FXUS66 KSTO 120519
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
920 PM PST THU MAR 11 2010

.DISCUSSION...
A MILDER DAY TODAY WITH MAX TEMPS UP SOME 2 TO 8 DEG FROM N TO S IN
THE VALLEY FROM WED...WITH DOUBLE DIGIT WARMER TEMPS IN THE SIERNEV.
THE NEXT COUPLE OF DAYS WILL BE COOLER...WITH A REBOUND IN TEMPS
AGAIN ON SUN.

SATELLITE SHOWS WAA CLOUDS SPREADING INLAND AS THE RIDGE ALOFT TAKES
ON A MORE POSITIVE TILT AHEAD OF THE DEEPENING AND PROGRESSIVE ERN
PAC TROF NEARING 135W. THE FRONTAL BAND CLOUDS ARE BECOMING MORE SW
TO NE ORIENTED AHEAD OF THE DEEPENING WHICH WILL KEEP THEM W OF THE
AREA OVERNITE...WITH THE PROGS SUGGESTING THEY WILL BE MOVING INLAND
BETWEEN 12Z-18Z FRI...AND INTO THE WRN PORTION OF OUR FORECAST AREA
BY AROUND 18Z OR SO. THAT MEANS THE ONSET OF STEADY PCPN WILL BEGIN
IN THE WRN SHASTA CO/COASTAL MTN ZONES FRI MORNING...THEN SPREADING
INTO THE VLY AND SIERNEV MAINLY BY MIDDAY OR EARLY AFTN. MANIFESTED
BY THE LARGE AREA OF CUMULIFORM CLOUDINESS OVER THE ERN PAC...THIS
WILL BE A VERY STRONG FRONT/HYPER-BAROCLINIC ZONE WITH A DEEP VORT
MAX/COLD POOL ALOFT. THE STRONG FRONT COULD RESULT IN A NCFR FOR THE
VALLEY AND SIERNEV FOOTHILLS. THE LARGE TEMP/DENSITY DISCONTINUITY
WILL ALSO CAUSE LARGE ENOUGH PRESSURE RISE/FALL COUPLETS TO RESULT
IN GUSTY SURFACE WINDS IN THE PROXIMITY OF THE FRONT. THE 12/00Z NAM
925 MBS WINDS HAVE WEAKENED TO 30+ KTS FROM THE EARLIER 45 KTS.
ALTHOUGH THIS MAY BE AN INDICATOR OF THE WINDS ALOFT...THE STRONG
CAA AND STEEPENING LAPSE RATES COULD RESULT IN GUSTS NEAR/AROUND
40KTS MAINLY OVER THE NRN HALF OF THE SAC VLY. THIS COULD RESULT IN
WIND ADVSRY CRITERIA FOR THE CENTRAL/NRN SAC VLY ASSOCIATED WITH
FROPA WHICH IS FORECAST TO BE LOCATED FROM ALTURAS... CHICO...NW OF
SAC AT 4 PM...AND THEN EAST AND SOUTH OF OUR AREA BY AROUND 06Z SAT.

THE LARGE SCALE ASCENT IS FORECAST TO BE QUITE IMPRESSIVE...BUT ONLY
FOR A SHORT TIME DUE TO THE PROGRESSIVE NATURE OF THE UPPER TROF.
OMEGA VALUES OF 20 UBAR/S ARE FORECAST FRI AFTN THROUGHOUT THE CWA
WITH STRONG OROGRAPHICS INTO THE SIERNEV. DESPITE THE FAST MOVEMENT
OF THE STORM...WE SHOULD EASILY REACH WARNING CRITERIA SNOWFALL IN
THE SIERNEV. THERE ARE ONLY TWO ELEMENTS THAT WILL KEEP QPFS
DOWN...THE 1ST IS THE FAST MOVEMENT OF THE STORM...AND THE 2ND IS
THE PW PLUME. THE BLENDED TPW PRODUCT SHOWS MOSTLY .90 PW WITHIN THE
PLUME...LESS THAN WHAT THE GFS IS FORECASTING. THIS IS STILL WET
ENOUGH FOR A GOOD PCPN EVENT...AND THE FACT THAT THE DYNAMICS ARE
VERY IMPRESSIVE WILL MORE THAN COMPENSATE FOR THE LOWER PW VALUES.

