FXUS66 KSTO 090441
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
840 PM PST TUE DEC 8 2009

.DISCUSSION...WATER VAPOR IMAGERY SHOWS AN INTERESTING PATTERN 
DEVELOPING OVER THE PACIFIC THIS EVENING...AS A NUMBER OF SYSTEMS 
ARE ROTATING AROUND EACH OTHER BETWEEN APPROXIMATELY 135W AND 165W.  
THE CLOSEST OF THESE SYSTEMS IS TRYING TO UNDERCUT A VERY HIGH 
AMPLITUDE RIDGE OF HIGH PRESSURE REMAINS OFF THE WEST 
COAST...SPREADING A FEW MID AND HIGH LEVEL CLOUDS TO THE NORTHERN 
SAN JOAQUIN VALLEY THIS EVENING.  HOWEVER...ON THE OTHER SIDE OF 
THIS HIGH AMPLITUDE RIDGE...ANOTHER WEAK AND DRY SYSTEM IS DIVING 
SOUTH TOWARDS NORTHERN CALIFORNIA THIS EVENING.  THIS SYSTEM WILL 
LIKELY HELP DISSIPATE OR SHUNT THESE MID AND HIGH LEVEL CLOUDS SOUTH 
OF THE WARNING AREA LATE TONIGHT.  IN THE MEANTIME THOUGH...THIS 
CLOUD COVER IS HELPING TO INSULATE THE TEMPERATURES.  FOR 
EXAMPLE...AREAS WITH CLEAR SKIES FROM SACRAMENTO NORTHWARD ARE 
SEEING TEMPERATURES THIS HOUR RUNNING UP TO 10 DEGREES COLDER THAN 
THIS TIME LAST NIGHT...WHILE TEMPERATURE IN THE NORTHERN SAN JOAQUIN 
VALLEY AND DELTA AREAS ARE UP TO 5 DEGREES WARMER.  WILL DO A QUICK 
UPDATE THIS EVENING FOR SKY COVER IN THE NORTHERN SAN JOAQUIN 
VALLEY...BUT KEEP THE CLOUD COVER CLEARING LATE TONIGHT.  
OTHERWISE...THE FREEZE WARNING LOOKS ON TRACK FOR ELEVATIONS BELOW 
2000 FEET.  DRIER CONDITION WILL REMAIN OVER THE REGION THROUGH THE 
NEXT 24 HOURS...WITH MORE WINTRY TYPE WEATHER RETURN LATE THURSDAY 
AND THIS WEEKEND.  PALMER

&&

.AVIATION...GENERALLY VFR CONDITIONS EXPECTED IN THE VALLEY THROUGH 
WEDNESDAY WITH PERIODS OF HIGH CLOUDS AND LIGHT WINDS. ALTHOUGH A 
BATCH OF LOW CLOUDS WITH BASES AROUND 6000 FEET ARE CURRENTLY IN THE 
DELTA AND THE NORTHERN SAN JOAQUIN VALLEY THIS EVENING BUT ARE 
EXPECTED TO SHIFT SOUTH OUT OF THE AREA AROUND 09Z. LOCAL MVFR 
CONDITIONS ARE POSSIBLE IN THE SACRAMENTO AREA AND THE NORTHERN SAN 
JOAQUIN VALLEY AFT 08Z UNTIL 18Z WITH BR. SUB-FREEZING SFC 
TEMPERATURES ARE EXPECTED THROUGH AROUND 18Z WEDNESDAY MORNING IN 
THE VALLEY.

&& 

.STO WATCHES/WARNINGS/ADVISORIES...
...FREEZE WARNING FROM 2 AM TO 9 AM PST WEDNESDAY FOR SACRAMENTO 
   VALLEY... DELTA AND NORTHERN SAN JOAQUIN VALLEY AND SURROUNDING 
   FOOTHILLS GENERALLY BELOW 2000 FEET.

&&

$$