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000
FXUS66 KMTR 160050 CCA
AFDMTR

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
549 PM PDT WED MAY 15 2013

...A CHANCE OF SHOWERS THURSDAY INTO FRIDAY MORNING...

.DISCUSSION...AS OF 2:16 PM PDT WEDNESDAY...COOL TEMPERATURES
ACROSS THE FORECAST AREA THIS AFTERNOON LOW 70S IN THE NORTH AND
EAST BAY AREA AND LOW TO MID 60S IN SAN FRANCISCO AND MONTEREY.
THE VISIBLE SATELLITE IMAGE CONTINUES TO SHOW MOSTLY SUNNY TO
PARTLY CLOUDY SKIES AROUND THE AREA WITH A BOUNDARY PUSHING IN
FROM THE NORTH.

A WELL DEFINED VORT MAX APPARENT ON THE SATELLITE WATER VAPOUR
IMAGE IS NOW POSITIONED AROUND 130W 45N. THE FORECAST MODELS HAVE
INITIALIZED WELL WITH THIS FEATURE AND THE GENERAL SYNOPTIC
PATTERN. BOTH THE 1200Z GFS40 AND ECMWF MOVE THIS FEATURE INTO THE
PACIFIC NORTHWEST LATER THIS EVENING. BOTH MODELS CONTINUE TO
DEPICT A DEEPENING TROUGH OF LOW PRESSURE OFF OF THE COAST WHICH
WILL MOVE INTO OUR FORECAST AREA THURSDAY INTO FRIDAY. THE LATEST
AMSU TPW IMAGE IS SHOWING TPW VALUES OF 1.00 TO 1.30 INCHES
ASSOCIATED WITH THIS DEVELOPING LOW. THIS SUGGESTS THAT THERE WILL
BE ENOUGH MOISTURE WITH THIS LOW TO PRODUCE SOME SHOWERS ACROSS
THE FORECAST AREA.

A CROSS SECTION WAS CARRIED OUT FROM NORTHERN SONOMA COUNTY THROUGH
SOUTHERN MONTEREY COUNTY UTILIZING THE 1200Z NAM12. THIS CROSS
SECTION SHOWED GENTLE LIFT AND INSTABILITY COMBINED WITH SUFFICIENT
MOISTURE TO PRODUCE LIGHT SHOWERS ACROSS THE CWA AS FAR SOUTH AS
THE SANTA LUCIAS FROM THURSDAY INTO FRIDAY MORNING. THEREFORE HAVE
INCREASED THE COVERAGE OF PRECIPITATION WITH THE AFTERNOON
PACKAGE. ALTHOUGH THE COVERAGE HAS BEEN INCREASED THE QPF REMAINS
LIGHT WITH THIS EVENT WHICH IS EXPECTED TO PRODUCE JUST ENOUGH
PRECIPITATING TO MAKE THE ROADS WET. HEAVIER DRIZZLE MAY BE A
POSSIBILITY ALONG THE COAST AS THE SYSTEM WORKS ITS WAY ASHORE.

A DRYING TREND BEGINS FRIDAY AFTERNOON ACROSS THE DISTRICT AS THE
TROUGH MOVES INLAND AND HIGH PRESSURE BUILDS OVER THE EASTERN
PACIFIC. THIS DRY WEATHER WILL LEAD INTO A NICE WEEKEND WITH
MOSTLY SUNNY SKIES AND SEASONABLY WARM TEMPERATURES FORECAST.

