Stonyford, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

823
FXUS66 KSTO 182140
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
240 PM PDT Wed Sep 18 2024

.Synopsis...
Cooler, unsettled weather through this evening with scattered
showers and thunderstorms, mainly over the mountains and foothills.
Lingering showers over the Sierra Nevada Thursday, otherwise
drier and warmer conditions into early next week.

&&

.Discussion...
A cool upper level low from the Gulf of Alaska is moving along the
California coast. Southerly flow form this low is bringing
moisture and unstable conditions. Latest radar shows showers and
thunderstorms developing over much of the Sierra crest and
extending into eastern Shasta County. There is 30-40% chance of
scattered showers and thunderstorms for eastern portions of the
Park Fire burn scar the rest of this afternoon and evening. The
main concern is for these storms moving from east to west into
that area, bringing the potential for heavy rainfall, which could
cause debris flows and flooding impacts there. A Flash Flood Watch
remains in effect for the Park Fire burn scar through 10 pm PDT
today. Convective Allowing Models (CAMs) currently show the some
of the strongest cells developing late this afternoon into the
evening. Easterly flow around the northern portion of the low
would track these storms into eastern portions of Tehama County
and northern Butte County.

Forecast rainfall amounts are around 0.10-0.50" over the Sierra,
southern Cascades and foothills. Highest rainfall is expected over
the Sierra crest, where up to an inch is possible. In addition to
rain, small hail is possible. Caltrans webcams are currently showing
some small hail on the ground on Highway 50 at Echo Summit. The
Valley has 10-20% chance of light rain showers this afternoon and
evening, with a 25% chance for the Delta. Rainfall amounts in the
Valley should be limited to just a trace to a few hundredths of an
inch.

As this system moves further into Southern California Thursday,
There will be another round of afternoon and evening thunderstorm
chances, but these should more limited to the Sierra crest,
mainly from I-80 southward. NBM probabilities have 15-30% along
the Sierra crest, with the highest chances south of US 50. Given
the center of the low bring further south, this will result in
more southeasterly steering flow and more downslope storm motion.

High pressure begins to build in Friday as eastern Pacific ridging
builds eastward. Temperatures begin to warm to near normal by
Saturday, with highs above normal on Sunday. Friday will see
afternoon highs warm to the mid 80s to low 90s in the Valley with
upper 60s to mid 80s across the mountains to foothills areas.
There will be some warming temperatures and some occasionally
breezy north winds in the Valley through the weekend, daytime
humidities lower back to upper teens to 20% over the Northern
Sacramento Valley Sunday into Monday.

&&


.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...
Dry weather is expected through the extended forecast period as
cluster analysis and ensemble guidance indicates high pressure
extending inland over Northern California. Temperatures will warm
up through the weekend and into early next week with highs in the
mid to upper 90s across the Valley and Delta. Areas of Moderate
HeatRisk return to the Delta, Valley, and foothills of the Sierra
Monday through Tuesday of next week. Light to breezy northerly
flow across the more wind-prone areas of the Sacramento Valley
(i.e. the northern Sac Valley and along the I-5 corridor in the
Sacramento Valley) Sunday through Tuesday, with gusts to 15 to 22
mph. Daytime humidities will decrease gradually through this
period into the upper teens to upper 20s, which may lead to
localized fire weather concerns in the northern Sacramento Valley
and adjacent foothills.

&&

.AVIATION...
Generally VFR conditions expected across interior NorCal next 24
hours. However, MVFR/IFR possible in any stronger
showers/thunderstorms through this evening, especially along the
Sierra and into adjacent foothills locations. Gusty and erratic
winds will be possible in the vicinity of thunderstorms as well.
Otherwise some gusts 20-30 kts along the Sierra after 06z, with
winds generally less than 12 kts elsewhere.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 10 PM PDT this evening for Central
Sacramento Valley-Northeast Foothills/Sacramento Valley-Northern
Sacramento Valley-Western Plumas County/Lassen Park.

&&

$$