FXUS66 KSTO 302341
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
330 PM PST MON NOV 30 2009
.DISCUSSION...
STRONG...HIGHLY AMPLIFIED RIDGE FORECAST TO REMAIN ALONG THE W COAST
FOR MUCH OF THIS WEEK...AND A STRETCH OF DRY WX WITH CHILLY MORNINGS
AND MILD DAYTIME TEMPS IS EXPECTED. WITH STRONG SUBSIDENCE...USUALLY
WIDESPREAD FOG IS A WELL DOCUMENTED PROBLEM THIS TIME OF YEAR...BUT
THE NAM 925 MBS WINDS INDICATE NLY FLOW...ALBEIT RELATIVELY LIGHT...
WILL PREVAIL OVER INTERIOR NORCAL UNTIL THU AFTERNOON. THIS
KATABATIC WIND FLOW IS NOT THE MOST EFFICIENT PATTERN FOR FOG...AND
WILL PRECLUDE THE WIDESPREAD FOG ASSOCIATED WITH STRONG SUBSIDENCE
PATTERN FOR THE NEXT FEW MORNINGS. WITH MUCH LIGHTER WINDS TODAY...
DEWPOINTS HAVE MADE A DRASTIC RECOVERY INTO THE LOW 40S COMPARED TO
YESTERDAY. IN THE SHORT TERM...WE WILL CONTINUE TO HI-LITE THE AREA
OF FOG IN THE GRIDDED FORECASTS NEAR THE I-5/HWYS 99 AND 70
CORRIDORS. BY THE END OF THE WEEK...FOG WILL BE A LITTLE MORE
WIDESPREAD AND A LITTLE MORE OF A NUISANCE IF SLY LOW LEVEL FLOW
DEVELOPS TOWARDS THE LATTER HALF OF THE WEEK.
STRONG TEMP INVERSIONS ASSOCIATED WITH THIS PATTERN WILL RESULT IN
STRONG RADIATIONAL COOLING AT NIGHT AND CHILLY MORNINGS...AND MILD
AFTERNOON TEMPS ESPECIALLY IN THE FOOTHILLS AND MTNS WELL UP INTO
THE TEMP INVERSION LAYER. THIS WILL RESULT IN ABOVE NORMAL MAX TEMPS
FOR THE WEEK OVER MANY SITES.
SHORT WAVE MOVING ACROSS B.C. AND PAC NW AND INTO THE NRN ROCKYS
TONITE AND TUE WILL FLATTEN THE RIDGE ALONG THE COAST ALLOWING SOME
HIGH LEVEL CLOUDINESS TO SPREAD OVER INTERIOR NORCAL AT TIMES. THE
RIDGE RE-AMPLIFIES IN THE WAKE OF THIS SYSTEM ON WED. OTHERWISE...A
STRONGER SHORT WAVE NEARING 35N/140W IS FORECAST TO DISSIPATE AS IT
RUNS INTO THE DOWNSTREAM RIDGE. THIS FIRST ATTEMPT AT UNDERCUTTING
THE RIDGE LOOKS TO BE A VERY UNSUCCESSFUL ATTEMPT. THIS MAY NOT BE
THE CASE FOR NEXT WEEKEND AS BOTH THE GFS AND ECMWF SHOW
UNDERCUTTING OF THE RIDGE...BUT DIFFER SIGNIFICANTLY ON HOW WET IT
MAY BE IN NORCAL. WHILE THE GFS BRINGS A COLD AIR DOWN FROM THE
ARCTIC...THE ECMWF BRINGS IT IN FROM THE GULF OF AK...AND IS MUCH
WETTER AS MOISTURE FROM TYPHOON NIDA CURRENTLY NEAR 140E MAY BECOME
ENTRAINED INTO THE UNDERCUTTING FLOW. THUS...THERE IS A HIGH DEGREE
OF UNCERTAINTY INVOLVED IN THE THE FORECASTS FOR THE UPCOMING
WEEKEND. JHM
.EXTENDED DISCUSSION (FRIDAY NIGHT THROUGH MONDAY)...THE MODELS HAVE
VARIOUS SOLUTIONS FOR THE WEEKEND AND INTO NEXT MONDAY BUT EITHER
WAY IT WILL MOST LIKELY BECOME COOLER AND WETTER FOR AT LEAST A
PORTION OF INTERIOR NORTHERN CALIFORNIA. THE 18Z GFS HAS A LOW
COMING DOWN INTO MONTANA FRIDAY NIGHT INTO SATURDAY. THE LOW THEN
RETROGRADES TO NEAR THE ORCA BORDER ON SUNDAY NIGHT AND OVER
NORTHERN CALIFORNIA ON MONDAY. THIS WOULD BRING COOLER TEMPERATURES
AND A CHANCE OF PRECIPITATION TO THE AREA BY SUNDAY AFTERNOON AND
INTO MONDAY. THE ECMWF HAS A LOW FROM THE GULF OF ALASKA OFF THE
PACIFIC NORTHWEST COAST ON FRIDAY NIGHT AND THEN IT MOVES SOUTH AND
COMBINES WITH ANOTHER LOW THAT MOVES EAST FROM 140 WEST SUNDAY NIGHT
AND THEN THE SYSTEM MOVES INLAND THROUGH CALIFORNIA ON MONDAY. A
MOISTURE PLUME IS EXPECTED WITH THIS SYSTEM WHICH WOULD BRING WETTER
WEATHER THAN THE GFS. THE ECMWF SHOWS 500 MB HEIGHTS OF 5300M WITH
THIS SYSTEM WHICH IS THREE STANDARD DEVIATIONS BELOW CLIMATOLOGY SO
THIS SYSTEM COULD BRING A SIGNIFICANT PRECIPITATION EVENT TO THE
AREA. THE GEM MODEL IS BETWEEN THE GFS AND ECMWF AND JUST BRING THE
LOW OVER THE PACIFIC NORTHWEST AND THROUGH CALIFORNIA ON SUNDAY.
THIS WOULD BRING A CHANCE OF PRECIPITATION SATURDAY INTO SUNDAY.
AFTER LOOKING AT THE VARIOUS SOLUTIONS THE FORECAST CURRENTLY LEANS
TO BELOW NORMAL TEMPERATURES AND ABOVE CLIMATOLOGY FOR THE POPS BUT
THERE IS STILL UNCERTAINTY IN THE TIMING...COVERAGE AND AMOUNT OF
PRECIPITATION.
&&
.AVIATION...
UPR RDG CONTS OVR NORCAL WITH NWLY FLOW ALF. VFR CONDS OVR INTR
NORCAL EXC AREAS OF MVFR IN BR FM VCNTY KMYV SWD AFT 06Z TIL 18Z
WITH LCL LIFR IN FOG BTWN 10Z-17Z MNLY SACRAMENTO AREA AND NRN SAN
JOAQUIN VLY.
&&
.STO WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
