FXUS65 KREV 212245
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
245 PM PST MON DEC 21 2009

SHORT TERM...
WEATHER SYSTEM ON TRACK TO MOVE THROUGH THE AREA LATE THIS AFTERNOON 
THROUGH TUESDAY. SNOW LEVELS ARE CURRENTLY RUNNING AROUND 6500-7000 
FEET BUT SHOULD QUICKLY DROP THIS EVENING AS A STRONG COLD FRONT 
MOVES INTO THE REGION FROM NORTH TO SOUTH. DISORGANIZED SHOWER 
ACTIVITY THIS AFTERNOON TO GRADUALLY BECOME MORE WIDESPREAD EARLY 
THIS EVENING AS THE UPPER JET AND FRONTAL FORCING BECOME BETTER 
ESTABLISHED. NUMEROUS SPATIAL PRECIP ISSUES WITH THIS SYSTEM AND AM 
A BIT CONCERNED THE INLAND TRAJECTORY OF THE LOW THROUGH CENTRAL NV 
WILL LIMIT SNOWFALL AMOUNTS OVER SIERRA AND EXTREME WRN NV. 

FOR THE SIERRA...SNOW LEVELS TO RAPIDLY DROP THIS EVENING AS 700 MB 
TEMPS PLUMMET TO BELOW -15C. ALTHOUGH LIQUID PRECIP AMOUNTS WILL NOT 
BE OVERLY IMPRESSIVE...GOOD SNOW RATIOS WILL AID IN ACCUMULATIONS. 
HOWEVER...THE INLAND TRAJECTORY THE LOW TAKES WILL LIMIT OROGRAPHIC 
LIFT OVER THE SIERRA. BELIEVE MOST OF THE PRECIP WILL FALL IN A 
SEVERAL HOUR PERIOD AS THE COLD FRONT AND ASSOCIATED FORCING PRODUCE 
A QUICK HITTING MODERATE TO HEAVY BAND OF SNOWFALL. AMOUNTS COVERED 
IN THE ADVISORY STILL LOOK ON TRACK...BUT WOULDN'T BE SURPRISED TO 
SEE THEM ON THE LOWER END DUE TO THE UNFAVORABLE TRACK/OROGRAPHICS. 
MONO COUNTY WILL GET SOME SNOW ESPECIALLY ALONG THE CREST NORTH OF 
MONO LAKE...BUT AMOUNTS BELOW ADVISORY CRITERIA AS PRECIP BAND 
WASHES OUT AS FORCING SHIFTS EAST. 

FOR WESTERN NV INCLUDING THE SURPRISE VALLEY: ANY PRECIP AHEAD OF 
THE FRONT WILL FALL PRIMARILY AS RAIN. IT WON'T BE UNTIL THE COLD 
FRONT MOVES THROUGH THIS EVENING THAT RAIN WILL QUICKLY TURN TO SNOW 
(AROUND 10-11PM IN RENO). THERE IS DECENT FRONTOGENESIS ALONG WITH 
MID LEVEL INSTABILITY (LI'S NEAR 0 TO +1) THAT WILL DEVELOP A 
RELATIVELY INTENSE BUT SHORT LIVED MESOSCALE SNOW BAND. WITH THE 
FAST MOVEMENT OF THE LOW/FRONT...DON'T BELIEVE THE BAND WILL LAST 
LONG ENOUGH TO WARRANT ADVISORIES FOR SNOW. MANY LOCATIONS WILL 
PICK UP A QUICK ONE TO TWO INCHES BUT THE DURATION OF ACCUMULATING 
SNOWFALL WILL BE ONLY A FEW HOURS FOLLOWED BY LIGHT SCATTERED SNOW 
SHOWERS. ACCUMULATING SNOWFALL SHOULD BE OVER BY THE MORNING 
COMMUTE. SNOWFALL COULD BE A BIT MORE PROLONGED OVER EASTERN 
PERSHING AND CHURCHILL COUNTIES BEING CLOSER TO THE CORE OF THE LOW. 
FREEZING RAIN IS LOOKING LESS LIKELY AS OBS ARE SHOWING ALMOST ALL 
VALLEYS ARE NOW ABOVE FREEZING WITH GOOD S-SWRLY WINDS IN MANY 
LOCATIONS.  

