SFOAFDSTO (05/24/13 1010)

FXUS66 KSTO 241714
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1014 AM PDT FRI MAY 24 2013

.SHORT TERM DISCUSSION...

STRONG BLOCKING PATTERN OVER WRN NOAM WILL DOMINATE NORCAL WX 
THROUGH THE HOLIDAY WEEKEND...IN WHAT COULD END-UP BEING "MEMORABLE" 
IF THE MODELS AND FORECAST WX (ESPECIALLY QPF) VERIFY FOR OUR CWA. 
FOR TODAY AND SAT...NORCAL WILL BE IN THE MILD WSWLY FLOW S OF
THE UPPER LOW OVER THE PAC NW. A WEAK SHORT WAVE WILL ROTATE
ACROSS THE FAR N TODAY SPREADING SOME HIGH CLOUDINESS OVER THE
AREA...BUT THE AIR MASS IS FORECAST TO REMAIN STABLE. THAT MAY
CHANGE SAT/SUN AFTERNOONS ACROSS THE FAR NRN MTNS WITH THE
FORECAST OF INCREASING INSTABILITY AS SUCCESSIVELY STRONGER SHORT
WAVES MOVE OVER THE AREA. MOISTURE IS MARGINAL SAT...BUT A LITTLE
MORE MOISTURE FORECAST ON SUN WITH SYNOPTIC COOLING ALSO LOWERING
TEMPS.

AS MENTIONED ABOVE...MON MAY TURN OUT TO CRACK THE TOP 5 WETTEST 
MEMORIAL DAYS IN DTS (DOWNTOWN SAC) IF THE MODELS VERIFY. ENERGY 
FROM THE GULF OF AK IS FORECAST TO PHASE WITH THE BLOCKING
LOW...WITH THE ENEGRY MOVING SEWD MON/TUE OVER CA/NV. GREATER
AREAL COVERAGE OF SHOWERS IS EXPECTED ON MON/MON NITE...GENERALLY
ENDING TUE...WITH VIRTUALLY ALL OF OUR CWA EXPECTED TO SEE SOME
SHOWERS. ANY QPF .08 INCH OR MORE WOULD CRACK THE TOP 5 WETTEST
MEMORIAL DAYS FOR DTS. THE SREF PLUME AVEARGE TEMPS ARE FORECASTING
SOME COOL MAXES FOR MON AS WELL...AGAIN POSSIBLY CRACKING SOME OF
THE TOP 5 COOLEST MEMORIAL DAYS. HOWEVER...THE LASTEST PLUME
SPREADS HAVE BECOME LESS CLUSTERED AROUND THE MEAN...RESULTING IN
LOW CONFIDENCE THAT A RECORD "COOL HIGH" WOULD OCCUR ON THAT DAY. 
   JHM

.PREVIOUS DISCUSSION...
NOT MUCH GOING ON IN THE ATMOSPHERE OVER NORTHERN CALIFORNIA
TODAY, BUT THE EARTH HAS BEEN ACTIVE LAST NIGHT AND INTO THIS
MORNING. FOLLOWING THE INITIAL 5.7 MAGNITUDE EARTHQUAKE ON THE
SOUTHEAST EDGE OF LAKE ALMANOR, THE AREA HAS HAD 40 AFTER SHOCKS
AS OF 415 AM PDT. THE LARGEST WAS 4.9 FELT AT OUR OFFICE IN
SACRAMENTO AROUND 100 AM PDT.

THE SEEMINGLY SEMI PERMANENT LOW OVER WASHINGTON IS STILL
DOMINATING OUR WEATHER PATTERN OVER NORTHERN CALIFORNIA. ROTATING
TROUGHS HAVE ELONGATED THE LOW FROM WEST TO EAST, TRANSLATING TO
A PLEASANT DAY WITH ONLY A FEW CLOUDS. TEMPERATURES ACROSS
NORTHERN CALIFORNIA WILL LIKELY BE AROUND 10F BELOW NORMAL TODAY. 

