000 FXUS65 KVEF 092100 AFDVEF AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LAS VEGAS NV 200 PM PDT THU JUL 9 2009 .SYNOPSIS...MOISTURE WILL INCREASE ACROSS THE AREA TONIGHT INTO FRIDAY AS THE FLOW ALOFT BECOMES SOUTHERLY. THIS WILL RESULT IN AN INCREASE IN CLOUDS TONIGHT AND THE POSSIBILITY OF AN ISOLATED THUNDERSTORM OVER MOHAVE COUNTY ON FRIDAY AFTERNOON. ON SATURDAY THE CHANCE FOR AN ISOLATED THUNDERSTORM WILL EXIST ACROSS MOST OF THE HIGHER ELEVATIONS ACROSS THE AREA. BY SUNDAY A SYSTEM MOVING INTO THE PACIFIC NORTHWEST WILL TURN THE FLOW ALOFT SOUTHWEST AND THIS WILL HELP TO DRY OUT THE AREA AND ALLOW FOR LITTLE IN THE WAY OF CLOUD COVER. HIGH TEMPERATURES WILL REMAIN AT OR ABOVE NORMAL THROUGH THE MIDDLE OF NEXT WEEK. && .SHORT TERM...OVERALL DRY AIR IS DOMINATING AT ALL LEVELS BUT THINGS WILL CHANGE TONIGHT AS THE UPPER LEVEL FLOW BECOMES MORE SOUTHERLY. AN UPPER LOW PRESENTLY OFF THE COAST OF WASHINGTON/OREGON IS PROGGED TO MOVE SOUTHWARD TO OFF THE SOUTHERN OREGON COAST TONIGHT WHICH IN RESPONSE SHIFTS THE FLOW ALOFT OVER OUR CWFA TO A DIRECTION MORE OUT OF THE SOUTH. THIS WILL RESULT IN INCREASING MOISTURE AT ALL LEVELS IN THE ATMOSPHERE. INITIALLY THE UPPER LEVELS WILL MOISTEN UP AND THIS WILL RESULT IN INCREASING HIGH LEVEL CLOUDS OVERNIGHT. HOWEVER THE MID-LEVELS AND EVENTUALLY LOW-LEVELS ARE ALSO PROGGED TO MOISTEN UP BY DAYBREAK FRIDAY WHICH AT THE LEAST WILL RESULT IN SOME A MID-LEVEL CLOUD DECK IN THE FEW TO SCT RANGE BUT ALSO INCREASE DEWPOINTS ACROSS THE AREA. OUTSIDE OF THE 12Z GFS WHICH HAD A SPURIOUS LOOKING MID-LEVEL DISTURBANCE RIPPLING THROUGH THE AREA...THERE REALLY APPEARS TO BE NO SIGNIFICANT TRIGGER FOR CONVECTION ON FRIDAY AFTERNOON OTHER THAN HEATING AND TERRAIN. THE BEST INSTABILITY WILL BE ACROSS THE EASTERN PARTS OF MOHAVE COUNTY WHERE LI/S APPROACH +2. THINK THE REALITY IS WE SEE A GOOD DEAL OF CLOUDS TONIGHT AND TOMORROW BUT IT APPEARS ANY REAL SHOT AT CONVECTION WAITS UNTIL SATURDAY AFTERNOON WHEN INSTABILITY IS GREATER ACROSS MOST OF THE AREA. AS A RESULT THUNDERSTORMS WILL BE POSSIBLE ACROSS MOST OF THE AREA THEN BUT GIVEN THE SIGNIFICANT LACK OF A TRIGGER THEY SHOULD DEVELOP OVER THE HIGHER ELEVATIONS. ON BOTH DAYS THE MAIN THREAT IN STORMS WILL BE GUSTY WINDS BUT A LOCALLY HEAVY DOWNPOUR IS NOT ENTIRELY IMPOSSIBLE IN THE EAST AS PWATS EXCEED 1 INCH THERE. TEMPS WILL WARM STEADILY AS HEIGHTS SLOWLY RISE IN RESPONSE TO A BIG RIDGE PRESENTLY OVER TEXAS THAT TRIES TO BUILD WEST. BY SUNDAY THE AFOREMENTIONED UPPER LOW OFF THE COAST OF OREGON MOVES INLAND AND TURNS THE FLOW ALOFT MORE SOUTHWEST. THIS WILL HELP TO DRY OUT MOST OF THE AREA THOUGH HAVE HELD ON TO SOME SLIGHT CHANCE POPS IN THE AFTERNOON IN MOHAVE AND LINCOLN COUNTIES AS THESE AREAS ARE OFTEN SLOW TO ENTIRELY DRY OUT. OTHERWISE TEMPS WILL CONTINUE TO WARM WITH