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000
FXUS66 KSTO 081022
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
322 AM PDT Thu Jun 8 2023

.SYNOPSIS...
Afternoon and evening shower and thunderstorm chances each day,
mainly over the mountains. Near to below average temperatures.

&&

.DISCUSSION...
Satellite imagery shows some passing clouds across interior
northern CA early this morning. Current temperatures are running
a few degrees warmer compared to 24 hours ago, with upper 50 to
low 60s across the southern Sacramento and northern San Joaquin
valleys and mid to upper 60s across the northern Sacramento
Valley. Highs this afternoon will peak in the low to mid 80s for
the Valley.

Upper low will continue to weaken and shift eastward today, but
enough moisture and instability will be in place to trigger
convection. HREF and Hi-Res guidance favor thunderstorm
development over the mountains, northeast foothills, and the
northern Sacramento Valley this afternoon and evening. HREF
probabilities of 0.50" in 1 hour (25-55%) favor the Sierra,
southern Cascades and western Shasta County. Primary impacts
associated with thunderstorms will be heavy rain, hail, gusty
winds, and lightning. Shower and thunderstorm activity may persist
into the overnight hours across portions of Shasta County and the
northeast foothills.

Decreasing thunderstorm coverage is expected Friday as westerly
flow increases, with the latest NBM advertising 15-30%
thunderstorm chances over the Sierra and portions of Shasta
County. Ensemble means in good agreement that another eastern
Pacific trough drops southeast and deepens into an upper low this
weekend and into early next week. This will result in increased
thunderstorm coverage, with the easterly component of the main
steering flow bringing thunderstorm chances into the foothills
and possibly the northern Sacramento Valley. The Extreme Forecast
Index (EFI) also supports better instability during this
timeframe.

High temperatures will warm slightly through the forecast period,
but will remain slightly below climatological normals. Expect Valley
highs generally in the low to mid 80s.

&&

.EXTENDED DISCUSSION (Monday THROUGH Thursday)...

Ensemble means continue to show an upper low spinning south of
the forecast area through early next week. This will result in
additional shower and thunderstorm chances, mainly over the
mountains. The EFI continues to depict anomalously high
instability values through at least Monday. By Tuesday, ensembles
depict the upper low weakening and shifting to the east, with
decreased thunderstorm chances (15-25%). Below normal daytime
temperatures early next week will be followed by near normal
temperatures by mid-week.

&&

.AVIATION...
General VFR conditions expected at TAF sites over the next 24
hours. Isolated to scattered showers and thunderstorms over the
Sierra Nevada, southern Cascades, and portions of the northern
Sacramento Valley through 09z Thursday (20-40% probability). The
main threats are gusty and erratic winds and lightning expected
near thunderstorms, which could impact KRDD and KRBL between
01-06Z Friday. Outside of thunderstorm influences, expect local
southerly wind gusts up to 15-20 kts across portions of the Valley
through 06Z Friday, and southwesterly up to 25-30 kts in the
vicinity of the Delta through 12Z Friday. Periods of SCT/BKN aoa 5
Kft through Thursday.

&&

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

$$