FXUS66 KMTR 240540
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
940 PM PST WED DEC 23 2009

.DISCUSSION...AS OF 9:00 PM PST WEDNESDAY...PRESENT FORECAST IS ON
TRACK WITH NO UPDATES ANTICIPATED TONIGHT. MAINLY CLEAR SKIES
CONTINUE OVER THE REGION. DRY WEATHER IS EXPECTED TO CONTINUE THROUGH
CHRISTMAS DAY.

A CHANCE OF RAIN REMAINS IN THE FORECAST FOR THE HOLIDAY WEEKEND. THE
ONCE DRIER GFS IS NOW MORE ALIGNED WITH THE WETTER ECMWF THOUGH THERE
ARE NOW DIFFERENCES IN TIMING THE ARRIVAL OF THE WEEKEND STORM. THE
GFS IS ABOUT 12 HOURS SLOWER SHOWING THE LOW MAINLY ARRIVING SUNDAY.
ASIDE FROM THIS THE MODELS DO AGREE ON THE INTENSIFICATION OF THE LOW
AS IT REACHES THE MENDOCINO COUNTY COAST DURING THE WEEKEND. DONT SEE
MUCH REASON TO CHANGE TIMING YET...BUT MAY NEED TO FINE TUNE THIS THE
CLOSER WE GET TO THE EVENT. FOR NOW IT APPEARS THE RAIN WILL QUICKLY
SPREAD ACROSS THE BAY AREA AND CENTRAL COAST BEGINNING PROBABLY LATER
IN THE DAY SATURDAY. THE WETTER ECMWF SHOWS 1 TO 1.5 INCHES OF RAIN
WHILE THE GFS FORECASTS ROUGHLY A HALF INCH OF RAIN. QPF ROUGHLY
SOMEWHERE IN MIDDLE IS THE MOST LIKELY CASE AS A STRONG JET DEVELOPS
ON THE BACK SIDE OF THE UPPER TROUGH SUNDAY SENDING IT SOUTHEAST TO
SOCAL. IN OTHER WORDS THE FRONT SHOULD MOVE THROUGH THE REGION FAIRLY
RAPIDLY SUNDAY WITH THE SHOWERS LINGERING LATE SUNDAY NIGHT AND
MONDAY MORNING. BOTH MODELS AGREE THE LOW WILL REACH NORTHERN MEXICO
AND ARIZONA BY MONDAY NIGHT THEN ITS OFF TO THE PLAINS BY WEDNESDAY
MORNING. A WEAK TO MODERATE UPPER LEVEL RIDGE TEMPORARILY MOVES IN
TUESDAY JUST PRIOR TO THE NEXT UPPER TROUGH ARRIVING WEDNESDAY
BRINGING THE NEXT CHANCE OF RAIN PER THE ECWMF. WOULD TEND TO GO WITH
THE ECMWF MODEL OUTPUT NOW SINCE THE GFS IS JUMPING ONBOARD WITH THE
STORMIER ECMWF PATTERN THE CLOSER WE GET TO THE EVENTS. QPF WITH THE
MID-WEEK STORM SHOULD BE LOWER GENERALLY UPWARDS OF A HALF AN INCH OF
RAIN.

&&

.AVIATION...AS OF 9:40 PM WEDNESDAY...HIGH PRESSURE OVER THE REGION
WILL MAINTAIN CLEAR SKIES AND LIGHT AND VARIABLE FLOW ACROSS THE
DISTRICT TONIGHT AND THURSDAY.

VICINITY OF KSFO...VFR CONDITIONS AND LIGHT WINDS EXPECTED THROUGH
THURSDAY.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MRY BAY AREA TERMINALS...VFR CONDITIONS AND LIGHT WINDS EXPECTED
THROUGH THURSDAY.

&&

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

$$

PUBLIC FORECAST: CANEPA
AVIATION/MARINE: CW

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO