694 FXUS65 KVEF 261121 AFDLAS MOJAVE DESERT/SOUTHERN GREAT BASIN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LAS VEGAS NV 415 AM PDT THU SEP 26 2002 .SYNOPSIS...A LOW PRESSURE SYSTEM OFF THE SOUTHERN CALIFORNIA COAST WILL MOVE INLAND FRIDAY AS ANOTHER DISTURBANCE DROPS SOUTH INTO THE NORTHERN GREAT BASIN. MARGINAL MOISTURE AND INSTABILITY WILL RESULT IN SHOWERS AND THUNDERSTORMS MAINLY OVER THE HIGHER TERRAIN OF SOUTH CENTRAL NEVADA AND NORTHWEST ARIZONA. A LOW PRESSURE SYSTEM WILL HANG BACK ACROSS WESTERN NEVADA SATURDAY CONTINUING THE THREAT OF SHOWERS AND THUNDERSTORMS ACROSS THE SIERRA AND SOUTH CENTRAL NEVADA. IT WILL BE BREEZY FRIDAY WITH A COOLING TREND THROUGH SATURDAY. .DISCUSSION...FOR THE SHORT TERM THROUGH SATURDAY MODELS IN FAIRLY DECENT AGREEMENT. SHORTWAVE THAT TRIGGERED A FEW SHOWERS AND THUNDERSTORMS LAST EVENING WEAKENING THIS MORNING AS IT MOVES EAST ACROSS SOUTHERN UTAH. FOR TODAY...AREA WILL BE BETWEEN SYSTEM IN THE NORTHERN BRANCH DIGGING SOUTH ACROSS THE PACIFIC NORTHWEST AND UPPER LOW OFF THE SOUTHERN CALIFORNIA COAST. TONIGHT AND FRIDAY...STRONGER/COLDER SHORTWAVE OVER THE PACIFIC NORTHWEST CONTINUES TO DIG SOUTH INTO THE NORTHERN GREAT BASIN...KICKING UPPER LOW OFF THE COAST INLAND INTO SOUTHERN CALIFORNIA. MODEL TIME HEIGHT SECTIONS INDICATE INCREASE IN MID LEVEL MOISTURE AND LIFT ACROSS THE SOUTHERN ZONES TONIGHT. ON FRIDAY...HAVE GONE AHEAD AND INTRODUCE SOME LOW GRADE POPS INTO NORTHWEST ARIZONA AND SPRING MOUNTAINS DUE TO MARGINAL INSTABILITY COMBINING WITH THE MOISTURE AND LIFT. IF ANYTHING DEVELOPS WILL BE CONFINED TO THE HIGHER TERRAIN. IN CENTRAL NEVADA...AGAIN COULD SEE SOME ISOLATED SHOWERS AND THUNDERSTORMS ALONG CONVERGENCE BOUNDARY ASSOCIATED WITH NORTHERN STREAM SHORTWAVE. SHORTWAVE OVER THE SOUTHERN ZONES EJECTS EAST INTO ARIZONA FRIDAY NIGHT WITH STORMS ENDING...BUT UP NORTH AN UPPER LOW CLOSES OFF OVER NORTHERN NEVADA. AVN MODEL DEPICTS MOISTURE AND DYNAMICS ALIGNED FROM NORTHERN INYO COUNTY INTO CENTRAL NEVADA THROUGH SATURDAY. PRESSURE GRADIENTS INCREASE FRIDAY FOR BREEZY CONDITIONS WHILE TEMPERATURES TAIL OFF SEVERAL DEGREES A DAY AS HEIGHTS/THICKNESSES LOWER. STILL ALOT OF DOUBT AND QUESTIONS WITH REGARDS TO UPPER PATTERN IN THE EXTENDED. 00Z GFS EJECTS WEAK TROUGH ACROSS THE AREA SATURDAY NIGHT...PLACING THE FORECAST AREA BETWEEN SYSTEMS SUNDAY. GFS SHOWS MUCH STRONGER/COLDER TROUGH DIGGING SOUTHEAST ACROSS THE INTERMOUNTAIN WEST TUESDAY AND WEDNESDAY. LATEST GUIDANCE MUCH COOLER THEN PREVIOUS RUNS. BUT ECMWF/UKMET CLOSE AN UPPER LOW OFF OVER NORTHERN CALIFORNIA OR EVEN OFF THE WEST COAST ONCE AGAIN KEEPING AREA UNDER MODERATE SOUTHWEST FLOW. HEIGHT DIFFERENCES BETWEEN AND ECMWF AND GFS OVER NORTHERN ARIZONA BY NEXT WEDNESDAY MORNING NEARLY 200 METERS. HAVE SPLIT OUT NEXT TUE-WED AND TEMPERED TEMPERATURES SLIGHTLY. COULD BE WAY OFF EITHER WAY. HOPEFUL FOR BETTER MODEL CONSENSUS NEXT RUNS. PIERCE .LAS...NONE.