FXUS65 KVEF 261700
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
855 AM PST SAT DEC 26 2009

.SYNOPSIS...HIGH PRESSURE OVER THE SOUTHWEST STATES WILL GIVE WAY 
LATE TODAY TO A SERIES OF WEAK STORMS AFFECTING THE REGION SUNDAY 
THROUGH NEW YEARS DAY. THIS PATTERN WILL BRING CONSIDERABLE 
CLOUDINESS AND POSSIBLY A FEW FLURRIES TO THE HIGHER PEAKS.
&&

.UPDATE...VARIABLE HIGH CLOUDS TO MOVE ACROSS THE CWA TODAY AS THE  
RIDGE OVER THE AREA BEGINS TO BREAK DOWN IN RESPONSE TO A TROUGH 
COMPLEX OFF THE WEST COAST. INITIAL SHORT WAVE TO PUSH INTO THE 
SOUTHERN SIERRA TONIGHT WITH VERY LITTLE QPF EXPECTED. OVERALL 
CURRENT SHORT TERM FORECAST ON TRACK. NO UPDATES PLANNED THIS 
MORNING.
&& 

.AVIATION...FOR MCCARRAN...NORTHEAST WINDS WILL DEVELOP AROUND 18Z 
TODAY AND LAST THROUGH 02Z SUNDAY AT 4-8 KTS...THEN WINDS WILL TEND 
TO FAVOR A SOUTHWEST DIRECTION AT 3-6 KTS. SCT-BKN HIGH CLOUDS TODAY 
AS A SYSTEM APPROACHES THE AREA. CLOUD BASES WILL LOWER TO AROUND 
12K FEET BY THIS EVENING.  

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST 
CALIFORNIA...MAINLY LIGHT WINDS FOLLOWING DIURNAL DIRECTIONAL 
TRENDS. THE EXCEPTIONS WILL BE IN AREAS THAT FAVOR ENHANCED NORTH TO 
NORTHEAST WINDS OF 10-15 KTS WHEN WINDS DO BLOW FROM THAT COMPONENT. 
AT KDRA THIS WILL BE AT NIGHT WHILE AT KEED AND ELSEWHERE ALONG THE 
COLORADO RIVER VALLEY THIS WILL BE IN THE LATE MORNING AND AFTERNOON 
HOURS. A CLEAR SKY THIS MORNING WILL GIVE WAY TO SCT-BKN CLOUDS BY 
THIS AFTERNOON WITH CLOUD BASES LOWERING TO BETWEEN 5K AND 12K FEET 
BY TONIGHT. SCT SHSN ARE EXPECTED IN THE EASTERN SIERRA TONIGHT AND 
MOUNTAIN OBSCURATIONS WILL BE LIKELY THEN. THERE IS A 20 PERCENT 
CHANCE THAT A SHSN COULD IMPACT KBIH BETWEEN 00Z AND 12Z SUNDAY BUT 
FOR NOW WILL JUST KEEP THE TAF DRY AS ODDS ARE IF SNOW FALLS IT WILL 
BE VERY LIGHT AND THE MORE LIKELY IMPACT WOULD BE MORE IN THE FORM 
OF LOWER CIGS.
&&

.PREV DISCUSSION...243 AM PST SAT SHORT TERM...SATELLITE SHOWS CLEAR 
SKIES AREAWIDE AT 2 AM...WITH A WELL DEFINED CIRRUS SHIELD ADVANCING 
EAST THROUGH CALIFORNIA. THESE CLOUDS WILL SPREAD ACROSS OUR AREA 
TODAY. SURFACE OBS SHOW LOCALLY GUSTY NORTH WINDS IN SUSCEPTIBLE 
SPOTS...BUT LIGHT WINDS AT MOST STATIONS. THE MODELS HAVE MADE MAJOR 
CHANGES IN THE MONDAY TIME FRAME...FOCUSING MUCH MORE ON THE 
SHORTWAVE TROUGH WHICH WAS LOCATED NEAR 40N 137W AT 2 AM. WATER 
VAPOR LOOP SHOWS THAT THIS WAVE HAS DEEPENED QUITE A BIT SINCE 24 
HOURS AGO...LENDING CREDENCE TO THE MODEL TRENDS. THIS WAVE IS 
FORECAST TO SWING EAST TO NEAR THE CA/OR COAST TOMORROW 
AFTERNOON...STALL FOR A DAY OR SO...THEN PHASE WITH THE NEXT 
SHORTWAVE /WHICH WAS PREVIOUSLY EXPECTED TO REMAIN WELL OFFSHORE/ 
OVER SOUTHERN CALIFORNIA NEAR THE END OF THE SHORT TERM MONDAY 
NIGHT. THIS SHOULD RESULT IN SLIGHTLY HIGHER PRECIP CHANCES FOR THE 
SOUTHWEST HALF OF OUR CWFA SUNDAY NIGHT...SPREADING EAST AND NORTH 
MONDAY AND MONDAY NIGHT. MOISTURE AVAILABILITY IS STILL A QUESTION 
MARK...SO MADE RELATIVELY SMALL UPWARD ADJUSTMENTS IN POPS. FUTURE 
SHIFTS MAY NEED TO RERAISE DEPENDING ON HOW THE WAVES EVOLVE AND 
INTERACT. AT A MINIMUM...SHOULD BE MORE CLOUDS THAN SUN THROUGH THE 
SHORT TERM AND QUITE A BIT OF VIRGA. MIGHT EVEN SEE A SNOWFLAKE OR 
TWO IN THE LAS VEGAS VALLEY EARLY SUNDAY MORNING...BUT THE LOW 
LEVELS LOOK SO DRY THAT THE CHANCE OF MEASURABLE PRECIP SHOULD BE 
NEAR ZERO.

