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000
FXUS66 KMTR 161623
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
923 AM PDT THU MAY 16 2013

.DISCUSSION...AS OF 09:15 AM PDT THURSDAY...LIGHT RAIN FALLING
ACROSS THE AREA WITH BOUNDARY MOVING THROUGH. KMUX RADAR
INDICATING RAIN BAND CURRENTLY EXTENDS FROM THE FAR EAST BAY
SOUTHWEST THROUGH MONTEREY HOWEVER THE INTENSITY OF THE RETURNS IS
MISLEADING AS LITTLE IS ACCUMULATING ON THE GROUND. PRECIP
REPORTS HAVE RANGED FROM A TRACE TO UP TO THREE HUNDREDTHS.
FORECAST POPS ON TRACK DUE TO LOW ACCUMULATION. RAIN WILL DIMINISH
LATE MORNING INTO AFTERNOON AS THE BOUNDARY CONTINUES EAST THOUGH
THE BALANCE OF THE DAY WILL REMAIN CLOUDY AND COOL.

&&

.PREV DISCUSSION...AS OF 3:00 AM PDT THURSDAY...KMUX RADAR IS STARTING
TO INDICATE SOME VERY LIGHT RETURNS THIS MORNING AS A SHORTWAVE
CURRENTLY OUT IN THE PACIFIC CONTINUES TO ADVANCE TOWARD THE
COAST. AS OF NOW, ALL OF THE ACTIVITY HAS BEEN TO OUR NORTH WITH
THE KBHX RADAR SHOWING RAINFALL NORTH OF MENDOCINO COUNTY (AND
MOUNT VACA RADAR INDICATING JUST VERY LIGHT RETURNS AROUND THE
NORTH BAY AT THIS TIME). AS THE MORNING PROGRESSES, RAIN WILL SLOWLY
PROGRESS MORE TO THE SOUTH AND POSSIBLY IMPACT OUR AREA TODAY.

CLIMATOLOGY CERTAINLY DOES NOT FAVOR RAIN THIS TIME OF YEAR,
ALTHOUGH IT WOULD NOT BE THAT UNUSUAL TO SEE SOME MINOR PRECIP
AMOUNTS FOR THE MIDDLE OF MAY. WHAT IS NOTABLE IS A CHUNK OF THE
MODEL GUIDANCE INDICATES THAT DESPITE THE HIGH PW VALUES ASSOCIATED
WITH THIS FEATURE (UP TO 1.25") THE BULK OF THE FAVORABLE ENERGY
WILL STAY TO THE NORTH. 06Z NAM RUN EVEN GOES AS FAR AS TO KEEP
THE ENERGY SOMEWHAT DISJOINTED NEAR OUR AREA (CASE IN POINT 500 MB
VORTICITY) AND ONLY DEPICTS POCKETS OF DRIZZLE AT THE COAST
THROUGH THE MORNING HOURS. AFTER LOOKING AT A FAIR NUMBER OF
SOLUTIONS DECIDED TO LOWER POPS AND QPF VALUES FOR ALL LOCATIONS.
CURRENT EXPECTATION IS ANY RAINFALL WE GET WILL BE VERY LIGHT
(LESS THAN A TENTH THROUGH TODAY) AND MANY LOCATIONS WILL END UP
STAYING DRY. BEST BET LOOKS TO BE FROM SANTA CRUZ COUNTY COASTLINE
NORTH TO THE SONOMA COAST. POPS WERE ALSO LOWERED FOR TONIGHT INTO
TOMORROW AS RAINFALL LOOKS INCREASINGLY UNLIKELY AFTER THE TROF
PASSAGE. EVEN IF IT DOESN`T RAIN, ONE THING THAT WILL BE NOTICED
WILL BE COOLER CONDITIONS TODAY (ESPECIALLY INLAND). HIGHS AT THE
COAST WILL BE IN THE UPPER 50S TO MID 60S WITH UPPER 60S TO MID
70S INLAND.

