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.
 &&
 
 

 
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