000
FXUS66 KMTR 201638
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
938 AM PDT MON MAY 20 2013

...CONTINUED SUNNY AND WARM TODAY...
...MUCH COOLER WITH BREEZY ONSHORE WINDS TUESDAY...

.DISCUSSION...AS OF 9:37 AM PDT MONDAY...NO FORECAST UPDATES
PLANNED FOR THIS MORNING. SKIES ARE CLEAR ACROSS THE ENTIRE BAY
AREA THIS MORNING AND TEMPERATURES WILL QUICKLY WARM WITH 850 MB
TEMPS MEASURED AT 16 CELSIUS ON THE 12Z KOAK SOUNDING AND AS WARM
AS 20 CELSIUS AT 900 MB. THE NORTHERLY GRADIENT DOWN THE COAST IS
6 MB WITH THE LARGE SCALE OFFSHORE GRADIENT FROM THE GREAT BASIN
BACK TO THE COAST AROUND 7 MB WHILE THE LOCAL SFO-SAC IS AROUND 1
MB ONSHORE. 24 HOUR TRENDS ARE ALREADY RUNNING 3-8 DEGREES WARMER
THAN YESTERDAY AFTER NORTHERLY BOUNDARY LAYER WINDS IN THE HILLS
KEPT OVERNIGHT LOWS RELATIVELY MILD. EXPECT WARM TO HOT WEATHER
TODAY WITH 70S AT THE BEACHES...80S INTO THE BAY AND 90S FOR THE
INLAND VALLEYS.

UPPER LEVEL TROUGH OF INTEREST THAT WILL INDUCE COOLING TREND
BEGINNING TOMORROW SHOWS UP NICELY ON WATER VAPOR JUST APPROACHING
45N/130W. THIS COLD CORE LOW WILL QUICKLY DROP TOWARDS FAR
NORTHERN CALIFORNIA/OREGON BORDER BY EARLY TUESDAY MORNING. 850 MB
TEMPS WILL PLUMMET...DROPPING TO AROUND 5-6 CELSIUS ACROSS
NORTHERN SONOMA COUNTY BY TUESDAY AFTERNOON. GUSTY ONSHORE WINDS
WILL KEEP TEMPERATURES IN THE UPPER 50S AT THE BEACHES...60S
INSIDE THE BAY AND ONLY 70S FOR THE INLAND VALLEYS OF THE BAY
AREA. ONLY THE FAR SOUTHERN SALINAS VALLEY WILL HOLD ONTO HOT
WEATHER FOR TUESDAY AFTERNOON. IN ADDITION TO THE COOLING TREND
THE GUSTY ONSHORE WINDS WILL BE MOST NOTICEABLE ALONG THE COAST
AND INTO THE WIND PRONE COASTAL GAPS AS WELL AS PLACES LIKE KSFO.
MODEL GUIDANCE INDICATES THE PERIOD OF STRONGEST WINDS WILL BE
TUESDAY AFTERNOON AND EVENING WHEN GUSTS TO AROUND 40 MPH WILL BE
MOSTLY LIKELY FOR PLACES LIKE KSFO AND POINT REYES.

WINDS WILL GRADUALLY EASE INTO WEDS MORNING. HOWEVER THE MAIN
UPPER LOW WILL STAY OVER THE WEST COAST. THE COMBINATION OF
ONSHORE WINDS AND COOL TEMPS ALOFT SHOULD KEEP MARINE CLOUDS TO A
MINIMUM IF AT ALL. EXPECT SUNNY AND SEASONABLY PLEASANT WEATHER
WITH AFTERNOON HIGHS IN THE 60S ALONG THE COAST WITH 70S FOR MOST
INLAND LOCATIONS WHICH IS A FEW DEGREES BELOW NORMAL FOR THE
SECOND HALF OF MAY. ONLY THE WARMEST INTERIOR SPOTS SHOULD REACH
THE 80S DURING THE AFTERNOON HOURS LATER THIS WEEK.

NO BIG CHANGES FORECAST RIGHT INTO THE WEEKEND WITH NEAR OR
SLIGHTLY BELOW NORMAL TEMPERATURES AND CONTINUED DRY WEATHER.

&&

.AVIATION...AS OF 4:59 AM PDT MONDAY...THE ACV-SFO GRADIENT IS
MODERATELY STRONG AT 6 MB AND IS FORECAST TO HOLD BETWEEN 4-6 MB
THROUGH EARLY TUE MORNING. THE WMC-SFO GRADIENT HAS INCREASED TO 7
MB OVERNIGHT BUT IS FORECAST TO DIMINISH TO 1-3 MB BY THIS
AFTERNOON. THE UKI-STS GRADIENT IS STRONG AT 2.7 MB WITH LITTLE
CHANGE IN STRENGTH EXPECTED THROUGH TONIGHT.

MODERATE TO HIGH CONFIDENCE VFR PREVAILS THROUGH EARLY TUE MORNING.
N-NW WINDS OVER THE COASTAL WATERS TUESDAY WILL HELP DRIVE IN SOME
STRATUS PROBABLY RIGHT TO THE IMMEDIATE COASTLINE. LOW CONFIDENCE
AS TO WHETHER OR NOT STRATUS WILL BE USHERED INLAND THOUGH AM
LEANING TOWARD A YES VOTE ON THAT ONE MOSTLY DUE TO A STRONG 5 MB
SFO-SAC GRADIENT PREDICTED TUE AFTERNOON PER THE LATEST NAM MODEL.
APPRECIABLE LOW-MID LEVEL COOLING (~ 80 METERS COOLING AT 500 MB
HEIGHT LEVEL FROM 21Z TODAY TO 21Z TUESDAY) WILL LIKELY RAISE
MARINE LAYER INVERSIONS OPENING THE WINDOW FOR A STRATUS INTRUSION.

VICINITY OF KSFO...VFR. SFO-SAC GRADIENT SHOULD REMAIN RATHER SUBDUED
TODAY DUE TO LARGER SCALE OFFSHORE GRADIENT WMC-SFO AT 7 MB. THE WMC-SFO
GRADIENT GRADUALLY TRENDS WEAKER THIS AFTERNOON. BY 23Z WEST WINDS
SHOULD BE A LITTLE STRONGER BUT WIND GUSTS SHOULD HOLD JUST BELOW
20 KNOTS.

KSFO BRIDGE APPROACH...VFR.

MONTEREY BAY AREA TERMINALS...NOCTURNAL RADIATIONAL COOLING PROCESSES
ARE NARROWING TEMPERATURE-DEWPOINT DEPRESSIONS BUT SO FAR SKIES ARE
REMAINING CLEAR. THESE SITUATIONS CAN REALLY GO EITHER WAY I.E.
GOING EITHER BRIEF CLOUDS OR STEADY CLEAR SKIES THROUGH DAYBREAK.
DIFFICULT TO SAY BUT WILL LEAN TOWARD CLEAR SKIES HOLDING ITS OWN
THROUGH DAYBREAK.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...PT ARENA TO PIGEON PT 10-60 NM

&&

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: CANEPA

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