FXUS65 KVEF 071249
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
450 AM PST MON DEC 7 2009

SYNOPSIS...A STRONG STORM CENTERED NEAR NORTHERN CALIFORNIA WILL 
BRING ABUNDANT PACIFIC MOISTURE ACROSS THE REGION TODAY FOR 
WIDESPREAD RAIN AND SNOW ALONG WITH GUSTY WINDS. THE SYSTEM WILL
QUICKLY SWING ACROSS SOUTHERN NEVADA TO THE FOUR CORNERS REGION 
TONIGHT LEAVING COOL AND DRY NORTHWEST FLOW BEHIND IT TUESDAY AND 
WEDNESDAY. THE WEATHER PATTERN WILL REMAIN UNSETTLED THROUGH THE 
WEEK AS ADDITIONAL PACIFIC SYSTEMS MOVE INLAND THURSDAY THEN AGAIN 
FOR THE WEEKEND.
&&

.SHORT TERM...THE LATEST RADAR...SATELLITE AND MODEL TRENDS 
INDICATED PRECIPITATION SHOULD DEVELOP AND BECOME FAIRLY WIDESPREAD 
ACROSS MUCH OF THE REGION BETWEEN 12Z AND 15Z. THE START TIME FOR 
THE WINTER STORM WARNING FOR EASTERN SAN BERNARDINO COUNTY...
SOUTHERN NEVADA AND NORTHWEST ARIZONA WAS CHANGED TO 14Z BECAUSE OF 
THE POTENTIAL TO IMPACT THE MORNING COMMUTE BETWEEN LAS VEGAS AND 
PAHRUMP AND TRAFFIC ALONG I-15 AT MOUNTAIN PASS. THE LATEST NAM AND 
GFS KEEP THE DEEP MOISTURE PLUME OVER SAN BERNARDINO...CLARK... 
LINCOLN AND MOHAVE COUNTIES TODAY AND THIS EVENING. INYO...ESMERALDA
AND CENTRAL NYE SHOULD BE SHADOWED BY THE SOUTHERN SIERRA. 
HOWEVER...LARGE SCALE ASCENT WITH THIS SYSTEM SHOULD OVERCOME SOME 
OF THE OROGRAPHIC EFFECTS AND PRODUCE 4 TO 8 INCHES OF SNOW FOR MUCH 
OF THIS AREA...ESPECIALLY LATE THIS AFTERNOON AND EVENING AS THE 
COLD CORE MOVES OVERHEAD. ALSO...THE OWENS VALLEY SHOULD SEE 3-6 
INCHES OF SNOW ACCUMULATIONS AND A SNOW ADVISORY WAS ISSUED. THE GFS 
NOW INDICATES THE BEST POTENTIAL FOR SUSTAINED PRECIP OVER LAS VEGAS 
BETWEEN 10 AM AND 6 PM PST. AS THE TROUGH SWINGS ACROSS THIS 
EVENING...THE DEEP MOISTURE LIFTS TO THE NORTHEAST AND LIMITED 
MOISTURE WITH THE COLD POOL MAY PRODUCE SNOW FLURRIES...BUT NOTHING 
TOO SIGNIFICANT IN THE LAS VEGAS VALLEY. PRECIPITATION WILL QUICKLY 
WIND DOWN AFTER 12Z TUESDAY OVER NORTHWEST ARIZONA. THE AREA THEN 
CLEARS AND REMAINS UNDER COOL NORTHWEST FLOW THROUGH WEDNESDAY. A 
WEAK IMPULSE MAY BRUSH NORTHERN LINCOLN COUNTY LATE TUESDAY FOR A 
FEW SNOW SHOWERS. THE NAM MOS GUIDANCE IS CONSIDERABLE LOWER THAN 
THE GFS AND THE OFFICIAL FORECAST IS CLOSER TO THE NAM GIVEN THE 
COOL PATTERN.
&&

