000
FXUS66 KMTR 251545
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
845 AM PDT SAT MAY 25 2013

...COOL HOLIDAY WEEKEND WITH SHOWERS POSSIBLE MEMORIAL DAY...

.DISCUSSION...AS OF 08:43 AM PDT SATURDAY...MORNING VISIBLE
SATELLITE IMAGERY REVEALS BROKEN STRATUS ACROSS PORTIONS OF THE
CWA. CLOUD COVER EARLY THIS MORNING IS MOST PREVALENT SAN MATEO
COAST...EAST BAY...MONTEREY THROUGH BOTH THE CARMEL AND SALINAS
VALLEYS. PASSING SHORTWAVE TROUGHS OVERHEAD AND A MODERATE 3-4 MB
N-S GRADIENT IS LIKE PREVENTING WIDESPREAD STRATUS THIS MORNING.
EXPECT THE CLOUD COVER TO GRADUALLY ERODE DURING THE MORNING HOURS
GIVING WAY TO PARTLY CLOUDY CONDITIONS THIS AFTERNOON. CURRENT
FORECAST FOR THIS AFTERNOON WILL SIMILAR TO YESTERDAY...SEASONABLY
COOL. HIGHS TODAY ARE EXPECTED TO BE IN THE 60S ALONG THE COAST
AND 70S INLAND...WHICH IS 3-6 DEGREES BELOW NORMAL FOR THIS TIME
OF YEAR.

CURRENT FORECAST FOR TODAY LOOKS GOOD AND NO UPDATES PLANNED AT
THIS TIME.

A BROAD TROUGH OF LOW PRESSURE WILL REMAIN ALONG THE PACIFIC
NORTHWEST COAST THROUGH MONDAY. A SERIES OF SHORTWAVE TROUGHS AND
UPPER LOWS WILL ROTATE THROUGH THE TROUGH. THE FIRST ONE WILL BE
TONIGHT THROUGH SUNDAY MORNING RESULTING IN POSSIBLY MORE STRATUS.
IN FACT...MODEL GUIDANCE...ESPECIALLY THE NAM INDICATES LIGHT
PRECIP ALONG THE COAST SUNDAY MORNING. TEMPERATURES WILL REMAIN
COOL ON SUNDAY AS WELL.

THE MAIN FOCUS OF THE FORECAST CONTINUES TO BE ON RAIN CHANCES ON
MEMORIAL DAY. WILL WAIT FOR THE NEW 12Z MODELS BEFORE MAKING ANY
CHANGES...BUT THE GENERAL TREND HAS CONTINUED TO BE SLOWER ON THE
ONSET OF PRECIP.

PREVIOUS DISCUSSION...OF THE ECMWF...NAM...AND GFS
SOLUTIONS...THERE REMAINS A FAIR AMOUNT OF DISAGREEMENT AND THIS
CONTRIBUTES TO A LOWER CONFIDENCE FORECAST. THE NAM AND GFS ARE IN
FAIRLY CLOSE AGREEMENT ON THE SOUTHWARD PROGRESS OF THE RAIN
DURING THE DAY ON MONDAY WITH THE ECMWF CONTINUING TO BRING IT
FARTHER SOUTH WITH HIGHER AMOUNTS. TIMING IS IN A BIT BETTER
AGREEMENT WITH EVEN THE ECMWF SLOWING THE ONSET FOR THE FORECAST
AREA UNTIL PRIMARILY AFTER 18Z MONDAY. SO ITS LIKELY THAT MONDAY
MORNING AND EARLY MORNING WILL BE PRIMARILY DRY EXCEPT FOR THE BAY
AREA NORTH WHERE SHOWER CHANCES WILL BE HIGHER. PRECIPITABLE WATER
AMOUNTS 1-1.25 INCHES SO THERE WILL BE ENOUGH MOISTURE PRESENT
ALONG WITH THE LIFT PRESENT FROM THE SURFACE COLD FRONT AND THE
UPPER TROUGH ENERGY. THE MODELS DO SHOW WHAT LOOKS LIKE BETTER
RAIN CHANCES LATER MONDAY AND OVERNIGHT BUT EVEN SO THERE REMAINS
UNCERTAINTY OVER THE AMOUNTS WHICH WILL NOT BE GREAT. SO THE
BOTTOM LINE WITH THE MONDAY FORECAST IS THAT THERE IS BETTER
CONFIDENCE IN THE TIMING BEING MORE FOCUSED ON HIGHER RAIN CHANCES
MONDAY AFTERNOON BUT THE SOUTHWARD EXTENT OF MEASURABLE RAIN
REMAINS IN QUESTION BUT WITH A BLENDED SOLUTION THE THE NORTH BAY
LOOKS IN LINE FOR THE BEST RAIN CHANCES. WILL KEEP LOW POPS FROM
THE BAY SOUTHWARD.

