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000
FXUS66 KMTR 170403
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
903 PM PDT THU MAY 16 2013

.DISCUSSION...AS OF 9:00 PM PDT THURSDAY...THE WEATHER SYSTEM THAT
PRODUCED SCATTERED LIGHT PRECIPITATION ACROSS OUR REGION EARLY
TODAY HAS MOVED WELL OFF TO OUR EAST AND RAIN HAS LONG SINCE
ENDED. SKIES BECAME MOSTLY CLEAR BY LATE IN THE DAY BUT RECENT
SATELLITE IMAGERY REVEALS EXPANDING AREAS OF LOW CLOUDS NEAR THE
OCEAN AND AROUND SF BAY. WITH PLENTY OF LOW LEVEL MOISTURE IN
PLACE...AS WELL AS MODERATE ONSHORE FLOW...WOULD EXPECT LOW CLOUDS
TO BECOME MORE WIDESPREAD AS THE NIGHT PROGRESSES. FRIDAY WILL
START OUT WITH PLENTY OF LOW CLOUD COVER...BUT WITH NO STRONG
MARINE INVERSION IN PLACE AND MODERATE NORTHWESTERLY FLOW TO
PROVIDE MIXING...EXPECT MOST AREAS TO CLEAR BY MIDDAY. ONLY A FEW
LOCATIONS NEAR THE OCEAN MAY REMAIN UNDER LOW CLOUDS INTO THE
AFTERNOON HOURS. TEMPERATURES WILL BE SLIGHTLY BELOW NORMAL IN
MOST AREAS TOMORROW AS WE REMAIN IN COOL NORTHWESTERLY FLOW.

A WARMING TREND IS FORECAST FROM SATURDAY THROUGH MONDAY AS AN
UPPER RIDGE OVER THE EASTERN PACIFIC GRADUALLY BUILDS JUST
OFFSHORE ALONG 130W. TEMPERATURES ARE EXPECTED TO WARM TO LEVELS
THAT ARE AT LEAST A FEW DEGREES ABOVE NORMAL BY SUNDAY. A MARINE
LAYER WILL DEVELOP BY FRIDAY NIGHT AND GRADUALLY BECOME MORE
SHALLOW OVER THE WEEKEND. BY SUNDAY...EXPECT ONLY PATCHY LOW
CLOUDS AND FOG NEAR THE IMMEDIATE COAST.

A SHORTWAVE TROUGH DROPPING INTO THE NORTHERN GREAT BASIN ON
SUNDAY WILL RESULT IN INCREASING NORTHERLY WINDS IN THE HILLS FROM
LATE SUNDAY INTO SUNDAY NIGHT AS SURFACE HIGH PRESSURE BUILDS TO
OUR NORTH AND NORTHEAST. THE STRONGEST WINDS WILL BE IN THE NORTH
AND EAST BAY HILLS. THE 00Z NAM FORECASTS NORTHERLY WINDS UP TO 30
KNOTS AT THE 925 MB LEVEL ACROSS THE NORTH BAY BY LATE SUNDAY
EVENING. GUSTY NORTHERLY WINDS WILL CONTINUE THROUGH SUNDAY
NIGHT...AND THEN RAPIDLY DIMINISH DURING THE DAY ON MONDAY. THESE
DRY NORTH WINDS WILL RAISE FIRE WEATHER CONCERNS...BUT AT THE
PRESENT TIME IT LOOKS AS THOUGH THE OFFSHORE WIND EVENT FROM LATE
SUNDAY NIGHT THROUGH EARLY MONDAY WON`T BE STRONG ENOUGH...OR LAST
LONG ENOUGH...TO WARRANT RED FLAG WARNINGS.

THE INCREASED NORTHERLY FLOW BEGINNING LATE SUNDAY WILL QUICKLY
DRY OUT THE AIRMASS ACROSS OUR REGION AND CLEAR ANY REMAINING LOW
CLOUDS AND FOG FROM THE COAST. MONDAY SHOULD BE A SUNNY DAY IN ALL
AREAS WITH TEMPERATURES WARMING INTO THE 70S NEAR THE OCEAN...AND
80S AND LOWER 90S INLAND. WE MAY EVEN SEE A FEW MID TO UPPER 90S
ACROSS THE SOUTHERN INTERIOR PART OF OUR AREA WHERE 850 MB TEMPS
ARE FORECAST TO CLIMB TO NEAR 20 DEG C.

