000
FXUS66 KMTR 140520
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1020 PM PDT MON MAY 13 2013

.DISCUSSION...AS OF 8:44 PM PDT MONDAY...CURRENT SATELLITE IMAGERY
DEPICTS MOST OF THE LOW CLOUDS THAT HUNG ON THROUGH THE AFTERNOON
HAVE ALL BUT DISSIPATED AHEAD OF A SHORT WAVE THAT IS FORECAST TO
MOVE INLAND OVERNIGHT. THE MAIN FORECAST CONCERN FOR TONIGHT WILL
BE HOW MUCH THE APPROACHING DISTURBANCE WILL AFFECT THE MARINE
LAYER. LATEST OBSERVATIONS SHOW THE MARINE LAYER CONTINUES TO
DEEPEN...HOWEVER THE QUESTION REMAINS HOW DEEP WILL THE MARINE
LAYER GET...OR WILL IT MIX OUT COMPLETELY AS THE SHORTWAVE TROUGH
MOVES ACROSS THE REGION? CURRENT THINKING IS THAT THERE WILL BE
FAR FEWER LOW CLOUDS TUESDAY MORNING THAN THERE WERE THIS MORNING
THEREFORE AN EVENING UPDATE WAS JUST ISSUED TO SCALE BACK ON THE
EXTENT OF THE LOW CLOUDS AND PATCHY FOG THROUGH THE OVERNIGHT AND
EARLY MORNING HOURS.

A QUICK LOOK AT THE GRADIENTS ACROSS THE REGION SHOWS A SIGNIFICANT
INCREASE IN THE NORTHERLY GRADIENT FROM ACV TO SFO WITH A ONLY A
SLIGHT CHANGE IN THE ONSHORE GRADIENT FROM SFO TO WMC. THIS CHANGE
HOWEVER HAS RESULTED IN STRONGER WINDS ACROSS THE REGION WITH PEAK
SUSTAINED WINDS AROUND 15 MPH WITH GUST TO AROUND 20 MPH IN MOST
LOCATIONS. A FEW LOCATIONS REPORTED SUSTAINED WINDS AROUND 25 MPH
WITH GUSTS TO OVER 30 MPH. THE INCREASE IN THE WINDS AND THE
DEEPENING OF THE MARINE LAYER DEFINITELY CONTRIBUTED TO THE COOLER
TEMPERATURES FELT ACROSS THE DISTRICT TODAY. MOST LOCATIONS
EXPERIENCED A FEW DEGREES OF COOLING BY THIS AFTERNOON WITH
COASTAL SITES ONLY REACHING IN TO THE LOWER 60S TO MID 70S WITH
MID 70S TO LOWER 80S INLAND. WARMEST INLAND AREAS REACHED INTO THE
MID 90S TO NEAR 100.

PREVIOUS DISCUSSION...FOR THE REST OF THE WEEK...500 MB HEIGHTS
WILL SLOWLY LOWER AS THE FLOW SWITCHES FROM ZONAL TO A LONGWAVE
TROF THAT WILL BE NEAR THE WEST COAST ON THURSDAY. THE FLOW AT THE
SURFACE WILL CONTINUE TO BE MODERATE FROM THE WEST WHILE THE
MARINE LAYER DEEPENS EVEN MORE. BY THURSDAY THE RANGE OF HIGHS
WILL BE MINIMAL -- JUST LOWER 60S AT THE COOLEST ON THE COAST TO
MID 70S FOR FAR INLAND SPOTS.

QUIET WEATHER IS EXPECTED INTO THE FIRST HALF OF NEXT WEEK AS THE
FLOW ALOFT REMAINS ZONAL WITH LITTLE DIFFERENCE IN 500 MB HEIGHTS
FROM DAY TO DAY. 6-10 DAY FORECAST CALLS FOR NEAR NORMAL TEMPERATURES
FOR MOST OF OUR AREA.

&&

.AVIATION...AS OF 10:20 PM PDT MONDAY...A STRONG ACV-SFO GRADIENT AND
MIXING FROM THE PASSAGE OF THE UPPER LEVEL TROUGH SHOULD MINIMIZE THE
AREAL COVERAGE OF STRATUS TONIGHT.

VICINITY OF KSFO...MVFR CIG POSSIBLE 07Z-14Z. VFR FORECAST TUESDAY.
WEST WIND GUSTS TO NEAR 30 KNOTS AFTER 21Z.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...PATCHY STRATUS WILL CONTINUE WITH TEMPO
CIGS POSSIBLE OVERNIGHT. VFR TUESDAY.

&&

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

&&

$$

PUBLIC FORECAST: CW
AVIATION/MARINE: CANEPA

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