FXUS66 KSTO 031423
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
620 AM PST THU DEC 3 2009

.SHORT TERM DISCUSSION (TODAY THROUGH SUNDAY NIGHT)...
METSAT FOG PRODUCT SHOWS COASTAL FOG THICKENING AND SPREADING TO 
ABOUT I-680 JUST EAST OF VALLEJO...OVER SUISUN BAY AND UP INTO 
CENTRAL SAC VALLEY NEAR MARYSVILLE AND INTO THE NRN SJ VALLEY.  SAC 
EXEC AND STOCKTON AIRPORTS HAD BEEN REPORTING ONE-QUARTER MILE WHILE 
OTHER SURROUNDING SITES HAVE STAYED 3-5 MILES.  KSMF AND KMHR NOW 
HAVE LESS THAN ONE-QUARTER MILE IN FOG.  VIS IN THE CENTRAL AND SRN 
SAC VALLEY...DELTA AND THE NRN SJ VALLEY WILL LIKELY LOWER NEAR 
SUNRISE.  THE FOG HAS SLOWED RADIATIONAL COOLING AT KSAC AND KSCK 
WHILE WITH INITIALLY LESS FOG COVERAGE AT KSMF THE TEMP HAD DROPPED 
TO 29F BEFORE INCREASING TO 30F.  A NORTH WIND OVER THE NRN SAC 
VALLEY HAS KEPT TEMPS IN THE MID 50S THIS MORN.  TODAY...500MB 
HEIGHTS INCREASE ABOUT 5DM AND THICKNESS INCREASES 2DM BUT 850MB 
DELTA IS NEGLIGIBLE.  THEREFORE...THE AREA MAY SEE A SLIGHT IN 
INCREASE IN TEMPS TODAY.  TOMORROW MAY SEE A SLIGHT DECREASE IN 
TEMPS AS SOME HIGH CLOUDS MOVE INTO THE AREA AHEAD OF THE UPPER 
TROUGH OVER SRN BC AND PAC NW.  A SLIGHT CHANCE OF PRECIP MAY IMPACT 
THE SIERRA SAT AND SAT NIGHT WITH AN INCREASE OCCURRING SUN.  BY SUN 
THE MODELS ARE IN SOME DISAGREEMENT WITH THE TROUGH AXIS PLACEMENT 
AND STRENGTH.  THE GFS IS CONSIDERABLE MORE DRY THAN THE ECMWF...SO 
WENT WITH PERSISTENCE FROM PREVIOUS FORECAST.    JMC

.EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY)...

MODELS VARY GREATLY NEXT WEEK AS ECMWF CONTINUES TO SHOW BREAK 
THROUGH OF WESTERLIES TO THE WEST COAST AND SIGNIFICANT PRECIP EVENT 
WITH FRONTAL SYSTEM TAPPING INTO SUB TROPICAL MOISTURE BY MID-WEEK. 
GEM AND GFS ARE SLOWER IN DEVELOPING PRECIPITATION AND INDICATE MUCH 
LIGHTER QPF. WITH SPLIT FLOW PATTERN AND GREAT VARIANCE IN EXTEND 
MODEL RUNS...CONFIDENCE FOR THE END OF FORECAST PERIOD REMAINS LOW.

&&

.AVIATION...
UPR RDG CONTS OVR NORCAL WITH NW-N FLOW ALF. VFR CONDS OVR INTR 
NORCAL EXC AREAS OF MVFR VSBY IN BR WITH LCL IFR/LIFR CONDS IN FG FM 
VCNTY KMYV SWD TIL ARND 18-20Z. ISOLD NE-E SFC WND GSTS 25-35 KTS 
OVR PTNS OF NRN INTR MTNS AND SIERNEV FTHLS/W SLPS.

&& 

.STO WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY THROUGH 1000 AM PST FOR THE CENTRAL AND SRN SAC 
VALLEY...DELTA AND NRN SAN JOAQUIN VALLEY. 

&&

$$