Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000
FXUS66 KMTR 262348
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
448 PM PDT TUE MAY 26 2015

.SYNOPSIS...A GRADUAL WARMING TREND IS EXPECTED THROUGH FRIDAY
ESPECIALLY INLAND AS HIGH PRESSURE BUILDS ALONG THE COAST. ANOTHER
COOLING TREND WILL COMMENCE THIS WEEKEND INTO EARLY NEXT WEEK AS
THE NEXT WEAK PACIFIC LOW APPROACHES THE COAST. MOSTLY DRY CONDITIONS
WILL CONTINUE INTO EARLY NEXT WEEK.

&&

.DISCUSSION...AS OF 01:25 PM PDT TUESDAY...

MARINE LAYER STILL AROUND 3000 FEET DEEP AND WELL MIXED WITH
CONSIDERABLE ONSHORE FLOW AND SFO TO SAC GRADIENT OVER 2 MB.
CLOUDS ARE MOST PREVALENT ALONG UPSLOPE SIDE OF COAST RANGE WITH
SOME BREAKS OVER THE WATERS. TEMPERATURES REMAIN COOL AND MOSTLY
IN THE 60S WITH SOME 80S INTERIOR MONTEREY CO. STRATUS WILL FILL
IN AND SPREAD INLAND FAIRLY QUICKLY AGAIN THIS EVENING.

MODELS IN REASONABLE AGREEMENT THROUGH EARLY NEXT WEEK WITH
RIDGING TO BUILD ALONG THE COAST THROUGH FRIDAY. UPPER LOW OVER
NORTHERN ROCKIES WILL BE SLOW TO PROGRESS EASTWARD...SO NOT
EXPECTING THE RIDGE TO AMPLIFY OR PROGRESS TOWARD THE COAST
QUICKLY. UPSHOT IS PERSISTENT ONSHORE FLOW FOR CENTRAL CALIFORNIA
AND REMAINING COOL ALONG THE COAST. RIDGE WILL ACT TO SUPPRESS
DEPTH OF MARINE LAYER AND BASED ON NAM BUFR SOUNDINGS...WOULD
EXPECT THE LAYER TO DROP CLOSER TO 2000 FEET TONIGHT AND PERHAPS
DOWN TO 1500 FEET DEEP OR LESS THURSDAY AND FRIDAY. CONFIDENCE IS
LOW REGARDING ACTUAL MARINE LAYER DEPTH...BUT CONFIDENCE IS MODERATE
WITH THE TREND FORECAST.

WARMING TREND SHOULD BEGIN WEDNESDAY INLAND AND CONTINUE THROUGH
FRIDAY. 850 MB TEMPERATURES CLIMB FROM ABOUT 15C TO 18C ALONG THE
COAST NEAR SAN FRANCISCO THE NEXT COUPLE DAYS WITH A LITTLE MORE
INTENSE WARMING INLAND. OVERALL...THE WARMING TREND SHOULD FORCE INLAND
TEMPERATURES CLOSER TO NORMAL...BUT STILL NO SIGN OF A MAJOR WARM
UP AT THIS TIME.

RIDGE PROGRESSES INLAND THIS WEEKEND AHEAD OF A WEAK PACIFIC
TROF. THE PARENT LOW ASSOCIATED WITH THIS FEATURE RESIDES AROUND
40N AND 150W AT TIME AND SHOULD GET EJECTED TOWARD THE COAST AND
INLAND BY MONDAY. FEATURE OPENS UP AND SHEARS INLAND LATE
SUNDAY...DEEPENING THE MARINE LAYER AND SPREADING COOLER AIR
INLAND. COULD SEE ANOTHER ROUND OF EXTENSIVE DRIZZLE AS EARLY AS
SUNDAY MORNING...BUT A BETTER CHANCE SUNDAY NIGHT AND EARLY
MONDAY WITH THE BIG MARINE PUSH. WOULD NOT RULE OUT A FEW LIGHT
SHOWERS NORTH BAY AS WELL...BUT SYSTEM APPEARS TO LACK SUFFICIENT
DYNAMICS FOR ANYTHING SIGNIFICANT.

MODELS DIVERGE SOMEWHAT TOWARD MIDWEEK WITH THE ECMWF CONTINUING
TO FEED THE WESTERN U.S. TROF WITH SHORT WAVE ENERGY WHILE THE GFS
IS MORE PROGRESSIVE. MAIN MESSAGE IN THE EXTENDED PERIOD IS
CONTINUED ONSHORE FLOW WITH EITHER ZONAL FLOW OR TROF LINGERING IN
NEAR THE WEST COAST.

&&

.AVIATION...AS OF 4:45 PM PDT TUESDAY...500 MB HEIGHTS WILL SLOWLY
INCREASE TONIGHT THROUGH WEDNESDAY INDICATING WEAK RIDGING FOR THE
PERIOD. LOW LEVEL TEMPERATURES ARE FORECAST TO REMAIN NEARLY UNCHANGED
THROUGH THE PERIOD AND BECAUSE OF THIS WOULD EXPECT LITTLE CHANGE
IN THE MARINE LAYER STRENGTH AND DEPTH. PRESENTLY THE MARINE LAYER
INVERSION IS 2600 TO 3000 FEET DEEP PER BODEGA BAY AND FORT ORD
PROFILERS. ONSHORE WINDS WILL USHER IN THE COASTAL LOW CLOUDS
OVERNIGHT.

MORNING NAM MODELED SURFACE GRADIENTS MATCHED UP FAIRLY WELL WITH
ACTUAL. THE ACV-SFO GRADIENT IS ON THE LIGHT SIDE...1.4 MB...BUT
THE ONSHORE WINDS BEING DRIVEN BY A MODERATE SFO-SAC GRADIENT IS
3.2 MB. THE NORTHERLY GRADIENT IS FORECAST TO REMAIN ON THE LIGHT
SIDE THROUGH WEDNESDAY NIGHT WHILE THE SFO-SAC VARIES FROM 1 TO 3
MB...STRONGEST THIS AFTERNOON AND AGAIN WEDNESDAY AFTERNOON.

VICINITY OF KSFO...VFR/MVFR WITH WINDS STAYING BELOW 20 KNOTS.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...MVFR CIGS RETURNING WITH IFR BEGINNING
10Z-12Z.

&&

.MARINE...AS OF 2:26 PM PDT TUESDAY...HIGH PRESSURE OVER THE
EASTERN PACIFIC WILL RESULT IN CONTINUED LIGHT ONSHORE FLOW AND
GENTLE SEA CONDITIONS THROUGH TONIGHT. WINDS VEER TOWARD THE
NORTHWEST AND INCREASE SLIGHTLY ON WEDNESDAY WITH GENTLE SEA
CONDITIONS EXPECTED THROUGH THE FORECAST PERIOD.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...NONE.

$$

PUBLIC FORECAST: KBB
AVIATION: CANEPA
MARINE: RGASS

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