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.