FXUS66 KMTR 020006
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
405 PM PST TUE DEC 1 2009

.DISCUSSION...AS OF 2:35 PM PST TUESDAY...QUIET WEATHER INTO THE
WEEKEND THEN THE STORM DOOR OPENS WITH MUCH WETTER PATTERN NEXT
WEEK.

WIDESPREAD CIRRUS CLOUDS AND COOLER AIRMASS HAS KEPT MANY LOCATION
SLIGHTLY COOLER TODAY COMPARED TO YESTERDAY...ESPECIALLY SOUTHERN
CWA.  HOWEVER...A FEW SPOTS IN THE EAST BAY ARE A FEW WARMER THAN
YESTERDAY.  OTHER ITEM OF NOTE THIS AFTERNOON...ARE SOME LOW CLOUDS
AND PATCHY FOG THAT DEVELOPED ALONG THE COASTAL N BAY SOUTHWARD
TOWARD THE SAN MATEO COAST.  WEBCAMS AND OBSERVERS BOTH INDICATE
THIS LAYER IS SHALLOW BUT REDUCES VISIBILITIES.

LONGWAVE PATTERN AT 500 MB SHOWS A DEEP UPPER LOW OVER NORTHERN
MEXICO WITH A RIDGE OVER THE WEST COAST AND A SECONDARY UPPER LOW
PUSHING THROUGH 140W. AS MENTIONED BEFORE...UPPER LEVEL MOISTURE IS
TRAPPED UNDER THE RIDGE PRODUCING CIRRUS CLOUDS.

SHORT TERM(TONIGHT-FRIDAY)...
LITTLE CHANGE WAS MADE TO THE OVERALL FORECAST WITH SEASONABLE
WEATHER CONDITIONS. HIGH PRESSURE IS FORECAST TO REMAIN IN PLACE
WITH A FEW DISTURBANCES UNDER CUTTING IT OR RIDING OVER THE TOP. THE
UPPER LEVEL MOISTURE WILL REMAIN IN PLACE FOR ONE MORE DAY WITH
MORE CIRRUS CLOUDS EXPECTED. THE HIGH CLOUDS WILL KEEP DAYTIME
TEMPERATURES COOLER AND NIGHTTIME TEMPERATURES WARMER.

LONG TERM(SATURDAY-TUESDAY)...
A COMBINATION OF THE ACTIVE PHASE OF THE MJO...REMNANTS OF SUPER-
TYPHOON NIDA AND AN INCREASE OF THE EAST ASIAN JET STREAM ARE
POINTING TO A VERY ACTIVE AND WET PATTERN FOR MUCH OF THE WEST COAST.

THERE ARE SOME DIFFERENCES AMONG THE MODELS AS TO BE EXPECTED THIS
FAR OUT...BUT ALL INDICATE A SERIES OF SYSTEMS MOVING THROUGH THE
REGION. THE MOST NOTABLE IS THE MIDDLE OF NEXT WEEK WITH REMNANTS
OF NIDA.

SATURDAY...THE UPPER RIDGE BREAKS DOWN AS AN ARCTIC INTRUSION PUSHES
WESTWARD IN THE PAC NW. THE THE CANADIAN MODEL IS THE FASTEST AND
THE EURO IS THE SLOWEST BY 12Z SUNDAY WITH THE UPPER TROUGH/LOW.
NONE THE LESS...THE BULK OF THE COLD AIR REMAINS N AND E OF THE CWA.
THAT BEING SAID...HAVE ADDED SOME LOW POPS OVER THE HILLS SATURDAY
NIGHT AS THE UPPER TROUGH MOVES INTO THE REGION. THE UPPER LOW
DIGS WESTWARD ON SUNDAY AS RIDGING SURGES N IN GULF OF AK AT 500MB.
AT THE SURFACE A WEAK LOW SKIRTS IN FROM THE WEST UNDER THE UPPER
LOW LATE SUNDAY. THIS WILL BRING EVEN MORE INSTABILITY SHOWERS ON
SUNDAY AND SUNDAY NIGHT. SNOW LEVELS DO LOWER DURING THIS TIME
FRAME...BUT THE JURY IS STILL OUT AS TO HOW MUCH COLD AIR MAKES IT
WESTWARD. PRECIP CHC INCREASE ON MONDAY WITH THE INFLUENCE FROM THE
UPPER TROUGH/LOW. CHC RAIN WILL REMAIN IN THE FORECAST ON MONDAY.
THERE COULD BE A BRIEF RESPITE ON TUESDAY AS THE UPPER TROUGH EXITS
TO THE EAST...BUT A MUCH STRONGER SYSTEM IS ON THE HORIZON.

