FXUS66 KSTO 271824
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1020 AM AM PST FRI NOV 27 2009

.DISCUSSION...
UPPER LEVEL FRONT HAS PUSHED OVER THE WRN HALF OF THE CWA...AND 
SEEMS TO BE MUCH FASTER THAN MODELED. EVEN THE 27/12Z WRF PCPN IS 
TOO SLOW AND NOT FAR ENOUGH SOUTH WITH THE QPF THIS MORNING. BACK 
UPSTREAM WE ARE SEEING THE BEGINNING OF THE FORMATION OF THE CLOSED 
LOW WITH A CIRCULAR BAND OF CLOUDS MOVING ALONG THE COAST. IT 
CERTAINLY LOOKS LIKE THE CLOSED UPPER LOW WILL BE DROPPING S-SEWD 
FOR THE REST OF THE DAY AND INTO THE WRN SAN JOAQUIN VALLEY BY 
06Z...THEN SWD INTO SOCAL ON SAT. SATELLITE IMAGERY SHOWS STRONG 
SUBSIDENCE BEHIND THE UPPER FRONT...DETACHING THE CLOSED LOW FROM 
THE MOISTURE TO THE E. THIS IS RESULTING IN LESS CONVECTIVE SHOWERS 
ALONG THE COAST DUE TO LOWER PW AIR. BUFKIT FORECAST SOUNDINGS 
INDICATE FOR SUU/SAC MARGINAL INSTABILITY THIS AFTERNOON THROUGH 
ABOUT 02Z AND THIN CAPE...A LITTLE OVER 100 J/KG. THE MID LEVEL CAA 
FROM THE CLOSED LOW IS FORECAST TO STEEPEN LAPSE RATES TO 8-9 DEG 
C/KM UP TO ABOUT 750 MBS DURING THE LATE AFTERNOON AND EVENING HRS. 
THERE MAY BE A RUMBLE OR TWO OF THUNDER...BUT THE MAIN PROBLEM FOR 
THE AFTERNOON WILL BE TO WORK ON THE TIMING OF THE WSW...AND THE 
EVENTUAL INCREASE IN WINDS. WITH THE FAST MOVEMENT...WE CAN LET THE 
WSW EXPIRE OR CANCEL IT FOR ZONE 68 WITH THE AFTERNOON PACKAGE...AND 
LET IT RIDE THIS EVENING IN ZONE 69. SRN ZONE 69 WILL STILL BE IN 
THE FAVORABLE NE QUAD OF THE UPPER WHERE CYCLONIC FLOW AND WRAP 
AROUND MOISTURE ARE LIKELY TO RESULT IN SOME SPILL-OVER OF PCPN FROM 
THE E SIDE OF THE SIERNEV TONIGHT AND INTO SAT. ELSEWHERE...WE CAN 
PROBABLY CUT BACK ON THE POPS BECAUSE OF LESS AREAL COVERAGE OF THE 
SHOWERS.  

NORTHERLY WINDS WILL BE INCREASING TONIGHT AND CONTINUE INTO SAT AS 
NLY PRESSURE GRADIENTS FROM THE PRESSURE RISES ACROSS THE PAC NW 
TODAY/TONITE. THIS IS DUE TO THE CLOSED LOW DROPPING S...AND A 
POSITIVELY TILTED RIDGE BUILDING INTO THE AREA. INCREASING 
ANTICYCLONIC FLOW ALOFT WILL RESULT IN A STRONG OFFSHORE FLOW 
PATTERN FOR THE NEXT COUPLE OF DAYS. BY 12Z SAT THE MFR-SAC GRADIENT 
IS FORECAST TO BE 15 MBS. THE PRESSURE GRADIENT BECOMES MORE NE-ELY 
SAT NITE AND SUN AS THE SURFACE HIGH MOVES FROM ORE INTO ID. STRONG 
SUBSIDENCE IS FORECAST OVER PORTIONS OF OUR AREA TONIGHT AND 
SAT...AND EVEN INTO SUN MORNING...AS MUCH AS 12 UB/S AT TIMES. CROSS 
SECTIONS REVEAL WINDS ALOFT ARE FORECAST TO BE STRONGER ON SAT THAN 
ON SUN...WITH STRONGER MID LEVEL CAA SAT MORNING AS WELL. WIND 
SPEEDS OF 45-50 KTS UP TO 10-12 KFT ARE FORECAST TONITE AND INTO 
SAT...AND IT LOOKS LIKE A PRIME TIME FOR WIND ADVSRY CRITERIA TO BE 
MET OVER A LARGE PORTION OF OUR FORECAST AREA. INCREASING 
ANTICYCLONIC FLOW WILL ALSO WARM THE AIR MASS ON SAT...WITH GREATER 
WARMING ON SUN.  JHM           

