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

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000
FXUS66 KMTR 231617
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
917 AM PDT TUE SEP 23 2014

.SYNOPSIS...NEAR SEASONAL CONDITIONS WILL CONTINUE ACROSS THE SAN
FRANCISCO AND MONTEREY BAY AREA TODAY. COOLER WEATHER AND CHANCES FOR
RAINFALL ARE THEN EXPECTED STARTING WEDNESDAY AS AN UPPER LEVEL SYSTEM
IMPACTS THE REGION.

&&

.DISCUSSION...AS OF 09:15 AM PDT TUESDAY...COASTAL CLOUDS THIS
MORNING HAVE BEEN LESS WIDESPREAD...MAINLY DUE TO A MORE
COMPRESSED AND WEAKER MARINE LAYER IN PLACE. AS A RESULT...MOSTLY
SUNNY CONDITIONS WILL BE THE NORM THROUGH THE AFTERNOON HOURS WITH
TEMPERATURES ONCE AGAIN WARMING TO NEAR OR SLIGHTLY ABOVE AVERAGE.
HAVE MADE A FEW ADJUSTMENTS TO THE FORECAST TO REFLECT CURRENT
TEMPERATURE TRENDS AND SKY COVER BASED OFF LATEST VISIBLE
SATELLITE IMAGERY. OTHERWISE...THE ONGOING FORECAST LOOKS ON
TRACK.

WILL BE WORKING ON UPDATING THE FORECAST FOR THIS AFTERNOON BASED
OFF THE LATEST 12Z FORECAST MODEL OUTPUTS. AT FIRST GLANCE...THE
BEST CHANCE FOR MEASURABLE PRECIPITATION WILL BE ACROSS THE
NORTHER PART OF THE SAN FRANCISCO BAY AREA. LESSER AMOUNTS ARE
EXPECTED INLAND AND FURTHER SOUTH DOWN INTO THE SANTA CRUZ
MOUNTAINS. MEANWHILE...MOST OF MONTEREY AND SAN BENITO COUNTIES
MAY ONLY RECEIVE A TRACE TO A FEW HUNDREDTHS OF AN INCH IF ANY AT
ALL.

&&

.PREV DISCUSSION...AS OF 3:00 AM PDT TUESDAY...SATELLITE SHOWS
FEWER CLOUDS EARLY THIS MORNING COMPARED TO PREVIOUS MORNINGS WITH
MUCH OF OUR CWA SEEING CLEAR SKIES. SURFACE FOR LOW STILL FROM THE
NW AND WITH SOME CLOUDS OVER OUR NW OUTER WATERS WILL NEED TO SEE
IF THEY ARE ABLE TO ADVANCE TO THE COAST OR NOT. TEMPERATURES ARE
RUNNING WITHIN A FEW DEGREES OF YESTERDAY, AND HIGHS ARE EXPECTED
TO BE CLOSE TO MONDAY -- MID 60S TO MID 70S AT THE COAST WITH MID
70S TO MID 80S INLAND.

ALL ATTENTION CONTINUES TO BE FOCUSED ON A STORM SYSTEM AROUND
45N/140W (OR 1100 MILES NW OF SAN FRANCISCO) THAT WILL ADVANCE TO
FIRST TO EH PACNW COAST LATE TODAY AND THEN DOWN TO NORCAL/SF BAY
REGION FOR WEDNESDAY INTO THURSDAY. RAIN WILL ADVANCE DOWN THE
COAST AS AN ASSOCIATED COLD FRONT APPROACHES. TIMING CONTINUES TO
SUGGEST ON WEDNESDAY AFTERNOON/EVENING FOR THE FAR NW PORTION OF
THE NORTH BAY...INTO THE SF BAY REGION WEDNESDAY NIGHT...AND DOWN
TO MONTEREY BAY AREA ON THURSDAY. THE VAST MAJORITY OF THE
MOISTURE WILL BE FOCUSED TO THE NORTH OF OUR AREA WITH SMALLER
AMOUNTS FORECAST AS YOU PROGRESS TO THE SOUTH. RAINFALL TOTALS BY
THURSDAY EVENING STILL LOOK LIKE LOCALLY MORE THAN 1/2" OVER THE
NORTH BAY WITH GENERALLY 1/10" TO 1/4" AROUND SF BAY PLUS THE
SANTA CRUZ MOUNTAINS. OTHER SPORTS WILL LIKELY PICK UP EVEN LESS
WITH INTERIOR MONTEREY COUNTY AND SAN BENITO COUNTIES EXPECTING
VERY LITTLE RAINFALL.

