will also be high, above 0.50" and this will lead
to heavy downpours. Somewhat fast storm motion should limit very
heavy rain over a single area but a quick 0.50-0.75" will be
possible with any thunderstorms.

The trough axis will push to our south Thursday night and showers
will diminish across the area. Northwest flow will develop on
Friday and this will keep isolated light showers in the forecast
Friday morning into the early afternoon with the best chances over
the higher elevations. We do see some CAPE build in over the
Sierra north of I-80 in the afternoon but the thunderstorm threat
looks very low.

This system will be able to pull in good moisture with it and the
IVT will be pushing up to near 500 kg/ms. This will lead to
somewhat impressive QPF totals for April. We are looking at 2-4"
over the Mountains, 1-2.50 over the foothills, and 0.30-1.0 in the
Valley expect for locally lower amounts in areas shadowed by the
Coastal Range. This system will bring even more impressive snow
amounts over the Sierra. We are looking at 1-2 feet of snow above
5000 feet with 3+ feet over some of the higher peaks from around
I-80 south. Mountain travel will become very difficult by the
overnight and is not recommended tomorrow as road conditions will
continue to be poor. Intense snow showers can be expected tomorrow
late morning into the afternoon with quick bursts of heavy snow
and near zero instability.

A ridge of high pressure builds in over the weekend and will
bring dry conditions and warm temperatures back to near seasonal
normals with mid 70s expected for the valley and mainly 50s in the
mountains.

-CJM

&&

.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...
Ridge of high pressure will be over the region on Sunday with
warmer temperatures and dry conditions. Temperatures will warm
into the mid 70s to lower 80s in the valley to the upper 50s to
upper 60s for the mountain valleys. These conditions will persist
through Monday but the ridge will begin to flatten out as a trough
begins to move into the Pacific Northwest. By Tuesday a weak dry
trough will be over California with some slight cooling each day
for Tuesday and Wednesday. The far northern part of the state
including the north end of the valley may have a chance to see a
little bit of precipitation from the tail end of that trough but
at this point it will most likely remain dry and breezy for both
days.

&&

.AVIATION...
A storm will impact interior Northern California over the next 24
hours. MVFR cigs mainly in the N Sac Valley beginning between
15-18Z with SHRA. Elsewhere in the Valley, cigs remain around
4000-6000 feet thru 06Z Thursday with SHRA after 00Z. Brief period
of LLWS possible at RDD between 13-18Z this morning before
surface winds increase this afternoon. In the northern and central
Sac Valley, southerly wind gusts from 25-40 kts possible from 15Z
Wednesday - 12Z Thursday. For Sac terminals southward, gusts
generally from 15- 25 kts, stronger in the Delta region.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 11 AM PDT Friday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

Wind Advisory until 5 AM PDT Thursday for Central Sacramento
Valley-Mountains Southwestern Shasta County to Western Colusa
County-Northeast Foothills/Sacramento Valley-Northern Sacramento
Valley.

&&