.LONG TERM...A BROAD UPPER LOW HEADS SOUTHEAST ACROSS THE AREA ON 
TUESDAY AFTERNOON. MODELS SHOW A LOT OF MID-LEVEL MOISTURE BUT GIVEN 
THE TRAJECTORY BEING NORTHWESTERLY THIS SHOULD RESULT IN A LOW 
THREAT OF PRECIP FOR MOST OF THE CWFA. AS A RESULT I HAVE KEPT IN 
GHOST POPS FOR JUST ABOUT ALL AREAS EXCEPT THE EASTERN SIERRA. 
CLOUDS LOOK A BETTER BET ALONG WITH SOME ENHANCED WINDS MAINLY DOWN 
THE COLORADO RIVER.

AFTER THIS SYSTEM HEADS OUT ANOTHER RIPPLE OF ENERGY IS PROGGED TO 
TRANSVERSE THE AREA AS NORTHWEST FLOW ALOFT REMAINS IN PLACE. THE 
00Z ECMWF WAS SHOWING LITTLE PRECIP WITH THIS FEATURE WHILE THE 00Z 
OPERATIONAL GFS/GFS ENSEMBLES AND GEM MODEL WERE SHOWING SOME 
SHOWERS WITH IT. OF NOTE IS THAT THE 06Z OPERATIONAL GFS HAS TRENDED 
MUCH DRIER WITH IT...SIMILAR TO THE ECMWF. POPS WERE INCREASED A 
LITTLE BUT MAINLY FOCUSED OVER THE HIGHER TERRAIN AND ESPECIALLY UP 
NORTH. THE TRAJECTORY OF THIS SYSTEM AND QUICK MOVING NATURE OF IT 
MAKES ME LEAN TOWARDS AGAIN ANOTHER THICK BATCH OF CLOUDS ROLLING ON 
THROUGH BEING THE MOST LIKELY IMPACT. NORTH WINDS SHOULD ALSO 
INCREASE ESPECIALLY OVER THE SOUTHERN GREAT BASIN AND LATER DOWN THE 
RIVER.

BY NEW YEARS EVE THERE IS EXCELLENT AGREEMENT WITH THE MODELS THAT 
AN UPPER LEVEL RIDGE WILL BUILD EASTWARD INTO THE WEST. OVERALL 
EXPECT TO SEE SOME WARMING BUT THIS MID-LEVEL MOISTURE SKIMMING BY 
TO THE NORTH WILL LIKELY SNEAK SOME EXTENT OF CLOUDS INTO THE AREA. 
WINDS LOOK LIGHT AND TEMPERATURES ARE EXPECTED TO BE AROUND NORMAL 
AS 2009 GIVES WAY TO 2010 WITH A SEASONABLE NIGHTTIME CHILL FOR NEW 
YEARS EVE. BY NEXT WEEKEND THE UPPER RIDGE MAY BEGIN TO BREAK DOWN 
AND ALLOW SYSTEMS PASSING BY TO THE NORTH TO PUSH FAR ENOUGH SOUTH 
TO BRING SOME VERY LIGHT SHOWERS TO NORTHERN PARTS OF THE AREA. 
LOWERED TEMPS THEN A LITTLE BUT OVERALL WE ARE NOT EXPECTING ANY 
MAJOR DROPS.  
&&

.VEF WATCHES/WARNINGS/ADVISORIES...
NV...NONE.
AZ...NONE.
CA...NONE.
&&

$$

JENSEN/MORGAN/STACHELSKI

HTTP://WEATHER.GOV/LASVEGAS