Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 270825
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
125 AM PDT Wed Mar 27 2024

.Synopsis...
The first of two weather systems will arrive today into Thursday,
bringing periods of mountain snow, rain, breezy winds, and
thunderstorm chances. The second storm is expected Friday into
Saturday morning, bringing similar Valley rain, but less mountain
snow for the holiday weekend. Drier weather by the end of the
weekend continuing into early next week.

&&

.Discussion...
Unsettled weather returns today, bringing mountain snow,
rain, breezy winds, and potential for thunderstorms with it.
Precipitation will begin later this morning over the Coastal
Range and northern Sacramento Valley, spreading southeast over the
northern Sierra by late morning/early afternoon, and eventually
the remainder of the Valley. Moderate to heavy snow is expected
overnight in the mountains at elevations above 5500 ft.

To this point, a Winter Storm Warning was issued for areas above
5500 ft in the Sierra and southern Cascades from 11 AM Wednesday
to 11 AM Thursday. Moderate to heavy snow and gusty winds are
expected during this time period, with snow totals around 6 to 12
inches (2 ft at highest peaks). Based on the latest hires data,
snowfall rates peak with 1-3"/hr begin around 6pm/8pm lasting
through 4am/6am for I-80 and Highway 50 respectfully. While this
is a low- end Warning event when looking at 24 hour snowfall
totals, moderate travel impacts are still to be expected due to
snow- covered roads, chain controls, and winds gusting up to 45
mph. Be sure to be prepared if you must travel during this time
period! Pack your car with an extra flashlight, food, and water in
case of an emergency.

Digging into the probabilities...the National Blend of Models
(NBM) is currently showing a 20 to 70% probability of at least 10
inches of snow above 5500 ft between Wednesday and Thursday. As
for rainfall totals, the NBM is projecting somewhere between 0.25
inches (50 to 80% probability) and 0.5 inches (20 to 60%
probability) for most of the Valley, with Shasta County, the
foothills and mountains below snow levels expecting closer to 1
inch (30 to 90% probability) to 1.5 inches (25 to 65%
probability).

Given the cold front moves through tonight, instability will be
limited, but there is a non-zero chance for a few embedded
lightning strikes as the front moves through tonight. Following
the front overnight tonight, expect a period of dry conditions
before more isolated to scattered showers and isolated
thunderstorms Thursday. The best thunderstorm chances (10-20%
probability), will be primarily between I-80 and Redding in the
Valley and foothills.

Friday morning will see additional precipitation as two upper-level
low pressure systems Fujiwara and dig along the CA coastline into
the weekend. The models have been struggling with the evolution
of these two system the last several days, but the latest forecast
track of the phased/dominant circulation has shifted slightly
further south, bringing the bulk of the upper level divergence
across southern CA. As a result, the latest forecast has trended
down some, and snow rates over the course of Friday will be less
than those overnight tonight, generally less than 0.50-1"/hr. Even
so, given that this weekend is also a holiday weekend and a
larger number of people may try to travel, it is especially
important to use caution if you must travel through the mountains.
Currently, the NBM is predicting 20 to 50% probability of at
least 6 inches of snow above 5000 ft on Friday, with some
additional snow expected on Saturday. Friday rainfall totals of
around 0.25 inches (30 to 80% probability) in the Valley and
around 0.75 inches (20 to 70% probability) for the foothills and
mountains. Additional thunderstorm chances (15 to 30% probability)
are possible Saturday morning into the afternoon as the upper-
low`s center will be close to the Bay Area, allowing for showers
and isolated thunderstorms mainly for the southern Sacramento
Valley to San Joaquin Valley and surrounding foothills.

//  SP/Peters

&&

.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...

Upper low off the SoCal coast Sunday with secondary low over NV
keeps a threat of showers and snow showers, mainly in the northern
and eastern foothills and mountains. Upper ridging builds into
the PacNW early next week with offshore flow over interior NorCal.
This will result in dry weather with above normal high temperatures.
Locally gusty north to east wind possible Monday and Tuesday,
mainly in the northern and eastern foothills/mountains.

&&

.AVIATION...

In Central Vly, areas MVFR/IFR spreading from NW to SE aft 18z
Tue. Areas Sly sfc wind up to 20 kts aft 18z Tue. In foothills and
mtns, widespread MVFR/IFR with lcl LIFR spreading from NW to SE
aft 18z Tue. Snow levels 5500-6500 today, lowering to 3500-4000
feet Thu morning. Areas S-SW sfc wind 15-25 kts with lcl gusts
30-40 kts over higher trrn aft 18z Tue.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 11 AM this morning to 11 AM PDT
Thursday for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

&&

$$


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