471
FXUS66 KSTO 272116
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
216 PM PDT SAT MAY 27 2023
SYNOPSIS
ISOLATED TO SCATTERED THUNDERSTORM CHANCES CONTINUE FOR THE
MOUNTAINS, MAINLY NORTHERN FOOTHILLS, AND NORTHERN HALF OF THE
SACRAMENTO VALLEY THROUGH THE HOLIDAY WEEKEND. THUNDERSTORM
CHANCES CONTINUE NEXT WEEK OVER THE MOUNTAINS. TEMPERATURES WILL
REMAIN NEAR OR SLIGHTLY BELOW NORMAL.
DISCUSSION
LOW PRESSURE AREA OVER ALONG THE PACIFIC NORTHWEST COAST WILL
DEEPEN ALONG THE COAST TO AROUND THE MENDOCINO COUNTY AREA
TONIGHT. IN THE NEAR TERM SHOWERS AND THUNDERSTORMS MAY FORM OVER
THE MOUNTAINS THIS AFTERNOON. ANY SHOWERS AND THUNDERSTORMS THAT
DO FORM SHOULD MOVE EAST OF THE CREST LATE THIS AFTERNOON TO
EARLY EVENING. THE FOCUS THEN BECOMES THE NORTHERN HALF OF THE
FORECAST AREA FOR THE OVERNIGHT HOURS. MAIN FOCUS WILL BE FROM
BUTTE COUNTY TO NORTHERN LAKE COUNTY NORTHWARD IN THE VALLEY AND
THE SURROUNDING MOUNTAINS. ACTIVITY LOOKS TO INCREASE IN THIS
AREA DURING THE EVENING WITH THE POTENTIAL FOR SOME LATE NIGHT
ACTIVITY WELL PAST MIDNIGHT. THUNDERSTORMS THAT FORM LOOK LIKE
THEY WILL CONTAIN VERY HEAVY RAIN AND SMALL HAIL. PRECIPITABLE
WATERS REMAIN VERY HIGH FOR THIS TIME OF YEAR OVER THE REGION
THROUGH TUESDAY WITH THE HIGHEST TONIGHT DURING THAT TIME PERIOD.
LOCAL FLOODING WITH THE STRONGER STORMS MAY BE POSSIBLE. AS THE
LOW DROPS SOUTHWARD IT SHOULD HELP TO KEEP PORTIONS OF THE VALLEY
BREEZY OVERNIGHT.
ON SUNDAY THE CENTER OF THE LOW WILL MOVE TO OFF THE COAST OF THE
BAY AREA. THUNDERSTORM ACTIVITY LOOKS LIKE IT MIGHT GET STARTED A
LITTLE EARLIER IN THE DAY BY LATE MORNING TO EARLY AFTERNOON.
THE FOCUS CONTINUES TO BE OVER THE MOUNTAINS WITH CHANCES
CONTINUING FOR PORTIONS OF THE CENTRAL SACRAMENTO VALLEY
NORTHWARD. VALLEY THUNDERSTORMS LOOK POSSIBLE BY MID AFTERNOON
LASTING THROUGH EARLY EVENING. ANY THUNDERSTORMS WILL CONTINUE TO
HAVE HEAVY RAIN WITH THEM BUT HAIL SIZE SHOULD INCREASE ON SUNDAY.
ON MONDAY THE CENTER OF THE LOW WILL MOVE TO THE CENTRAL COAST AND
CONTINUE TO MOVE SOUTHWARD INTO SOUTHERN CALIFORNIA ON TUESDAY.
CONTINUED AFTERNOON AND EVENING THUNDERSTORMS BOTH DAYS. THESE
TWO DAYS THUNDERSTORMS WOULD HAVE THE BEST CHANCE OF MAKING IT
INTO THE MOTHERLODE BY LATE AFTERNOON OR EARLY EVENING.
THUNDERSTORMS ARE EXPECTED TO MOVE TOWARDS THE FOOTHILLS THAT FORM
OVER THE HIGHER ELEVATIONS. SLIGHT CHANCES CONTINUE EACH DAY FOR
THE FAR NORTHERN END OF THE VALLEY AS WELL. ANY HOLIDAY TRAVELERS
MAY WANT TO KEEP THE TIMING IN MIND.
TEMPERATURES WILL GENERALLY BE BELOW NORMAL FOR THIS TIME OF
YEAR THROUGH TUESDAY WHICH MAY HELP TO KEEP PEOPLE OUT OF THE
WATER THIS HOLIDAY WEEKEND. RIVERS AND LAKES CONTINUE TO BE VERY
COLD. WATER TEMPERATURES ARE MAINLY IN THE 50S FOR THE VALLEY
TRANSITIONING TO THE 40S IN THE FOOTHILLS.
EXTENDED DISCUSSION (WEDNESDAY THROUGH SATURDAY)
WEDNESDAY A TROUGH OF LOW PRESSURE WILL EITHER BE THROUGH
CALIFORNIA OR JUST TO THE WEST WHILE A LOW PRESSURE AREA IS EITHER
OVER SOUTHERN CALIFORNIA OR ARIZONA DEPENDING ON THE
DETERMINISTIC MODELS. CLUSTERS INDICATE A WEAK TROUGH OVER THE
REGION. ALL SEEM TO POINT TO CONTINUED AFTERNOON AND EVENING
THUNDERSTORMS OVER THE MOUNTAINS REGARDLESS OF EXACT POSITIONING
OF THE LOWS.
THURSDAY IS WHEN THE MODELS DIVERGE SO CONFIDENCE BECOMES LOW THE
NEXT FEW DAYS. LOW PRESSURE AREA WILL EITHER BE OVER CALIFORNIA OR
THE PACIFIC NORTHWEST. WEAKER TROUGHING IS INDICATED BY THE
CLUSTERS SO THERE MAY BE LESS MOUNTAIN THUNDERSTORM ACTIVITY.
ENSEMBLES CONTINUE TO KEEP THUNDERSTORMS OVER THE CREST EXTENDING
INTO THE SOUTHERN CASCADES AT THIS TIME. FRIDAY AND SATURDAY THERE
WILL BE A LOW PRESSURE AREA IN THE GULF OF ALASKA BUT THE EXTENT
OF HOW DEEP IT IS AT THIS TIME REMAINS UNCERTAIN. ENSEMBLES KEEP
SOME AFTERNOON AND EVENING THUNDERSTORMS ACTIVITY FROM AROUND THE
TAHOE REGION SOUTHWARD ALONG THE CREST. IT IS ALSO INDICATING
A WARMING TREND TO NEAR NORMAL OR SLIGHTLY ABOVE TEMPERATURES
LATE NEXT WEEK AND INTO THE WEEKEND.
AVIATION
VFR CONDITIONS NEXT 24 HOURS EXCEPT FOR ISOLATED MVFR CONDITIONS
POSSIBLE IN SHOWERS/THUNDERSTORMS, MAINLY OVER MOUNTAINS. GUSTY
AND ERRATIC WINDS EXPECTED NEAR THUNDERSTORMS. SURFACE WIND
GENERALLY AT OR BELOW 15 KTS EXCEPT VICINITY OF DELTA WITH
SOUTHWESTERLY WIND UP TO 25 KNOTS.
STO WATCHES/WARNINGS/ADVISORIES
NONE.
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