AREA FORECAST DISCUSSION

 
 FXUS65 KPSR 092217
 AFDPSR
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE PHOENIX AZ
 315 PM MST TUE FEB 9 2010
 
 .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. 
 
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 .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).    
 
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 .AVIATION...
 KPHX AND KIWA...
 SFC WINDS FROM THE SOUTH/SOUTHEAST SLOWLY INCREASING ACROSS THE 
 PHOENIX AREA THIS AFTN. FAIR CONFIDENCE WINDS WILL REMAIN FROM
 THE SOUTH TONIGHT...AHEAD OF THE DEEP UPPER LOW IN CALIF. 
 ALSO...CLOUDS AT/ABOVE 15 THSD FT ON THE INCREASE...WITH PRECIP
 SPREADING FROM WEST TO EAST AFT 10/12Z. BY 10/15Z THE LOWER 
 CIGS...8-10 THSD FT WILL FILTER INTO THE METRO AREA ALONG WITH LGT 
 RAIN. 
 
 KIPL AND KBLH...
 NORTH-SOUTH LINE OF LGT SHOWERS WITH CIGS 6-8 THSD FT WILL BRUSH 
 ACROSS CALIF DESERTS THRU 10/00Z. ADDITIONAL SHOWERS LIKELY TO BRING 
 BEST CHANCE OF SHOWERS AFT DARK AT BOTH KIPL/KBLH. GOOD CONFIDENCE 
 THAT LOWER VSBYS WILL ACCOMPANY THE PRECIP AND CIGS...AND 5-7 MILES 
 VSBYS STILL LOOK GOOD. GUSTY WINDS ALSO MAY REACH 20-25 KTS SPCLY 
 ASSOCD WITH ISOLD TSTMS. TIMING OF CLEARING TREND STILL GOOD BY WED 
 AFTERNOON.
 
 AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
 
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 .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.
   
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 .PSR WATCHES/WARNINGS/ADVISORIES...
 
 AZ...NONE.
 
 CA...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 10 AM PST     
      WEDNESDAY CAZ030.
 
 
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 NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
 
 WEATHER.GOV/PHOENIX
 
 DISCUSSION...DG
 AVIATION...SIPPLE
 FIRE WEATHER...ELLIS
 
 
 

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