000 FXUS65 KPSR 100526 CCA AFDPSR AREA FORECAST DISCUSSION...............COR NATIONAL WEATHER SERVICE PHOENIX AZ 1025 PM MST TUE FEB 9 2010 CORRECTION FROM VANDENBURG SNOW LEVEL MENTIONED IN DISCUSSION .SYNOPSIS... A LOW PRESSURE SYSTEM WILL BRING RAIN AND MOUNTAIN SNOW SHOWERS... AS WELL AS A SLIGHT CHANCE OF THUNDERSTORMS...OVER FAR SOUTHEAST CALIFORNIA AND THE LOWER COLORADO RIVER VALLEY TONIGHT INTO EARLY WEDNESDAY...AND MAINLY OVER SOUTHWEST AND SOUTH-CENTRAL ARIZONA WEDNESDAY AND WEDNESDAY EVENING. DRIER CONDITIONS WILL PREVAIL THURSDAY AS THE LOW MOVES OFF TO OUR EAST...THOUGH IT WILL REMAIN RATHER COOL. DRY AND WARMER WEATHER WILL COMMENCE FRIDAY AND CONTINUE THROUGH EARLY NEXT WEEK AS A RIDGE OF HIGH PRESSURE BECOMES ESTABLISHED OVER THE WESTERN UNITED STATES. TEMPERATURES WILL BE SEVERAL DEGREES ABOVE NORMAL SATURDAY THROUGH AT LEAST NEXT TUESDAY. && .DISCUSSION... A POWERFUL DEVELOPING PACIFIC LOW PRESSURE SYSTEM THAT HAD BEEN MOVING QUICKLY DOWN THE WEST COAST FROM OREGON MONDAY/MONDAY NIGHT ARRIVED IN SOUTHERN CA TUESDAY AFTERNOON WITH A BANG. HEAVY RAIN... THUNDERSTORMS AND MORE DEVELOPED FROM SANTA BARBARA TO SAN DIEGO ...AND OVER THE ADJACENT COASTAL MOUNTAINS. ITS A COLD STORM...AND WEATHER BALLOON SOUNDINGS DETECTED THE SNOW LEVEL RANGED FROM 3000 FEET AT VANDENBURG AFB...WITH THE COLD CORE STORM CENTER...TO 5000 FEET AT SAN DIEGO. THE DRA SOUNDING NEAR LAS VEGAS DETECTED A SNOW LEVEL AT 4800 FEET. MODELS SO FAR ARE DOING A GREAT JOB IN THE SHORT TERM...MEANING THE LOW PRESSURE SYSTEM CONTINUED TO MOVE SOUTH/SOUTHEAST. THE EUROPEAN AND GFS MODELS SINK THIS SYSTEM SOUTH INTO NORTHERN BAJA CA BY 12Z WED. THERE IS A CAVEAT THOUGH. ABUNDANT SATELLITE DERIVED 300 AND 250 MB JET STREAM WINDS...DERIVED FROM THE SUBTROPICAL CLOUD PLUME ACROSS BAJA CA AND NORTHWEST MEXICO AT 00Z...SHOWED A SUBTROPICAL JET SLIGHTLY IN EXCESS OF 130 KNOTS. THE CAVEAT IS...A SUBTROPICAL JET THIS STRONG MAY SERVE TO LIMIT THE SOUTHWARD MOVEMENT OF THE LOW PRESSURE SYSTEM...WITH THE SYSTEM TRACKING A LITTLE FARTHER NORTH INTO SOUTHERN AZ THAN MODELS FORECAST. MORE MOISTURE AND DYNAMICS COULD BE DIRECTED TOWARD PHOENIX AND VICINITY ON WED (OF MOST OF SOUTH CENTRAL AZ) WITH ISOLATED THUNDERSTORMS. BACK TO SNOWFALL. A WINTER WEATHER ADVISORY FOR JOSHUA TREE NATIONAL PARK IN SOUTHEAST CA WILL CONTINUE TONIGHT. WE WILL OPT TO UPDATE THE ADVISORY FOR MORE SNOW...AND TAKE THE ACCUMULATING SNOW LEVEL DOWN TO 3500 FEET. 3 TO 5 STORM TOTAL INCHES ABOVE 3500 FEET IS NOW EXPECTED IN JOSHUA TREE. UPDATES WILL COME OUT SHORTLY. REASONING... APPEARS FROM THE COASTAL WEATHER BALLOON SOUNDINGS THAT THE 3000 FOOT SNOW LEVEL IS FOLLOWING THE MINUS 8 DEGREE C ISOTHERM...WHICH MOVES INTO JOSHUA TREE AROUND 06Z OR 10 PM PST. 3000 FEET WILL BE THE SNOW LINE...BUT ACCUMULATIONS LIKELY ABOVE 3500 FEET. PRECIPITATION IN SOUTHEAST CA AND THE COLORADO RIVER VALLEY...SOME HEAVY RAIN SHOWERS WITH ISOLATED THUNDERSTORMS WILL SPREAD ACROSS THE SOUTHEAST CA DESERTS SHORTLY...THEN MOVE INTO THE COLORADO RIVER VALLEY LATER TONIGHT. SHOWERS WILL THEN SPREAD EAST ACROSS MOST OF SOUTHERN AZ ON WEDNESDAY AS THE UPPER LOW TRACK EAST NEAR THE INTERNATIONAL BORDER. UPDATES FOR THE SNOW ADVISORY WILL COME OUT SHORTLY...OTHERWISE REMAINDER OF FORECASTS LOOK OK FOR NOW. PREVIOUS DISCUSSION BELOW STILL APPLIES EXCEPT FOR A CHANGE IN SNOW LEVELS AND ACCUMULATIONS IN SOUTHEAST CA. PREVIOUS DISCUSSION... UPPER LOW THAT WILL AFFECT OUR