FXUS65 KREV 252252
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
252 PM PST WED NOV 25 2009

.SHORT TERM...
ECMWF HAS REMAINED FAIRLY CONSISTENT WITH ITS HANDLING OF NEXT
TROF DROPPING INTO THE RGN ON FRIDAY. GFS AND NAM HAVE NOW PICKED
UP ON TREND FROM THE ECMWF OF DEVELOPING A CUT OFF LOW IN THE BASE
OF THE TROF LATE FRIDAY OVER CNTRL CA AND DROPPING IT SOUTH INTO
SRN CA BY SATURDAY. THIS LEADS TO A BIT MORE CONFIDENCE IN THE
OVERALL FORECAST PATTERN THIS CYCLE. BUT SOME DISCREPANCIES REMAIN
AND DETAILS ARE NOT COMPLETELY CLEAR YET.

RIDGE WINDS SHOULD BEGIN INCREASING LATE THURSDAY AS H700 WINDS
INCREASE AHEAD OF THE TROF. WHILE LOW LVL WINDS WILL REMAIN LIGHT
THROUGH MOST OF THURSDAY THE INCREASING WINDS ALOFT SHOULD HELP TO
INCREASE MIXING THUS WILL GO WITH TEMPS ABOUT 5 DEGREES WARMER IN
THE VALLEYS FOR THURSDAY OVER TODAY. CLOUDS SHOULD BEGIN TO
INCREASE LATE THURSDAY EVENING. ECMWF SPREADS PCPN INTO THE FAR NRN
CWA FASTER THAN THE OTHER MODELS THURSDAY NIGHT. THE TREND HAS
BEEN FOR A SLOWING OF THE OVERALL SYSTEM. NAM IS SLOWEST WITH
PCPN SPREADING INTO THE CWA ASCD WITH THIS SYSTEM. BUT NAM HAS A
TENDENCY TO UNDER FORECAST PCPN ONSET. GFS IS A GOOD COMPROMISE
NOW AND WILL TREND TOWARD ITS SOLUTION WITH LOW POPS FAR NW CWA
LATE THURSDAY NIGHT.

PCPN INCREASES IN AREAL COVERAGE FRIDAY FROM NORTHWEST TO SOUTH.
ECMWF AND GFS SPREAD PCPN SOUTH THROUGH THE DAY ALONG WITH COLDER
H700 TEMPS AND FALLING SNOW LEVELS. QPF DOES NOT APPEAR TOO GREAT
AT THIS POINT AND SYSTEM DOES DROP SOUTH FAIRLY QUICKLY SO SNOW
ACCUMULATIONS IN THE MTNS SHOULD BE SOMEWHAT LIMITED. COLD FRONT
PASSES THROUGH THE RGN LATE FRIDAY EVENING AND THIS SHOULD CUT OFF
MOST PCPN. HOWEVER...WITH MODELS TRYING TO DROP A CUT OFF LOW INTO
SRN CA BY SATURDAY MRNG THINK EASTERLY UPSLOPE FLOW IN THE MID
LVLS WILL DVLP ALONG THE SRN SIERRA. THIS WOULD RESULT IN
SCATTERED SHOWERS LINGERING IN THE SRN SIERRA THROUGH MUCH OF
SATURDAY. RAISED POPS RATHER SIGNIFICANTLY FOR FRIDAY AND FRIDAY
NIGHT WITH HIGHEST POPS IN THE SIERRA AND LASSEN COUNTY TO ACCOUNT
FOR BAND OF FRONTAL PCPN THAT SHOULD BE FAIRLY SOLID AS IT WORKS
SOUTH FRIDAY AFTN/EVNG. ALSO INCREASED POPS TO ACCOUNT FOR SHOWERS
IN THE SRN SIERRA SATURDAY.

UNFORTUNATELY 25/18 UTC NAM NOW SHOWS CUT OFF LOW DROPPING TO
SOUTH JUST ALONG OR OFF SHORE SATURDAY. UNDER THIS SCENARIO AREAS
EAST OF THE SIERRA WOULD SEE FAR LESS PCPN...AND POSSIBLY NONE.
25/18 UTC GFS DOES NOT SUPPORT THIS SOLUTION. BUT WILL NEED TO
MONITOR FOR POSSIBILITY OF DECREASING POPS EAST OF THE SIERRA. MLF

.LONG TERM...SUNDAY THROUGH WEDNESDAY...
DECENT MODEL AGREEMENT THROUGH THE EXTENDED PERIOD. THE SYSTEM FROM
FRI NIGHT/SAT DROPS SOUTH INTO THE DESERT SOUTHWEST AND CLOSES OFF
ON SUNDAY. THE GFS BRINGS THE SYSTEM SLIGHTLY FURTHER WEST THAN
THE ECMWF...BUT EITHER WAY THIS WOULD PUT THE CWA UNDER A COOL
NORTHEASTERLY FLOW ALOFT. RIDGE ALOFT PUSHES INLAND FOR THE EARLY
PART OF THE WEEK AHEAD OF A WAVE SLATED TO MOVE INTO THE NORTHWEST
MONDAY EVENING. THIS WILL HELP TO MIX OUT THE VALLEY INVERSIONS
WITH TEMPS WARMING A FEW DEGREES MONDAY AND TUESDAY. MOISTURE WILL
BE TOO FAR NORTH TO BRING MENTIONABLE POPS INTO THE FORECAST AT
THIS TIME. AS THE WAVE CONTINUES EASTWARD...A NORTHERLY FLOW WILL
SET UP ALOFT AGAIN BRINGING COOLING ONCE AGAIN TO THE AREA ON
WEDNESDAY. DF &&

.AVIATION...
VFR UNDER CLEAR SKIES WITH LIGHT SURFACE WINDS THROUGH THANKSGIVING.
FOG IS POSSIBLE AT KTRK THE NEXT FEW NIGHTS...BUT WITH SUCH A DRY
AIR MASS IN PLACE...IT WILL BE SHALLOW AND PATCHY AT BEST.

A SYSTEM IS FORECAST TO MOVE INTO THE WEST COAST THURSDAY NIGHT...
IMPACTING THE SIERRA FRIDAY NIGHT INTO SATURDAY MORNING. THIS
WILL BRING INCREASED WINDS AND CHANCE FOR SHOWERS AND MOUNTAIN
OBSCURATION. DF &&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...NONE.
CA...NONE.
&&

$$

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