FXUS66 KSTO 070500
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
900 PM PST SUN DEC 6 2009
.DISCUSSION...
COLD CANADIAN UPPER LOW DROPPING INTO FAR NORTHERN INTERIOR PORTION
OF CAL THIS EVENING WITH ASSOCIATED CYCLONIC FLOW DRAWING MOISTURE
ONSHORE AND RESULTING IN SCATTERED SHOWERS OVER PORTIONS OF THE CWA.
SPOTTER REPORTS EARLIER THIS EVENING REPORTING LIGHT SNOW AS LOW AS
2000 FEET. IR IMAGERY SHOWING LESS CLOUD COVER NEAR THE LOW
CENTER...DEEPER INTO THE COLD AIR. AT THE SAME TIME... MOISTURE IS
BEING DRAWN INLAND WITH A MARKED INCREASE FROM STATE ROUTE 20
SOUTHWARD. AS A RESULT...BY MONDAY MORNING A STRONG N-S PWS GRADIENT
SETS UP OVER INTERIOR NORCAL WITH VALUES RANGING FROM AROUND .1-.2
INCHES OVER SHASTA COUNTY...TO AROUND .5-.6 INCHES FROM THE
SACRAMENTO AREA INTO THE NORTHERN SAN JOAQUIN VALLEY. THIS WILL
RESULT IN SIGNIFICANTLY LESS PRECIP OVER THE NORTHERN HALF OF THE
CWA...ESPECIALLY IN THE VALLEY...HOWEVER WITH THE COLD AIR MASS...
VERY HIGH SNOW RATIOS ARE POSSIBLE WITH THIS EVENT. GFS SHOWING 7H
SOUTHWESTERLY FLOW 30-45 KTS OVER THE MOTHERLODE AND WEST SLOPES OF
THE NORTHERN SIERRA NEVADA OVERNIGHT INTO MONDAY MORNING. FARTHER
NORTH...OROGRAPHIC FLOW OVER WESTERN PLUMAS/LASSEN PARK AREA IS ONLY
ABOUT 10-30 KTS THIS EVENING...DECREASING OVERNIGHT INTO MONDAY
MORNING. THIS AREA IS ALSO IN THE DRIER AIR AND THUS SNOW AMOUNTS
EXPECTED TO BE SIGNIFICANTLY LESS. FOR THE CENTRAL VALLEY...FORECAST
BECOMES MORE DIFFICULT WITH PLACEMENT OF COLD ENOUGH AIR FOR SNOW
YET ENOUGH MOISTURE FOR PRECIP. BOTH 00Z NAM12 AND 18Z GFS SHOWING
LESS THAN A TENTH OF PRECIP NORTH OF THE LINE MENTIONED EARLIER.
THIS REGION WILL DEFINITELY BE COLD ENOUGH FOR SNOW LATER TONIGHT
INTO MONDAY MORNING...BUT WILL BE LACKING SIGNIFICANT MOISTURE. AS A
RESULT...EXPECTING LITTLE TO NO ACCUMULATIONS OF SNOW NORTH OF
MARYSVILLE TOMORROW MORNING. TO THE SOUTH...MOISTURE BECOMES
GREATER...HOWEVER THERE IS QUESTION AS TO HOW FAR THE COLDER AIR
WILL MOVE SOUTH OVERNIGHT. SOUTHWEST SURFACE WINDS THIS EVENING IN
THE SACRAMENTO AREA WITH EXTENSIVE CLOUD COVER PUTTING A DAMPER ON
COOLING...HOWEVER LOCAL WRF_NMM SURFACE WINDS PROGGING MORE
FAVORABLE NORTHWEST WIND DEVELOPMENT IN THIS AREA LATER TONIGHT. 18Z
GFS BUFKIT SOUNDINGS FOR THE CENTRAL VALLEY HAVE TRENDED TO ALL
RAIN. 00Z NAM BUFKIT SOUNDING ALSO SHOWING MAINLY RAIN IN THE VALLEY
WITH SOME RAIN/SNOW MIX POSSIBLE IN THE MORNING FROM SAC AREA
SOUTHWARD. AT THIS TIME...CURRENT AVAILABLE MODEL DATA SUGGESTING
PRIMARILY A RAIN/SNOW MIX IN THE VALLEY MONDAY MORNING WITH BEST
CHANCES FOR ANY ACCUMULATING SNOW TO BE BETWEEN MARYSVILLE AND
SACRAMENTO AND TOWARDS THE FOOTHILLS. WILL CONTINUE TO ANALYZE DATA
AS IT BECOMES AVAILABLE BUT IN THE MEANTIME WILL MAKE SOME CHANGES
TO FORECAST AND TREND DOWN SNOW AMOUNTS ADVERTISED IN THE VALLEY.