THE WARMING TREND WILL COME TO AN ABRUPT END ON TUESDAY AS A COLD
UPPER TROUGH APPROACHES FROM THE NORTHWEST. TUESDAY`S COOLING WILL
MOSTLY BE DUE TO INCREASING ONSHORE FLOW IN ADVANCE OF THE UPPER
TROUGH. BUT THEN A MUCH COOLER AIRMASS WILL SWEEP ACROSS OUR AREA
DURING THE SECOND HALF OF NEXT WEEK AND DROP TEMPERATURES WELL
BELOW NORMAL...ESPECIALLY FOR INLAND AREAS...BY WEDNESDAY AND
THURSDAY. NEARLY ALL PRECIP WITH THIS COOL SYSTEM IS FORECAST TO
REMAIN TO OUR NORTH DURING THE SECOND HALF OF NEXT WEEK.

&&

.AVIATION...AS OF 5:30 PM PDT THURSDAY...THE WEAK PACIFIC FRONTAL
SYSTEM THAT BROUGHT WIDESPREAD CLOUD COVERAGE AND A FEW LIGHT SHOWERS
EARLIER IN THE DAY HAS NOW PROGRESSED EASTWARD OF OUR DISTRICT. IT
HAS HOWEVER LEFT A RELATIVELY MOIST AIR MASS IN ITS WAKE...ESPECIALLY
IN THE BOUNDARY LAYER. MARINE STRATUS PRESENTLY LIES ALONG MUCH OF
THE COAST SOUTH OF THE GOLDEN GATE AND HAS ALREADY BEGUN EXTENDING
INLAND AROUND MONTEREY BAY. THE ONSHORE PRESSURE GRADIENT IS
MODERATELY STRONG...4 MB BETWEEN KSFO AND KSAC AT 00Z. LATEST
MODEL OUTPUT AND STATISTICAL GUIDANCE CONTINUE TO INDICATE STRATUS
WILL EXPAND AND EXTEND WELL INLAND TONIGHT...WITH CIGS EXPECTED
TO DEVELOP AT ALL TERMINALS EXCEPT PERHAPS KSTS DURING THE EVENING
HOURS. CONFIDENCE IS LOWER HOWEVER WITH RESPECT TO DETAILS OF
TIMING AND CIG HEIGHT CATEGORY AS HERE SOLUTIONS VARY MORE WIDELY.

VICINITY OF KSFO...CURRENT FORECAST HOLDS OFF CIG DEVELOPMENT UNTIL
LATE EVENING BUT CONFIDENCE IN TIMING ISN`T HIGH AND BELIEVE
THERE IS SOME RISK OF EARLIER ONSET. LATEST SATELLITE AND WEBCAM
IMAGERY SHOWS SOME LOW CLOUDINESS OVER THE BAY TO THE EAST OF THE
TERMINAL...BUT ALSO HINT AT IT BEING ORGANIZED IN THE FORM OF GRAVITY
WAVE ROLLS...AND IF SO SHOULD DIMINISH DURING THE EVENING AS THE
GENERATING ONSHORE FLOW OVER THE SAN MATEO PENINSULA HILLS
WEAKENS. PRESENT WEST WINDS OF A BIT OVER 20 KT AT THE TERMINAL
WILL GRADUALLY DIMINISH OVER THE NEXT SEVERAL HOURS.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...MVFR CIG HAS ALREADY DEVELOPED AT
KSNS AND IS EXPECTED TO DEVELOP AT KMRY WITHIN THE NEXT HOUR OR SO.
CIG AT KMRY EXPECTED TO LOWER TO IFR BY LATER THIS EVENING AND
POSSIBLY ALSO AT KSNS.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             SCA...SF BAY UNTIL 8 PM

&&

$$

PUBLIC FORECAST: DYKEMA
AVIATION/MARINE: BLIER/MM

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