000
FXUS66 KSTO 170427
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
927 PM PDT THU MAY 16 2013

.SHORT TERM DISCUSSION...

MAIN CONCERN CONTINUES TO BE THE SHORT TERM WITH THE STRONG
THUNDERSTORM THAT DEVELOP WEST OF I-5 EARLIER CONTINUES TO HOLD
TOGETHER. CURRENTLY THE SYSTEM IS AROUND I-5 AND TO THE EAST BUT
LAST VOLUME SCAN OF RADAR SHOWS MORE ACTIVITY FLARING UP BACK
TOWARDS THE WEST. INTENSE HEAVY RAINFALL WILL CONTINUE THE NEXT
FEW HOURS UNDER THE CORE OF THESE STORMS MIXED WITH MAINLY SMALL
HAIL.

THE LOW PRESSURE AREA HAS BECOME NEGATIVELY TILTED THIS EVENING IS
IS HELPING TO ENHANCE SHOWERS AND THUNDERSTORMS. THE THROUGH AXIS
WILL MOVE THROUGH THE VALLEY OVER THROUGH ABOUT MIDNIGHT SO EXPECT
SOME SHOWERS TO CONTINUE IN FRONT OF THE TROUGH AXIS...HEAVY
AT TIMES. THE ACTIVITY WILL GRADUALLY CONTINUE TO PUSH TO THE
EAST AND NORTHEAST AS THE THROUGH PUSHES INLAND.

FURTHER SOUTH SHOWERS CONTINUE MAINLY FROM AROUND I-80 NORTH IN
THE FOOTHILLS AND MOUNTAINS BUT SHOULD CONTINUE TO DIMINISH
BETWEEN NOW AND MIDNIGHT.

FROM PREVIOUS DISCUSSION...

UPPER TROUGH WILL MOVE EAST INTO THE GREAT BASIN TOMORROW...BUT
LINGERING MOISTURE WILL KEEP SHOWER CHANCES OVER THE SIERRA.
TEMPERATURES WILL REMAIN SLIGHTLY BELOW NORMAL WITH VALLEY
READINGS IN THE MID TO UPPER 70`S. UPPER RIDGE WILL BUILD INTO
NORCAL SATURDAY WITH A DRY NORTHWEST UPPER FLOW DEVELOPING.
TEMPERATURES WILL WARM INTO THE LOW 80`S FOR VALLEYS.

UPPER TROUGH WILL DEEPEN OVER THE ROCKIES ON SUNDAY WITH GUSTY
NORTH WINDS DEVELOPING ON THE BACKSIDE OF THIS FEATURE OVER THE
SAC VALLEY. GUSTS UP TO 30 MPH WILL BE POSSIBLE. TEMPERATURES WILL
WARM INTO THE MID-UPPER 80`S FOR VALLEY LOCATIONS.



.EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY)

WARMING TREND CONTINUES INTO THE EARLY PART OF THE EFP WITH THE ERN
PAC RIDGE BUILDING INTO NORCAL IN THE WAKE OF THIS WEEKEND`S
DEPARTING UPPER TROF AND AHEAD OF THE DEVELOPING DEEP UPPER LEVEL
CLOSED LOW FOR EARLY NEXT WEEK. NWLY FLOW OFF THE COASTAL RANGE AND
NLY PRESSURE GRADIENTS ON MON EXPECTED TO RESULT IN SOME ADIABATIC
WARMING EFFECTS AS WELL. MAX TEMPS SOME 6-12 DEG ABOVE NORMAL ARE
EXPECTED ON MON AND SURPASSING 90 IN THE VALLEY. THEN A BIG
COOLING TREND IS FORECAST FOR THE REST OF THE WEEK. MEDIUM RANGE
MODELS FORECAST ENERGY FROM THE GULF OF AK TO FORM A DEEP CLOSED
LOW (-1 TO -2 500 MBS HEIGHT ANOMALY) OVER THE PAC NW ON TUE WITH
A BIG REX BLOCK ALONG THE W COAST LASTING INTO THE WEEKEND. SO
THIS LOW WILL INFLUENCE NORCAL WX FOR QUITE AWHILE. MAX TEMPS ARE
EXPECTED TO FALL TO NEAR NORMAL ON TUE...THEN SOME 4-10 DEG BELOW
NORMAL WED/THU WITH HIGHS MAINLY IN THE 70S IN THE VALLEY...AND
50S-60S MTNS. ENSEMBLES INDICATE SOME SPREAD IN THE MODELING
DURING THIS TIME WHICH COULD RESULT IN SOME LOCAL TIMING OR
MAGNITUDE OF COOLING ISSUES AT POINT LOCATIONS...NTL THE TREND IS
WHAT WE ARE AFTER AT THIS TIME. IF THE UPPER LOW STAYS N OF OUR
AREA PER THE 16/12Z GFS/ECMWF THE PRECIP IS ALSO LIKELY TO STAY N
OF OUR CWA FOR THE MOST PART...BUT WE DID INCLUDE A SMALL POP OVER
THE NRN ZONES/PARTS OF NRN SIERNEV WED/THU TO ACCOUNT FOR MODEL
SPREADS AND MODEL DIFFERENCES E.G. THE 16/12Z GEM. INCREASING OR
STRENGTHENING WSW FLOW ALOFT ALSO CONDUCIVE FOR WINDY CONDITIONS
OVER THE MTNS.   JHM

&&

.AVIATION...

SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS MAINLY OVER THE MTNS
WILL CONTINUE THIS EVENING AS THE UPPER LEVEL TROF MOVES INLAND.
VFR CONDITIONS EXPECTED IN THE VALLEY...WITH AREAS OF MVFR AND
LOCAL IFR CONDITIONS OVER MTNS. ISOLATED THUNDERSTORMS POSSIBLE
THROUGH THE EVENING FROM NRN SAC VLY AND SHASTA CO MTNS...AND SWD
INTO WRN PLUMAS COUNTY. ONSHORE FLOW RESULTING IN GUSTY SOUTHWEST
WINDS TO 35 KTS IN THE CARQUINEZ STRAIT...AND SIERNEV...THIS
EVENING TAPERING OVERNIGHT.


&&

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

$$