Special Marine Warning 2, NWS San Francisco Bay Area, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
243 PM PDT THU APR 12 2012

.DISCUSSION...AS OF 2:30 PM PDT THURSDAY...UPPER LEVEL LOW NEAR
45/135 MOVING SOUTHEAST. FRONTAL SYSTEM MOVED RAPIDLY THROUGH THE
SFO AND MRY BAY AREA THIS MORNING DUMPING ABOUT ONE-HALF INCH OF
RAIN DISTRICTWIDE. CLEARING HAS TAKEN PLACE OVER THE AREA TODAY
BUT RADAR IS SHOWING SHOWERS OFFSHORE WHICH WILL MOVE ONSHORE
LATER THIS AFTERNOON. LIGHTNING STRIKES HAVE BEEN REPORTED OFF
THE NORTHERN CALIFORNIA COAST SO THERE IS A SLIGHT CHANCE OF
THUNDERSTORMS IN THE CWA.

THINGS GET INTERESTING TONIGHT AS THE UPPER TROUGH AXIS APPROACHES
THE AREA. RAIN AND THUNDERSTORM CHANCES WILL PICK UP AFTER 00Z.
MODELS SHOW DECENT UPWARD VERTICAL VELOCITIES AND SOME DIRECTIONAL
WIND SHEAR IN THE LOWER LEVELS. AS A RESULT THERE IS THE
POSSIBILITY OF SEVERE WEATHER TONIGHT WITH LOCALLY HEAVY RAIN AND
STRONG THUNDERSTORMS. THESE STRONG THUNDERSTORMS COULD CONTAIN
GUSTY WINDS TO 50 MPH AND HAIL UP TO ONE-HALF INCH DIAMETER.

RAIN WILL TURN TO SHOWERS FRIDAY AS THE TROUGH AXIS PASSES
THROUGH AND THE UPPER LOW ITSELF MOVES OVER THE AREA. THERE WILL
BE LESS DIRECTIONAL WIND SHEAR AND VERTICAL VELOCITY ON FRIDAY
BUT 500 MB TEMPERATURES DROP TO -30 DEGREES C INCREASING
CONVECTIVE INSTABILITY. SO THERE WILL AGAIN A CHANCE OF
THUNDERSTORMS WITH SMALL HAIL. SNOW LEVELS WILL LOWER TO 3000
FEET.

RAINFALL AMOUNTS THROUGH FRIDAY ARE EXPECTED TO BE ONE-HALF TO
ONE INCH WITH LOCALLY HIGHER AMOUNTS IN AREAS OF HEAVY PRECIP.
SHOWERS WILL DECREASE FRIDAY NIGHT AS THE LOW MOVES SOUTHEAST OF
THE AREA BUT SOME SHOWERS WILL PERSIST ALONG THE MONTEREY COUNTY
COAST IN THE MOIST NORTHWEST FLOW. THERE WAS SOME CONCERN FOR COLD
TEMPERATURES FRIDAY NIGHT BUT BELIEVE THERE WILL BE ENOUGH WIND
AND CLOUDS TO KEEP TEMPERATURES WELL ABOVE FREEZING. DRY AND
WARMER WEATHER IS FORECAST FOR THE WEEKEND AS A LARGE UPPER LEVEL
RIDGE BUILDS OFF THE WEST COAST. THIS RIDGE WILL KEEP STORMS NORTH
OF THE AREA NEXT WEEK WITH ONLY A SLIGHT CHANCE OF RAIN IN THE FAR
NORTH BAY AROUND MIDWEEK. LOOKING BEYOND...LONG RANGE MODELS SHOW
NO REAL CHANCE OF RAIN THROUGH THE END OF THE MONTH.

&&

.AVIATION...AS OF 11:05 AM PDT THURSDAY...THE CURRENT VISIBLE
SATELLITE IMAGE IS SHOWING SKIES BEGINNING TO SCATTER OUT AROUND
THE CENTRAL COAST. THIS WILL ALLOW FOR A PERIOD OF SUNSHINE WHICH
WILL ENHANCE THE DEVELOPMENT OF CONVECTIVE CLOUDS THIS AFTERNOON.
THESE CONVECTIVE CLOUDS WILL PRODUCE SHOWERS WHICH MAYBE HEAVY AT
TIMES IN SOME LOCATIONS. LINGERING INSTABILITY COMBINED WITH LIFT
PRODUCED BY THE TROUGH AXIS WILL ALLOW FOR A SECOND ROUND OF RAIN
TONIGHT WITH THE POSSIBILITY OF AN ISOLATED THUNDERSTORM.

.VICINITY OF KSFO...PRIMARILY VFR CIGS BKN-OVC035 THIS MORNING
INTO THE AFTERNOON HOURS WITH A SHOWER IN THE VICINITY. LIGHT
SHOWERS ARE EXPECTED TO BEGIN BY 2100Z WITH CIGS DROPPING TO
BKN025 BY 0200Z. SOUTH SOUTHWEST WINDS EXPECTED TO REACH 10 TO 15
KT WITH GUSTS TO 20 KT. WINDS WILL BECOME SOUTH SOUTHEAST FOR A
PERIOD AFTER 0200Z. LIGHT RAIN WITH PERIODS OF HEAVIER RAIN AND
ISOLATED THUNDERSTORMS ARE EXPECTED OVERNIGHT.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MONTEREY BAY AREA TERMINALS...PRIMARILY VFR CIGS SCT025 BKN-OVC050
THIS MORNING INTO THE AFTERNOON HOURS WITH A SHOWER IN THE
VICINITY. LIGHT SHOWERS ARE EXPECTED TO BEGIN BY 2200Z WITH CIGS
DROPPING TO BKN025 BY 0200Z. SOUTH SOUTHWEST WINDS EXPECTED TO
REACH 10 TO 15 KT WITH GUSTS TO 20 KT. WINDS WILL BECOME SOUTH
SOUTHEAST AFTER 0200Z AT KSNS. LIGHT RAIN IS EXPECTED OVERNIGHT.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PT ARENA TO PIGEON PT 10-60 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM UNTIL 3 PM
             SCA...PT REYES TO PIGEON PT 0-10 NM UNTIL 2 PM
             SCA...SF BAY UNTIL 9 PM

&&

PUBLIC FORECAST: W PI
AVIATION/MARINE: LARRY

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