FXUS66 KSTO 052310
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
310 PM PST SAT DEC 5 2009
.DISCUSSION...
A VERY COLD LOW PRESSURE SYSTEM OVER THE NORTHWEST INTERIOR STATES
IS FILTERING VERY COLD AIR TODAY. NORTHERLY WINDS WILL REMAIN BREEZY
THROUGH THE AFTERNOON BEFORE TAPERING THIS EVENING.
A NUMBER OF LOCATIONS IN THE CENTRAL VALLEY TONIGHT WILL EXPERIENCE
FREEZING TEMPERATURES TONIGHT AS A RESULT OF THE COLD AIR MOVING
OVER THE REGION. THE SYSTEM WILL CONTINUE TO RETROGRADE SOUTHWEST
OVER NORTHERN CALIFORNIA ON SUNDAY AND SUNDAY NIGHT. AS THE SYSTEM
BACKS OVER THE PACIFIC IT WILL PICK UP SOME MOISTURE FROM MOVING
OVER THE OCEAN AS WELL AS MOISTURE FROM THE LOW PRESSURE AREA OUT
NEAR 140W. THE COLD AIR IN PLACE WILL ALLOW FOR VERY LOW SNOW
LEVELS...POSSIBLY OVER PORTIONS OF THE CENTRAL VALLEY MONDAY
MORNING. LIGHTER PRECIPITATION IS EXPECTED OVER THE FAR NORTH WITH
HIGHER PRECIPITATION TOTALS AS YOU MOVE SOUTHWARD WITH THIS STORM.
THE CURRENT WINTER STORM WATCH LOOKS GOOD BUT HAVE EXPANDED IT TO
INCLUDE SOUTHERN LAKE COUNTY. PRECIPITATION AMOUNTS STILL REMAIN A
LITTLE UNCERTAIN AT THIS TIME BUT THEY COULD RANGE FROM A TRACE TO A
FEW HUNDREDTHS OVER THE FAR NORTH END OF THE VALLEY TO UP TO A
QUARTER INCH OR SO OVER THE NORTHERN SAN JOAQUIN VALLEY...WHILE THE
WESTERN SLOPES COULD RANGE FROM A QUARTER OF AN INCH NEAR LASSEN
PARK UP TO AN INCH FOR THE WEST SLOPES OF THE SIERRA NEVADA. DUE TO
THE COLD DRY AIR RAIN TO SNOW RATIOS WILL BY VERY HIGH. THE HIGHEST
PRECIPITATION TOTALS ARE EXPECTED SOUTH OF HIGHWAY 70.
BEHIND THE SYSTEM EVEN COLDER AIR WILL ADVECT OVER THE REGION AND
SKIES SHOULD BE CLEARING MONDAY NIGHT FOR THE VALLEY WITH WINDS NOT
EXPECTED TO BE A MAJOR FACTOR BEHIND THE SYSTEM. THAT SETS THE STAGE
FOR EVEN COLDER TEMPERATURES AT NIGHT FOR TUESDAY MORNING.
.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.
&&
.UPDATED AVIATION...
OCCASIONAL WIND GUSTS UP TO 25 KTS MAY CONTINUE FOR THE NEXT HOUR OR
TWO IN THE KRBL VCNTY TIL 01Z...HOWEVER WIND SPEEDS ARE ON THE
DECLINE AS LIGHT TO MODERATE NORTHERLY WINDS CONTINUE IN THE VALLEY
THIS EVENING. APPROACHING STORM WILL CAUSE WINDS TO TRANSITION
OVERNIGHT BECOMING LIGHT SOUTHWESTERLY AROUND 12Z. PATCHY FOG
DEVELOPMENT MAY AGAIN AFFECT PORTIONS OF THE SOUTHERN SAC TO
NORTHERN SAN JOAQUIN VALLEYS CAUSING IFR CONDS WITH LCL LIFR
POSSIBLE 13-17Z. 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...
&&
$$
