FXUS65 KVEF 021759
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
959 AM PST WED DEC 2 2009

.SYNOPSIS...HIGH PRESSURE WILL KEEP A DRY WEATHER PATTERN OVER THE 
SOUTHWEST MUCH OF THE WEEK...BUT COOLER TEMPERATURES AND LOCALLY 
GUSTY NORTH WINDS CAN BE EXPECTED THURSDAY AND FRIDAY. THE HIGH 
PRESSURE RIDGE WILL BREAK DOWN GOING INTO THE WEEKEND...LEADING TO A 
SIGNIFICANT PATTERN CHANGE WITH A SERIES OF STRONG PACIFIC STORMS 
IMPACTING THE REGION LATE IN THE WEEKEND THROUGH NEXT WEEK.
&&

.UPDATE...A CLEAR SKY UNDER A COOLER NORTHERLY FLOW WILL BE THE MAIN 
STORY TODAY THROUGH FRIDAY. THE 12Z NAM AND GFS MOS GUIDANCE STILL 
SHOW A GOOD POTENTIAL FOR NEAR FREEZING TEMPERATURES FOR SOME OF THE 
LAS VEGAS EARLY FRIDAY MORNING AND SUBFREEZING TEMPS VALLEYWIDE BY 
EARLY SATURDAY MORNING. THE GOING FORECAST HAS THESE TRENDS COVERED 
AND NO UPDATE IS PLANNED.
&&

.PREV DISCUSSION.../237 AM PST WED DEC 2 2009/

.SHORT TERM...SATELLITE SHOWS HIGH CLOUDS ROUGHLY SOUTHWEST OF A 
LINE FROM TONOPAH TO KINGMAN...WITH CLEAR SKIES TO THE NORTHEAST. 
SURFACE OBS SHOW LIGHT WINDS AND SEASONABLY CHILLY TEMPS AREAWIDE. 
THERE WILL BE TWO SYSTEMS OF CONCERN THROUGH THE SHORT TERM...THE 
DEEP LOW BEING CARVED OUT OVER THE NORTHERN PLAINS TODAY AND 
THURSDAY AND THE STORM COMING OUT OF THE GULF OF ALASKA INTO THE 
NORTHERN ROCKIES FRIDAY. SATELLITE SHOWS THE FIRST SYSTEM OVER 
HUDSON BAY EARLY THIS MORNING. THIS CIRCULATION WILL RETROGRADE 
SOUTHWEST ALONG THE MANITOBA/ONTARIO BORDER AND MERGE WITH ANOTHER 
CIRCULATION WHICH WAS OVER NORTH DAKOTA THIS MORNING...FORMING A BIG 
LOW WHICH WILL MEANDER OVER MINNESOTA THROUGH THURSDAY. A TROUGH 
WILL EXTEND FROM THIS LOW CENTER ALL THE WAY BACK TO THE DESERT 
SOUTHWEST...AND WILL COMBINE WITH HIGH AMPLITUDE RIDGING ALONG THE 
WEST COAST TO PRODUCE ROBUST NORTHERLY FLOW OVER THE EASTERN HALF OF 
OUR CWFA. THIS WILL PULL COLDER AND MUCH DRIER AIR DOWN INTO OUR 
AREA...AND ALSO SUPPORT GUSTY NORTH WINDS IN THE SUSCEPTIBLE AREAS 
SUCH AS THE COLORADO RIVER VALLEY. THE AFOREMENTIONED SECOND SYSTEM 
WILL DIG OUT OF BRITISH COLUMBIA/ALBERTA ON FRIDAY...FORCING THE 
WEST COAST RIDGE WESTWARD AND QUICKLY BACKING OUR MID LEVEL FLOW 
FROM NORTHERLY TO WESTERLY. THIS WILL SUPPORT AN INFLUX OF HIGH 
CLOUDS...AS NOTED ON 500-300 MB MOISTURE PROGS. NOW FOR THE SENSIBLE 
WEATHER IMPACTS. HIGH TEMPERATURES WILL COME DOWN 5 TO 15 DEGREES 
FROM TODAY TO FRIDAY...WITH THE GREATEST DROPS IN THE EASTERN ZONES. 
THERE WILL ALSO BE SOME RISK OF THE FIRST FREEZE OF THE SEASON IN 
LAS VEGAS THURSDAY AND FRIDAY NIGHTS. HOWEVER...THE NORTH WINDS 
ASSOCIATED WITH THE FIRST SYSTEM COULD KEEP TEMPS UP THURSDAY 
NIGHT...AND THE HIGH CLOUDS ASSOCIATED WITH THE SECOND SYSTEM COULD 
DO THE SAME FRIDAY NIGHT. THUS...THE RISK OF FREEZING TEMPERATURES 
WILL BE HIGHER IN THE OUTLYING AREAS OF THE VALLEY...AND LOWER IN 
THE HEAVILY DEVELOPED AREAS WHERE URBAN HEAT ISLAND EFFECTS ARE 
GREATEST. IF WINDS DECOUPLE THURSDAY NIGHT OR THE HIGH CLOUDS ARE 
DELAYED INTO SATURDAY...FREEZE WARNINGS COULD BE NEEDED.

