AREA FORECAST DISCUSSION

 
 FXUS65 KTWC 070415
 AFDTWC
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE TUCSON AZ
 915 PM MST FRI NOV 6 2009
 
 .SYNOPSIS...EXPECT CONSIDERABLE HIGH CLOUDINESS INTO SATURDAY AS A 
 LOW PRESSURE SYSTEM MOVES SOUTH OF OUR AREA. OTHERWISE...DRY 
 CONDITIONS WITH ABOVE NORMAL DAYTIME TEMPERATURES WILL OCCUR THROUGH 
 THE MIDDLE OF THE UPCOMING WEEK.
 
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 .DISCUSSION...WEAK UPPER LOW CENTERED NEAR THE BAJA SPUR WILL MOVE 
 SLOWLY EWD TONIGHT AND SAT. MAIN IMPACT FROM THIS SYSTEM ON SE AZ 
 WILL BE CONSIDERABLE MID AND MOSTLY HIGH-LEVEL CLOUDS RESULTING IN 
 MOSTLY CLOUDY SKIES INTO SAT MORNING. SOME CLEARING FROM WEST-EAST 
 DURING THE AFTERNOON ALTHOUGH AMPLE MOISTURE MAINLY ABOVE 500 MB TO 
 RESULT IN AT LEAST PARTLY CLOUDY SKIES SAT AFTERNOON. LIGHT WINDS TO 
 PREVAIL THE REST OF TONIGHT AND SAT. NO UPDATES NECESSARY AT THIS 
 TIME. PLEASE REFER TO THE PREVIOUS DISCUSSION BELOW FOR ADDITIONAL 
 FORECAST DETAIL.
 
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 .AVIATION...EXPECT VFR CONDITIONS WITH VARIABLE CLOUDS AT OR ABOVE 
 15K FT AGL AND SURFACE WINDS MOSTLY LESS THAN 10 KTS TO OCCUR INTO 
 SATURDAY EVENING. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
 
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 .FIRE WEATHER...DRY CONDITIONS WITH LIGHT TERRAIN DRIVEN SURFACE 
 WINDS AND ABOVE NORMAL DAYTIME TEMPERATURES WILL PREVAIL THROUGH THE 
 MIDDLE OF THE UPCOMING WEEK.
 
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 .PREV DISCUSSION...HEIGHTS/THICKNESSES CONTINUE TO SHOW A GRADUAL 
 DECLINE SATURDAY AND SUNDAY...WITH THE EXPECTATION WE WILL SHAVE OFF 
 ANOTHER DEGREE OR TWO SATURDAY AND HOLD IN THE LOWER 80S SUNDAY. 
 SUNDAY WILL BE OUR COOLEST DAY...SO TO SPEAK...STILL WELL ABOVE 
 NORMAL FOR NOVEMBER. ANOTHER WARMING TREND IS EXPECTED MONDAY AND 
 TUESDAY EARLY NEXT WEEK...AS FLAT UPPER RIDGING QUICKLY BUILDS INTO 
 THE DESERT SOUTHWEST. BUMPED UP AFTERNOON MAX TEMPS FOR MONDAY AND 
 TUESDAY ABOUT 1-2 MORE DEGREES...WITH MID TO UPPER 80S EXPECTED ON 
 THE LOWER DESERTS TUESDAY AFTERNOON. THICKNESSES STILL DO NOT 
 SUPPORT A RETURN OF THE 90S...A BIT OF GOOD NEWS.
 
 RATHER LARGE UNCERTAINTY WITH THE SECOND HALF OF NEXT WEEK. A STRONG 
 LOW PRESSURE TROUGH IS EXPECTED TO BE NEAR THE PACIFIC NORTHWEST 
 NEXT TUESDAY AFTERNOON. HOW THIS TROUGH EVOLVES AND AFFECTS THE 
 DESERT SOUTHWEST LATE NEXT WEEK IS VARYING WILDLY BETWEEN MODELS AND 
 FROM RUN TO RUN. 12Z GFS PROGS A 548 DM 500 MB LOW OVER UTAH NEXT 
 FRIDAY...WITH BASICALLY A BIG WIND EVENT FOR SOUTHEAST ARIZONA. 00Z 
 ECMWF ALSO HAD A STRONG CUTOFF LOW NEAR LAS VEGAS AT ABOUT THE SAME 
 TIME...BUT 12Z ECMWF CAME IN WITH A MUCH BROADER TROUGH ACROSS THE 
 NORTHERN ROCKIES WITH MUCH LESS AMPLITUDE. AT THIS POINT...ALL I DID 
 WAS KNOCK ABOUT 5 DEGREES OFF NEXT FRIDAY`S MAX TEMPS...AND KEPT 
 SOME ISOLATED POPS IN THE WHITES DURING THE THURSDAY/FRIDAY TIME 
 FRAME. DID TRIM INHERITED POPS DOWN ACROSS THE SOUTHERN CWA AS 
 MAJORITY OF CURRENT MODELS SUGGEST THE TRAJECTORY OF THIS SYSTEM 
 WILL FAVOR MOSTLY WIND FOR SOUTHEAST ARIZONA.
 
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 .TWC WATCHES/WARNINGS/ADVISORIES...NONE.
 
 

 
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