409
FXUS66 KSTO 142023
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
123 PM PDT Sat Sep 14 2024

.Synopsis...
Warm and dry weather continues today, then periods of unsettled
weather Sunday into next Wednesday with scattered showers and
isolated thunderstorms along with periods of gusty wind. Drier
and warmer weather returns Thursday into next weekend.

&&

.Discussion...
Dry weather continues today with high temperatures expected to be
close to the max temps Friday. Satellite shows a line of cirrus
clouds making their way over Shasta County early this afternoon
but overall a quiet weather day with dry Valley conditions.

This looks to change tomorrow afternoon ahead of a weather system
moving in from the Pacific NW. Chances for rain start Sunday
afternoon over the Coastal Range and northern Shasta County. By
mid-afternoon chances for rain spread north of I-80 with the NBM
giving a 35-75% of seeing rain, higher as you travel northward.
With this, there is a 15-25% chance of thunderstorms from Hwy. 32
northward, highest over northern Shasta County and Southern
Cascades mountains. Currently, hi-res models are showing
convection being constrained to mainly the Coastal Range and
northern Shasta County. However, given the upper low`s track of
moving from west to east across the Central Valley, there is the
potential for showers and isolated thunderstorms to extend further
down the Valley. Any thunderstorms that do develop will be
capable of gusty winds, small hail, and lightning, as well as
brief heavy rainfall which may lead to flooding/debris flow
impacts for recent burn scar areas. Overall confidence is low,
given the discrepancies in the model`s placement of convection
versus the synoptic forcing possible further down the Valley.

As the low moves through the Valley, it keeps the thunderstorm
threat into Monday morning, more contained to higher terrain of
the Sierra/Coastal Range. By Monday afternoon, chances will taper
off giving a brief break in active weather and cooler
temperatures over the area. From Sunday afternoon to late Monday
morning,

The next round of precipitation will start Tuesday PM into
Wednesday as energy ahead of a larger trough passage occurs
Tuesday evening. Late Tuesday evening will see rain begin over the
Coastal Range before extending further into the Valley Wednesday
morning bringing another round of showers, isolated
thunderstorms, breezy winds, and cooler, moist air.

Tomorrow through midweek will see below normal
temperatures with Valley highs in the 70s and mid 50s to low 70s
over the mountains and foothills.

&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Another low pressure is projected to move into interior NorCal
Wednesday morning, bringing another chance of showers and
potential thunderstorms to NorCal. The NBM is showing more
widespread showers/storms for the Central/Northern Valley and the
Sierra Nevada. Current probabilities of exceeding 0.50" inches of
rainfall from Wednesday-Thursday night are around 30-60%, with the
highest probs in the northern Sierra and Burney Basin. Still some
disagreement on the track of the low, so these probabilities will
likely change as will the total QPF forecast as models come into
better consensus. Low pressure will then move off into the Great
Basin Thursday night/Friday morning and an upper level ridge will
then develop in the eastern Pacific. Pressure gradients will be
orientated north to south on Thursday, so the potential for breezy
and locally gusty northerly winds will exist. High temperatures
will then climb back into the mid 80s to low 90s as we move into
the weekend as our heights rise and ridging dominates the synoptic
pattern.

&&

.AVIATION...

VFR conditions over interior NorCal next 24 hrs. Sfc wind mainly
at or below 12 kts except vcnty of Delta SWly sfc wind up to 20
kts possible aft 00z Sun.


&&

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

$$