MEANWHILE AND MUCH FARTHER TO THE WEST...THE FORMER SUPER TYPHOON
NIDA EJECTS NE IN THE WEST PACIFIC AND HELPS TO ENHANCE THE EAST
ASIAN JET. AS A RESULT...THE OLD TROPICAL FEATURE BEGINS TO BOMB OUT
NEAR 175W 935-945MB LOW (12Z SAT-00Z SUN). NEXT QUESTION IS WHEN DOES
THIS SYSTEM MOVE EASTWARD?  THE MODELS HAVE SOME AGREEMENT IN KEEPING
THE LOW W OF 170W THROUGH 00Z MONDAY...BUT THEN THEY BRING IT
EASTWARD WITH LOTS OF GUSTO AND MOISTURE. THE EURO IS THE QUICKEST
WITH THE ONSET OF MOISTURE AND THE GFS/CANADIAN ARE CLOSER TOGETHER.
THINK THE EURO MAY BE A LITTLE TO QUICK AND THE CANADIAN WOULD BE A
GOOD COMPROMISE. THAT MEANS...LATE TUESDAY INTO WEDNESDAY THE REAL
ONSET OF MODERATE RAINFALL COULD START TO AFFECT MUCH OF THE REGION.
THE EXACT DETAILS REGARDING RAINFALL AMOUNTS AND TIMING ARE STILL
SOMEWHAT UNCERTAIN GIVEN THAT IT IS STILL A WEEK OUT...BUT IF THE
GUIDANCE IS IN THE BALLPARK COPIOUS AMOUNTS OF RAINFALL CAN BE
EXPECTED.

A LOT CAN HAPPEN BETWEEN NOW AND THEN...BUT ONE THING IS FOR SURE
THE PATTERN LOOKS IMPRESSIVE FOR NEXT WEEK.  STAY TUNED.

&&

.AVIATION...AS OF 4:05 PM TUESDAY...SCATTERED TO BROKEN HIGH
CLOUDS HAVE SPREAD OVER THE REGION WITH LOW CLOUDS AND FOG
CONFINED TO THE IMMEDIATE COAST. GRADIENTS ARE VERY WEAK ONSHORE AT
THE PRESENT TIME AND THE MARINE LAYER IS SHALLOW. THUS...DO NOT
EXPECT LOW CLOUDS AND FOG TO BE AN ISSUE AT ANY TERMINALS THROUGH THE
EVENING RUSH. THERE IS A CHANCE THAT IFR CIGS AND VSBYS MAY DEVELOP
LATE TONIGHT LOCALLY INTO SF BAY...BUT CHANCES APPEAR LOW GIVEN
LACK OF ANY APPRECIABLE ONSHORE PUSH. WINDS WILL REMAIN LIGHT.

VICINITY OF KSFO...VFR CONDITIONS WITH SCT-BKN HIGH LEVEL CLOUDS.
LIGHT ONSHORE WINDS THROUGH 04Z AND THEN LIGHT AND VARIABLE
THEREAFTER.  SLIGHT POSSIBILITY OF IFR CIGS/MVFR VSBYS FORMING AT
KSFO FROM 12-15Z WEDNESDAY MORNING.

KSFO BRIDGE APPROACH...VFR CONDITIONS WITH ONLY SCT-BKN CIRRUS
CLOUDS.

MRY BAY AREA TERMINALS...VFR CONDITIONS WITH SCT-BKN HIGH LEVEL
CLOUDS. GENERALLY LIGHT WEST WINDS WITH A SHIFT TO EAST AND
SOUTHEAST OVERNIGHT. SLIGHT CHANCE OF IFR CIGS/VSBYS AT KMRY FROM 12-
14Z WED MORNING.

&&

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

$$

PUBLIC FORECAST: MM
AVIATION/MARINE: BJT/DYKEMA

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO