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000
FXUS66 KSTO 161634
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
934 AM PDT THU MAY 16 2013

.SHORT TERM DISCUSSION...

UPPER TROUGH IS ALONG THE COAST WITH MOISTURE FEED MOVING INTO
NORCAL. MUCH OF THE MOISTURE WITH THIS SYSTEM IS AT MID-LEVELS
WITH TOP DOWN MOISTENING OF THE ATMOSPHERE NECESSARY FOR PRECIP
TO REACH THE SURFACE. BAND OF RAIN MOVING THROUGH THE AREA HAS
BECOME ENHANCED AS IT MOVES TO A PACIFIC HOUSE-JACKSON-STOCKTON-
MODESTO LINE...WHERE UP TO 0.15 IS POSSIBLE THROUGH NOON.
GENERALLY ONLY TRACE AMOUNTS OF RAIN HAVE BEEN REPORTED FARTHER
WEST INCLUDING THE SACRAMENTO AREA. PRECIP BAND WILL SHIFT EAST
AND DISSIPATE THIS AFTERNOON WITH THE SHOWERS BECOMING SCATTERED
IN NATURE. THE BEST PRECIP CHANCES THIS AFTERNOON WILL BE OVER THE
SIERRA AND FOR AREAS NORTH OF CHICO WHERE THE BEST LIFT WILL BE
LOCATED.

PREVIOUS DISCUSSION...

WEATHER SYSTEM MOVING INTO NORCAL GOT AN EARLY START THIS MORNING.
THE FIRST WAVE OF MOISTURE MOVED INTO THE NORCAL COASTLINE
AFTER MIDNIGHT AND A FEW SHOWERS STARTING POPPING UP IN THE
NORTHERN SACRAMENTO VALLEY AFTER 1 AM. WE EVEN GOT A LIGHTNING
STRIKE FROM ONE OF THE CELLS BUT NOT MUCH RAIN HIT THE GROUND. THE
ONLY OBSERVATION SO FAR FROM THIS EARLY BATCH OF SHOWERS WAS AT
SOLDIER MOUNTAIN MEASURING A TENTH OF AN INCH.

THUS THE TONE FOR TODAY`S WEATHER PATTERN HAS BEEN SET...COOLER,
SHOWERY CONDITIONS EXPECTED TODAY INTO TOMORROW. MODELS HAVE BEEN
SHOWING MARGINAL INSTABILITY FOR OUR CWA AS THE SYSTEM MOVES
EASTWARD. HAVE KEPT SLIGHT CHANCE OF THUNDERSTORMS IN THE
FORECAST NEAR LASSEN PARK & BURNEY BASIN FOR TODAY AND ALONG THE
SIERRA CREST FOR TOMORROW. HOWEVER CONFIDENCE IS NOT HIGH THAT
THUNDERSTORMS WILL BE NUMEROUS ACROSS ALL OF NORCAL. SOME OF THE
LIMITING FACTORS ARE THE INCOMING CLOUDS THAT WILL INHIBIT SURFACE
HEATING TODAY COUPLED WITH THE COOLER AIRMASS ALREADY IN PLACE NEAR
THE SURFACE. TODAY`S DAYTIME HIGHS WILL RANGE 7-15 DEGREES BELOW
NORMAL. VALLEY HIGHS SHOULD REACH INTO THE LOW 70S.

RAIN TOTALS WILL BE UP TO 0.15" IN THE VALLEY AND UP TO AROUND A HALF
INCH ACROSS THE MOUNTAINS. LOCALLY HIGHER AMOUNTS OF RAIN ARE
POSSIBLE IF THUNDERSTORMS DEVELOP. SNOW LEVELS CONTINUE TO BE
FAIRLY HIGH NEAR 7500 FT SO ANY SNOW ACCUMULATION WILL BE LIGHT
AND SHOULD REMAIN ABOVE PASS LEVELS.