AS THE LOW TRACKS INTO THE GREAT BASIN TUESDAY AFTERNOON...EASTERLY 
WINDS WILL INCREASE AND LOOK TO BE QUITE GUSTY OVER THE SIERRA 
RIDGES. THIS COULD ALSO KEEP SOME LIGHT UPSLOPE INSTABILITY SNOW 
SHOWERS GOING INTO EARLY EVENING...BUT WITH LITTLE IF ANY 
ACCUMULATION. EXPECT COLD OVERNIGHT LOWS WITH STRENGTHENING VALLEY 
INVERSIONS TUESDAY NIGHT INTO WED AS RIDGING BUILDS BACK INTO THE 
REGION.  MILNE

.LONG TERM...THURSDAY THROUGH MONDAY...
UPPER RIDGE OFF THE WEST COAST ON THURSDAY MOVES SLOWLY EAST WITH 
AXIS OVER WRN NV BY EARLY SATURDAY MORNING. INVERSION CONDITIONS 
WITH MENTION OF FZFG WILL BE KEPT IN THE FORECAST THRU CHRISTMAS DAY 
AND SATURDAY...ALTHOUGH CONDS MAY IMPROVE MORE QUICKLY ON SAT AS 
HIGH CLOUD COVERAGE AND SW FLOW ALOFT INCREASES. DRY CONDS WILL 
PREVAIL THRU SAT WITH TEMPS HELD BELOW NORMAL IN VALLEYS DUE TO THE 
INVERSION AND LIGHT WINDS.

FOR SUNDAY-MONDAY...MEDIUM RANGE GUIDANCE BEGINS TO DIVERGE ON 
HANDLING TROF APPROACHING THE WEST COAST. WHILE THE CONSENSUS FAVORS 
A SPLITTING SYSTEM AS IT MOVES ONSHORE WITH MOST OF THE ENERGY 
DIVING TO FAR SRN CA...THE 12Z GFS AND ALMOST HALF OF THE ENSEMBLE 
MEMBERS BRING SOME LIGHT PRECIP TO THE SIERRA AS EARLY AS SAT NGT 
AND CONTINUING THRU SUN-SUN NGT AS THE SYSTEM BECOMES NEGATIVELY 
TILTED. OVERALL IT DOES NOT LOOK FAVORABLE FOR A SIGNIFICANT PRECIP 
EVENT SO POPS WILL BE LIMITED TO SLGT CHANCE MAINLY FOR THE SIERRA 
FROM SAT NGT-MON. THE GFS IS SEVERAL DEGREES COOLER AT 700 MB THAN 
THE ECMWF BUT BOTH MODELS TRENDED COOLER FROM PREV RUNS...SO SNOW 
LEVELS WERE LOWERED BY A FEW HUNDRED FEET. LITTLE CHANGE IN MAX 
TEMPS THRU NEXT MON AS MOST AREAS REMAIN BELOW NORMAL...ALTHOUGH 
NIGHTS WILL PROBABLY NOT BE AS COLD DUE TO THICKER AND MORE 
WIDESPREAD CLOUD COVERAGE. MJD 

&&

.AVIATION...
FOR KTVL-KTRK...CURRENT MVFR CONDS TO WORSEN TO IFR AROUND 00Z WITH 
LIFR AT TIMES BTWN 02Z-12Z AS PRECIP CHANGES TO ALL SNOW AND 
INCREASES IN INTENSITY. VSBY TO IMPROVE AFT 12Z ALTHOUGH CIGS LIKELY 
TO REMAIN MVFR WITH OCNL IFR IN SCT -SHSN THRU MOST OF TUESDAY.  

FOR KRNO-KLOL...VFR CIGS/VSBY TO PREVAIL THRU 04Z EVEN DURING BRIEF 
-SHRA AT BOTH SITES. BTWN 04Z-07Z...CIGS LOWERING TO MVFR AS -RA 
INCREASES AHEAD OF COLD FRONT PASSAGE. CHANGEOVER TO -SN EXPECTED 
AROUND 07Z WITH SHORT PERIODS OF IFR CIGS/VSBY THRU 12Z. CONDS 
IMPROVING AFT 12Z WITH MAINLY VFR CIGS/VSBY EXCEPT FOR OCNL MVFR IN 
ISOLD-SCT -SHSN MAINLY BEFORE 20Z. WINDS SHIFTING TO NW AND NORTH 
LATE TONIGHT THRU TUES AM AFTER COLD FRONT PASSAGE WITH GUSTS TO 25 
KT. MJD

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER WEATHER ADVISORY UNTIL 9 AM PST TUESDAY FOR NVZ002.

CA...WINTER WEATHER ADVISORY UNTIL 9 AM PST TUESDAY FOR CAZ071-072.

&&

$$

HTTP://WEATHER.GOV/RENO