FXUS65 KVEF 061303
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
500 AM PST SUN DEC 6 2009

.SYNOPSIS...A COLD LOW PRESSURE SYSTEM DROPPING OUT OF CANADA WILL 
MOVE INTO NORTHERN CALIFORNIA TODAY. THIS WILL RESULT IN LOCALLY 
STRONG AND GUSTY WINDS TODAY AND TONIGHT FOR THE SOUTHERN SIERRA AND 
SOUTHERN NEVADA MOUNTAINS. WIDESPREAD VALLEY RAIN AND MOUNTAIN SNOW 
WILL DEVELOP ACROSS MUCH OF THE AREA ON MONDAY THROUGH MONDAY NIGHT.
UNSETTLED WEATHER WILL THEN BE OVER THE REGION THROUGH THE REMAINDER 
OF THE WEEK.
&&

.SHORT TERM...THE MAIN FEATURES TO WATCH ARE THE COLD LOW OVER 
WASHINGTON/OREGON AND THE MOISTURE PLUME BETWEEN CALIFORNIA AND
HAWAII. THE MODELS WERE IN FAIRLY GOOD AGREEMENT WITH THE EVOLUTION 
OF THE SYSTEM THROUGH TUESDAY AND THE GFS SOLUTION WAS USED AS THE 
BASIS FOR THE FORECAST. THE MAIN ISSUE TODAY WILL BE STRONG WINDS 
DEVELOPING OVER THE SOUTHERN SIERRA AND THE SPRING MOUNTAINS/SHEEP 
RANGE TONIGHT. ALTHOUGH DOWNSLOPE CONDITIONS DO NOT APPEAR REAL 
FAVORABLE...RIDGETOP WINDS WILL BE HIGH AND THIS COULD IMPACT UPPER 
SLOPES. REPLACED THE HIGH WIND WATCH WITH A HIGH WIND WARNING FOR 
THE SOUTHERN SIERRA AND A WIND ADVISORY FOR THE SOUTHERN NEVADA 
MOUNTAINS THROUGH TONIGHT. THINGS BECOME MORE INTERESTING TONIGHT 
AND EARLY MONDAY AS THE PACIFIC MOISTURE GETS PULLED ACROSS SOUTHERN 
CALIFORNIA AND SOUTHERN NEVADA MONDAY MORNING. LIGHT PRECIPITATION 
COULD BEGIN BEFORE 12Z MONDAY BUT IT STILL APPEARS THE MAIN 
COMBINATION OF BROAD UPWARD FORCING AND DEEP MOISTURE WILL COME 
TOGETHER FOR MOST OF THE AREA AFTER 18Z MONDAY. IT APPEARS 21Z 
MONDAY TO 06Z TUESDAY WILL BE THE BEST WINDOW FOR MODERATE TO HEAVY 
RAIN AND SNOW ACROSS MOST OF THE FORECAST AREA. NORTHWEST ARIZONA 
WILL CONTINUE TO SEE GOOD POTENTIAL THROUGH 12Z TUESDAY. SIGNIFICANT 
SNOW ACCUMULATIONS SHOULD BE ABOVE 4000 FEET AND THE WINTER STORM 
WATCH REMAINS IN EFFECT. HOWEVER...ADDED DEATH VALLEY...EASTERN SAN 
BERNARDINO COUNTY AND CENTRAL/SOUTHERN MOHAVE COUNTY. THE LOW CENTER 
IS FORECAST TO SWING ACROSS SOUTHERN NEVADA BETWEEN 06Z AND 12Z 
TUESDAY AND MOISTURE WILL BE LIMITED IMMEDIATELY FOLLOWING IT. 
PRECIPITATION WILL TURN SHOWERY WITH THE COLD CORE AND LIGHT SNOW 
SHOWERS COULD STILL BE OBSERVED AT ELEVATIONS OF 2500-3000 FEET 
MONDAY NIGHT. TUESDAY WILL DRY OUT UNDER NORTHWEST FLOW ON THE BACK 
SIDE OF THE SYSTEM.

