000
FXUS66 KMTR 160406
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
906 PM PDT WED MAY 15 2013

.DISCUSSION...AS OF 9:05 PM PDT WEDNESDAY...IT`S A COOL AND BREEZY
EVENING ACROSS THE REGION AS A BROAD UPPER TROUGH DEEPENS NEAR
THE WEST COAST. WIND GUSTS AS HIGH AS 45 MPH WERE REPORTED AT SAN
FRANCISCO AIRPORT JUST BEFORE 6 PM PDT THIS EVENING AND CURRENT
OBSERVATIONS REVEAL SEVERAL LOCATIONS GUSTING UP TO 35
MPH...MAINLY NEAR THE OCEAN AND IN THE HILLS. THE MODELS INDICATE
THAT ONSHORE GRADIENTS WILL RELAX OVERNIGHT AS SURFACE HIGH
PRESSURE WEAKENS OFFSHORE. SO...EXPECT WINDS TO GRADUALLY
DIMINISH THROUGH THE REMAINDER OF THE NIGHT.

SATELLITE IMAGERY CURRENTLY SHOWS A SHORTWAVE TROUGH OFFSHORE
NEAR 40N/137W. THIS SHORTWAVE WILL APPROACH THE COAST LATE TONIGHT
AND THEN MOVE INLAND ACROSS NORTHERN CALIFORNIA BY LATE THURSDAY.
THE MODELS ALL SHOW AT LEAST SOME SCATTERED LIGHT PRECIP ACROSS
THE SF BAY AREA TOMORROW MORNING AS THE SHORTWAVE DRAWS CLOSE TO
THE COAST. BELIEVE IT`S LIKELY THIS SYSTEM WILL PRODUCE MEASURABLE
RAINFALL ACROSS AT LEAST A PORTION OF OUR AREA GIVEN THE RATHER
MOIST AIRMASS CURRENTLY FEEDING INTO IT. AMSU SATELLITE DATA
INDICATES A PLUME OF HIGH PW AIR STREAMING FROM NEAR THE
PHILIPPINES ALL THE WAY ACROSS THE PACIFIC...WITH 1.25 INCH PW
VALUES IN THE VICINITY OF THE APPROACHING SHORTWAVE TROUGH. LOOKS
LIKE THE BEST CHANCE OF RAIN WILL BE FROM AROUND SUNRISE THROUGH
LATE MORNING...AND MAINLY FROM SANTA CRUZ COUNTY NORTHWARD. THE
MORNING COMMUTE IN THE SF BAY AREA COULD BE WET. AFTER AN
EXTENDED DRY PERIOD...EVEN LIGHT AMOUNTS OF RAIN CAN RESULT IN
SLICK ROADWAYS.

THE MODELS INDICATE PRECIP WILL TAPER OFF THURSDAY AFTERNOON AND
PROBABLY END BY LATE THURSDAY EVENING AS THE UPPER TROUGH AXIS
SHIFTS INLAND AND TO OUR EAST. FRIDAY WILL BE A PARTLY
CLOUDY...BREEZY AND COOL DAY ON THE BACKSIDE OF THE UPPER TROUGH.

A WARMING TREND IS FORECAST TO COMMENCE ON SATURDAY AS AN UPPER
RIDGE OVER THE EASTERN PACIFIC BEGINS TO BUILD INLAND.
TEMPERATURES SHOULD WARM ABOVE NORMAL BY SUNDAY AND WARMTH MAY
EXTEND ALL THE WAY TO THE COAST BY MONDAY IF LIGHT OFFSHORE FLOW
DEVELOPS AS INDICATED BY THE GFS.

&&

.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: DYKEMA
AVIATION/MARINE: CANEPA

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