MODELS HAVE BACKED OFF A BIT FROM THE CONVECTIVE PARAMETERS AND
AGREE WITH THE PREVIOUS SHIFT THAT REMOVING THEM FROM THE
FORECAST FOR LATE WEDNESDAY INTO THURSDAY WAS THE RIGHT CALL.

BEHIND THE FRONTAL PASSAGE THE LONGWAVE TROF AND MAIN UPPER LEVEL
LOW WILL MOVE OVERHEAD ON FRIDAY. THIS WILL LEAD TO SCATTERED
SHOWERS ACROSS AT LEAST THE NORTHERN HALF OF OUR AREA. SYNOPTIC
SETUP WOULD ALSO SUGGEST THE POSSIBILITY OF THUNDER SO WILL NEED
TO SEE WHAT THE HIGHER RESOLUTION MODELS SAY AS IT GETS A LITTLE
CLOSER. ADDITIONAL RAINFALL AMOUNTS FOR FRIDAY SHOULD BE UNDER
1/10" IN ALMOST ALL SPOTS. THE LOW IS EXPECTED TO SLOWLY DEPART
TO THE EAST LATE ON SATURDAY.

FOR NEXT WEEK...THE STORM TRACK IS FORECAST TO SHIFT BACK WELL TO
THE NORTH AS A RIDGE BUILDS NEAR THE WEST COAST. TEMPERATURES
WILL AVERAGE OUT A BIT ABOVE NORMAL.

&&

.AVIATION...AS OF 4:35 AM PDT TUESDAY...LATE DEVELOPING STRATUS
ACROSS MUCH OF THE REGION THIS MORNING. CIGS ARE GENERALLY
1000-1500 FEET...BUT THE MARINE LAYER IS PATCHY IN NATURE.
THEREFORE...EXPECTING A RELATIVELY EARLY BURN OFF. EXPECTING VFR
THIS AFTERNOON WITH SOME CIGS RETURNING LATE TONIGHT. CONF IS
MEDIUM.

VICINITY OF KSFO...MVFR CIGS ACROSS THE EAST BAY AND OVER KSFO.
EXPECTING EARLY BURN OFF AND WILL CURRENTLY FORECAST 17Z...BUT IT
COULD BE EARLIER. VFR THIS AFTERNOON WITH GUSTY WEST WINDS.

KSFO BRIDGE APPROACH...AT THIS TIME...THE APPROACH IS MOSTLY
CLEAR...BUT CIGS ARE ON THE FRINGES. PATCHY CIGS WILL LIKELY
IMPACT THE APPROACH...BUT IT MAY NOT BE CONSTANT.

MONTEREY BAY AREA TERMINALS...IFR CIGS THROUGH 17-18Z. VFR THIS
AFTERNOON.

&&

.MARINE...AS OF 09:15 AM PDT TUESDAY...LIGHT TO MODERATE NORTHWEST
FLOW WILL CONTINUE ALONG THE CENTRAL COAST AS HIGH PRESSURE
REMAINS OVER THE EASTERN PACIFIC. A COLD FRONT WILL MOVE THROUGH
THE REGION WEDNESDAY BRINGING A CHANCE FOR RAIN AND INCREASING
NORTHWESTERLY SWELL.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...NONE.

$$

PUBLIC FORECAST: RGASS
AVIATION: MM
MARINE: AC

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