.EXTENDED DISCUSSION (TUESDAY THROUGH FRIDAY)...
UNCERTAINTY OF FORECAST INCREASES TOWARD THE END OF THE EXTENDED 
PERIOD. ALL THE MEDIUM RANGE MODELS SHOW THE STRONG MEAN WEST COAST 
RIDGE PERSISTING THROUGH THE EXTENDED PERIOD OF THE FORECAST...BUT 
DIFFER IN TIMING AND HANDLING OF SIGNIFICANT SHORT WAVE ENERGY 
MOVING INTO THE RIDGE TOWARD THE END OF NEXT WEEK. GFS IS MOST 
AGGRESSIVE DIGGING ANOTHER SYSTEM SOUTHEASTWARD INTO CALIFORNIA FROM 
THE GULF OF ALASKA LATE IN THE WEEK WHILE THE GEM AND ECMWF ARE 
WEAKER AND SLOWER. MODELS CONTINUE TO HINT AT MORE SIGNIFICANT 
CHANGES OUT AROUND DAY 10 AS THE WEST COAST RIDGE RETROGRADES TO 
140W AND FORMS A STRONG BLOCK OVER THE GULF OF ALASKA/WESTERN BC 
WHICH MAY EVENTUALLY BE UNDERCUT SETTING THE STAGE FOR A POTENTIALLY 
MORE PROLONGED WET PERIOD FOR NORTHERN CALIFORNIA.

&&

.AVIATION...
COLD FRONT AROUND SACRAMENTO AND NORTHEAST TO AROUND CARIBOU AT 
1630Z AND IS MOVING SOUTHEAST THROUGH THE AREA TODAY.  VFR/MVFR 
CONDITIONS EXPECTED IN THE VALLEY TODAY WITH SHOWERS AND MVFR/IFR 
CONDITIONS WITH LOCAL LIFR CONDITIONS EXPECTED IN THE MOUNTAINS WITH 
PRECIPITATION. CONDITIONS WILL DETERIORATE TO IFR IN SHSN AND BR 
ACROSS THE NORTHERN SIERRA NEVADA THIS MORNING AND CONTINUE THROUGH 
ABOUT 06Z TO 12Z SATURDAY. SNOW LEVELS AROUND 4000 IN THE NORTH TO 
AROUND 5500 FEET IN THE SOUTH. GUSTY SOUTHERLY WILL TURN NORTHERLY 
BEHIND THE FRONT TODAY. NORTHERLY WINDS ARE EXPECTED TO INCREASE 
SATURDAY MORNING. VFR CONDITIONS WITH GUSTY NORTHERLY WINDS ARE 
EXPECTED ON SATURDAY. HSO

&& 

.STO WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY 8 AM THROUGH 6 PM TODAY WESTERN PLUMAS 
COUNTY/LASSEN PARK.

WINTER WEATHER ADVISORY 10 AM THROUGH 10 PM TODAY WEST SLOPE 
NORTHERN SIERRA NEVADA.

&&

$$