000
FXUS66 KSTO 201151
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
330 AM PST THU NOV 20 2008
.DISCUSSION...
UPPER LEVEL TROF APPROACHING THE NRN CA COAST MOVING ENEWD AT ABOUT
40 KTS...FORECAST TO MOVE INTO ERN ORE BY 00Z FRI. HIGH LEVEL
MOISTURE ENTRAINED INTO THE SWLY FLOW AHEAD OF THE TROF IS MAINLY
SPREADING ACROSS THE SRN PORTION OF THE FORECAST AREA FROM I-80
SWD...WITH DRIER MID LEVEL FLOW TO THE N. SATELLITE TRENDS INDICATE
THE SRN MOISTURE WILL GRADUALLY BE THINNING FROM W TO E DURING THE
EARLY MORNING...ALTHO LEE ENHANCED AC/CI WILL CONTINUE E OF THE
SIERNEV CREST. GIVEN THE NARROW TEMP/DEWPOINT SPREADS WON`T GIVE UP
ON POSSIBLE FOG FORMING DURING THE EARLY MORNING...ALTHO SELY WINDS
FROM 5-7 KTS MAKE IT LESS FAVORABLE THAN YESTERDAY MORNING`S CALM
WINDS. LAST LOOK AT THE FOG PRODUCT SHOWED A COUPLE OF PATCHES OF
STRATUS/POSSIBLE FOG DEVELOPING AROUND FOLSOM AND IN THE CENTRAL SAC
VLY W OF KBAB WHERE THE AREAL COVERAGE WAS BECOMING MORE EXTENSIVE.
THE TROF IS ASSOCIATED WITH A COLD FRONT THAT WILL BE MOVING INLAND
DURING THE MORNING HOURS. THERE IS A LACK OF ENHANCEMENT WITH THE
OFFSHORE FRONT S OF 40N...AND SSMI RAIN RATES WERE RAPIDLY
DISAPPEARING. HOWEVER...EKA RADAR DETECTING SOME LIGHT ECHOES ALONG
THE N COAST. SINCE THE COLD FRONT IS RUNNING INTO DRY/LOW PW AIR OFF
THE COAST AS IT MOVES EWD...WE ARE NOT LOOKING AT SIGNIFICANT PCPN
WITH THIS SYSTEM. THE 20/00Z GFS CROSS SECTIONAL ANALYSIS INDICATES
MOISTURE/CLOUDS BELOW 850-700 MBS...MAINLY AHEAD OF AND WITH THE
FRONT...WILL BE SPREADING INLAND THIS MORNING...THEN DECREASING THIS
AFTERNOON/EVENING. DYNAMICS/UPWARD VERTICAL MOTION FORECAST TO
WEAKEN RAPIDLY DURING THE AFTN AS THE UPPER TROF MOVES INTO ERN ORE.
THUS WE HAVE LIMITED POPS MAINLY TO THE MORNING OVER THE NRN PORTION
OF THE FORECAST AREA...AND DECREASED AREAL COVERAGE OF POPS IN THE
AFTERNOON. SYNOPTIC COOLING FROM THIS SYSTEM EXPECTED TO LOWER MAX
TEMPS TODAY SOME 3 TO 6 DEG OVER MOST OF THE AREA.
IN THE WAKE OF THE UPPER SYSTEM AND COLD FRONT...NLY/DOWNSLOPE FLOW
WILL DEVELOP OVER THE AREA...LIKELY PRECLUDING FOG DEVELOPMENT...
EXCEPT WHERE THE GRADIENT IS WEAKER IN THE NRN SAN JOAQUIN VLY THIS
COMING NITE. POST FRONTAL AIR MASS WILL ALSO RESULT IN A CHILLY
NIGHT. THE NEXT UPSTREAM TROF IS FORECAST TO TRACK FURTHER N LATE
FRI NIGHT AND EARLY SAT...AND WE HAVE CONFINED OUR MENTION OF LOW
POPS TO SAT MORNING FOR NOW.
MEDIUM RANGE MODELS TAKING A MORE SIMILAR APPROACH THAN PREVIOUS
RUNS WITH DEVELOPMENT OF A CLOSED-LOW VCNTY 30N/130W BY 00Z
TUE...ALTHO THE CANADIAN MODEL IS ABOUT 10 DEG FURTHER W THAN THE
EURO/GFS. WHILE THE CANADIAN KEEPS NORCAL DRY AND WARM UNDER A
STRONG UPPER LEVEL RIDGE THROUGH THE 144 HR PERIOD...THE EURO/GFS
WOBBLE THE CLOSED EWD TOWARD THE CA COAST TUE/WED INCREASING THE
CHANCES FOR PCPN IN NORCAL. THESE SOLUTIONS HAVE SOME SUPPORT FROM
GFS ENSEMBLE RUNS...BUT WITH CLOSED/AND OR CUT-OFF LOWS OFF THE
COAST THIS TIME OF YEAR...CONFIDENCE IS NOT VERY HIGH ON THIS
TIMING. IF MEMORY RECALL IS ACCURATE...WE ONLY HAD 2 DAYS OF RAIN IN
NOV AT DTS IN 2007 WITH JUST UNDER ONE INCH OF PCPN FOR THE
MONTH...AS AN OMEGA-REX BLOCK FORMED OFF THE W COAST RESULTING IN A
DRY NOV...AND A VERY LATE START TO OUR WET SEASON. THE CANADIAN MAY
BE HINTING AT THAT SCENARIO. WE ARE CAUTIOUSLY OPTIMISTIC THAT THE
WETTER-LOOKING MODELS WILL VERIFY BASED ON SOME ENSEMBLE SUPPORT.
JHM
&&
.AVIATION...
PATCHY FOG...MIST AND LOW STRATUS CLOUDS ARE DEVELOPING THIS MORNING
IN PORTIONS OF THE CENTRAL VALLEY. AREAS WITH IFR CIGS AND VIS ARE
EXPECTED ACROSS PORTIONS OF SACRAMENTO AND NORTHERN SAN JOAQUIN
VALLEYS AND DELTA THROUGH THE MORNING. CURRENTLY AREAS OF STRATUS
AND FOG ARE NEAR AND EAST OF KMHR...WEST OF KBAB...AND EAST AND
NORTH OF KRDD. EXPECT THESE AREAS TO GROW AS SKIES CLEAR SOME AS
HIGH CLOUDS SHIFT EASTWARD. CLOUDS WILL INCREASE LATER THIS MORNING
OVER THE NORTHERN MOUNTAINS AND THE NORTHERN SACRAMENTO VALLEY WITH
A SLIGHT CHANCE OF LIGHT RAIN INTO THE AFTERNOON. FOG WILL DIMINISH
WITH THE INCREASING CLOUDS BY LATE MORNING. SOUTHWEST WINDS GUSTS UP
TO 35 MPH OVER MOUNTAIN RIDGES THIS AFTERNOON AS A COLD FRONT PASSES
THROUGH. EK
&&
.STO WATCHES/WARNINGS/ADVISORIES...NONE.
$$