.LONG TERM...THE ACTION DOES NOT STOP WITH THE DEPARTURE OF THE 
EARLY WEEK SYSTEM AS AN ACTIVE STORM TRACK REMAINS IN PLACE ACROSS 
THE SOUTHWESTERN U.S.. WEDNESDAY SHOULD BE A BIT OF A BREAK IN 
BETWEEN SYSTEMS AS A WEST-NORTHWEST FLOW ALOFT SETS UP. ALL OF THE 
MODELS HAVE TRENDED SLOWER WITH THE NEXT SYSTEM PROGGED ENTER THE 
PICTURE...HOWEVER WE SHOULD STILL SEE A CONSIDERABLE AMOUNT OF HIGH 
LEVEL CLOUDS OVERSPREAD THE REGION FROM THE WEST ON WEDNESDAY. GIVEN 
THIS AND WEAK MIXING...HIGH TEMPS WILL BE QUITE CHILLY AND RUN SOME 
12 DEGREES BELOW NORMAL. CLOUDS WILL CONTINUE TO MOVE IN ON 
WEDNESDAY NIGHT...HOWEVER...IT LOOKS LIKE ANY REAL SHOT AT 
PRECIPITATION OUTSIDE OF THE SIERRA AND SAN BERNARDINO COUNTY 
DESERTS SHOULD HOLD OFF UNTIL AFTER DAYBREAK THURSDAY. THUS POPS 
WERE LOWERED FOR WEDNESDAY NIGHT.

THE 00Z MODELS DID NOT LOOK AS IMPRESSIVE WITH THIS NEXT SYSTEM AS 
THEY SEEM TO DAMPEN OUT MUCH OF THE MOISTURE BEFORE THE SYSTEM WORKS 
ACROSS THE AREA. THIS MAY WIND UP BEING A SYSTEM THAT IS LARGELY A 
CLOUD MAKER AND FEATURES PRECIPITATION...BUT ONLY GENERATES SMALL 
AMOUNTS IN THE VALLEYS AND MAINLY WETS (OR SNOWS IN) THE HIGHER 
ELEVATIONS. NEVERTHELESS THERE REMAINS GENERAL AGREEMENT THAT THIS 
SYSTEM WILL CROSS THE AREA THURSDAY - LIKELY IN THE AFTERNOON INTO 
FRIDAY MORNING - SO FOCUSED POPS IN THESE TIME FRAMES. INITIALLY 
SNOW LEVELS WILL START LOW BUT SHOULD RISE THROUGH THE EVENT TO 
5000-6000 FEET. ONE CONCERN AT THE ONSET OF PRECIPITATION IS 
LOW-LEVEL COLD AIR WILL BE IN THE VALLEYS ESPECIALLY UP NORTH...SO 
PRECIPITATION MAY START HERE AS SNOW OR SNOW/RAIN MIX BEFORE 
CHANGING OVER TO ALL RAIN. THIS SYSTEM HEADS EAST BY FRIDAY NIGHT.

THERE SHOULD BE A SHORT-LIVED BREAK FRIDAY NIGHT INTO SATURDAY 
MORNING BEFORE THE THIRD SYSTEM OF THE WEEK HEADS ON IN. THE LATEST 
MODELS NOW TAKE THIS SYSTEM WELL TO OUR NORTH WHICH WOULD YIELD A 
WARMER SYSTEM WITH HIGHER SNOW LEVELS AND ALSO FOCUS THE BEST 
CHANCES FOR PRECIPITATION OVER THE NORTHERN PARTS OF THE AREA. 
HOWEVER SINCE THE MODELS MAY STILL BOUNCE AROUND WITH WHERE THEY 
PLACE THE LOW...GHOST POPS AT A MINIMUM WERE WENT WITH WITH SLIGHT 
CHANCE TO CHANCE POPS OVER THE HIGHER TERRAIN. HIGH TEMPS OVERALL 
SHOULD BE WARMER GIVEN THE PACIFIC ORIGIN OF THE AIR MASS THEN.  
&&

