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

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KMTR 212150
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
250 PM PDT SUN SEP 21 2014

.SYNOPSIS...LITTLE CHANGE IN THE WEATHER IS FORECAST OVER THE NEXT
FEW DAYS. LOOK FOR A CONTINUED FAIRLY DEEP MARINE LAYER RESULTING
IN WIDESPREAD NIGHT AND MORNING LOW CLOUDS. A PACIFIC STORM SYSTEM
WILL BRING RAIN TO OUR AREA FOR WEDNESDAY INTO THURSDAY WITH MOST
OF IT FOCUSED ON THE LOCATIONS NORTH OF SAN FRANCISCO. SHOWERS ARE
POSSIBLE FROM THURSDAY AFTERNOON INTO FRIDAY EVENING.

&&

.DISCUSSION...AS OF 3:00 PM PDT SUNDAY...ANOTHER ROUND OF SUNNY
SKIES INLAND WITH WIDESPREAD CLOUDS ALONG THE COAST. IN FACT, MANY
COASTAL SPOTS HAVE STAYED CLOUDY ALL DAY. EVEN A GOOD PORTION OF
SAN FRANCISCO HAVE NOT HAD ANY BREAKS FROM THE CLOUDS. MARINE
LAYER STANDS OVER 2000 FEET WITH THE ONSHORE GRADIENT AROUND 2.5
MB FROM THE WEST. THIS WILL HELP TO BRING CLOUDS QUICKLY BACK INTO
OUR CWA OVERNIGHT.

QUIET WEATHER CAN BE EXPECTED FOR MONDAY AND TUESDAY AS A LONGWAVE
TROF SLOWLY ADVANCES FROM THE PACIFIC WHILE THE RIDGE CONTINUES TO
PROGRESS TO THE EAST. SURFACE FLOW SHOULD REMAIN GENERALLY
WESTERLY ALONG WITH THE MARINE LAYER STICKING CLOSE TO 2,000 FEET.
HIGHS WILL VARY LITTLE EACH DAY FROM TODAY`S READINGS. GENERALLY
MID 60S TO MID 70S AT THE COAST WITH MID 70S TO MID 80S INLAND.

THINGS GET MORE INTERESTING FOR WEDNESDAY AND THURSDAY AS A
PACIFIC STORM SYSTEM AND ASSOCIATED COLD FRONT MOVE INTO THE PACNW
DOWN TO OUR REGION. MODEL GUIDANCE REMAINS FAIRLY CONSISTENT WITH
THE TIMING AND BRINGS THE LEADING EDGE OF RAIN INTO THE NORTH BAY
BY WEDNESDAY AFTERNOON AND THEN INTO SF BAY REGION TO AROUND SANTA
CRUZ WEDNESDAY NIGHT INTO EARLY THURSDAY. ONE ENCOURAGING SIGN IS
MODEL TRENDS HAVE BEEN A BIT WETTER COMPARED TO SOLUTIONS FROM THE
PAST FEW DAYS, SO POPS WERE INCREASED FOR ALMOST ALL SPOTS NORTH
OF MONTEREY COUNTY. SOME INSTABILITY IS ALSO NOTED WEDNESDAY NIGHT
INTO THURSDAY, SO AT THIS TIME THUNDER CANNOT BE RULED OUT. THE
GOOD NEWS IS ANY STORMS THAT PRODUCE LIGHTNING SHOULD BE WET WHICH
WILL HELP TO LESSEN THE FIRE WEATHER RISK. THUNDER WAS LEFT OUT OF
THE GRIDS FOR NOW, HOWEVER ONCE THE HIGHER RESOLUTION RUNS COME IN,
IT MAY BE ADDED IN. STILL A LITTLE EARLY TO COME UP WITH SPECIFICS
FOR RAINFALL AMOUNTS, HOWEVER BASED OFF BOTH THE OPERATIONAL RUNS
PLUS THE ENSEMBLES, LOOKS LIKE PARTS OF THE NORTH BAY COULD EASILY
PICK UP MORE THAN 1/2" OF RAIN. FOR URBAN SPOTS AROUND THE BAY
RIGHT NOW CLOSER TO 1/10"-1/4" LOOKS MORE LIKELY. FOR SANTA CRUZ
COUNTY SOUTHWARD GENERALLY LESS THAN 1/10" CAN BE EXPECTED
ALTHOUGH A STRAY SHOWER OR TWO COULD BRING LOCALLY HIGHER AMOUNTS
IN THE SANTA CRUZ MOUNTAINS. TO GIVE YOU AN IDEA HOW MUCH RAIN WE
WOULD NEED TO CATCH UP TO NORMAL, SAN FRANCISCO IS NEARLY 22"
BEHIND WHERE IT SHOULD BE LOOKING BACK TO THE START OF 2013!