.LONG TERM...THE NEXT SYSTEM THE MODELS WERE SHOWING CONTINUES TO 
LOOK LESS AND LESS IMPRESSIVE. ALL OF THE MODELS SHOW IT APPROACHING 
THE CALIFORNIA COAST FROM THE WEST BY THURSDAY MORNING BUT WEAKEN IT 
CONSIDERABLY AS IT MOVES INLAND...MOVING IT ACROSS SOUTHERN NEVADA 
AS A WEAK RIPPLE OF ENERGY. OVERALL THIS WILL BE LARGELY A CLOUD 
MAKER WITH PERHAPS JUST ENOUGH MOMENTUM TO SQUEEZE OUT A FEW LIGHT 
SHOWERS ESPECIALLY OVER THE HIGHER ELEVATIONS. THE GFS ENSEMBLE MEAN 
WAS SHOWING BETWEEN A 20 AND 40 PERCENT CHANCE OF A TENTH OF AN INCH 
ACROSS OUR ENTIRE AREA AND GIVEN THIS OPTED TO KEEP POPS UP A LITTLE 
HIGHER AS THIS STILL LOOKS TO BE A SYSTEM ON THE WAY...BUT JUST ONE 
THAT WON'T BRING US MUCH IN THE WAY OF PRECIPITATION. THE ABUNDANT 
CLOUD COVER THOUGH WILL KEEP HIGH TEMPS CHILLY. SNOW LEVELS WILL BE 
AROUND 5000 FEET BUT LOW-LEVEL COLD AIR TRAPPED IN THE VALLEYS UP 
NORTH MAY CAUSE THEM TO FALL LOWER AT THE ONSET OF THE PRECIPITATION 
THERE THURSDAY...ALLOWING FOR SOME SNOW TO FALL ENTIRELY OR MIX WITH 
THE RAIN BEFORE CHANGING OVER. THIS SYSTEM HEADS EAST BY FRIDAY 
EVENING.

THERE SHOULD BE SOME DRYING THAT TAKES PLACE FOR FRIDAY NIGHT AND 
SATURDAY MORNING. AFTERWARDS THE THIRD SYSTEM OF THE WEEK ENTERS THE 
PICTURE FROM THE PACIFIC. THIS ONE IS EXPECTED TO HEAD FURTHER 
NORTH...THUS PUTTING US IN MORE OF A WEST/SOUTHWEST FLOW AHEAD OF 
IT. AS A RESULT...IT WILL BE WARMER AND SNOW LEVELS WILL BE HIGHER. 
THE BEST CHANCES FOR PRECIPITATION WILL BE OVER THE NORTHERN HALF OF 
THE AREA WITH SOME INDICATIONS NOT MUCH MAY TAKE PLACE FURTHER 
SOUTH. AGAIN PRECIP MAY INITIALLY START AS SNOW OR MIX WITH IT IN 
THE VALLEYS UP NORTH BEFORE GOING OVER TO RAIN. THE SIERRA IS LIKELY 
TO SEE THE BEST CHANCES FOR PRECIP WITH THIS SYSTEM AND PAINTED IN 
THE HIGHEST POPS THERE. OTHERWISE LOOK FOR HIGH TEMPS TO MAKE A RUN 
AT NORMAL LEVELS FOR THE WEEKEND...WHICH WILL CERTAINLY BE A BREAK 
FROM THE CHILL AROUND MOST OF THIS WEEK. THIS SYSTEM SHOULD HEAD 
EAST BY SUNDAY EVENING...ALLOWING FOR SOME DRYING BY SUNDAY NIGHT 
INTO MONDAY.
&&

