FXUS66 KSTO 051801
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1000 AM PST SAT DEC 5 2009
.DISCUSSION...
A VERY COLD LOW PRESSURE SYSTEM OVER THE NORTHWEST INTERIOR STATES
IS FILTERING VERY COLD AIR TODAY. NORTHERLY FLOW WILL GRADUALLY HELP
TO DISSIPATE THE LOW CLOUDS OVER THE SOUTHERN SACRAMENTO AND
NORTHERN SAN JOAQUIN VALLEY SO LOOK FOR SUNNY SKIES TO DEVELOP OVER
THOSE AREAS BY EARLY AFTERNOON.
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. 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 OVER THE NORTHERN SAN JOAQUIN
VALLEY...WHILE THE WESTERN SLOPES COULD RANGE FROM A QUARTER OF AN
INCH UP TO AN INCH. DUE TO THE COLD DRY AIR RAIN TO SNOW RATIOS WILL
BY VERY HIGH.
BEHIND THE SYSTEM EVEN COLDER AIR WILL ADVECT OVER THE REGION AND
SKIES SHOULD BE CLEARING MONDAY NIGHT 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 APPEAR TO BE ON TRACK WITH A WET WEATHER PATTERN
DEVELOPING AS A STRONG PACIFIC JETSTREAM UNDERCUTS THE UPPER RIDGE
OVER ALASKA BRINGS A WARMER AIRMASS...RAISING SNOW LEVELS. THE ECMWF
CONTINUES TO BE THE FASTEST AND WETTEST MODEL WITH THE GEM AND GFS
ABOUT 12-18 HOURS SLOWER. OUR FORECAST TIMING TRENDS MORE TOWARD THE
ECMWF. GREAT OROGRAPHIC FLOW MAY RESULT IN SIGNIFICANT PRECIP
AMOUNTS OR AT LEAST CONTINUOUS WIDESPREAD PRECIP THROUGH THURSDAY.
THEN THE JET STREAM SHIFTS SOUTH OF OUR AREA INTO CENTRAL AND SRN
CAL. JMC
&&
.UPDATED AVIATION...
UPPER LEVEL LOW PRESSURE SYSTEM AROUND IDAHO AND MONTANA WILL MOVE
SOUTH INTO NEVADA AND UTAH BY SUNDAY MORNING. A PIECE OF ENERGY
MOVES AROUND THE BACK SIDE OF THE LOW ACROSS NORTHERN CALIFORNIA
TODAY WITH ANOTHER WAVE MOVING THROUGH SUNDAY MORNING. THIS WILL
BRING NORTHERLY WINDS AND SOME CLOUDS TO THE AREA TODAY FOR
GENERALLY VFR/MVFR CONDITIONS. ALTHOUGH AREAS OF LOW CLOUDS AND FOG
WILL BRING AREAS OF IFR/LIFR CONDITIONS UNTIL AROUND 18Z TO THE
VALLEY FROM AROUND MARYSVILLE AND SOUTH TO THE NORTHERN SAN JOAQUIN
VALLEY AND THE DELTA REGION.
&&
.STO WATCHES/WARNINGS/ADVISORIES...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.
...FROST ADVISORY IN EFFECT FROM 2 AM TO 9 AM PST SUNDAY BELOW 2000
FEET FOR INTERIOR CALIFORNIA...
...HARD FREEZE WATCH IN EFFECT FROM LATE MONDAY NIGHT THROUGH
TUESDAY MORNING BELOW 2000 FEET FOR INTERIOR CALIFORNIA...
&&
$$
