FXUS66 KSTO 060500
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
900 PM PST SAT DEC 5 2009
.DISCUSSION...
DRY COLD FRONT CONTINUING TO PUSH SOUTH INTO CENTRAL PORTION OF
STATE THIS EVENING...USHERING IN CP AIR. SURFACE HIGH FOLLOWING IN
ITS WAKE HAS STRENGTHENED N-S SURFACE PRESSURE GRADIENT OVER
INTERIOR NORCAL RESULTING IN GUSTY NORTHERLY WIND. GRADIENT FORECAST
TO DECREASE TONIGHT WITH BOUNDARY LAYER DECOUPLING OVERNIGHT. AS A
RESULT...STRONG RADIATIONAL COOLING EXPECTED OVERNIGHT WITH LOW
DEWPOINTS COULD RESULT IN SOME VALLEY FROST POSSIBLE IN WIND
SHELTERED AREAS SUNDAY MORNING.
NEXT BLAST OF COLD AIR WORKING ITS WAY SOUTH ALONG DOWNSTREAM SIDE
OF HIGH AMPLITUDE RIDGE NEAR 140W. WATER VAPOR SHOWING WAVE NOW
CROSSING WESTERN WASH AND IS PROGGED TO DROP INTO THE FAR NORTHERN
INTERIOR OF CAL SUNDAY AFTERNOON. THIS SHORT WAVE HAS LIMITED
MOISTURE BUT THE VERY COLD AMS WILL ALLOW FOR EASY SATURATION. AS
THE UPPER LOW SLOWLY DROPS SOUTH SUNDAY NIGHT INTO MONDAY THROUGH
INTERIOR NORCAL...ASSOCIATED OVER-WATER CYCLONIC FLOW INCREASES. AS
A RESULT...MODEL QPFS SHOW AN INCREASE SOUTHWARD OVER THE CWA...BUT
DIFFER AMONG THEMSELVES ON THE AMOUNTS. VALLEY PRECIP SUNDAY
AFTERNOON THROUGH MONDAY EVENING LOOKS TO BE FROM LESS THAN A TENTH
IN THE NORTHERN SAC VALLEY TO NEAR ONE HALF INCH OVER PORTIONS OF
THE NORTHERN SAN JOAQUIN VALLEY. ALSO...SNOW LEVELS WILL DROP
SIGNIFICANTLY SUNDAY NIGHT INTO MONDAY...TO AROUND 500 FEET IN THE
NORTHERN INTERIOR...WITH SOME SNOW POSSIBLE IN THE NORTHERN
SACRAMENTO VALLEY MONDAY MORNING BUT LITTLE TO NO ACCUMULATION
EXPECTED. GOOD OROGRAPHIC ENHANCEMENT WITH CYCLONIC FLOW AND HIGH
SNOW RATIOS COULD RESULT IN SIGNIFICANT MOUNTAIN SNOW AMOUNTS...
SOUTH OF A KUKI-KSVE LINE SUNDAY NIGHT THROUGH MONDAY. PRECIP WINDS
DOWN IN THE NORTHERN SAN JOAQUIN VALLEY BY MONDAY EVENING AND
LINGERS IN THE SOUTHERN SIERRA INTO TUESDAY MORNING. OVERNIGHT LOWS
MONDAY NIGHT EXPECTED TO BE COLDER UNDER CLEARING SKIES AND
GENERALLY LIGHT WIND.
PCH
.EXTENDED DISCUSSION (WEDNESDAY THROUGH SATURDAY)...THE MODELS STILL
VARY ON HOW FAR SOUTH THE JET STREAM THAT IS UNDERCUTTING THE RIDGE
OF HIGH PRESSURE OVER ALASKA WILL GO AND THE TIMING OF WAVES MOVING
ONSHORE. ALTHOUGH IT LOOKS LIKE THE WET WEATHER PATTERN MAY CONTINUE
THROUGH THE WEEK OVER AT LEAST PORTIONS OF INTERIOR NORTHERN
CALFORNIA AS PIECES OF ENERGY FROM THE PACIFIC MOVE INTO CALIFORNIA.
THE ECMWF AND GEM BOTH BRING IN MORE PRECIPITATION DURING THE DAY
WEDNESDAY AND THE GFS IS SLOWER BRINGING IT IN WEDNESDAY EVENING AND
A LITTLE FURTHER NORTH COVERING ALL THE CWA. SNOW LEVELS WILL BE
HIGHER (AROUND 4000 TO 5000 FEET) WITH THIS SYSTEM COMING IN FROM
THE PACIFIC COMPARED TO MONDAYS SYSTEM. PRECIPITATION MAY TAPER OFF
ON FRIDAY AND POSSIBLY EVEN A BRIEF BREAK IN THE PRECIPITATION IN
THE VALLEY BUT MORE PRECIPITATION IS EXPECTED FRIDAY NIGHT INTO
SATURDAY.
&&
.AVIATION...
NORTHERLY WIND SPEEDS HAVE BEEN ON THE DECLINE THIS
EVENING...HOWEVER THE NORTH-SOUTH GRADIENT IS STILL A DECENT 3 MB
FROM RDD-SAC. TAF SITES REPORTING SPEEDS AROUND 7-15 KTS IN THE
VALLEY. HAVE TAKEN OUT MENTION OF FOG IN THE TAFS SINCE WIND SPEEDS
SHOULD REMAIN ABOVE 5 KTS THROUGH THE EVENING AND INHIBIT MOST FOG
DEVELOPMENT...PLUS...AIRMASS IS PRETTY DRY WITH LARGE
TEMPERATURE/DEWPOINT SPREADS. LIGHT TO MODERATE NORTHERLY WINDS
CONTINUE IN THE VALLEY THIS EVENING. APPROACHING STORM WILL CAUSE
WINDS TO TRANSITION OVERNIGHT BECOMING LIGHT TO MODERATE SOUTHERLY
AFTER 12Z. JBB
&&
.STO WATCHES/WARNINGS/ADVISORIES...
...FROST ADVISORY IN EFFECT FROM 2 AM TO 9 AM PST SUNDAY BELOW 2000
FEET FOR INTERIOR CALIFORNIA...
...WINTER STORM WATCH SUNDAY NIGHT AND MONDAY FOR THE WEST SLOPES OF
THE NORTHERN SIERRA NEVADA... WESTERN PLUMAS COUNTY AND THE LASSEN
PARK AREA...NORTHERN SIERRA NEVADA FOOTHILLS AND MOTHERLODE.
...WINTER STORM WATCH SUNDAY NIGHT AND MONDAY MORNING FOR SOUTHERN
LAKE COUNTY...
...HARD FREEZE WATCH IN EFFECT FROM LATE MONDAY NIGHT THROUGH
TUESDAY MORNING BELOW 2000 FEET FOR INTERIOR CALIFORNIA...
&&
$$
