429
FXUS66 KSTO 102133
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
233 PM PDT SAT OCT 10 2026
FOR ADDITIONAL DETAILS ON WEATHER AND EXPECTED IMPACTS OVER THE
NEXT 7 DAYS, PLEASE VISIT WEATHER.GOV/STO/BRIEFING.
KEY MESSAGES
- RED FLAG WARNING IN EFFECT FROM 7 AM SUNDAY TO 5 AM MONDAY
DUE TO GUSTY NORTH WINDS AND LOW RELATIVE HUMIDITY FOR
NORTHERN SACRAMENTO VALLEY AND ADJACENT FOOTHILLS.
- PATTERN CHANCE THIS WEEKEND-EARLY NEXT WEEK: COOLER
TEMPERATURES, CHANCES FOR PRECIPITATION, ISOLATED
THUNDERSTORMS, AND MOUNTAIN SNOW.
- POTENTIAL FOR FIRST MEASURABLE SNOW OF THE SEASON IN THE
SIERRA SUNDAY PM - MONDAY, SOUTH OF US 50 AND ABOVE 6000
FEET.
- LINGERING MOUNTAIN SHOWERS WITH CONTINUING BELOW-NORMAL
TEMPERATURES ON TUESDAY, FOLLOWED BY DRY AND WARMING TREND
MID- TO LATE NEXT WEEK.
DISCUSSION
..TODAY
A WEAK COLD FRONT IS TRAVERSING NORTHERN CALIFORNIA THIS
AFTERNOON. LATEST VISIBLE SATELLITE DEPICTS A NARROW AREA OF MID-
LEVEL CLOUDS STREAMING SOUTHEAST ACROSS THE AREA, WHILE CUMULUS
CLOUDS ARE DEVELOPING ALONG THE SIERRA THIS AFTERNOON. MOSTLY DRY
WEATHER IS EXPECTED TO PREVAIL TODAY, BUT THERE IS A LOW CHANCE
(LESS THAN 10%) OF LIGHT MOUNTAIN SHOWERS FOR THE HIGHER TERRAIN
IN SHASTA COUNTY. AFTERNOON TEMPERATURES ARE RUNNING 15 TO 25
DEGREES COOLER COMPARED WITH YESTERDAY'S READINGS, WITH HIGHS
GENERALLY IN THE 70S. BREEZY ONSHORE WINDS WILL CONTINUE TO WEAKEN
THROUGH THIS EVENING.
COLD TEMPERATURES ARE FORECAST TO THE MOUNTAINS, WITH OVERNIGHT
TEMPERATURES IN THE MID 20S TO MID 30S IN THE SIERRA TONIGHT.
..SUNDAY-MONDAY
A COLD AN UPPER-LEVEL TROUGH OVER THE PACIFIC NW WILL EVOLVE INTO
A CLOSED LOW AND CONTINUE DIGGING SOUTHWARD, APPROACHING THE AREA
EARLY SUNDAY. IN ADDITION, SOME MOISTURE ADVECTION FROM REMNANT OF
RACHEL WILL NOSE INTO PORTIONS OF THE SIERRA NEVADA. THIS WILL
PROMOTE AN INCREASING CHANCE OF WETTING MOUNTAIN SHOWERS TO THE
SIERRA AND FOOTHILLS SUNDAY AND MONDAY. COLDER AIR ALOFT WILL
BRING SOME SHALLOW INSTABILITY SUNDAY AND MONDAY, CAPABLE OF PRODUCE
BRIEF HEAVY DOWNPOURS AND A CHANCE OF ISOLATED THUNDERSTORMS.
RAINFALL TOTAL AMOUNTS FORECAST FROM A QUARTER TO HALF OF AN INCH
FOR THE SIERRA, WITH THE HIGHEST AMOUNTS SOUTH OF I-80. WHILE FEW
HUNDREDTHS FOR THE SIERRA FOOTHILLS. SOME CAMS ARE SHOWING SOME
NOCTURNAL SHOWERS MOVING ACROSS THE AREA FROM THE SOUTH- SOUTHWEST
SUNDAY NIGHT INTO MONDAY.
