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363
FXUS66 KMTR 241752
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1052 AM PDT FRI OCT 24 2014

.SYNOPSIS...MOSTLY SUNNY CONDITIONS ARE EXPECTED TODAY...ASIDE
FROM SOME MORNING FOG AND LOW CLOUDINESS NEAR THE COAST AND IN THE
NORTH BAY VALLEYS. HOWEVER...INCREASING RAIN CHANCES WILL THEN
RAPIDLY SPREAD IN FROM THE NORTHWEST LATER TONIGHT AND SATURDAY
MORNING AS A STRONGER AND WETTER PACIFIC WEATHER SYSTEM MOVES
INTO NORTHERN AND CENTRAL CALIFORNIA. RESIDUAL SHOWERS ARE
EXPECTED TO TAPER OFF SATURDAY EVENING...WITH DRY WEATHER RETURNING
DISTRICTWIDE SUNDAY AND CONTINUING INTO AT LEAST THE FIRST HALF OF
NEXT WEEK.

&&

.DISCUSSION...AS OF 9:06 AM PDT FRIDAY...STRATUS AND PATCHY FOG
EXTENDS ALONG THE COAST FROM SAN MATEO COUNTY SOUTHWARD. PATCHY
DENSE FOG ALSO EVIDENT IN NORTH BAY VALLEYS AND PARTS OF THE SOUTH
BAY. WITH THE SHORTER DAYS FOG AND CLOUDS WILL BE SLOW TO CLEAR
THIS MORNING AND SHOULD PERSIST ALONG THE COAST ALL DAY. OTHERWISE
MOST AREAS WILL BY MOSTLY SUNNY TODAY. WOULD EXPECT STRATUS TO
SPREAD INLAND THIS EVENING AND MIX OUT QUICKLY WITH THE APPROACH
OF THE COLD FRONT AND INCREASING SOUTH WINDS.

DETAILS ARE STARTING TO EMERGE FROM THE LATEST NAM RUN REGARDING
TIMING OF RAINFALL AND CONVECTIVE POTENTIAL. GFS NOT AS ROBUST AS
NAM WITH CONVECTION BEHIND FRONTAL BOUNDARY SATURDAY
AFTERNOON...BUT IMPRESSIVE CAPE FROM NAM RAISES POTENTIAL FOR
THUNDERSTORMS EVEN INTO BAY AREA AND SANTA CRUZ MOUNTAINS BY
SATURDAY AFTERNOON. EXTENDED SLIGHT CHANCE OF THUNDERSTORMS
FURTHER SOUTH IN THE GRID FORECASTS FOR SATURDAY AFTERNOON.

WILL ALSO EVALUATE POTENTIAL FOR WIND ADVISORY ALONG THE COAST AND
IN THE MOUNTAINS FROM SANTA CRUZ MOUNTAINS AND SAN MATEO COAST
NORTHWARD LATE TONIGHT AND AT LEAST INTO SATURDAY MORNING. WINDS
COULD BE GUSTY ENOUGH TO KNOCK DOWN SOME LARGER TREE LIMBS GIVEN
THE WEAKENED STATE OF TREES WITH THE DROUGHT.

EXPECTING WINDS TO INCREASE RAPIDLY AFTER MIDNIGHT WITH A QUICK
MOVING FRONTAL BAND AND MOSTLY LIGHT RAIN LATE TONIGHT AND EARLY
SATURDAY SPREADING SOUTHEAST ACROSS THE AREA. COLD POCKET
ASSOCIATED WITH OFFSHORE TROF MOVES THROUGH THE AREA SATURDAY
AFTERNOON AND SHOULD TRIGGER PLENTY OF SHOWERS AND POSSIBLE
THUNDERSTORMS ESPECIALLY NORTH BAY DOWN TO BAY AREA.

&&

.PREV DISCUSSION...ASIDE FROM THE AFOREMENTIONED MORNING LOW
CLOUDINESS AND FOG...MOSTLY SUNNY CONDITIONS ARE EXPECTED TODAY
WITH AFTERNOON HIGHS AROUND THE BAYS GENERALLY IN THE LOWER 70S.

TONIGHT AND SATURDAY...RAIN CHANCES WILL RAPIDLY DEVELOP FROM THE
NORTHWEST DURING THE OVERNIGHT HOURS AS A COLD FRONTAL RAIN BAND
AHEAD OF THE NEXT AND STRONGER PACIFIC LOW PRESSURE SYSTEM APPROACHES.
GENERAL TREND OF RECENT MODEL RUNS HAS BEEN TO SPEED THINGS UP A
BIT. CONSENSUS TIMING OF LATEST OUTPUT FROM THE NAM...GFS AND
ECMWF DETERMINISTIC SOLUTIONS HAS RAIN BEGINNING IN SANTA ROSA
AROUND A COUPLE OF HOURS BEFORE SUNRISE ON SATURDAY...SAN
FRANCISCO DURING THE FIRST PART OF THE MONTEREY...AND WITH A GOOD
CHANCE SOUTH TO NEAR MONTEREY BY MID-TO-LATE MORNING. AND THEN
AFTER A SHORT BREAK...ANOTHER ROUND OF PRECIP...THIS TIME MORE
SHOWERY IN NATURE...IS LIKELY AS THE COOL UPPER LEVEL TROUGH AXIS
QUICKLY FOLLOWS THROUGH. RAINFALL AMOUNTS THROUGH SATURDAY EVENING
COULD POTENTIALLY BE AS MUCH AS 0.75 TO 1.0 INCHES IN WETTEST SPOTS OF
THE COASTAL NORTH BAY HILLS...BUT OTHERWISE GENERALLY 0.25 INCHES
OR LESS ASIDE PERHAPS FROM A BIT MORE AT SOME LOCATIONS IN THE
SANTA CRUZ MTNS. AND SHOULD NOTE THAT SOME PORTIONS OF INTERIOR
MONTEREY AND SAN BENITO COUNTIES MAY WELL NOT RECEIVE ANY RAIN AT
ALL.