&&

.AVIATION...AS OF 5:40 PM PDT WEDNESDAY...A SURFACE PRESSURE
GRADIENT FROM HIGHER PRESSURE OVER MENDOCINO COUNTY TO LOWER
PRESSURE OVER THE SACRAMENTO VALLEY WAS CAUSING LOCALLY GUSTY NW
WINDS IN THE NORTH BAY THIS AFTERNOON. THE WIND AND LOCAL GRADIENTS
ARE 2X AS STRONG AS THE MOST RECENT MODEL FORECAST SHOWS FOR THE
NORTH BAY THIS EVE. OTHERWISE THE ONSHORE GRADIENT SFO-SAC MATCHES
THE MODEL FORECAST SHOWING 4 MB. MARINE LAYER INVERSIONS ARE
LIFTING AND WEAKENING WITH TIME WHICH IS ALLOWING DRY AIR TO
CONTINUOUSLY MIX INTO THE MARINE LAYER LEADING TO A LACK OF
STRATUS CLOUDS OVER THE AREA. AS LOW LEVEL COOLING CONTINUES
TONIGHT THROUGH THURSDAY EXPECT SOME STRATUS TO REDEVELOP BUT
CLOUD TYPE SHOULD TREND OVER TO STRATOCUMULUS AS LOW LEVEL
STABILITY CONTINUES TO DISSIPATE. MID AND HIGH CLOUDS ARRIVING
TONIGHT SHOULD HELP SLOW DOWN LOW CLOUD REDEVELOPMENT TIL MUCH
LATER TONIGHT. A FEW SHOWERS ARE POSSIBLE THURSDAY AS A DEEPENING
TROUGH PASSES OVER THE AREA.

VICINITY OF KSFO...WEST WINDS TO 30-35 KNOTS IS FORECAST TIL 04Z.
AN AIRPORT WEATHER WARNING FOR WINDS CONTINUES TIL 04Z. IN GENERAL
A DRIER N WIND COMPONENT TO THE WIND OVER THE NORTH BAY MANY TIMES
HELPS DELAY THE ARRIVAL OF LOW CLOUDS AT KSFO BUT IN THIS CASE
TODAY SATELLITE SHOWS THERE WAS AND STILL IS LITTLE TO NO LOW CLOUD
COVERAGE TO SPEAK OF ANYWAY. OVERALL CONFIDENCE LEVEL IS HIGH THAT
VFR WILL CONTINUE FOR THE EVENING VOLUME. LOWER CONFIDENCE REGARDING
CLOUD COVER FORECAST LATE TONIGHT AND THURSDAY MORNING. NAM MODEL
PREDICTS 3-4 MB ONSHORE GRADIENT FROM SFO-SAC THURSDAY
AFTERNOON/EVE SO GUSTY WEST WINDS SHOULD RETURN.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...SATELLITE SHOWS LITTLE IN THE WAY OF
STRATUS EXCEPT FOR WHAT IS PILING UP OVER THE PENINSULA. MARINE
LAYER INVERSION IS WEAKENING AS IT RISES TO ROUGHLY 3 THOUSAND
FEET DEEP PER THE FORT ORD PROFILER. BLEND OF SURFACE COOLING
FAVORING CLOUDS AND LOW LEVEL DRIER AIR MIXING INTO THE MARINE
LAYER FROM ABOVE MEANS LOW CONFIDENCE FORECAST REGARDING CLOUD
COVER DURATION. TEMPO MVFR CIGS ARE THEREFORE FORECAST TIL 06Z-
07Z WHEN NIGHT-TIME COOLING AND LOW LEVEL COOLING WILL PROBABLY
FAVOR PREVAILING MVFR CIGS FOR THE LATE NIGHT THROUGH THURSDAY
MORNING.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...SF BAY UNTIL 9 PM
             SCA...MRY BAY UNTIL 9 PM
             SCA...PIGEON PT TO PT PINOS 0-10 NM UNTIL 9 PM
             SCA...PT ARENA TO PT REYES 0-10 NM UNTIL 3 AM
             SCA...PT REYES TO PIGEON PT 0-10 NM UNTIL 3 AM
             SCA...PT ARENA TO PIGEON PT 10-60 NM UNTIL 3 AM
             SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 3 AM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM

&&

$$

PUBLIC FORECAST: LARRY
AVIATION/MARINE: CANEPA

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