475
FXUS66 KSTO 201639
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
900 AM PDT TUE MAY 20 2008
DISCUSSION
GOOD ONSHORE AND UPVALLEY FLOW IN THE SACRAMENTO VALLEY THIS MORNING
WITH SFO-RNO SURFACE PRESSURE GRADIENT ALMOST 6 MB THIS MORNING.
FORT ORD PROFILER SHOWS THE MARINE LAYER DEEPENED TO AROUND 1800
FEET THIS MORNING WITH THE APPROACHING TROUGH. THE DEEPER MARINE
LAYER AND GOOD ONSHORE FLOW BROUGHT SOME LOW CLOUDS INTO SUISUN THIS
MORNING (SUU REPORTED SCT005).
TEMPERATURES ARE EXPECTED TO BE SIGNIFICANTLY COOLER EVERYWHERE
TODAY WITH THE TROUGH AND ASSOCIATED COLD FRONT MOVING THROUGH THE
AREA. ALTHOUGH TEMPERATURES WILL JUST DROP BACK DOWN TO NEAR NORMAL
FOR THIS TIME OF YEAR. SOME INSTABILITY OVER THE HIGHER TERRAIN THIS
AFTERNOON INTO TONIGHT AS A SHORTWAVE AND THE COLD FRONT MOVE
THROUGH. THIS INSTABILITY AND SOME MOISTURE WILL BRING ISOLATED
SHOWERS AND THUNDERSTORMS TO THE HIGHER TERRAIN...ESPECIALLY THE
NORTHEASTERN MOUNTAINS THIS AFTERNOON AND EVENING AND THEN THE
NORTHERN SIERRA NEVADA OVERNIGHT.
THE ONSHORE FLOW WILL TURN NORTHERLY BEHIND THE TROUGH TONIGHT. THE
MFR-RDD GRADIENT INCREASES DURING THE DAY TOMORROW WITH THE MFR-RDD
GRADIENT EXPECTED TO BE ABOUT 10MB AND THE MFR-SAC ABOUT 14 MB AT 5
PM TOMORROW AFTERNOON. THE JET NOSES INTO THE AREA TOMORROW
AFTERNOON BUT MOVES OVER NORTHERN CALIFORNIA WITH 250 MB WINDS AT
ABOUT 140 KTS ON THURSDAY. 700MB WINDS 40 TO 50 KTS WEDNESDAY
MORNING AND UP TO 50 TO 65 KNOTS THURSDAY MORNING INDICATING GOOD
UPPER LEVEL SUPPORT. THE SURFACE GRADIENT AND UPPER LEVEL SUPPORT
WILL BRING GUSTY NORTHERLY WINDS ACROSS THE AREA TOMORROW INTO
FRIDAY. WILL CONSIDER ISSUING AN ADVISORY WITH THE AFTERNOON
PACKAGE.
THE TROUGH FORMS A CLOSED LOW OVER UTAH LATE WEDNESDAY INTO
THURSDAY. THE MODEL THEN SHOWS THIS LOW RETROGRADING BACK INTO
CALIFORNIA THURSDAY INTO FRIDAY. THIS WILL BRING NEAR TO BELOW
NORMAL TEMPERATURES WEDNESDAY THROUGH FRIDAY. THE CLOSED LOW OVER THE AREA
MAY BRING SOME INSTABILITY OVER THE AREA FRIDAY INTO SATURDAY FOR
ANOTHER THREAT OF SHOWERS AND THUNDERSTORMS OVER THE HIGHER TERRAIN.
ALTHOUGH THE MODEL SOLUTION VARY WITH THIS LOW SO OUR CONFIDENCE IS
NOT REAL HIGH FOR THE WEEKEND INTO EARLY NEXT WEEK.
AVIATION
UPPER LEVEL TROUGH OF LOW PRESSURE WILL MOVE ACROSS
NORTHERN CALIFORNIA TODAY AND TONIGHT...SPREADING MAINLY MID AND
HIGH LEVEL CLOUDS ACROSS THE REGION. HOWEVER...ISOLATED SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON AND EVENING OVER THE
NORTHERN MOUNTAIN AND SIERRA AS WELL AS NORTHERN SACRAMENTO
VALLEY...WITH LOCAL MVFR CONDITIONS POSSIBLE. AHEAD OF THE COLD
FRONT...GUSTY SOUTHWESTERLY WINDS WILL CONTINUE OVER THE
REGION...WITH GUSTS UP TO 40 KTS POSSIBLE OVER THE MOUNTAINS. THE
STRONGEST WINDS IN THE VALLEY WILL BE NEAR THE CARQUINEZ
STRAIT...WITH SUSTAINED WINDS OF 25-30KTS AND GUSTS UP TO 40KTS
CONTINUING THROUGH THE EARLY EVENING. WINDS WILL SHIFT TO THE NORTH
THIS EVENING BEHIND THE FRONT. THE NORTH WINDS WILL INCREASE AND
SPREAD DOWN THE VALLEY TONIGHT AND WEDNESDAY...WITH GUSTY CONDITIONS
DEVELOPING ACROSS THE REGION.
STO WATCHES/WARNINGS/ADVISORIES
FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY AFTERNOON
FOR THE ENTIRE FIRE WEATHER DISTRICT EXCEPT FOR ELEVATIONS ABOVE
3000 FEET OVER THE WEST SLOPES OF THE NORTHERN SIERRA NEVADA AND
EXTREME SOUTHERN CASCADE RANGE.
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