FRI NITE AND EARLY SAT...PCPN WILL WIND DOWN FROM W TO E. IT LOOKS
LIKE A CHILLY N WIND BEHIND THE FRONT ON SAT...WITH 850 MBS TEMPS
BELOW 0 DEG C AROUND SAC. WOULD PREFER TO LOWER MOS GUIDANCE MAX
TEMPS ON SAT WITH VALLEY HIGHS ONLY IN THE MID TO UPPER 50S...AND A
VERY CHILLY DAY IN THE MTNS. TEMPS ARE EXPECTED TO REBOUND ON SUN AS
HIGH PRESSURE BUILDS OVER THE AREA IN THE WAKE OF THE STORM. THE
GUIDANCE IS REALLY PULLING BACK ON THE WARMING FOR SUN...E.G. THE
03/07 MEXRDD FORECAST A 79 ON SUN AND NOW THE 03/12 FORECAST IS
70...SIMILARLY FOR SAC THE MEX DROPS FROM 70 TO 66. SO THE FIRST 70
FOR SAC MAY BE ON HOLD FOR A COUPLE OF DAYS. JHM


.PREVIOUS DISCUSSION...
INCOMING WINTER STORM WILL BE ANOTHER RELATIVELY MILD ONE. THE
SYSTEM IS SLOWING A BIT SO TIMING WAS ADJUSTED BY A FEW HOURS BUT
STILL EXPECTING IT TO MOVE ONSHORE TONIGHT ALONG THE NORTH COAST AND
PUSH INTO THE STO CWA OVERNIGHT. FRIDAY SHOULD BE WET JUST ABOUT
EVERYWHERE BUT THE HEAVIEST PRECIPITATION LOOKS TO COME THROUGH
FRIDAY EVENING AND OVERNIGHT. BAD TIMING FOR COMMUTERS AND WEEKEND
TRAVELERS BUT THE PERIOD OF HEAVIEST PRECIP LOOKS TO BE JUST A FEW
HOURS. PRECIP WILL TAPER OFF FROM THE COASTAL AND NORTHERN MOUNTAIN
BY OVERNIGHT ON FRIDAY BUT WILL LINGER IN THE SIERRA NEVADA RANGE
INTO THE SATURDAY MORNING HOURS.

SNOW LEVELS WILL BE 4000 TO 5000 FEET ACROSS THE AREA... A BIT LOWER
TO START IN THE COASTAL MOUNTAINS AND A BIT HIGHER IN THE SIERRA.
SNOW AMOUNTS WILL BE FAIRLY STEADY OTHER THAN THE STRONGER BURST
FRIDAY AFTERNOON ALONG THE COAST AND IN THE EVENING IN THE SIERRA.
TOTAL ACCUMULATIONS OF TWO TO SIX INCHES IN THE COASTAL AND NORTHERN
MOUNTAINS WITH GUSTY WINDS RESULTED IN A WINTER WEATHER ADVISORY FOR
THE AREA FOR FRIDAY.

IN THE SIERRA... SNOW LEVELS BEGIN HIGHER BUT A DEEP COLD POOL OF
AIR SWINGS ACROSS THE AREA EARLY SATURDAY MORNING AND DROP THE
LEVELS DOWN INTO THE FOOTHILLS. THE MAIN QUESTION IS WHETHER THERE
WILL BE MUCH SNOW STILL FALLING WHEN THIS OCCURS. DEBATED ABOUT AN
ADVISORY FOR THE SIERRA FOOTHILL SATURDAY MORNING BUT HELD OFF FOR
NOW AND JUST PUT FLURRIES AND LIGHT SNOW OF UP TO AN INCH IN THOSE
AREAS. OTHERWISE THE HIGHER ELEVATIONS WILL GET A GOOD FRESH LAYER
OF SNOW OF ONE TO TWO FEET TOTAL ACCUMULATION. HEAVY SNOW AND GUSTY
WINDS FOR THE AREA RESULTED IN A WINTER STORM WARNING FOR MOST OF
FRIDAY THROUGH SATURDAY MORNING.