AFTER THE UNSETTLED WEATHER AND SHOWER CHANCES DIMINISH ON
TUESDAY...THE ECMWF AND GFS ARE IN DECENT AGREEMENT ON THE TROUGH
PROGRESSING INTO THE INTER MOUNTAIN WEST AND THIS LEAVES OUR AREA
IN THE TRANSITIONAL ZONE BETWEEN THE TROUGH TO THE EAST AND THE
BUILDING RIDGE OVER THE PACIFIC. THIS WILL CONTRIBUTE TO A
CONTINUED LOWER CONFIDENCE FORECAST GIVEN THE POTENTIAL FOR LARGE
CHANGES IN THE EXTENDED WITH THE HIGHLY AMPLIFIED PATTERN. FOR NOW
WILL REFLECT A BLENDED MOS SOLUTION WHICH SUPPORTS A SLOW MID WEEK
WARMING TREND FOLLOWED BY A RETURN TO HOTTER WEATHER BY LATE WEEK.

&&

.AVIATION...AS OF 4:41 AM PDT SATURDAY...THE CURRENT SATELLITE IR
FOG PRODUCT AND THE SUOMI DAY NIGHT VIS IMAGE SHOWS STRATUS ALONG
THE SAN FRANCISCO COAST AND MONTEREY BAY AREA. STRATUS IS ALSO
APPARENT IN SAN FRANCISCO BAY THIS MORNING. HOWEVER...STRATUS IN
THE SAN FRANCISCO BAY APPEARS TO BE PRIMARILY NEAR KOAK AND
SLIGHTLY EAST OF KSFO AND THE APPROACH. STRENGTHENING ONSHORE FLOW
SHOULD RESULT IN A BREEZY DAY AT THE TERMINALS ESPECIALLY AS THE
SEA BREEZE SETS UP THIS AFTERNOON.

VICINITY OF KSFO...MVFR CIGS WILL PASS OVER KSFO FROM TIME TO TIME
THIS MORNING WHILE PREVAILING AT KOAK THROUGH 1800Z. SOUTHWEST WINDS
WILL INCREASE TO 15 KT BY 1700Z WITH FURTHER INCREASES TO 25 KT
WITH GUSTS TO 32 KT BY 2200Z.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...MVFR CIGS WILL PREVAIL THIS MORNING
IMPROVING TO VFR BY 1800Z AT KSNS. CIGS MAY STICK AROUND ALL DAY
AT KMRY TODAY WITH IMPROVEMENTS TO OVC020 BY 1700Z. GUSTY ONSHORE
WINDS ARE EXPECTED TO REACH 10 TO 15 KT WITH GUSTS TO AROUND 25 KT
AS THE SEA BREEZE ESTABLISHES ITSELF THIS AFTERNOON.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...PT ARENA TO PIGEON PT 10-60 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM
             SCA...PT ARENA TO PT REYES 0-10 NM
             SCA...PT REYES TO PIGEON PT 0-10 NM
             SCA...SF BAY IN EFFECT AT 1 PM

&&

$$

PUBLIC FORECAST: MM/LJ
AVIATION/MARINE: LARRY

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