THIS SYSTEM WILL BRING THE FIRST MEASURABLE SNOWFALL OF THE
SEASON IN THE SIERRA SUNDAY NIGHT TROUGH MONDAY. SNOW LEVELS ARE
EXPECTED TO BE ABOVE 7500 FEET THROUGH SUNDAY, BEFORE LOWERING
BETWEEN 6000-7000 FEET LATE SUNDAY NIGHT INTO MONDAY. FORECAST
AMOUNTS ARE BETWEEN 0.5-4 INCHES MAINLY ABOVE 7000 FEET, WITH 2-4
INCHES POSSIBLE AT THE HIGHEST PEAKS. HOWEVER, UNCERTAINTY REMAINS
ON THE EXACT SNOW AMOUNTS.
IN ADDITION, NORTHERLY WINDS ARE FORECAST TO DEVELOPED AND
INCREASING ALONG THE SACRAMENTO VALLEY TONIGHT THROUGH SUNDAY. GUST
30 TO 40 MPH ARE EXPECTED, WITH THE STRONGEST WINDS ALONG AND
WEST OF THE I-5 CORRIDOR SUNDAY MORNING. WINDS SLIGHTLY DIMINISH
SUNDAY AFTERNOON, BUT REMAIN BREEZY INTO MONDAY MORNING. DAYTIME
RELATIVE HUMIDITIES ARE EXPECTED TO RETURN TO THE LOW 20S ON
SUNDAY, WITH SOME AREAS INTO THE TEENS POSSIBLE. CRITICAL WEATHER
CONDITIONS ARE EXPECTED DUE TO THE GUSTY NORTH WINDS AND LOW
RELATIVE HUMIDITIES OVER NORTHERN SACRAMENTO VALLEY AND ADJACENT
FOOTHILLS. A FIRE WEATHER WARNING IS IN EFFECT FROM 7 AM SUNDAY
TO 5 AM MONDAY.
..TUESDAY-FRIDAY
HIGH PRESSURE AND UPPER-LEVEL RIDGE WILL BUILD IN QUICKLY IN THE
WAKE OF THE AFOREMENTIONED CLOSED LOW TRANSLATING EASTWARD. ANY
LINGERING MOUNTAIN SHOWERS ARE EXPECTED TO DISSIPATE TUESDAY
MORNING AS DRIER AIRMASS MOVES IN. GENERALLY DRY WEATHER, WITH
CONTINUING BELOW NORMAL TEMPERATURES IS EXPECTED ON TUESDAY.
ENSEMBLE MEMBERS ARE IN A GOOD AGREEMENT WITH THE UPPER-LEVEL
RIDGE CONTINUE BUILDING ON WEDNESDAY, BEFORE AMPLIFY AND BRING
ABOVE -AVERAGE 500 MB HEIGHTS OVER THE WESTERN CONUS THURSDAY AND
FRIDAY. THIS WILL BRING A DRIER AND WARMING TREND ACROSS NORTHERN
INTERIOR CALIFORNIA, WITH HIGH TEMPERATURES BACK TO THE 80S. BREEZY
NORTH TO NORTHEAST WINDS ARE ANTICIPATED FOR THE SACRAMENTO
VALLEY AND ADJACENT FOOTHILLS, AND TO THE SIERRA THURSDAY AND
FRIDAY. THERE IS A POTENTIAL FOR ELEVATED FIRE WEATHER CONDITIONS
DUE TO BREEZY NORTH WINDS AND LOW RELATIVE HUMIDITY (15-25%) OVER
THE SACRAMENTO VALLEY AND ADJACENT FOOTHILLS.
AVIATION
VFR CONDITIONS CONTINUE ACROSS INTERIOR NORCAL NEXT 24
HOURS. BREEZY WINDS OVER THE SOUTHERN SAC. VALLEY WITH WINDS 8 TO
12 KTS AND GUSTS UP TO 20 KTS UNTIL AROUND 03Z SUNDAY BEFORE
WEAKENING THROUGH THE EVENING. NORTH TO NORTHEAST WIND DEVELOP
OVER THE NORTHERN SAC. VALLEY (RDD,RBL) WITH WINDS 10TO 15 KTS
GUSTING UP TO 20 TO 30 KTS INTO 18Z SATURDAY. THE DELTA WILL
CONTINUE TO SEE GUSTY SOUTHWEST WINDS UP TO 15 TO 25 KTS UNTIL 06Z
SUNDAY.
STO WATCHES/WARNINGS/ADVISORIES
RED FLAG WARNING FROM 7 AM SUNDAY TO 5 AM PDT MONDAY FOR CENTRAL
GLENN CO & INTERSTATE 5-N. SAC VALLEY IN TEHAMA COUNTY-SHASTA
METRO.
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