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AREA FORECAST DISCUSSION

 
 FXUS65 KVEF 121052
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
350 AM PDT SUN OCT 12 2008

.SYNOPSIS...AN UNSEASONABLY COLD LOW PRESSURE SYSTEM WILL LINGER
OVER THE REGION TODAY THEN GRADUALLY MOVE EAST MONDAY. A DISTURBANCE
MOVING DOWN THE BACK SIDE OF THE SYSTEM TONIGHT WILL BRING GUSTY
NORTH WINDS TO MUCH OF THE AREA MONDAY THROUGH TUESDAY...ESPECIALLY
DOWN THE COLORADO RIVER VALLEY. UNSEASONABLY COLD TEMPERATURES WILL
PERSIST THROUGH MONDAY BEFORE WARMER TEMPERATURES RETURN TO THE AREA
BY THE MIDDLE OF THE WEEK.
&&

.SHORT TERM...THE UPPER LOW OVER THE GREAT BASIN AND INTERMOUNTAIN
REGION WILL MAKE LITTLE OR NO EASTWARD PROGRESS TODAY. THE 00Z/06Z
MODELS CONTINUE TO A SHOW A VORTICITY SPOKE DIVING FROM SOUTHERN
IDAHO DOWN THROUGH SOUTHERN NEVADA BY THIS EVENING. EVIDENCE OF THIS
COULD BE SEEN ON RECENT SATELLITE LOOPS AND IT APPEARS TO BE BEST
DEPICTED BY THE GFS. THE MAIN IMPACT OF THIS FEATURE WILL BE A
REINFORCING SHOT OF COLD AIR AND SUBSIDENCE WHICH WILL INCREASE
NORTHERLY WINDS ACROSS THE AREA...ESPECIALLY THE COLORADO RIVER
VALLEY...TONIGHT AND MONDAY. IT IS ALSO WORTH NOTING THAT SUFFICIENT
MOISTURE AND ASCENT ARE INDICATED WITH THIS DISTURBANCE TO PRODUCE
SOME SHOWERS OVER SOUTH CENTRAL NEVADA AND POSSIBLY THE SOUTHERN
NEVADA MOUNTAINS THIS AFTERNOON AND EARLY EVENING. THE GFS INDICATES
THE UPPER LOW WILL CLOSE OFF AND MAKE SLOW PROGRESS ACROSS NORTHERN
ARIZONA MONDAY THEN OPEN UP AS IT MOVES INTO THE SOUTHERN ROCKIES
TUESDAY. NORTH WINDS WILL PERSIST ACROSS THE FORECAST AREA TUESDAY
THEN DECREASE TUESDAY NIGHT AS ZONAL FLOW DEVELOPS.

.LONG TERM...AFTER A WEEKEND FEATURING TEMPERATURES MORE TYPICAL OF
DECEMBER MANY PEOPLE MAY BE WONDERING WHERE FALL WENT. THE GOOD NEWS
IS MUCH WARMER WEATHER WILL RETURN TO THE AREA BY THE LATTER HALF OF
THIS WEEK. THE MID AND UPPER LEVEL FLOW WILL BECOME SOUTHWESTERLY ON
WEDNESDAY AHEAD OF A SHORTWAVE TROUGH THAT MOVES ACROSS THE PAC NW.
ALTHOUGH MODEL FORECAST SOUNDINGS SHOW A SHALLOW INVERSION THAT WILL
KEEP THE LOWEST LEVELS FROM MIXING...HIGH TEMPS SHOULD STILL WARM BY
4 TO 8 DEGREES OVER TUESDAY. FURTHER WARMING IS EXPECTED TO TAKE
PLACE ON THURSDAY AS AN UPPER RIDGE BUILDS EASTWARD INTO THE
SOUTHWESTERN CONUS. ALTHOUGH THE RIDGE WILL SLIDE EASTWARD ON FRIDAY
A SOUTHWEST FLOW ALOFT WILL KEEP HIGH TEMPS ABOVE NORMAL ACROSS THE
AREA. EVEN THOUGH WE WILL REMAIN IN A SOUTHWEST FLOW ALOFT ON
SATURDAY...AN UPPER TROUGH APPROACHING THE PAC NW WILL HELP TO LOWER
HEIGHTS ACROSS THE AREA ALLOWING FOR A SUBTLE DROP IN TEMPS AND
PUSHING THEM BACK CLOSER TO NORMAL. THE MODELS BEGIN TO DIVERGE BY
SUNDAY...WITH THE 00Z GFS AND 06Z DGEX SHOWING AN UPPER LOW
ASSOCIATED WITH THE SOUTHERN BRANCH OF THE JETSTREAM MOVING ACROSS
SOCAL INTO ARIZONA ON MONDAY...WHILE THE 00Z ECMWF DIVES A DEEP
UPPER TROUGH SOUTHWARD TOWARDS THE GREAT BASIN BY MONDAY NIGHT. FOR
NOW I DEPICTED SOME CLOUDS IN THE GRIDS FOR THIS TIME FRAME...BUT
WHAT IS UNCERTAIN IS JUST HOW MUCH COOLING TAKES PLACE AND IF ANY
POPS NEED TO BE INTRODUCED.
&&

.AVIATION...FOR MCCARRAN...GUSTY NORTH WINDS EARLY THIS MORNING WILL
LESSEN SOME AS THE MORNING PROGRESSES AS SURFACE PRESSURE GRADIENTS
SLOWLY WEAKEN...BUT IT STILL LOOKS LIKE NORTH WINDS AROUND 10 KTS
WILL PREVAIL THIS AFTERNOON INTO TONIGHT. FEW-SCT CLOUDS ARE
EXPECTED AOA 10K FEET TODAY...MAINLY OVER THE SURROUNDING MOUNTAINS
WITH A CLEAR SKY TONIGHT.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...AN UPPER LOW WILL REMAIN OVER THE THE AREA TODAY.
ENOUGH MOISTURE ON THE BACK SIDE OF THIS SYSTEM WILL STILL ALLOW FOR
ISOLATED SHSN ACROSS LINCOLN COUNTY AS WELL AS SCT-BKN CLOUDS WITH
CIGS AS LOW AS 6-8K FEET AND POSSIBLE MTN OBSCURATION. OTHERWISE
EXPECT GENERALLY NORTH WINDS ACROSS THE AREA AT 10-15 KTS WITH GUSTS
OF 20-25 KTS ESPECIALLY ACROSS THE SOUTHERN GREAT BASIN...THE OWENS
VALLEY AND DOWN THE COLORADO RIVER. WINDS WILL LESSEN SOME
OVERNIGHT...BUT GUSTS AROUND 15 KTS ARE STILL POSSIBLE DOWN THE
COLORADO RIVER. FEW-SCT CLOUDS AOA 10K FEET...BECOMING CLEAR
TONIGHT.
&&

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




ADAIR/STACHELSKI

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