.AVIATION...FOR MCCARRAN...NORTHEAST WINDS AT 8-12 KTS ARE EXPECTED 
THROUGH AROUND 22Z SUNDAY BEFORE WINDS TURN TO THE SOUTH. WINDS WILL 
TAKE ON MORE OF A SOUTH-SOUTHWEST COMPONENT BETWEEN 05Z AND 08Z 
MONDAY. FEW-SCT CLOUDS AROUND 15K FEET THROUGH THIS EVENING. CLOUD 
LAYERS WILL INCREASE TONIGHT WITH BASES LOWERING IN ADVANCE OF AN 
APPROACHING STORM SYSTEM THAT WILL AFFECT THE LAS VEGAS VALLEY 
MONDAY AFTERNOON INTO EARLY TUESDAY MORNING. CEILINGS WILL LIKELY 
DROP BELOW 5K FEET THEN AND THERE IS A 60 PERCENT CHANCE OF CEILINGS 
DROPPING BELOW 3K FEET AND VSBY LOWERING BELOW 5 MILES AT TIMES 
MONDAY EVENING. PRECIPITATION WILL REMAIN ALL RAIN IN THE VALLEY 
WITH LOCAL MOUNTAINS BEING OBSCURED. MECHANICAL TURBULENCE WILL BE 
POSSIBLE MONDAY INTO EARLY TUESDAY MORNING DUE TO STRONG WINDS 
ALOFT.  

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST 
CALIFORNIA...WINDS WILL INCREASE FROM THE SOUTH BETWEEN 18Z AND 20Z 
SUNDAY WITH GUSTS OVER 20 KTS IN FAVORED AREAS. FEW-SCT CLOUDS AOA 
15K FEET. TONIGHT WINDS WILL LESSEN SOME BUT STILL REMAIN MAINLY 
FROM THE SOUTH AT 6-12 KTS. ONLY EXCEPTION OF NOTE LOOKS TO BE IN 
THE OWENS VALLEY WHERE A DOWNVALLEY WIND SHOULD DEVELOP TONIGHT. 
CLOUD LAYERS WILL INCREASE TONIGHT AND WITH BASES LOWERING IN 
ADVANCE OF AN APPROACHING STORM SYSTEM. THE MAIN IMPACTS FROM THIS 
SYSTEM WILL BE FROM LATE MONDAY MORNING THROUGH EARLY TUESDAY 
MORNING. MVFR/IFR CIGS AND VSBY WILL BE LIKELY ACROSS MUCH OF THE 
AREA AT TIMES ESPECIALLY MONDAY EVENING. PRECIPITATION IS EXPECTED 
AREAWIDE WITH SNOW LEVELS LOWERING TO AROUND 3500 FEET BEFORE 
PRECIPITATION ENDS MONDAY NIGHT. MOUNTAIN OBSCURATIONS ARE EXPECTED. 
MECHANICAL TURBULENCE WILL BE POSSIBLE MONDAY INTO EARLY TUESDAY 
MORNING DUE TO STRONG WINDS ALOFT.  
&&

.VEF WATCHES/WARNINGS/ADVISORIES...
NV...WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 4 AM PST MONDAY FOR 
     NVZ018-019.
     WINTER STORM WATCH FROM MONDAY MORNING THROUGH LATE MONDAY 
NIGHT      FOR NVZ014-015-018-019.
AZ...WINTER STORM WATCH FROM MONDAY MORNING THROUGH LATE MONDAY 
NIGHT      FOR AZZ001-003.
CA...WINTER STORM WATCH FROM MONDAY MORNING THROUGH LATE MONDAY 
NIGHT      FOR CAZ522-524.
     WINTER STORM WATCH FROM LATE TONIGHT THROUGH MONDAY EVENING FOR 
     CAZ519-521.
     HIGH WIND WARNING FROM 10 AM THIS MORNING TO 10 PM PST THIS 
     EVENING FOR CAZ519.
&&

$$

ADAIR/STACHELSKI

HTTP://WEATHER.GOV/LASVEGAS