UPPER TROUGH WILL MOVE EAST INTO THE GREAT BASIN ON FRIDAY...BUT
LINGERING MOISTURE WILL LIKELY KEEP A CHANCE OF SHOWERS (AND
SLIGHT CHANCE OF THUNDERSTORMS) CONTINUING OVER THE SIERRA. AS
CLOUDS SCATTER OUT DURING THE DAY ON FRIDAY...TEMPERATURES WILL
WARM UP A BIT BUT REMAIN SLIGHTLY BELOW NORMAL. VALLEY TEMPS
SHOULD PEAK IN THE MID TO UPPER 70`S. UPPER RIDGE WILL BUILD INTO
NORCAL SATURDAY WITH DRY NORTHWEST UPPER FLOW. TEMPERATURES WILL
WARM INTO THE LOW 80`S FOR VALLEYS WITH ADDITIONAL WARMING ON
SUNDAY. JBB



.EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY)

UPPER RIDGING CONTINUES AND MONDAY SHOULD MARK THE WARMEST DAY OF
THE WEEK WITH DAYTIME HIGHS RANGING 5-10 DEGREES ABOVE NORMAL.
VALLEY HIGHS WILL WARM UP TO THE LOW 90S.

THE EXTENDED MODELS ALL INDICATE THAT A STRONG CLOSED LOW WILL
DEVELOP OVER THE CANADIAN COASTLINE AND BEGIN TO DIG SOUTHWARD ON
TUESDAY. MODELS VARY SOMEWHAT ON THE DETAILS OF THIS STORM, BUT IT
LOOKS AS THOUGH THE CENTER OF THE STORM WILL LINGER OVER THE
PACIFIC NW FROM TUESDAY INTO THURSDAY. ON FRIDAY THIS SYSTEM
SHOULD WEAKEN AND LIFT NORTHWARD. FOR THE EXTENDED FORECAST
PERIOD...HAVE COOLED TEMPERATURES AND ADDED SLIGHT CHANCES OF RAIN
TO THE NORTHERN TERRAIN OF OUR CWA. THIS SYSTEM WILL ALSO CAUSE
BREEZY NORTH WINDS FOR THE VALLEY AND GUSTY WESTERLY FLOW OVER THE
MOUNTAINS. AT THIS POINT...WEDNESDAY APPEARS TO BE THE COOLEST DAY
BUT TEMPERATURES SHOULD STILL BE IN THE MID TO UPPER 70S FOR THE
VALLEY. THE CHALLENGE OF THIS FORECAST IS HOW FAR SOUTH THE LOW
WILL ACTUALLY TRACK AND HOW MUCH MOISTURE WILL END UP IMPACTING
NORCAL. JBB


&&

.AVIATION...

VFR/MVFR CONDITIONS WITH AREAS OF IFR CONDITIONS IN THE VALLEY
AND WIDESPREAD IFR CONDITIONS AND LOCAL LIFR CONDITIONS IN THE
MOUNTAINS. ISOLATED THUNDERSTORMS ARE POSSIBLE FROM EASTERN SHASTA
COUNTY AND DOWN TO WESTERN PLUMAS COUNTY THIS AFTERNOON AND
EVENING. PRECIPITATION IS EXPECTED TO TAPER OFF OVERNIGHT AND INTO
FRIDAY. ISOLATED THUNDERSTORMS ARE POSSIBLE FROM EASTERN SHASTA
COUNTY AND DOWN THE SIERRA ON FRIDAY AFTERNOON AND EVENING AS THE
TROUGH SHIFTS TO THE EAST. ONSHORE FLOW RESULTING IN GUSTY
SOUTHEAST TO SOUTHWEST WINDS TO 35 KTS IN THE CARQUINEZ STRAIT...
UP TO 45 KTS IN THE SIERNEV...TO 25 KTS IN THE SAC VALLEY AND
NORTHWEST WIND GUSTS UP TO 30 KTS IN THE NRN SAN JOAQUIN VALLEY.

&&

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

$$