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000
FXUS66 KMTR 250551
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1051 PM PDT FRI MAY 24 2013

...CONTINUED COOL THROUGH THE HOLIDAY WEEKEND...
...RAIN CHANCES MONDAY AND MONDAY NIGHT...BUT FORECAST UNCERTAINTY
IS INCREASING...

.DISCUSSION...AS OF 9:20 PM PDT FRIDAY...THE SYNOPTIC PATTERN HAS
BEEN ESSENTIALLY UNCHANGED SINCE MIDWEEK WITH AN UPPER LOW CENTERED
OVER THE PACIFIC NORTHWEST AND A TROUGH EXTENDING SOUTH ALONG THE
WEST COAST. THE MODELS AGREE THAT A LONGWAVE UPPER TROUGH WILL
REMAIN ANCHORED IN PLACE ALONG THE WEST COAST THROUGH AT LEAST THE
MIDDLE PART OF NEXT WEEK...WHICH WILL MEAN CONTINUED COOLER-THAN-
NORMAL WEATHER...ESPECIALLY INLAND...THROUGH THE LONG HOLIDAY
WEEKEND AND BEYOND. IN ADDITION...THERE IS A REASONABLY GOOD
CHANCE THAT RAINFALL COULD OCCUR ACROSS AT LEAST PORTIONS OF OUR
FORECAST AREA ON MEMORIAL DAY AND MONDAY NIGHT.

NO SIGNIFICANT CHANGES ARE FORECAST IN THE SHORT TERM. IN
FACT...SATURDAY LOOKS TO BE A DAY MUCH LIKE TODAY WITH MOSTLY
SUNNY SKIES...EXCEPT FOR A FEW CLOUDS NEAR THE OCEAN...ALONG WITH
RELATIVELY COOL TEMPERATURES. A SERIES OF SHORTWAVE TROUGHS
MOVING ACROSS NORTHERN CA CONTINUE TO KEEP THE LOW LEVELS MIXED ENOUGH
TO PREVENT DEVELOPMENT OF WIDESPREAD LOW CLOUDS. SKY GRIDS WERE
UPDATED EARLIER THIS EVENING TO SIGNIFICANTLY REDUCE LATE NIGHT
AND MORNING LOW CLOUDS FOR TONIGHT/SATURDAY MORNING.

A STRONGER SHORTWAVE TROUGH IS FORECAST TO SWING ACROSS NORTHERN
CA LATE SATURDAY NIGHT. THE NAM SHOWS INCREASING NORTHWESTERLY
WINDS AND MOISTURE IN THE BOUNDARY LAYER AND WE MAY SEE SOME LOCAL
DRIZZLE AND FOG DEVELOP ON NORTHWEST-FACING SLOPES OF THE COASTAL
RANGES LATE SATURDAY NIGHT INTO SUNDAY MORNING...ALONG WITH MORE
WIDESPREAD LOW CLOUD COVER ACROSS COASTAL AREAS IN GENERAL. BUT
THIS DOES NOT LOOK LIKE A SITUATION WITH WIDESPREAD FOG NEAR SEA
LEVEL THAT WOULD OCCUR WITH A MARINE LAYER IN PLACE. AND COOL
ADVECTION ON SATURDAY NIGHT WOULD MEAN LITTLE CHANCE WE WILL SEE
THE DEVELOPMENT OF A MARINE LAYER. EVENING FORECAST UPDATE
INCLUDED A REDUCTION IN THE AMOUNT OF NIGHT AND MORNING FOG ON
SATURDAY NIGHT AND SUNDAY. COOL ADVECTION SATURDAY NIGHT AND
SUNDAY MORNING WILL MEAN SLIGHTLY COOLER TEMPS IN MOST AREAS ON
SUNDAY.