TEMPERATURES WILL BE QUITE COOL SATURDAY MORNING BUT WILL REBOUND
WELL ON SATURDAY AFTERNOON AND BY SUNDAY THE MAX TEMPS WILL BE
PUSHING 70 DEGREES IN MOST PORTIONS OF THE CENTRAL VALLEY.


.EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY)...
RIDGE OF HIGH PRESSURE OVER THE AREA ON MONDAY WITH TEMPERATURES IN
THE THE LOWER TO MID 70S IN THE VALLEY TO THE 50S IN THE MOUNTAINS.
MONDAY COULD BE THE WARMEST DAY OF THE YEAR SO FAR IN SOME PLACES
(THIS COULD BE THE FIRST TIME DOWNTOWN SACRAMENTO REACHES 70 DEGREES
THIS YEAR). THE RIDGE SHIFTS TO THE EAST ON TUESDAY AS A WEATHER
SYSTEM APPROACHES THE PACIFIC NORTHWEST BRINGING COOLER
TEMPERATURES. THIS SYSTEM WILL BRUSH BY THE NORTHERN MOUNTAINS
BRINGING A SLIGHT CHANCE OF LIGHT PRECIPITATION ON TUESDAY. THE
MODELS VARY FOR WEDNESDAY AND THURSDAY BUT EITHER WAY INTERIOR
NORTHERN CALIFORNIA LOOKS LIKE IT WILL BE DRY. THE GFS HAS THE RIDGE
SHIFTED FURTHER WEST ALLOWING A SYSTEM TO DROP INTO THE PACIFIC
NORTHWEST BRINGING MORE CLOUDS AND A LITTLE COOLER TEMPERATURES THAN
THE ECMWF WITH THE RIDGE FURTHER EAST INTO CALIFORNIA.

&&

.AVIATION...
VFR CONDITIONS THROUGH TONITE OVER INTERIOR NORCAL WITH RAPIDLY
DETERIORATING CIGS/VSBYS TO MVFR AROUND 12Z FRI AND LOCAL IFR
CONDITIONS OVER NRN SAC VLY AROUND 18Z FRI. LOCAL MVFR CIGS/VSBYS
POSSIBLE IN SRN SAC AFT 18Z FRI...WITH WIDESPREAD IFR/LIFR
CIGS/VSBYS IN SNOW OVER SIERNEV AS WELL. SNOW LEVEL 5000-6000
KFT...LOWERING INTO THE LOWER FOOTHILL ELEVATIONS BEHIND THE FRONT.

OFFSHORE COLD FRONT EXPECTED TO MOVE ACROSS MOST OF INTERIOR NORCAL
BETWEEN 18Z FRI - 00Z SAT...TO ABOUT THE I-80 CORRIDOR BY 00Z...AND
THEN S AND E OF THE FORECAST AREA AROUND 06Z. BAND OF MODERATE TO
HEAVY PCPN EXPECTED VCNTY OF FRONT. SLY WINDS ALSO EXPECTED TO
INCREASE OVER THE CENTRAL VLY WITH GUSTS IN EXCESS OF 30KTS IN
PROXIMITY OF CDFNT AND POSSIBLE LLWS. PCPN AND WIND EXPECTED TO
DECREASE AFTER 00Z SAT OVER INTERIOR NORCAL WITH LINGERING SHOWERS
INTO EARLY SAT MORNING.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
..WINTER WEATHER ADVISORY 4 AM TO 10 PM FRIDAY ABOVE 4000 FEET FOR
SHASTA COUNTY MOUNTAINS INCLUDING THE COASTAL RANGE DOWN THROUGH
NORTHERN LAKE COUNTY..
..WINTER STORM WARNING 10 AM FRIDAY UNTIL 4 AM SATURDAY ABOVE 4500
FEET FOR THE WEST SLOPES OF THE SIERRA NEVADA INCLUDING LASSEN PARK
AND WESTERN PLUMAS COUNTY..

&&

$$




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