AS THIS WILL BE THE FIRST SIGNIFICANT PRECIP EVENT IN SOME
TIME ACROSS MUCH OF THE AREA...ROADWAYS WILL BECOME ESPECIALLY
SLICK AS ACCUMULATED SURFACE OILS MIX IN ESPECIALLY DURING THE
FIRST HOUR OR SO OF PRECIP. ALSO...HAVE INCLUDED MENTION OF A
SLIGHT CHANCE OF THUNDERSTORMS OVER THE NORTH BAY ON
SATURDAY...GIVEN SUBSTANTIAL SURFACE-BASED CAPE VALUES EVIDENT IN
MODEL OUTPUT SOUNDINGS...ESPECIALLY THOSE FROM THE NAM. 500 MB
TEMPS REALLY DON`T GET ALL THAT COLD...ONLY DOWN INTO THE -18C TO
TO -20C RANGE EVEN WITH THE UPPER LEVEL TROUGH PASSAGE. BUT
SURFACE TEMPS AND ESPECIALLY DEW POINTS ARE PROJECTED TO BE HIGH
ENOUGH TO COUNTERBALANCE THAT...THE LATTER IN PARTICULAR
REFLECTING THE UNUSUALLY WARM SEA SURFACE TEMPS THAT CONTINUE IN
OUR COASTAL WATERS. THERE MAY BE A FEW RESIDUAL SHOWERS SATURDAY
EVENING...BUT DRY CONDITIONS ARE PROJECTED TO RETURN DISTRICTWIDE
BY THE LATE NIGHT HOURS.

SUNDAY THROUGH WEDNESDAY...DRY CONDITIONS ARE EXPECTED DISTRICTWIDE
ASIDE FROM JUST A SLIGHT CHANCE OF SOME LIGHT PRECIP IN THE NORTH
BAY AS MIDWEEK APPROACHES AND LONGER RANGE MODEL SOLUTIONS THEN
BEGIN TO DIVERGE A BIT AS TO WHETHER THE PRECIP BAND STARTS TO
SAG BACK DOWN TOWARDS OUR NORTHERN BOUNDARY.

IN THE EVEN LONGER TERM...HAVE NOTED THAT THE ECMWF IN PARTICULAR
HAS REMAINED CONSISTENT OVER ITS LAST SEVERAL RUNS IN PROJECTING
ANOTHER ROUND OF WET WEATHER FOR OUR AREA AROUND NEXT WEEKEND.

&&

.AVIATION...AS OF 10:52 AM PDT FRIDAY...FOR 18Z TAFS. NO CONCERNS
FOR THIS AFTERNOON WITH MAINLY CLEAR SKIES AND SOME LIGHT
SOUTHERLY WINDS DEVELOPING BUT THEY SHOULD TREND SOUTHWEST THIS
AFTERNOON. FAIRLY IMPRESSIVE LOW WILL DEEPEN OFF THE COAST LATER
THIS AFTERNOON AND EVENING WITH INCREASING SOUTHEAST FLOW
DEVELOPING LATER THIS EVENING AND OVERNIGHT. PRETTY HIGH
CONFIDENCE FOR STRONG SOUTHEAST WINDS AND WET RUNWAYS FOR SATURDAY
MORNING. T-STORMS EVEN POSSIBLE SATURDAY AFTERNOON BUT WONT SHOW
THAT IN TAF AT THIS TIME.

VICINITY OF KSFO...VFR SKIES THIS AFTERNOON AND EVENING. LIGHT
SOUTHEAST WINDS THROUGH EARLY AFTERNOON SHOULD TREND SOUTHWEST AND
NOT IMPACT OPERATIONS. INCREASING SOUTHEAST WINDS OVERNIGHT WILL
LIKELY CAUSE ISSUES FOR SATURDAY MORNING PLANNING.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...CLEAR FOR KSNS THIS AFTERNOON WITH
CLOUD BANK CURRENTLY HOVERING OVER KMRY. EXPECT PARTIAL CLEARING
AT THE COAST. SOUTHERLY WINDS SHOULD DEVELOP OVERNIGHT WITH SOME
-SHRA BY AROUND 12-15Z SATURDAY.

&&

.MARINE...AS OF 10:52 AM PDT FRIDAY...HIGH PRESSURE OFF THE
SOUTHERN CALIFORNIA COAST WILL WEAKEN AS A DEEPENING LOW PRESSURE
SYSTEM APPROACHES FROM THE WEST.  THE LOW WILL LIFT NORTHEAST ON
SATURDAY MOVING INLAND OVER THE PACIFIC NORTHWEST SATURDAY NIGHT.
SOUTH WINDS WILL INCREASE TODAY THROUGH SATURDAY THEN SWITCH TO
NORTHWEST SATURDAY NIGHT AND SUNDAY. THE LOW WILL BRING A SLIGHT
CHANCE OF THUNDERSTORMS TO THE NORTHERN WATERS SATURDAY.

&&

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

&&

$$

PUBLIC FORECAST: KBB
AVIATION/MARINE: RWW

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