THE PRIMARY FORECAST CHALLENGE CONCERNS RAIN CHANCES FOR MEMORIAL
DAY. THE MODELS AGREE THAT A SYSTEM DROPPING SOUTHEAST OUT OF THE
SOUTHERN GULF OF ALASKA WILL SPREAD RAIN INTO NORTHERN CALIFORNIA
BY LATE MONDAY. HOWEVER...THERE IS QUITE A BIT OF DISAGREEMENT
BETWEEN THE MODELS REGARDING HOW FAR SOUTH PRECIPITATION WILL
REACH. THE 12Z ECMWF IS MOST BULLISH WITH DIGGING THE UPPER TROUGH
SOUTH INTO CALIFORNIA AND SPREADS PRECIP ACROSS MOST OF THE SF BAY
AREA BY LATE MONDAY AND THOUGH OUR ENTIRE FORECAST AREA BY LATE
MONDAY NIGHT. THE 00Z NAM DOES NOT DIG THE UPPER TROUGH NEARLY AS
FAR TO THE SOUTH...COMPARED TO THE ECMWF...AND MOSTLY WASHES OUT
THE SURFACE COLD FRONT PRIOR TO IT REACHING OUR CWA.
CONSEQUENTLY...THE GFS FORECASTS ALMOST NO PRECIP IN OUR AREA ON
MONDAY AND MONDAY NIGHT. THE 00Z NAM OFFERS A SOLUTION SOMEWHERE
IN BETWEEN THE OTHER TWO MODELS. IT`S INTERESTING TO NOTE THAT THE
00Z NAM`S QPF IS ONLY ABOUT HALF OF THE 18Z NAM. THUS...THE NAM IS
TRENDING DRIER SIMILAR TO THE GFS. WILL WAIT UNTIL THE 00Z ECMWF
IS IN BEFORE MAKING WHOLESALE CHANGES TO POPS FOR MONDAY AND
MONDAY NIGHT. FOR NOW HAVE ONLY REDUCED POPS ACROSS THE SOUTHERN
PART OF OUR FORECAST AREA ON MONDAY AS IT APPEARS THAT EVEN THE
WETTEST MODEL SOLUTION BRINGS RAIN NO FARTHER SOUTH THAN SANTA
CRUZ BY LATE MONDAY AFTERNOON.

THE MODELS ALSO DISAGREE CONCERNING THE EVOLUTION OF THE SYNOPTIC
PATTERN NEXT WEEK. THE ECMWF GRADUALLY SHIFTS THE LONGWAVE TROUGH
TO THE EAST...RESULTING IN GRADUAL WARMING DURING THE SECOND HALF
OF THE WEEK. THE 00Z GFS HOLDS THE LONGWAVE TROUGH AXIS NEAR THE
WEST COAST AND MAINTAINS COOL WEATHER RIGHT ON THROUGH THE WEEK.
THE CURRENT FORECAST CALLS FOR GRADUAL WARMING DURING THE SECOND
HALF OF THE WEEK...BUT THAT MAY CHANGE DEPENDING ON WHAT THE 00Z
ECMWF SHOWS.

&&

.AVIATION...AS OF 10:45 PM PDT FRIDAY...SKIES ARE MAINLY CLEAR. VFR
IS HOLDING SO FAR BUT LOCALIZED LOW CLOUDS ARE FORECAST OVERNIGHT.

VICINITY OF KSFO...WEST WINDS HAVE DECREASED. VFR.

KSFO BRIDGE APPROACH...VFR.

MONTEREY BAY AREA TERMINALS...MVFR CIGS FORECAST THIS EVENING. IFR
OVERNIGHT.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PIGEON PT TO PT PINOS 0-10 NM UNTIL 3 AM
             SCA...PT ARENA TO PIGEON PT 10-60 NM
             SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             SCA...PT ARENA TO PT REYES 0-10 NM
             SCA...PT REYES TO PIGEON PT 0-10 NM

&&

$$

PUBLIC FORECAST: DYKEMA
AVIATION/MARINE: CANEPA

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