005
FXUS66 KSTO 121807
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1107 AM PDT WED AUG 12 2026
FOR ADDITIONAL DETAILS ON WEATHER AND EXPECTED IMPACTS OVER THE
NEXT 7 DAYS, PLEASE VISIT WEATHER.GOV/STO/BRIEFING.
KEY MESSAGES
- SHOWER AND THUNDERSTORM CHANCES SOUTH OF HIGHWAY 50 TODAY, WITH
BEST CHANCES SOUTH AND EAST OF OUR AREA.
- RED FLAG WARNING IN EFFECT FROM 5 AM THURSDAY UNTIL 9 PM
THURSDAY FOR A MIX WET/DRY THUNDERSTORMS AND STRONG OUTFLOW
WINDS FOR ELEVATIONS ABOVE 5000 FEET IN THE SIERRA.
- SLIGHTLY COOLER, BUT STILL HOT, THROUGH WEDNESDAY, FOLLOWED BY
NOTABLY COOLER TEMPERATURES FOR THE REMAINDER OF THE WEEK.
- REDUCED MOUNTAIN THUNDERSTORM CHANCES CONTINUE ON FRIDAY AROUND
10-15% CHANCE AS WE DRY INTO THE WEEKEND.
DISCUSSION
CURRENT SATELLITE SHOWS SCATTERED HIGH CLOUDS ACROSS
OUR CENTRAL VALLEY AND OVER THE SIERRA WITH A SLOT OF MORE
CUMULUS AND CONVECTIVE CLOUD COVER STREAMING ACROSS OUR SOUTHEAST
LATE THIS MORNING. THIS IS AHEAD OF OUR TROUGH AND PRESENT
MONSOONAL MOISTURE FUELING ACTIVITY TODAY LEADING TO A 10-25%
CHANCE OF MOUNTAIN THUNDERSTORMS THIS EVENING, MAINLY CONFINED THE
SIERRA SOUTH OF 50 LOOKING THROUGH TODAY'S HI-RES FORECAST RUNS.
CONFIDENCE REMAINS LOWER IN THE SHORT TERM SO IT COULD BE VERY
POSSIBLE OUR AREA DOESN'T SEE ANY RESULTING PRECIPITATION FOR THIS
AFTERNOON AND EVENING BUT WOULD BE UNDER THE THREAT OF GUSTY
OUTFLOW BOUNDARIES AND INCREASED CLOUD COVER WITH THUNDERSTORMS
DEVELOPMENT STAYING TO OUR SOUTHEAST.
LOOKING TO LATE THIS EVENING INTO EARLY THURSDAY MORNING, GIVEN
THE INCREASED MOISTURE IN THE AREA WE COULD SEE SHOWERS OVER OUR
SOUTHEAST ACROSS THE UPPER FOOTHILLS (10-20% CHANCE WETTING RAIN
BELOW 5000 FEET) AND MOUNTAINS WITH A MIX OF DRY AND WET
THUNDERSTORMS POSSIBLE BEGINNING TOMORROW MORNING ABOVE 5000 FEET
OVER THE SIERRA CREST. THIS THREAT WILL CONTINUE AND EXPAND ALONG
THE MOUNTAIN AND BY THE AFTERNOON BE 10-30% ACROSS THE SIERRA
CREST. MODELS HAVE DONE A POOR JOB HANDLING OUR MONSOONAL MOISTURE
SO CONFIDENCE REMAINS LIMITED BUT GIVEN THE FUEL PICTURE AND
THUNDER THREAT...
WE HAVE ISSUED A RED FLAG WARNING FOR THE SIERRA SOUTH OF
INTERSTATE 80 ACROSS FIRE ZONE 136 SIERRA (EL DORADO-AMADOR) ABOVE
5000 FT AND FIRE ZONE 139 SIERRA (CAL-TUO) ABOVE 5000 FEET FROM 5
AM TO 9 PM THURSDAY A FOR A MIX OF WET AND DRY STORMS COMBINED
WITH GUSTY OUTFLOW WINDS FROM ANY DEVELOPED STORM. THIS WILL
SUPPORT NEW FIRE STARTS AND RAPID SPREAD, EVEN IF WETTING RAIN
FALLS WITHIN STORM CORES. PLEASE CONTINUE TO PRACTICE
FIRE/THUNDERSTORMS SAFETY AND STAY UP TO DATE WITH THE LATEST
FORECAST CONDITIONS AS THINGS COULD CHANGE QUICKLY GIVEN THE LOW
CONFIDENCE NATURE OF SUMMER THUNDERSTORM FORECASTING.
LASTLY, THIS PATTERN WILL BRING NOTABLY COOLER TEMPERATURES
ACROSS INTERIOR NORCAL THURSDAY AND FRIDAY, WITH HIGHS IN THE 80S
ACROSS THE VALLEYS, MID 90S TO MID 80S FOR THE FOOTHILLS AND 60S
FOR THE MOUNTAINS.
MONSOONAL MOISTURE WILL GRADUALLY PUSH BACK OUT OF THE AREA AFTER
FRIDAY. AS RESULT, THUNDERSTORMS CHANCES BEGIN TO DECREASE TO 10%
OR LESS ALONG THE SIERRA CREST HEADING INTO THE WEEKEND AS BELOW
NORMAL TEMPERATURES AND DRIER WEATHER SETTLE IN ELSEWHERE.
AVIATION
VFR CONDITIONS PREVAIL ACROSS INTERIOR NORCAL NEXT 24 HOURS.
BREEZY ONSHORE FLOW WILL CONTINUE TODAY, WITH SURFACE WINDS BELOW
15 KTS WITH GUSTS UP TO 25 KTS THIS AFTERNOON AND EVENING AS DELTA
BREEZE INCREASES. MOUNTAIN THUNDERSTORM CHANCES INCREASE AROUND
20Z TODAY THROUGH 05Z THURSDAY; THEN RETURN AROUND 12Z THURSDAY
MORNING. NON-ZERO CHANCE (2-4%) OF ISOLATED T-STORM IN SOUTHERN
SACRAMENTO VALLEY AND NORTHERN SAN JOAQUIN VALLEY TAF SITES FROM
AROUND 12-18Z THURSDAY.
STO WATCHES/WARNINGS/ADVISORIES
RED FLAG WARNING FROM 5 AM TO 9 PM PDT THURSDAY FOR SIERRA (CAL-
TUO) ABOVE 5000 FT-SIERRA (EL DORADO-AMADOR) ABOVE 5000 FT.
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