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FXUS66 KSTO 122158
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
258 PM PDT Fri Apr 12 2024


.Synopsis...
Chances for isolated thunderstorms (15-30%) continue this afternoon
and evening ahead of a weather system, brining mountain snow,
rain showers, gusty winds, and isolated thunderstorms Saturday and
Sunday.

&&

.Discussion...
Late this morning, radar showed a line of thunderstorms
developed over in the northeast foothills and a line of showers
over the Coastal Range. Conditions have weakened with now just
showers extending over the foothills and Coastal Range. Today`s
weather challenge will be diagnosing thunderstorm potential as we
have 15-30% chance of thunderstorm development, highest over the
Sierra. Confidence is low in strength and location as mitigating
factors have muddled our convective picture for this afternoon.
Current runs of forecasted model reflectivity show showers
developing this morning over Lassen and move northeastward with a
secondary round of showers south of Hwy. 50 and moving north. The
secondary round of showers looks to have better potential for
stronger storms as there is more lift and moisture available to
access, with the caveat of an slightly unfavorable shear direction
of west- southwesterly. With any thunderstorm that develops,
small hail, lightning, gusty winds, and brief heavy rain showers
are possible. Winds today also will breezy with south gusts of 15
to 35 MPH, strongest north of Sacramento.

As today`s showers and thunderstorm potential drops off tonight,
our next weather system will look to impact NorCal bringing
periods of light to moderate rainfall and mountain snow, breezy
winds, and isolated thunderstorms. Precipitation begins with
light showers extending into the Northern Sacramento Valley early
Saturday morning with a line of rain moving in the west side of
the Valley later Saturday morning. Precipitation amounts are
forecasted to be 0.25-0.75" in the Valley with 0.75-2.00" over the
foothills and mountains. Highest amounts will be in the Northern
Sacramento Valley and Coastal Range areas. NBM probabilities of
an half inch is relatively low for the Valley with only 15-45%
chance, highest in the foothills and areas southeast of
Sacramento. Thunderstorm and convective activity may help realize
rain amounts with the Northern San Joaquin having a 10-20% chance
of thunderstorm development Saturday afternoon and evening.

Additionally with this system, winter weather over the Sierra will
bring minor travel impacts as snow picks up Saturday morning and
continues through Sunday afternoon. Snow levels Saturday morning
are 5000 to 7000 feet, lowering by Saturday afternoon to 4000 to
5275 feet and 3500 to 4500 feet by Sunday morning. Amounts are
forecasted to be 2 to 6 inches, up to a foot at peaks and areas of
the Central Sierra, south of Hwy. 108 south of Strawberry.
Heaviest snowfall will be late Saturday morning for the areas
south of Hwy. 108 and Saturday night for areas north of I-80. NBM
probabilities of 6 inches or more are 10-20% outside of the Lassen
Park area and areas south of Hwy. 108 which get up to 55% chance.
Winds over the mountains will gusts up to 45 MPH on Saturday, so
visibilities may be reduced if heavier bands of snowfall occur
during the periods of gusty winds.

Overall, conditions dry and warm after Sunday night as ridging
begins to overtake the forecast area again. Monday afternoon highs
warm to the upper 60s and low 70s. Dry weather looks to be the
dominant forecast pattern as we enter early next week.
&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
Dry and increasingly warm temperatures are expected next week.
Clusters show the trajectory for an upper trough to move into the
Great Basin (inside slider track) is diminishing, with the track
shifting more over the Rockies. This has reduced the potential for
strong, gusty north to east winds for the middle of next week.
Currently the NBM is projecting northerly wind gusts to around
20-25 mph for the western side of the Sacramento Valley on
Wednesday. High temperatures trend above normal through the work
week, with Valley highs in the mid 70s to around 80. &&

.AVIATION...
VFR conditions next 24 hours except areas MVFR with
showers and local IFR/LIFR with isolated thunderstorms over the
Sierra and mountains of Shasta County into this evening. Areas
southerly surface wind gusts 20-30 kts through 04Z. &&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$