.AVIATION...FOR MCCARRAN...CLOUD BASES WILL CONTINUE TO LOWER THIS 
MORNING AND DROP TO 5K FEET BY 21Z MONDAY. SOME LIGHT SHOWERS WILL 
BE AROUND BY LATER THIS MORNING AND TURN INTO MORE OF A STEADIER 
RAIN BY 21Z TODAY. THE BIG QUESTION IS JUST HOW LOW DO CIGS GO AFTER 
THIS. WE RARELY THROW THE TERM IFR IN A KLAS AVIATION DISCUSSION 
BUT THIS IS ONE OF THOSE TIMES WHERE ESPECIALLY WITH RESPECT TO CIGS 
IT MAY BE REACHED. IT IT DOES...IT WILL BE BETWEEN 23Z MONDAY AND 
07Z TUESDAY WHEN RAIN SHOULD BE STEADIEST AND THE ATMOSPHERE IS 
SATURATED OR CLOSE TO IT. FOR VSBY EXPECT IT TO BE BETWEEN 3 AND 5 
SM BUT IF ANY HEAVIER DOWNPOURS OCCUR IT COULD GO LOWER. WINDS WILL 
BE SOUTHERLY THROUGH THE DAY AND BECOME GUSTY AROUND 03Z TUESDAY 
WITH GUSTS TO AROUND 25 KTS EXPECTED. RAIN SHOULD END BY 07Z TUESDAY 
WITH SKIES GRADUALLY CLEARING AFTERWARDS. DUE TO THE STRONG WINDS 
ALOFT MECHANICAL TURBULENCE IS EXPECTED. MOUNTAINS WILL BE OBSCURED 
AROUND THE VALLEY WITH SNOW LEVELS DROPPING TO 3500 FEET OR SO LATER 
TONIGHT.  

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST 
CALIFORNIA...A STORM SYSTEM WILL MOVE ACROSS THE AREA TODAY INTO 
TONIGHT BRINGING MVFR TO IFR CIGS AND VSBY...MAINLY THIS AFTERNOON 
INTO EARLY TONIGHT WHEN PRECIPITATION IS STEADIEST AND HEAVIEST. 
SNOW LEVELS WILL DROP THROUGH THE DAY AND GET AS LOW AS 2500 TO 3500 
FEET BY TONIGHT. FOR THE TAFS...KBIH WILL SEE ALL SNOW AND VSBY HERE 
AS A RESULT WILL BE AN ISSUE...DROPPING TO AT LEAST 2SM AND EVEN 
LOWER IF IT SNOWS HEAVIER THAN EXPECTED. FOR KDRA...SOME SNOW MAY 
MIX IN JUST BEFORE PRECIPITATION ENDS AROUND 08Z/09Z TUESDAY. ALL 
OTHER TAF SITES WILL SEE JUST RAIN. PRECIPITATION WILL END BETWEEN 
06Z AND 12Z TUESDAY WITH CLOUDS SLOWLY CLEARING OUT. WINDS WILL BE 
GUSTY MAINLY OVER THE MOJAVE DESERT AFTER 03Z TUESDAY WHEN THE STORM 
BEGINS TO DEPART...AND GUSTS OVER 25 KTS ARE EXPECTED THEN. MOUNTAIN 
OBSCURATIONS ARE EXPECTED THROUGH TONIGHT AND DUE TO THE STRONG 
WINDS ALOFT MECHANICAL TURBULENCE WILL BE POSSIBLE.
&&

.VEF WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WARNING UNTIL 4 AM PST TUESDAY FOR NVZ015-018-019.
     WINTER STORM WARNING FROM 10 AM THIS MORNING TO 10 PM PST THIS 
     EVENING FOR NVZ014.
AZ...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR AZZ001-003.
CA...WINTER STORM WARNING UNTIL 4 AM PST TUESDAY FOR CAZ524.
     WINTER STORM WARNING UNTIL 10 PM PST THIS EVENING FOR CAZ519-521.
     WINTER STORM WARNING FROM 10 AM THIS MORNING TO 10 PM PST THIS 
     EVENING FOR CAZ522.
     WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR CAZ520.
&&

$$

ADAIR/STACHELSKI

HTTP://WEATHER.GOV/LASVEGAS