THE NEXT SLIGHT CHANCE OF PRECIPITATION RETURNS SATURDAY
AFTERNOON INTO SUNDAY OVER THE NORTHERN MOUNTAINS AS ANOTHER WEAK
SHORTWAVE ROTATES AROUND THE LOW ACROSS NORTHERN CALIFORNIA. THIS
WILL ALSO INCREASE CLOUD COVER OVER THE FORECAST AREA.
INSTABILITY WITH THIS SYSTEM MAY BE ENOUGH TO TOUCH OFF A FEW
ISOLATED THUNDERSTORMS FROM THE BURNEY BASIN THROUGH WESTERN
PLUMAS COUNTY AND LASSEN PARK SUNDAY AFTERNOON.

A MUCH MORE ROBUST WEST TO NORTHWESTERLY JETSTREAM WILL HELP TO
FILL AND KICK OUT THE PAC NW LOW LATE SUNDAY. BUT THIS LOW/TROUGH
WILL BE REPLACED ON MEMORIAL DAY BY ANOTHER TROUGH FROM THE ERN
PAC WITH OVER AN INCH OF PRECIPITABLE WATER AND INCREASED UPPER
LEVEL DYNAMICS. IN LIGHT OF THIS, A GOOD CHANCE OF SHOWERS MAY
SPREAD ACROSS INTERIOR NORTHERN CALIFORNIA MONDAY AND CONTINUE
THROUGH TUESDAY. WE ARE NOT EXPECTING WIDESPREAD SIGNIFICANT
RAINFALL AMOUNTS, BUT BE AWARE THAT LOCALIZED HEAVIER AMOUNTS CAN
OCCUR WITHIN MORE INTENSE STORMS. SOME OF THE NORTHERN MOUNTAINS
AND COASTAL RANGE COULD RECEIVE UP TO 0.25 INCH WHILE THE VALLEY
WILL LIKELY REMAIN LESS THAN 0.1 INCH. EVEN THOUGH THE MAIN TROUGH
PASSES LATE TUESDAY, DIMINISHING SHOWERS MAY CONTINUE LATER INTO
THE WEEK.

AFTERNOON MAX TEMPERATURES WILL GRADUALLY WARM THROUGHOUT THE
WEEK, BUT STILL REMAIN JUST BELOW NORMAL.     JCLAPP

&&

.EXTENDED DISCUSSION (TUESDAY THROUGH FRIDAY)

A TROUGH REMAINS OVER THE WEST COAST NEXT WEEK BRINGING BELOW
NORMAL TEMPERATURES AND PERIODS OF POSSIBLE PRECIPITATION THROUGH
THE WEEK. THE MODELS ARE IN GOOD AGREEMENT WITH A DISTURBANCE
MOVING THROUGH NORTHERN CALIFORNIA ON MONDAY. THIS WILL BRING A
CHANCE OF RAIN TO INTERIOR NORTHERN CALIFORNIA ON MEMORIAL DAY.
TEMPERATURES ARE EXPECTED TO DROP TO AROUND 70 IN THE VALLEY AND
MID 40S TO MID 50S IN THE MOUNTAINS MONDAY. PRECIPITATION IS
EXPECTED TO TAPER OFF ON TUESDAY. MODELS VARY FOR THE REST OF THE
WEEK AND TIMING OF WAVES SO THERE IS UNCERTAINTY IN THE DETAILS.
FORECAST GOES WITH A CHANCE OF SHOWERS OVER NORTHERN SACRAMENTO VALLEY
AND NORTHERN MOUNTAINS AND A SLIGHT CHANCE OVER THE SIERRA FOR
WEDNESDAY AND THURSDAY WITH A POSSIBLE WAVE MOVING THROUGH THE
NORTH.

&&

.AVIATION...

VFR CONDITIONS CONTINUE. WINDS GENERALLY 5 TO 15 KNOTS AT TAF
SITES. LIGHT TO MODERATE WEST TO SOUTHWEST WINDS OVER RIDGETOPS. JBB

&&

.STO WATCHES/WARNINGS/ADVISORIES...
NONE.
&&