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

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000
FXUS66 KMTR 211601
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
901 AM PDT MON APR 21 2014

.SYNOPSIS...DAYTIME TEMPERATURES WILL BE SLIGHTLY COOLER TODAY
WITH AN INCREASE IN MID TO HIGH LEVEL CLOUDS IN ADVANCE OF AN
APPROACHING FRONTAL BOUNDARY. LIGHT SHOWERS WILL BE POSSIBLE TONIGHT
THROUGH EARLY TUESDAY MORNING AS THE WEAK FRONT MOVES ACROSS THE
REGION. DRY WEATHER AND NEAR NORMAL TEMPERATURES RETURN WEDNESDAY
BEFORE RAIN CHANCES RE-ENTER THE PICTURE BY FRIDAY.

&&

.DISCUSSION...AS OF 9:01 AM PDT MONDAY...WEAK FRONTAL BAND IS
APPROACHING NORTHERN CALIFORNIA THIS MORNING WITH MAINLY MID AND
HIGH CLOUDS OVER THE NORTH BAY. RADAR IS SHOWING SOME ELEVATED
RETURNS WITH MOISTURE IN THE HIGH CLOUDS BUT THERE IS A DEEP AND
DRY SUB-CLOUD LAYER SO NOT EXPECTING ANY PRECIP TODAY THROUGH
EARLY THIS EVENING. BAND OF ORGANIZED CLOUDS ABOUT 200 MILES
OFFSHORE IS ASSOCIATED WITH THE SURFACE BOUNDARY WITH SOME COLD
AIR CUMULUS NOTED ON SATELLITE OUT BEYOND 130W. ITS THIS AREA OF
CLOUDS THAT WILL LIKELY GENERATE SOME LIGHT SHOWERS OVERNIGHT
INTO EARLY TUESDAY. BEST CHANCES WILL BE OVER THE NORTH BAY AND
ALONG THE COAST BUT QPF NUMBERS REMAIN VERY LIGHT. OFFICIAL RFC
DATA SUGGESTS ONLY A HUNDREDTH OR TWO WITH PERHAPS UP TO A TENTH
IN THE NORTH BAY HILLS. NAM MODEL SUGGESTS THE BEST CHANCE OF
SHOWERS WILL BE DURING THE OVERNIGHT AND PRE-DAWN HOURS WITH ANY
SHOWERS ENDING BY ABOUT 15Z TUESDAY WITH MINIMAL IMPACT FOR THE
MORNING COMMUTE.

DRYING TREND FOR THE DAY TUESDAY WITH STRONG SUBSIDENCE ALOFT
LEADING TO PARTLY CLOUDY SKIES IN GENERAL. STRONG NORTHWEST WINDS
WILL PERSIST ALONG THE COAST AND IN THE HILLS WITH A WELL MIXED
ATMOSPHERE AND COOLER AIR ALOFT CREATING RELATIVELY STEEP LAPSE
RATES CONDUCIVE TO GOOD MIXING. UPSHOT IS FOR COOL AND BREEZY
WEATHER NEAR THE COAST AND BAYS.

HIGH PRESSURE REBUILDS TUESDAY NIGHT THROUGH THURSDAY WITH
SEASONABLE WEATHER AND MOSTLY CLEAR SKIES. SOME FAIRLY COLD
OVERNIGHT LOWS WILL BE POSSIBLE WEDS MORNING WITH UPPER 30S IN THE
NORTH BAY VALLEYS AND WIDESPREAD LOWER TO MID 40S DUE TO LIGHT
WINDS AND LOW DEWPOINTS BY SUNRISE WEDS.

MAIN FORECAST FOCUS WILL DEAL WITH RAIN CHANCES ON FRIDAY. THE
GEM AND GFS MODELS REMAIN BULLISH IN DROPPING A COLD AND WET
TROUGH INTO NORTHERN CALIFORNIA AND THE BAY AREA BY 12Z FRIDAY.
THE ECMWF HAS THE TROUGH AS WELL BUT NOT NEARLY AS WET WITH A
SLIGHTLY MORE NORTHWARD TRAJECTORY AND LESS OVER-WATER. WILL AWAIT
ALL OF THE 12Z GUIDANCE BEFORE ADJUSTING THE EXTENDED FORECAST
FOR THE AFTERNOON PACKAGES.

&&

.AVIATION...AS OF 4:45 AM PDT MONDAY...VFR. SKIES ARE CLEAR EXCEPT
FOR SOME HIGH CLOUDS DRIFTING IN FROM THE WEST. CLOUDINESS INCREASES
LATE TODAY INTO TUESDAY. SHOWERS POSSIBLE NORTH BAY LATE TONIGHT.

VICINITY OF KSFO...VFR.

KSFO BRIDGE APPROACH...VFR.

MONTEREY BAY AREA TERMINALS...VFR TODAY. LOW CLOUDS ARE POSSIBLE BY
THE EVENING.

&&

.MARINE...AS OF 4:45 AM PDT MONDAY...NORTHWEST SWELL ARE DECREASING
THIS MORNING AND ARE EXPECTED TO SLOWLY SUBSIDE THROUGH THE DAY.
SWELL PERIODS WILL ALSO BE DECREASING SLOWLY TO 13 SECONDS BY THIS
AFTERNOON.

A ROUGH BAR ADVISORY DOES CONTINUE THROUGH TONIGHT. ON TUESDAY NW
WINDS WILL INCREASE TO SMALL CRAFT CRITERIA FOR THE COASTAL WATERS.
NW WINDS OVER THE BAY WATERS WILL NOT BE AS GUSTY.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...ROUGH BAR ADVISORY FOR SF BAR

&&

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: CANEPA

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