SFOAFDSTO (05/14/13 0434)

FXUS66 KSTO 141137
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
437 AM PDT TUE MAY 14 2013

.SHORT TERM DISCUSSION...

TODAY WILL BE FAIRLY SIMILAR TO YESTERDAY. TEMPERATURES AT 3 AM
WERE THE SAME OR WITHIN A FEW DEGREES COMPARED TO 24 HOURS AGO AND THE
SFO-SAC ONSHORE GRADIENT CONTINUES TO BE AROUND 2.5 TO 3 MB.

THE MAIN DIFFERENCE TODAY IS THAT A WEAK WAVE WILL MOVE EASTWARD
ACROSS CENTRAL CALIFORNIA. THERE IS LITTLE MOISTURE ASSOCIATED
WITH THIS WAVE BUT IT WILL INTRODUCE INSTABILITY ALONG THE CREST OF
THE CENTRAL AND SOUTHERN SIERRA. THERE IS A SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS SOUTH OF THE LAKE TAHOE REGION. THIS
WAVE IS ALSO DEEPENING THE MARINE LAYER. THE FORT ORD PROFILER
SHOWS THAT THE MARINE LAYER DEPTH HAS RISEN FROM 1000 FT YESTERDAY
TO ALMOST 2000 FT EARLY THIS MORNING. HOWEVER...THERE'S NOT MUCH
MARINE STRATUS IN THE BAY AREA AT THIS TIME SO DOUBT THERE WILL BE
ANY BIG PUSH OF STRATUS INTO THE DELTA.

AFTER THIS WAVE PASSES A BROADER TROUGH WILL DEVELOP ALONG THE
WEST COAST. THE AIRMASS ALOFT WILL BE IN A COOLING TREND AS THIS
TROUGH LOWERS 500 MB HEIGHTS ON WEDNESDAY AND DAYTIME HIGHS WILL
LOWER ABOUT 5-7 DEGREES (VALLEY HIGHS IN THE LOW TO MID 80S).
THE TROUGH WILL DEEPEN ON THURSDAY AND ADDITIONAL COOLING WILL
PUSH DAYTIME HIGHS BELOW NORMAL (VALLEY HIGHS IN THE MID TO UPPER
70S). 

THE MAIN IMPACTS OF THIS TROUGH WILL BE FELT ON THURSDAY AND
FRIDAY WITH COOLING, INCREASED CLOUDS, ENHANCED ONSHORE FLOW AND
MOISTURE. CHANCE OF RAIN ON THURSDAY AND FRIDAY WILL PRIMARILY BE
ACROSS THE COASTAL...NORTHERN...AND SIERRA TERRAIN AS WELL AS
SPREADING INTO THE CENTRAL AND NORTHERN SACRAMENTO VALLEY. QPF
ESTIMATES AT THIS TIME WILL TOTAL FROM A FEW HUNDREDTHS OF RAIN IN
THE VALLEY UP TO A QUARTER OF AN INCH ACROSS THE MOUNTAINS FOR THE
THURS-FRI PERIOD. SNOW LEVELS WILL LOWER TO AROUND 7500-8000 FT SO
THIS COULD RESULT IN A COUPLE INCHES OF SNOW WHERE SHOWERS OCCUR
OVER THE MOUNTAINS. JBB

.EXTENDED DISCUSSION (SATURDAY THROUGH TUESDAY)

BY EARLY SATURDAY MORNING THE TROUGH AXIS WILL BE EAST OF
CALIFORNIA AND OVER THE GREAT BASIN. 500 MB HEIGHTS WILL INCREASE
AND THE AIRMASS ALOFT WILL WARM. WEEKEND TEMPERATURES FOR THE
VALLEY WILL BE IN THE 80S AND THEN WARM INTO THE LOW 90S BY
MONDAY. HIGH PRESSURE RIDGING WILL IMPACT THE WEST COAST ON MONDAY
AND TUESDAY WITH DRY WEATHER AND ABOVE NORMAL TEMPERATURES.

&&

.AVIATION...

VFR CONDITIONS NEXT 18 HOURS. WEAK NW WINDS IN NRN SAC VALLEY AND
SW TO W WINDS THROUGH DELTA AND INTO SRN SAC AND NRN SAN JOAQUIN
VALLEYS TODAY. DIURNAL WINDS DOMINATE. ISOLD AFTERNOON TSTMS MAY
DEVELOP OVER SIERRA CREST SOUTH OF ALPINE COUNTY. 30% CHANCE OF
MARINE STRATUS CIG INTO KMHR AND KSAC WED MORN.   JCLAPP


&&

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