000
FXUS66 KSTO 040533
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
933 PM PST FRI FEB 3 2012

.DISCUSSION...
WEAK UPPER RIDGE OVER NORCAL REMAINS THROUGH THE WEEKEND WITH LITTLE
CHANGE IN THE WEATHER EXPECTED. MINOR UPDATES TO FORECAST FOR
TONIGHT AND SATURDAY WITH SLIGHTLY LOWER DEWPOINTS IN THE SAC AREA
SOUTHWARD INTO THE NORTHERN SAN JOAQUIN PORTENDING LESS POTENTIAL
FOR WIDESPREAD FOG TONIGHT AND EARLY SATURDAY...AND POSSIBLY A
LITTLE COOLER MIN TEMPS EARLY SATURDAY WITH PATCHY FROST IN THE
VALLEY. UPDATES OUT.

&&

.PREVIOUS SHORT TERM DISCUSSION...
RIDGE ALONG THE W COAST TRANSITIONS TO AN OMEGA-REX BLOCK OVER THE
WRN STATES THROUGH THE WEEKEND. CURRENT 500 MBS STREAMLINE ANALYSIS
SHOWS A METEOROLOGICAL COL/SADDLE JUST INLAND FROM THE COAST
RESULTING IN LIGHTER WINDS AND WEAKER UPPER AIR SUPPORT THAN
YESTERDAY. THE NLY AND ELY GRADIENTS HAVE DRASTICALLY WEAKENED THIS
AFTERNOON WHICH HAS ALLOWED DEWPOINTS AND HUMIDITIES TO RECOVER.
AFTERNOON TEMPS WERE RUNNING SOME 1 TO 9 DEG COOLER THAN
YESTERDAY...AND WITH A LACK OF SIGNIFICANT ADIABATIC WARMING
TODAY...MAX TEMPS SHOULD END-UP A LITTLE COOLER OVER MOST LOCATIONS
THAN YESTERDAY.

DURING THE WEEKEND...THE REX PORTION OF THE BLOCK IS FORECAST TO
RETROGRADE...WHICH MAY KEEP WEAK CYCLONIC FLOW AND MINOR COOLING
OVER NORCAL AS SUGGESTED BY THE NAM...BUT MUCH LESS SO AS SUGGESTED
BY THE GFS. WE HAVE FAVORED THE LATTER...AND KEPT THE COLDER AIR AND
ANY POSSIBLE BACKWASH CLOUDINESS EAST OF THE CREST. GIVEN THE WRN
STATES BLOCKING PATTERN...THE MORNING RH PROGS SHOWED A LOT LESS
MOISTURE W OF 130W SPREADING INLAND ON SUN AS THEY DID YESTERDAY.
THUS...WITH MOSTLY CLEAR SKIES...LIGHT WINDS AND RECOVERING
DEWPOINTS...LOW CLOUDS AND PATCHY DENSE FOG ARE POSSIBLE IN THE
VALLEY DURING THE NEXT COUPLE OF MORNINGS.

THE MOISTURE AHEAD OF THE TROF IS CURRENTLY ELONGATING/STRETCHING AS
IT NEARS 130W. A DEFORMATION AXIS JUST INLAND FROM THE COAST IS
EXPECTED TO ERODE/BLOCK MUCH OF THE HIGHER CLOUDINESS FROM SPREADING
INLAND UNTIL SUN NITE/MON. THE GFS DOES NOT SPREAD MOISTURE AT/BELOW
700 MBS UNTIL MON NITE WHEN WE INTRODUCE OUR INITIAL POPS.

CAUTIOUS OPTIMISM CONTINUES FOR AT LEAST A LITTLE/SOME QPF FALLING
IN OUR AREA MAINLY TUE. THE TROF IS FORECAST TO SPLIT AS IT NEARS
THE COAST AND RUNS INTO THE WRN BLOCK. SPLITTING SYSTEMS DON`T
PRODUCE SIGNIFICANT PRECIP...BUT IT WILL BE AT LEAST...SOMETHING.

NCEP GLOBAL ENSEMBLE MEAN OUT THROUGH THE MIDDLE OF THE MONTH DOES
NOT REALLY SHOW APPRECIABLE CHANGE...MAINLY KEEPING THE RIDGE
ALONG THE COAST AND SUGGESTING OCCASIONAL WEAKENING OR SPLITTING
TROFS AFFECTING NORCAL.  JHM

&&

.EXTENDED DISCUSSION (TUESDAY THROUGH FRIDAY)...
MODELS CONTINUE TO DIFFER WITH HANDLING OF THE SYSTEM FOR LATE
MONDAY THROUGH TUESDAY. ECMWF HI-RES...WHICH HAS BEEN THE MOST
CONSISTENT RUN TO RUN...CONTINUES TO CLOSE OFF THE LOW WELL WEST OF
THE CWA TUESDAY THEN DIG IT SOUTH OFF THE CALIFORNIA COAST TUESDAY
NIGHT INTO WEDNESDAY. LATEST 12Z RUN KEEPS THE CWA DRY THROUGH THE
EVENT. 18Z OPER GFS CONTINUES THE TREND OF THE LAST SEVERAL RUNS
WHERE IT KEEPS THE WAVE MORE CONSOLIDATED AS IT MOVES ONSHORE OVER
NORCAL THEN DIGS AND CLOSES IT OFF AS IT TRACKS THROUGH. THE LATEST
GEM SOLUTION LOOKS MORE LIKE THE ECMWF HI-RES BUT TRACKS THE LOW
CLOSER TO THE COAST WITH SOME MAINLY LIGHT QPF OVER THE CWA TUESDAY.
CURRENT FORECAST FOLLOWS THIS COMPROMISE SOLUTION WITH HIGHER POPS
ADVERTISED FARTHER WEST ON TUESDAY WITH LINGERING SHOWERS MAINLY
SOUTHERN PORTIONS OF THE CWA TUESDAY NIGHT INTO WEDNESDAY MORNING AS
THE LOW MOVES FARTHER SOUTH ALONG THE CALIFORNIA COAST.

MODELS IN AGREEMENT IN REBUILDING RIDGING ALONG THE WEST COAST
BEHIND THIS SYSTEM WITH DRY WEATHER FORECAST THROUGH THE REMAINDER
OF THE WEEK.  PCH

&&

.AVIATION...
HIGH PRESSURE CONTINUES OVER THE AREA WITH GENERAL VFR CONDITIONS.
PATCHY FOG WILL BRING IFR/LIFR TO THE NORTHERN SAN JOAQUIN AND
SOUTHERN SACRAMENTO VALLEYS SATURDAY MORNING THROUGH ABOUT 18Z.
GENERALLY LIGHT WINDS EXPECTED THROUGH TOMORROW. EK

&&

.STO WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$