AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA 240 PM PDT SUN MAR 15 2009
.DISCUSSION...AS OF 2:30 PM PDT SUNDAY...A FEW SHOWERS HAVE MOVED ACROSS THE SAN FRANCISCO BAY AREA TODAY WITH MOST RAIN FALLING IN THE HIGHER TERRAIN. OVER THE LAST SIX HOURS RAINFALL TOTALS HAVE PEAK AT 1/10 INCH...PLACING THE MAXIMUM STORM TOTAL...AND I USE THAT TERM LOOSELY...AT 1/4 INCH. THE MAIN PART OF THE STORM IS STILL APPROACHING AND CAN BE SEEN ON THE IR SATELLITE IMAGERY AS A WEST TO EAST ORIENTED COLD FRONT EXTENDING WESTWARD OFFSHORE FROM THE OREGON/CALIFORNIA BORDER. THE PARENT LOW IS CENTERED JUST WEST OF VANCOUVER ISLAND AND MOVING TO THE EAST. THE COLD FRONT IS SLIPPING SOUTHEASTWARD AND IS EXPECTED TO STALL JUST NORTH OF THE SAN FRANCISCO BAY AREA LATE IN THE DAY ON MONDAY. THIS WILL CAUSE ON AND OFF SHOWERS FROM THE SANTA CRUZ MOUNTAINS NORTHWARD TONIGHT AND MONDAY. SOUTH OF THE SANTA CRUZ MOUNTAINS ISOLATED SHOWER MAY DEVELOP...MAINLY OVER THE HIGHER TERRAIN. ADDITIONAL RAINFALL TOTALS WILL RANGE FROM AN INCH IN THE NORTH BAY MOUNTAINS TO JUST A FEW HUNDREDTHS IN THE VALLEYS.
ON TUESDAY WEAK RIDGING WILL BUILD INTO SOUTHERN CALIFORNIA PROVIDING A DRIER AIRMASS AND WARMER CONDITIONS. THE GFS WARMS THE AREA QUICKLY WHILE THE ECMWF AND NAM ARE MORE CONSERVATIVE. SINCE HPC IS TRENDING TOWARD THE ECMWF AND AWAY FROM THE GFS...AND THE RIDGE WILL REMAIN WEAK...THE FORECAST WILL TREND TOWARD THE NAM/ECMWF SOLUTIONS AND WILL TAKE A CONSERVATIVE APPROACH TO THE WARMING.
AT THE WEEKEND...ANOTHER SHORT WAVE WILL BREAK FREE FROM THE ANCHORED LOW IN THE GULF OF ALASKA PROVIDING THE NEXT CHANCE FOR RAIN. THE ECMWF AND GFS HAVE THE SAME IDEA OF MOVING THE SHORT WAVE OUT OF THE GULF...BUT DIFFER IN TIMING AND DETAILS. THE GFS IS MORE PROGRESSIVE AND BRINGS THE MOISTURE ASSOCIATED WITH THE TROUGH INTO NORTHERN CALIFORNIA SOONER THAN THE ECMWF. THEREFORE...WILL INTRODUCE SLIGHT CHANCE POPS IN THE FORECAST ON FRIDAY AND GRADUALLY INCREASE THEM THROUGH THE WEEKEND.
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.AVIATION...AS OF 4:55 PM PDT SUNDAY...SATELLITE PICTURES SHOW FRONTAL SYSTEM OFF THE SONOMA COAST THAT WILL SPREAD MORE LOW CLOUDS INTO THE AREA AFTER 03Z. LATEST MODELS KEEP CEILING HEIGHTS AROUND 1500 FEET OVERNIGHT WITH RAIN CONFINED TO THE NORTH BAY AND NRN SFO BAY AREA. CEILINGS WILL LIFT BY MONDAY AFTERNOON. WINDS WILL BE SOUTH 5-10 KT BECOMING WEST BY MONDAY AFTERNOON.
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.MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...NONE.
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PUBLIC FORECAST: EVANS AVIATION/MARINE: LARRY/W PI
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