FXUS65 KREV 021015
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
215 AM PST WED DEC 2 2009

.SHORT TERM...WATER VAPOR IMAGERY DEPICTS A SWATH OF DRY AIR BEING 
PUSHED ACROSS THE CWA FROM THE NORTH BY A LOW PRESSURE SYSTEM TO THE 
NORTHEAST. THIS NORTHERLY FLOW WILL KEEP THE TEMPERATURE COOLING 
TREND THROUGH THE WEEK AND LIGHT WINDS WILL CONTINUE TO BLOCK MIXING 
AND KEEP INVERSIONS IN PLACE. 

BY FRIDAY AFTERNOON AN UPPER LOW WILL BEGIN ITS DESCENT TOWARDS THE 
GREAT BASIN...CENTERED OVER THE IDAHO/MONTANA BORDER. 00Z 
OPERATIONAL MODEL RUNS ARE ALL IN AGREEMENT THAT THE TIMING OF THE 
DESCENT WILL BE SLOWER THAN PREVIOUSLY THOUGHT. AS THE LOW MOVES 
IN...UPPER LEVEL FLOW WILL INCREASE SLIGHTLY AND SHIFT TO THE WEST. 
CURRENTLY...GUIDANCE SUGGESTS IT WILL NOT ARRIVE EARLY ENOUGH NOR BE 
STRONG ENOUGH TO BREAK INVERSIONS FRIDAY...THEREBY KEEPING 
TEMPERATURES COOL THROUGH THE SHORT TERM. THE POSSIBILITY TO MIX OUT 
FRIDAY STILL EXISTS HOWEVER...AS MORE OF AN INCREASE IN WINDS COULD 
BREAK INVERSIONS AND INCREASE AFTERNOON HIGHS SIGNIFICANTLY. IN 
ADDITION TO THE CHANGE IN FLOW...UPPER LEVEL MOISTURE IN THE FORM OF 
HIGH CLOUDS WILL MOVE OVER THE CWA FRIDAY AFTERNOON AS THE LOW 
APPROACHES. LABELLE

.LONG TERM...SATURDAY THROUGH TUESDAY...
THERE SEEMS TO BE BETTER AGREEMENT AT LEAST THRU MON WITH FIRST 
SURGE OF COLD AIR ARRIVING SAT FOLLOWED BY A SECOND SURGE SUN 
NGT-MON. MODELS DIFFER AFTER THAT WITH THE GFS/CANADIAN DRIER AND 
COLDER WITH A RETURN TO MILDER AND WETTER CONDS A LITTLE LATER IN 
THE WK. THE ECMWF IS MAINTAINING A STRONGER SURGE OF PAC ENERGY 
MON-WED WITH CONTINUOUS PCPN AND RISING SNOW LVLS. THE GFS WAS 
FOLLOWED THRU MON WITH A BLEND OF GFS/ECMWF TUE INTO THE PRELIM 
GRIDDED FCST WED/WED NGT.

STG FRONTGEN IS INDICATED WITH CDFNT SAT/SAT NGT. HOWEVER MOISTURE 
WL BE QUITE LIMITED AND CONFINED MAINLY TO SHALLOW COLD AIRMASS. 
FAST MOVEMENT OF FRONT AND LIMITED MOISTURE SHOULD PRECLUDE ANYTHING 
MORE THAN SLGT CHC MENTION OF SHOWERS. SNOW LVLS DROP DRAMATICALLY 
AND ANY PCPN SHOULD BE IN THE FORM OF LGT SNOW. DO NOT ANTICIPATE 
SIGNIFICANT IMPACTS SAT-SUN WITH JUST PLAIN COLD CONDS FOR SUN. 
CURRENT FCST TEMPS ON SUN MAY BE A FEW DEGREES TO WARM WITH 20S AND 
30S MOST AREAS POSSIBLE IF THE MORE AGGRESSIVE GFS PANS OUT.

SECONDARY SYSTEM PIVOTS AROUND PACNW/NRN ROCKIES UPR LOW WITH 
LONGWAVE FEATURE RETROGRADING TO NR THE PACNW COAST AND ASSOCIATED 
JET EXTENDING FM THE EPAC INTO CA-NV. BOTH THE GFS/ECMWF AS WELL AS 
THE GEFS/CANADIAN ENSEMBLES SEEM TO INDICATE A DECENT POTENTIAL OF 
SNOW WITH THIS FEATURE SUN NGT INTO MON WITH A COMBINATION OF JET 
DYNAMICS AND INCRG INSTBY/UPR LVL FRONTGEN SUGGESTING GOOD 
POTENTIAL FOR SPILLOVER. POPS WERE INCREASED TO LIKELY SUN NGT-MON 
FOR THE SIERRA AND PARTS OF WRN NV WHERE ACCUMULATING SNOW COULD 
RESULT IN IMPACTS TO TRAVEL INCLUDING THE MON MRNG COMMUTE. 

FOR MON NGT-TUE A SLGT CHC-CHC OF PCPN WAS MAINTAINED DUE TO 
CONTINUED UNCERTAINTY. WHILE CONFIDENCE IS A BIT LOW AT THE END OF 
THE PD...STRONGER SIGNALS POINT TO A SURGE OF WET AND MILDER PAC 
ENERGY WED-THU. HOHMANN
&&

.AVIATION...
HI PRES OVR THE W COAST WL CONT TO BRING VFR CONDS AND LGT WINDS. 
SHALLOW FZFG WILL LIKELY GENERATE ONCE AGAIN OVER COLD SIERRA LAKES 
IN MONO COUNTY THIS MRNG ALTHOUGH CONDS WERE A BIT DRIER AND 
DEVELOPMENT MAY BE MORE LIMITED...MAINLY 12Z-17Z. 

FOR KTRK/KTVL...ELY GRADIENT WL LIKELY PREVENT FZFG FORMATION AND WL 
KEEP OUT OF THE TAFS. HOHMANN
&&

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

$$

HTTP://WEATHER.GOV/RENO