HIGHS POSSIBLY TAKING A RUN AT THE 110 DEGREE MARK IN LAS VEGAS AS HEIGHTS RISE FURTHER AND 700 MB TEMPS APPROACH +16C. SEE THE CLIMATE SECTION BELOW FOR SOME STATS ON 110 DEGREE HIGHS IN LAS VEGAS. AS THE SYSTEM CROSSES THE PAC NW SUNDAY NIGHT WINDS WILL PICK UP SOME OUT OF THE SOUTHWEST AND BECOME LOCALLY BREEZY. .LONG TERM...LITTLE CHANGE TO THE MONDAY THROUGH FRIDAY PERIOD. THE BIG RIDGE WHICH WILL BE THE MAIN PLAYER SLOWLY MIGRATES FROM NEW MEXICO TO ARIZONA/UTAH THROUGH THE PERIOD...WITH ENOUGH WESTWARD RIDGING TO BLOCK MEXICAN MOISTURE AT LEAST THROUGH THURSDAY. THUS...DRY WEATHER AND HOT TEMPERATURES ARE EXPECTED. THERE IS A GOOD CHANCE OF KLAS REACHING 110F FOR THE FIRST TIME THIS SEASON DURING THIS PERIOD. THE 12Z ECMWF HAS TRENDED TOWARD THE 12Z GFS IN DEPICTING SOME WEAKENING OF THE WESTWARD EXTENSION OF THE HIGH BY FRIDAY...WHICH WOULD ALLOW SOME MOISTURE TO INVADE OUR AREA FROM THE SOUTHEAST. HEDGED IN THIS DIRECTION ON FRIDAY BY ADDING SOME CLOUDS AND RAISING POPS A BIT...BUT KEPT THEM BELOW 15 PERCENT. IF FUTURE MODEL RUNS LOOK SIMILAR...POPS CAN BE TRENDED HIGHER. && .AVIATION...FOR MCCARRAN...MID AND HIGH LEVEL CLOUDS WILL INCREASE TONIGHT AND FRIDAY...BUT CIGS ARE EXPECTED TO REMAIN ABOVE 120. THERE IS A VERY SMALL CHANCE FOR A THUNDERSTORM OVER THE MOUNTAINS NEAR THE AIRPORT ON SATURDAY...THEN CLOUDS WILL DECREASE SATURDAY NIGHT. GUSTY SOUTHWEST WINDS WILL CONTINUE IN THE AFTERNOONS AND EVENINGS THROUGH THE WEEKEND. FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST CALIFORNIA...MID AND HIGH LEVEL CLOUDS WILL INCREASE FROM SOUTHEAST TO NORTHWEST THIS EVENING THROUGH FRIDAY. THERE WILL BE A SLIGHT CHANCE OF THUNDERSTORMS OVER THE DESERT AREAS SOUTHEAST OF INTERSTATE 15 FRIDAY AND SATURDAY...AND OVER THE HIGHER TERRAIN OF THE SOUTHERN GREAT BASIN SATURDAY. CLOUDS AND THUNDERSTORM CHANCES WILL DECREASE AREAWIDE SUNDAY. GUSTY SOUTHWEST WINDS WILL CONTINUE IN THE AFTERNOONS AND EVENINGS THROUGH THE WEEKEND. && .CLIMATE...MANY PEOPLE HAVE BEEN COMMENTING ON THE LACK OF HEAT SO FAR THIS SUMMER IN LAS VEGAS. IT IS INTERESTING TO NOTE THAT ONLY 3 YEARS EVER IN LAS VEGAS HAVE NOT SEEN THE TEMPERATURE REACH AT LEAST 110 DEGREES. THEY ARE 1965...1976 AND 1982. WHAT DO ALL OF THESE YEARS HAVE IN COMMON? THEY WERE ALL YEARS WHEN WE WERE GOING INTO AN EL NINO. LOOKING AT THE 18 YEARS GOING INTO AN EL NINO EPISODE THERE WERE 11 YEARS WHERE THERE WAS A BELOW AVERAGE NUMBER OF DAYS WITH 110 DEGREE OR BETTER...2 YEARS NEAR NORMAL AND 5 YEARS WITH AN ABOVE NORMAL TOTAL. THE NORMAL NUMBER OF DAYS AT OR ABOVE 110 DEGREES IN LAS VEGAS IN A YEAR IS 8.8. IT WILL BE INTERESTING GIVEN THE CURRENT TRENDS IN THE PACIFIC TO SEE WHAT THIS YEAR HOLDS. && .VEF WATCHES/WARNINGS/ADVISORIES... NV...NONE. AZ...NONE. CA...NONE. && $$ STACHELSKI/MORGAN HTTP://WEATHER.GOV/LASVEGAS