WEATHER DURING THE NEXT COUPLE OF DAYS WAS CENTERED SW OF SAN FRANCISCO AS OF 21Z (2 PM MST)...AND CONTINUED TO MOVE TOWARD THE SSE AT ABOUT 20 KNOTS. AS MENTIONED THIS MORNING...NUMERICAL MODELS ARE IN GOOD AGREEMENT REGARDING TRACK OF THIS LOW...KEEPING IT ON A PATH THAT PARALLELS THE CALIFORNIA COAST DURING THE NEXT 18 HRS...PLACING IT JUST WEST OF SAN DIEGO BY 12Z WEDNESDAY...THEN MOVING IT SLOWLY EAST ALONG THE INTERNATIONAL BORDER TO JUST SOUTH OF THE ARIZONA-NEW MEXICO BORDER BY 12Z THURSDAY. AS SUCH...STRONGEST FORCING/UVV AND BEST CHANCE FOR PRECIPITATION WILL TRACK ACROSS FAR SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA TONIGHT...ACROSS SOUTHERN QUARTER OF ARIZONA ON WEDNESDAY...AND OVER SOUTHEAST ARIZONA WEDNESDAY NIGHT (PRINCIPAL UPPER SUPPORT AND BEST CHANCE FOR PRECIPITATION DOES AN 'END RUN' AROUND SOUTH-CENTRAL ARIZONA). GIVEN ONLY MODEST MOISTURE AVAILABILITY AS WELL AS THE FACT THE STORM WILL TRACK WELL SOUTH OF OUR FORECAST AREA...PRECIP TOTALS FROM THIS STORM WILL BE RATHER MODEST...LESS THAN ONE HALF INCH AT MOST LOCALES. TOTALS IN EXCESS OF ONE THIRD INCH...BUT LESS THAN ONE HALF INCH...WILL BE MOST LIKELY OVER FAR SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA TONIGHT INTO WEDNESDAY MORNING...AND OVER THE HIGHER TERRAIN OF SOUTH- CENTRAL ARIZONA WEDNESDAY NIGHT. PRECIP AMOUNTS WILL VARY QUITE A BIT FROM SITE TO SITE...SINCE CONVECTIVE SHOWERS AND A FEW THUNDERSTORMS ARE EXPECTED. STRONG RIDGING DEVELOPS BEHIND THE LOW THURSDAY WHICH WILL QUICKLY BRING THE THREAT OF PRECIP TO AN END. GFS/ECMWF IN GOOD AGREEMENT THAT A MUCH DIFFERENT AND RATHER PERSISTENT LONG WAVE PATTERN WILL BECOME ESTABLISHED THIS WEEKEND THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. RIDGE AXIS SETS UP NEAR 120W (FAR WESTERN UNITED STATES) WHILE BROAD TROUGH WILL BE CENTERED NEAR 90W (EASTERN UNITED STATES). THIS PATTERN PROMISES TO BRING DRY CONDITIONS WITH DAYTIME HIGHS SEVERAL DEGREES ABOVE NORMAL THIS WEEKEND INTO EARLY NEXT WEEK...WITH WARMEST DAYTIME HIGHS TOWARD THE END OF THIS FORECAST PACKAGE (EARLY NEXT WEEK). && .AVIATION... KPHX AND KIWA... THROUGH 11Z WED...SCT CLDS BASED NEAR 8 THSD WITH INCREASING HIGH CLOUDS ABOVE. FROM 11Z TO 14Z...CLOUDS LOWERING AND BECOMING BKN 8 THSD MSL. 14Z WED THROUGH 23Z WED...BKN TO OVC CLDS BASED NEAR 5 THSD AGL WITH SCATTERED RAIN SHOWERS. KIPL AND KBLH... COLD FRONT APPROACHING THROUGH 14Z. CLDS LOWERING AND BECOMING BKN TO OVC 4 TO 5 THSD FT AGL WITH SCT SHWRS AND ISOLATED THUNDERSTORMS. VISIBILITY IN HEAVIER SHOWERS FALLING TO NEAR 3 MILES. AFT 14Z CLOUDS BECOMING SCT TO OCNL BKN NEAR 5 THSD AGL WITH A FEW SHOWERS. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... WEDNESDAY NIGHT THROUGH MONDAY... SOME LINGERING SHOWERS ARE EXPECTED WEDNESDAY NIGHT...MAINLY EAST OF PHOENIX. HIGH PRESSURE ALOFT FROM THE PACIFIC WILL BRING A RETURN TO RELATIVELY DRIER AIR AND A RECOVERY OF TEMPERATURES THURSDAY AND FRIDAY WITH FURTHER WARMING THIS COMING WEEKEND. MINIMUM RELATIVE HUMIDITY IS EXPECTED TO GENERALLY REMAIN ABOVE 20 PERCENT WITH GOOD TO EXCELLENT RECOVERY AT NIGHT. SOME BREEZINESS FROM THE NORTH AND NORTHEAST IS EXPECTED THIS WEEKEND...ESPECIALLY DOWN THE LOWER COLORADO RIVER VALLEY. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 10 AM PST WEDNESDAY CAZ030. && $$ NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT WEATHER.GOV/PHOENIX DISCUSSION...VASQUEZ/DG AVIATION...VASQUEZ FIRE WEATHER...ELLIS