AFTER ANOTHER COOL DAY ON FRIDAY, TEMPERATURES WILL BE ON THE
REBOUND AS A RIDGE OF HIGH PRESSURE STARTS TO BUILD IN FROM THE
PACIFIC OVER THE WEEKEND. 500 MB HEIGHTS WILL RISE FROM 570 DM TO
582 DM WHILE 850 MB TEMPS WILL INCREASE FROM 7-9C TO 14-16C ON
SUNDAY. LOOK FOR UPPER 70S TO MID 80S FOR INLAND LOCATIONS WITH
MID 60S TO MID 70S FOR THE COAST. THE WARMING WILL CONTINUE INTO
MONDAY AS 850 MB TEMPS CONTINUE TO RISE AND THE RIDGE AXIS MOVES
EVEN CLOSER TO OUR CWA. SOME INDICATION THAT WE COULD EVEN SEE A
SLIGHT OFFSHORE WIND ON MONDAY WHICH WOULD HELP TO BOOST
TEMPERATURES AT THE COAST.

ANOTHER SWING IN TEMPS CAN BE EXPECTED AS AN UNUSUALLY COLD SYSTEM
DROPS DOWN FROM CANADA (INTERESTING NOTE, THE SYSTEM IS ORIGINATING
IN ALASKA AS A PIECE OF ENERGY BREAKS AWAY FROM A VERY LATE SEASON
STORM). 850 MB TEMPS WILL DROP BACK TO AROUND 2C BY THURSDAY.
HIGHS WILL RETREAT BACK TO UPPER 50S TO MID 60S AT THE COAST WITH
60S TO LOWER 70S FOR MOST INLAND LOCATIONS.

&&

.AVIATION...AS OF 5:05 AM PDT THURSDAY...WINDS HAVE EASE A BIT
OVERNIGHT WITH ALL TERMINALS REPORTING WINDS UNDER 10 KT EXCEPT
KSFO THAT CONTINUES TO REPORT SUSTAINED WINDS AROUND 20 KT. WINDS
WILL RAMP UP ONCE AGAIN THIS AFTERNOON WITH MODERATE ONSHORE FLOW
AROUND 15 KT WITH GUSTS NEAR 20 KT AS A WEAK COLD FRONT MOVES
ACROSS THE REGION. A SLIGHT CHANCE OF SHOWERS POSSIBLE TODAY. HAVE
LEFT VCSH IN TAFS. PATCHY LOW CLOUDS WILL SCATTER OUT BETWEEN
17Z-18Z OVER AFFECTED TERMINALS WITH CIGS EXPECTED TO RETURN
AFTER MIDNIGHT TONIGHT OVER MOST SITES.

VICINITY OF KSFO...IFR CIGS WILL PERSIST UNTIL 17Z THIS MORNING.
VFR CONDITIONS WITH MAINLY HIGH CLOUDS ARE THEN EXPECTED THROUGH
THIS EVENING. IFR CIGS EXPECTED TO RETURN AROUND MIDNIGHT TONIGHT.
STRONG ONSHORE FLOW AROUND 20 KT WILL CONTINUE OVER KSFO THROUGH
TODAY WITH GUSTS TO NEAR 30 KT THIS AFTERNOON. LIGHTER ONSHORE
FLOW EXPECTED OVER KOAK.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...IFR-MVFR CIGS WILL PERSIST UNTIL
17Z-18Z THIS MORNING WITH STRATUS RETURNING AS EARLY AS 03Z THIS
EVENING OVER KMRY. MODERATE ONSHORE FLOW AROUND 5 TO 10 KT WILL
PERSIST THROUGH THE MORNING THEN INCREASE TO AROUND 15 KT WITH
GUSTS TO NEAR 20 KT THIS AFTERNOON.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             SCA...SF BAY FROM 11 AM

&&

$$

PUBLIC FORECAST: AC/BELL
AVIATION/MARINE: CW

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