ALTHOUGH RAIN CHANCES WILL BE ON THE DECREASE FOR THE SECOND HALF
OF THURSDAY, A 120 KT JET STREAM IS FORECAST TO BE OVERHEAD WHILE
THE LONGWAVE TROF AXIS IS STILL TO OUR WEST. DUE TO THAT KEPT
SHOWERS GOING A BIT LONGER THAN QPF IS SUGGESTING IN CASE WE GET
SOME POST FRONTAL ACTIVITY INTO THURSDAY NIGHT AND MAYBE EVEN
FRIDAY. SIMILAR TO WEDNESDAY NIGHT INTO THURSDAY, THE BEST CHANCE
FOR RAINFALL WILL BE FOR THE NORTHERN THIRD OF THE CWA.

FOR THE WEEKEND INTO NEXT WEEK, THERE IS LESS AGREEMENT BETWEEN
THE MODELS WITH THE PROGRESSIVE NATURE OF THE TROF. SOME OF THEM
HAVE THE TROF ADVANCING TO THE EAST OVER THE WEEKEND WITH A RIDGE
OF HIGH PRESSURE BUILDING IN WHILE OTHERS HAVE AN ASSOCIATED UPPER
LEVEL LOW BECOMING NEARLY STATIONARY NEAR OUR CWA. IN THE CASE OF
THE SECOND SCENARIO, MOISTURE WOULD WRAP AROUND THE LOW AND
POSSIBLY MOVE BACK INTO OUR CWA BY SUNDAY. DUE TO THE LARGE
DISAGREEMENT, FOR NOW WILL KEEP A GENERALLY DRY WEEKEND/EARLY NEXT
WEEK FORECAST GOING WITH SEASONABLE TEMPS.

&&

.AVIATION...AS OF 9:57 AM PDT SUNDAY...THE STRATUS CLOUD COVERAGE
IS NEARLY IDENTICAL TO YESTERDAY MORNING BUT THE MARINE LAYER IS
SOMEWHAT DEEPER THIS MORNING. THE 12Z OAK SOUNDING SHOWS PRECIP
WATER VALUE UP TO 1.33" A POSITIVE CHANGE FROM LAST EVE AND
YESTERDAY MORNING WITH A HIGHER DISTRIBUTION OF HUMIDITY FROM THE
SURFACE TO LOW LEVELS AND THEN AGAIN IN THE MIDDLE LEVELS OF THE
ATMOSPHERE. ALL IN ALL THIS SUGGESTS THE STRATUS CLOUDS MAY TAKE A
LITTLE LONGER TO MIX OUT TODAY. FORECAST IS MOSTLY HINGING ON THE
ONSHORE (SFO-SAC) GRADIENT...PRESENTLY 2-3 MB...AND IS FORECAST
TO BE APPROX THE SAME THIS AFTERNOON AND AGAIN MONDAY AFTERNOON.
OVERALL THINK THE OCEAN BASED STRATUS CLOUD PATTERN WILL PERSIST
OVER THE NEXT 24-36 HOURS WITH THE USUAL LATE NIGHT/EARLY MORNING
INLAND STRATUS COVERAGE. THERE COULD BE A FEW PATCHES OF MOSTLY
NON-MEASURABLE VERY LIGHT DRIZZLE.

VICINITY OF KSFO...SLIGHTLY LONGER MVFR CIGS ARE FORECAST TODAY PER
COORD WITH THE NWS/CWSU OAKLAND OFFICE. AS OF THIS WRITING STRATUS
CLOUDS ARE BEGINNING TO SCATTER OUT SW OF MOFFETT FIELD OTHERWISE STILL
FAIRLY EXTENSIVE OVER THE BAY AREA. SCT015 VFR CONDITIONS ARE FORECAST
BY 1930Z.

KSFO BRIDGE APPROACH...STRATUS CLOUDS COULD LINGER UP TO 45 MIN
LONGER IN THE APPROACH.

MONTEREY BAY AREA TERMINALS...EXTENSIVE STRATUS CLOUD COVERAGE
NORTH CENTRAL COAST THIS MORNING. CLOUDS SHOULD MIX OUT BETWEEN
19Z-20Z.

&&

.MARINE...AS OF 9:57 AM PDT SUNDAY...LIGHT WINDS AND SEAS WILL
CONTINUE OVER THE COASTAL WATERS THROUGH EARLY TO MID WEEK. FOR
THE MID TO LATE WEEK TIME FRAME MODERATE TO LARGE NORTHWEST SWELL
WILL ENTER THE WATERS.

&&

.CLIMATE...AUTUMN OFFICIALLY BEGINS (AUTUMNAL EQUINOX) AT 7:29 PM
PDT ON MONDAY SEPTEMBER 22.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...SF BAY NORTH OF THE BAY BRIDGE UNTIL 9 PM

&&

$$

PUBLIC FORECAST: BELL
AVIATION/MARINE: CANEPA

VISIT US AT WEATHER.GOV/SANFRANCISCO

FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSBAYAREA
WWW.TWITTER.COM/NWSBAYAREA
WWW.YOUTUBE.COM/NWSBAYAREA





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.