PCH
.PREVIOUS DISCUSSION...
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 VERY COLD TEMPERATURES AT NIGHT FOR TUESDAY MORNING. THE COLD
AIR STAYS IN PLACE THROUGH AT LEAST WEDNESDAY MORNING SO THE HARD
FREEZE WATCH INCLUDES BOTH DAYS.
.EXTENDED DISCUSSION (THURSDAY THROUGH SUNDAY)...
WET WEATHER PATTERN FOR THURSDAY THROUGH THE WEEKEND AS SEVERAL
SHORTWAVES MOVE THROUGH THE WESTERLY FLOW INTO CALIFORNIA. THESE
STORMS ARE EXPECTED TO BE WARMER WITH SNOW LEVEL LEVELS AROUND 4000
FEET. AT THIS POINT...THE STORM FRIDAY NIGHT INTO SATURDAY LOOKS
LIKE THE WETTEST (WITH PRECIPITABLE WATER VALUES UP TO AN INCH) AND
STRONGEST (WITH A 120KT JET MOVING INTO NORTHERN CALIFORNIA).
&&
.AVIATION...
LOCAL SOUTHWEST WINDS GUSTS 40 TO 50 MPH POSSIBLE OVER THE
MOUNTAINS. LIGHT TO MODERATE SOUTHEASTERLY TO SOUTHWESTERLY VALLEY
WINDS CONTINUE EXCEPT LIGHT NORTHERLY WINDS IN NRN SAC VLY. CURRENT
TAF CIGS RANGING BKN-OVC 060-100 WITH SCT CLOUDS AROUND 030-050. -RA
IN A LINE ORIENTED WEST-EAST FROM SF BAY AREA TO SAC METRO TOWARDS
THE SIERRA FOOTHILLS. -SN AT HIGHER ELEVATIONS ALONG SIERRA
SLOPES...MAINLY SOUTH OF HWY 70. LIFR/IFR VSBYS REPORTED IN SNOW
SHOWERS IN FOOTHILLS/MOUNTAINS AT KPVF...KBLU...KTVL. CIGS SHOULD
LOWER OVERNIGHT FOR VALLEY TAF SITES RANGING 2000-5000 FT WITH LCL
CIGS AT 1000-1500 FT DURING SHOWERS...PRIMARILY IN THE KSMF-KMOD
VCNTY. SHOWERS IN VALLEY LIKELY TO BE RA WITH A RA/SN MIX POSSIBLE
BETWEEN 10-18Z. JBB
&&
.STO WATCHES/WARNINGS/ADVISORIES...
...WINTER STORM WARNING IN EFFECT FOR THE SIERRA NEVADA FROM 3 PM
THIS AFTERNOON TO 6 PM PST MONDAY FOR HEAVY SNOW...
...WINTER STORM WARNING IN EFFECT FROM 4 AM TO NOON PST MONDAY FOR
THE SOUTHERN SACRAMENTO AND NORTHERN SAN JOAQUIN VALLEY INCLUDING
THE DELTA FOR SNOW...
...WINTER WEATHER ADVISORY IN EFFECT FROM 4 AM TO NOON PST MONDAY
FOR THE CENTRAL SACRAMENTO VALLEY FOR SNOW...
...WINTER WEATHER ADVISORY IN EFFECT FROM 10 PM THIS EVENING TO 3 PM
PST MONDAY THE NORTHEAST FOOTHILLS/SACRAMENTO VALLEY AND SOUTHERN
LAKE COUNTY FOR SNOW...
...HARD FREEZE WATCH FOR LATE MONDAY NIGHT AND TUESDAY MORNING AND
AGAIN LATE TUESDAY NIGHT AND WEDNESDAY MORNING FOR INTERIOR NORTHERN
CALIFORNIA BELOW 2000 FEET...
&&
$$
