950
FXUS66 KSTO 121939
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1239 PM PDT FRI SEP 12 2025
FOR ADDITIONAL DETAILS ON WEATHER AND EXPECTED IMPACTS OVER THE
NEXT 7 DAYS, PLEASE VISIT WEATHER.GOV/STO/BRIEFING.
DISCUSSION
SYNOPSIS
ISOLATED SHOWERS AND THUNDERSTORMS TODAY OVER THE SIERRA CREST
SOUTH OF INTERSTATE 80 AS A WEATHER SYSTEM EXITS THE REGION. NEAR
NORMAL TEMPERATURES AND DRIER WEATHER THEN ARRIVE BY THE WEEKEND.
WARMING AND DRYING TREND TO ABOVE NORMAL TEMPERATURES AND
PERIODICALLY BREEZY NORTHERLY WINDS EXPECTED EARLY NEXT WEEK.
KEY MESSAGES
* TODAY:
- ISOLATED SHOWER/THUNDERSTORMS ALONG THE SIERRA CREST SOUTH OF
INTERSTATE 80 TODAY AS A WEATHER SYSTEM EXITS THE REGION
- PROBABILITY OF THUNDERSTORMS: 15-25% ALONG SIERRA CREST
SOUTH OF INTERSTATE 80, HIGHEST CHANCES SOUTH OF HIGHWAY 50
- PROBABILITY OF RAIN > 0.1" : 10-30% ALONG SIERRA CREST SOUTH
OF INTERSTATE 80
- SLIGHT WARMUP TO NEAR NORMAL TEMPERATURES TODAY WITH VALLEY
HIGH TEMPERATURES IN THE 80S, WITH 60S TO 70S AT HIGHER
ELEVATIONS AND PERIODICALLY BREEZY ONSHORE WINDS
* SATURDAY - SUNDAY:
- TRANSIENT RIDGING ALOFT IS EXPECTED SATURDAY AS THE EXITING
TROUGH PUSHES EASTWARD, THEN A PROGRESSIVE SHORTWAVE TROUGH
LOOKS TO TRAVERSE THE PACIFIC NORTHWEST ON SUNDAY
- HIGH TEMPERATURES IN THE 80S TO LOW 90S EXPECTED AT LOWER
ELEVATIONS, WITH 70S TO LOW 80S AT HIGHER ELEVATIONS
- SLIM (5-10%) CHANCE FOR AN ISOLATED LIGHT SHOWER/THUNDERSTORM
ACROSS SHASTA COUNTY MOUNTAINS ON SUNDAY AS THE SHORTWAVE MOVES
THROUGH
* EARLY TO MID NEXT WEEK:
- THE SHORTWAVE TROUGH EJECTS EASTWARD EARLY MONDAY, FOLLOWED
RAPIDLY BY AMPLIFYING RIDGING, ALLOWING FOR DRIER AND WARMER
WEATHER FOR MUCH OF NEXT WEEK
- INCREASING NORTHERLY WINDS EXPECTED SUNDAY NIGHT INTO MONDAY,
STRONGEST ALONG AND WEST OF INTERSTATE 5
- PROBABILITY OF WIND GUSTS > 20 MPH: 50-90% FOR THE
SACRAMENTO VALLEY, DELTA AND ADJACENT TERRAIN
- AREAS OF MODERATE HEATRISK TUESDAY-WEDNESDAY IN THE SOUTHERN
SACRAMENTO VALLEY, DELTA, AND NORTHERN SAN JOAQUIN VALLEY
- WARMING TREND BRINGS VALLEY HIGH TEMPERATURES TO THE 90S
CHANGES FROM PREVIOUS FORECAST
- SLIGHT DECREASE IN AREAL COVERAGE OF MODERATE HEATRISK EARLY TO
MID NEXT WEEK
- VERY SLIGHT DECREASE IN WIND GUST FORECAST FOR MONDAY
- POTENTIAL FOR THE RETURN OF MOUNTAIN SHOWERS AND THUNDERSTORMS
LATE NEXT WEEK, MAINLY OVER THE SIERRA
AVIATION
VFR CONDITIONS EXPECTED AT INTERIOR NORCAL TAF SITES NEXT 24
HOURS, ALTHOUGH SOME MVFR/IFR POTENTIAL IN ISOLATED TSRA ALONG
SIERRA CREST SOUTH OF INTERSTATE 80 FROM 20Z - 04Z SATURDAY.
GENERALLY LIGHT WINDS LESS THAN 12 KTS EXPECTED, WITH SOME GUSTS
15-20 KTS THROUGH DELTA AND ADJACENT VALLEY FROM 22Z - 09Z
SATURDAY.
STO WATCHES/WARNINGS/ADVISORIES
NONE.
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