.LONG TERM...DEFINITELY THERE WILL BE A MAJOR CHANGE IN THE WEATHER 
NEXT WEEK TOWARDS A MORE ACTIVE AND WET PERIOD. BROAD MODEL 
AGREEMENT ON SETTING UP A STRONG LOW IN THE PACIFIC NORTHWEST BY 
SUNDAY AND THAT A GOOD FETCH OF SUBTROPICAL MOISTURE WILL BE DRAWN 
IN. THE DIFFERENCES ARE IN THE DETAILS OF THE WAVES THAT WILL ROTATE 
AROUND IT INTO OUR AREA....THUS THE FORECAST IS A BIT BROAD BRUSHED. 
MOST OF THE LATEST MODEL RUNS WILL HAVE THE LOW OPEN UP AND MOVE OUT 
LATE MONDAY AND TUESDAY. THIS APPEARS TO BE THE BEST TIME FOR 
PRECIPITATION CHANCES. IT IS NOT OUT OF THE QUESTION TO SEE GOOD 
SNOW FALLS AT HIGHER ELEVATIONS THEN...BUT DEPENDING ON SOLUTION 
CHOSEN SNOW LEVELS COULD BE HIGH AND THE AMOUNT OF PRECIPITATION 
SHADOWING COULD BE SIGNIFICANT DOWN STREAM FROM THE SIERRA. 
CONFIDENCE IS UP A BIT AND DID RAISE POPS IN MOST AREAS WITH THE 
SIERRA BEING RAISED THE MOST.
&&

.AVIATION...FOR MCCARRAN...THE DIURNAL PATTERN OF THE LAST FEW DAYS 
IS EXPECTED TO CONTINUE TODAY AS WELL...WITH NORTHEAST WINDS IN THE 
AFTERNOON AND SOUTHWEST IN THE EVENING AND OVERNIGHT. WIND SPEEDS 
WILL BE BELOW 7 KNOTS. NO SIGNIFICANT CLOUDS ARE EXPECTED.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST 
CALIFORNIA...WINDS WILL REMAIN RELATIVELY LIGHT OVER THE AREA 
THROUGH THURSDAY MORNING FOLLOWING LOCAL DIURNAL PATTERNS. GUSTIER 
NORTH WINDS WILL DEVELOP THURSDAY AFTERNOON...PRIMARILY DOWN THE 
COLORADO RIVER VALLEY...IMPACTING LOCATIONS LIKE LAUGHLIN AND 
NEEDLES. WIND GUSTS TO 25 MPH SHOULD BE ANTICIPATED IN THOSE 
LOCATIONS ON THURSDAY AFTERNOON. NO SIGNIFICANT CLOUDS ARE EXPECTED.
&&

.FIRE WEATHER...LOCALLY GUSTY NORTH WINDS...ESPECIALLY DOWN THE 
COLORADO RIVER VALLEY...WILL USHER IN A VERY DRY AIRMASS ON 
THURSDAY. MINIMUM RELATIVE HUMIDITY VALUES WILL DROP INTO THE LOW 
TEENS AND SINGLE DIGITS THURSDAY AND FRIDAY. HOWEVER...WIND GUSTS 
ARE EXPECTED TO GENERALLY REMAIN BELOW 30 MPH.
&&

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

$$

ADAIR/GORELOW/MORGAN/JACQUES

HTTP://WEATHER.GOV/LASVEGAS