FXUS66 KSTO 280531
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
930 PM PST FRI NOV 27 2009

.DISCUSSION...WATER VAPOR IMAGERY SHOWS OUR TROUGH OF LOW PRESSURE 
DIGGING SOUTH ACROSS NORTHERN CALIFORNIA THIS EVENING...WITH THE 
MAIN UPPER LEVEL LOW NOW MOVING OVER THE NORTHERN SAN JOAQUIN 
VALLEY.  THE COMPOSITE RADAR IMAGERY CLEARLY SHOWS SHOWERS ROTATING 
AROUND THIS LOW...WITH ONE BAND OF PRECIPITATION LIFTING NORTHWARD 
OVER THE SIERRA THAT STARTS TO WRAP BACK TOWARDS THE WEST...WHILE 
ANOTHER CLUSTER OF SHOWERS ARE MOVING SOUTHWARD DOWN THE VALLEY.  
THIS CLUSTER OF SHOWERS IN THE VALLEY WAS QUITE IMPRESSIVE EARLIER 
THIS EVENING...AS THE RADAR SCOPE SHOWED A NUMBER OF THUNDERSTORMS 
FROM THE MARYSVILLE AREA SOUTHWARD.  THE MOST IMPRESSIVE OF THESE 
STORMS MOVED SOUTHWARD THROUGH ROSEVILLE...CITRUS HEIGHTS...AND 
RANCHO CORDOVA...PRODUCING RAIN RATES UP TO AN INCH AN HOURS AND 
ENOUGH HALF INCH HAIL TO COAT THE GROUND.  

MEANWHILE...IR SATELLITE IMAGERY AND COMPOSITE RADAR IMAGERY IS 
REALLY STARTING TO SHOW SOME ENHANCEMENT OF THE BAND THAT IS 
WRAPPING BACK ACROSS THE SIERRA.  HEAVY SNOW CONTINUES AT SOUTH LAKE 
TAHOE...AND THIS BAND IS PUSHING WEST OF THE CREST.  ALTHOUGH THE 
WINTER WEATHER ADVISORY WAS ALLOWED TO EXPIRE EARLIER FOR THE WEST 
SLOPE...HAVE RE-ISSUED A NEW ONE FOR TONIGHT.  BELIEVE THAT THE BEST 
ACCUMULATIONS WILL BE SOUTH OF HIGHWAY 50...WITH AN ADDITIONAL 4 TO 
7 INCHES OF SNOW POSSIBLE AT THE HIGHEST ELEVATIONS.  HAVE UPDATED 
THE FORECAST THIS EVENING TO REFLECT THESE TRENDS.    

THE OTHER MAIN CONCERN FOR THE FORECAST THIS EVENING IS WITH THE 
INCREASING NORTHERLY GRADIENT FOR LATE TONIGHT AND TOMORROW BEHIND 
THE CURRENT TROUGH.  MODELS HAVE CONSISTENTLY BE FLIP FLOPPING ON 
HOW STRONG THE GRADIENT WILL BE.  HOWEVER...00Z RUNS OF THE NAM AND 
GFS ARE NOW SHOWING BETWEEN 8 TO 10 MBS BETWEEN REDDING AND 
SACRAMENTO...WITH 35 TO 50 KT WINDS AT 925 AND 850 MB.  BELIEVE A 
WIND ADVISORY MAY BE NEEDED TOMORROW FOR THE VALLEY LOCATIONS...WITH 
THE STRONGEST WINDS OCCURRING ON THE WEST SIDE OF THE VALLEY...BUT 
WILL HOLD OFF AND LET THE MID SHIFT MAKE THE CALL.  

OTHERWISE...EXPECT SHOWERS TO LINGER OVER THE SIERRA TOMORROW...WITH 
DRIER CONDITIONS ELSEWHERE.  PALMER

&&

.AVIATION...VFR CONDITIONS SPREADING OVER THE SACRAMENTO VALLEY WITH 
JUST SOME LIGHT LINGERING SHOWERS OVER THE NORTHERN SAN JOAQUIN 
VALLEY WHICH WILL END BY AROUND 06Z. SNOW SHOWERS OVER THE NORTHERN 
SIERRA ARE INTENSIFYING AND WILL BRING AREAS OF IFR/LIFR OVERNIGHT 
THROUGH 12Z...MAINLY IN HEAVIER SNOW SOUTH OF HIGHWAY 50. PATCHY BR 
MAY FORM OVER THE SOUTHERN SACRAMENTO VALLEY IN LIGHT WINDS THIS 
EVENING. NORTH WINDS WILL GRADUALLY INCREASE OVERNIGHT ACROSS THE 
VALLEY WITH GUSTS PICKING UP TO AROUND 30 KT AT DAWN. WINDS OVER THE 
NORTHERN SACRAMENTO VALLEY WILL INCREASE FURTHER TO AROUND 35 KT 
AFTER 14Z SATURDAY. MOUNTAINS GUSTS TO 40 KT POSSIBLE 
TONIGHT...INCREASING TO 50 KT ON SATURDAY. VFR CONDITIONS EXPECTED 
ACROSS MOST THE AREA ON SATURDAY WITH JUST SOME LINGER MORNING SNOW 
SHOWERS OVER THE NORTHERN SIERRA.

&& 

.STO WATCHES/WARNINGS/ADVISORIES...
...WINTER WEATHER ADVISORY UNTIL 4 AM PST SATURDAY FOR WEST SLOPE 
   NORTHERN SIERRA NEVADA.
...WIND ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST SATURDAY FOR 
   CLEAR LAKE/SOUTHERN LAKE COUNTY-MOUNTAINS SOUTHWESTERN SHASTA 
   COUNTY TO NORTHERN LAKE COUNTY-NORTHEAST FOOTHILLS/SACRAMENTO 
   VALLEY-WESTERN PLUMAS COUNTY/LASSEN PARK.
...WIND ADVISORY FROM 1 AM TO 4 PM PST SATURDAY FOR WEST SLOPE 
   NORTHERN SIERRA NEVADA.

&&

$$