FXUS66 KSTO 111805
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1000 AM PST FRI DEC 11 2009
.DISCUSSION...
SHORT WAVE TROF MOVING ONTO THE CA COAST IS FORECAST TO SWING
THROUGH THE AREA TODAY. THIS SYSTEM HAS SPLIT...WITH A CLOSED
CIRCULATION OFF THE N COAST AND A STRONGER PIECE OF ENERGY OFF THE
CENTRAL COAST CAUSING AN ENHANCED AREA OF CLOUDS IN THE WARM SECTOR
OF THE SURFACE CYCLONE. INTERIOR NORCAL NOW IS BETWEEN THESE TWO
FEATURES WITH THE BACKEDGE OF THE MAIN STRATIFORM BAND OF PCPN
MOVING INTO THE WRN PORTION OF THE VALLEY. THE GFS W-E CROSS
SECTIONS SHOW THE DEPTH OF THE MOISTURE DECREASING SIGNIFICANTLY
THIS AFTERNOON WITH STILL ENOUGH MOISTURE AND INSTABILITY IN THE
LOWER 8-10 KFT TO SQUEEZE OUT A LITTLE LIGHT PCPN IN THE
VALLEY...WITH WEAK UPSLOPE FLOW CONTINUING LIGHT PCPN OVER THE W
SLOPES SIERNEV AFTER THE MAIN PCPN BAND MOVES THROUGH.
THE 12Z MODELS CONTINUE THE TREND SET BY THE 00Z RUNS OF SLOWING THE
TIMING OF THE SAT STORM. IT STILL LOOKS LIKE A VERY POTENT
STORM...CAPABLE OF PRODUCING THIS SEASON'S SNOWIEST STORM SO
FAR...IT JUST WILL BE ARRIVING ABOUT 6-12 HRS LATER THAN FORECAST
YESTERDAY. THAT MEANS A LONGER BREAK IN THE PCPN THAN EXPECTED
EARLIER...GOOD NEWS FOR THE BIG H.S. FOOTBALL GAME TONITE AT UCD.
THE SLOWER TIMING OF THE SAT STORM ALSO MEANS WE NEED TO ADJUST THE
CHANCE OF POSSIBLE THUNDERSTORMS...START THEM LATER AND CARRY THEM
INTO THE EVENING PER THE CAPE FORECASTS OF THE WRF/NAM. ALSO THE
PEAK WINDS FOR THE VALLEY NOW SEEM TO BE TARGETED OVER THE NRN SAN
JOAQUIN VALLEY AND SRN SAC VLY...FROM MOD-MYV AROUND THE 00Z SUN
TIME FRAME AS THE SURFACE OCCLUDED FRONT WILL BE SLOWER TO MOVE
INLAND AS WELL. THE NAM 925 MBS SHOW A CORE OF 45 KTS SLY WINDS IN
THIS AREA.
A VERY STRONG AND TEXT BOOK JET STRUCTURE IS FORECAST TO EFFECT
NORCAL SAT AFTN INTO SUN EVENING...WITH NORTH IN THE THERMALLY
INDIRECT CIRCULATION OF THE UPPER JET FROM 00Z-06Z SUN. STRONG UPPER
LEVEL DIVERGENCE WILL ENHANCE UPWARD MOTION OVER INTERIOR NORCAL
WITH STRONG 12-20 UBAR/S OMEGA FORECAST BY THE GFS CROSS SECTIONS
DURING THIS TIME. WINDS...AND PCPN INTENSITY SHOULD BE QUITE STRONG
DURING THIS TIME PERIOD.
THE SYSTEM SHOULD WIND DOWN OVER INTERIOR NORCAL LATER IN THE DAY ON
SUN/SUN EVENING...WITH SHORT WAVE RIDGING PROVIDING A BREAK IN THE
PCPN ON MON...ALTHOUGH WARM ADVECTION CLOUDS AND POSSIBLE LIGHT PCPN
WILL LIKELY SPREAD EWD ACROSS THE AREA DURING THE DAY. MOIST WSWLY
FLOW IS FORECAST TO DEVELOP BY THE MIDDLE OF NEXT WEEK AS LOW
PRESSURE DEVELOPS 150-170W SENDING MORE PCPN TOWARD NORCAL POSSIBLY
FROM TUE THROUGH THU. JHM
.EXTENDED DISCUSSION (TUESDAY THROUGH FRIDAY)...
ONLY MINOR TWEAKS TO EXTENDED FORECAST AS MODELS CONTINUE TO HINT AT
MOISTURE RIDING OVER A RIDGE NEAR THE WEST COAST. THIS MOISTURE...
ASSOCIATED WITH A STRONG STORM DEVELOPING IN THE GULF OF ALASKA WILL
BRING A SLIGHT CHANCE TO CHANCE OF RAIN/SNOW TO NORTHERN CALIFORNIA.
MOISTURE WILL GET PUSHED NORTH OF OUR CWA AND INTO PAC NW AROUND
THURSDAY EVENING AS RIDGE APPEARS TO AMPLIFY OVER THE WEST COAST.
THUS ANY SHOWER ACTIVITY SHOULD PRIMARILY BE NORTH OF INTERSTATE 80
FROM THURSDAY AFTERNOON INTO SATURDAY.
&&
.AVIATION...
RADAR IMAGERY SHOWS HEAVIER SHOWERS IN THE VALLEY NOW SHIFTING
EASTWARD INTO THE SIERRA. LIGHT SHOWERS WITH BR CONTINUING OVER
VALLEY TAF SITES BRINGING MVFR VISIBILITIES WITH IFR/LIFR CEILINGS.
SNOW LEVELS WILL BE ON THE RISE BECOMING AROUND 4500 TO 5500 FT IN
THE NEXT 24 HRS...BUT LOCAL FREEZING RAIN IS POSSIBLE THIS MORNING
IN MOUNTAIN VALLEYS WITH TRAPPED COLD AIR. PRECIPITATION WILL
CONTINUE OFF AND ON FOR ALL TAF SITES THROUGH TONIGHT. LIGHT NORTH
ACROSS THE SACRAMENTO VALLEY AND WITH LIGHT SOUTHWESTERLY WINDS OVER
THE NORTHERN SAN JOAQUIN VALLEY. SOUTHWEST GUSTS TO 25KT IN THE
SIERRA.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
...WINTER WEATHER ADVISORY TODAY UNTIL 10 PM PST TONIGHT FOR THE
WEST SLOPES OF THE NORTHERN SIERRA NEVADA-WESTERN PLUMAS
COUNTY/LASSEN PARK.
...WINTER STORM WATCH FROM LATE FRIDAY NIGHT THROUGH SUNDAY MORNING
FOR WEST SLOPE NORTHERN SIERRA NEVADA-WESTERN PLUMAS
COUNTY/LASSEN PARK.
&&
$$
