AREA FORECAST DISCUSSION

 
 FXUS65 KTWC 250424
 AFDTWC
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE TUCSON AZ
 920 PM MST TUE NOV 24 2009
 
 .SYNOPSIS...HIGH PRESSURE ALOFT WILL PROVIDE DRY CONDITIONS WITH 
 ABOVE NORMAL DAYTIME TEMPERATURES THROUGH FRIDAY. A PACIFIC WEATHER 
 SYSTEM WILL THEN MOVE FROM THE NORTH ACROSS SOUTHEAST ARIZONA THIS 
 WEEKEND. THIS SYSTEM WILL BRING COOLER TEMPERATURES...SOME BREEZES...
 AND A SLIGHT CHANCE OF SHOWERS TO THE WHITE MOUNTAINS SUNDAY. DRY 
 WITH A GRADUAL WARMING TREND EARLY NEXT WEEK.
 
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 .DISCUSSION...SATELLITE IMAGERY WAS SHOWING MOSTLY CLEAR SKIES OVER 
 THE AREA THIS EVENING. EXPECT THIS TO CONTINUE OVERNIGHT. CURRENT 
 FORECAST LOOKED ON TRACK...SO NO UPDATES NEEDED. PLEASE REFER TO THE 
 SECTIONS BELOW FOR MORE DETAILS. 
 
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 .AVIATION...CLEAR SKIES AND SURFACE WINDS GENERALLY LESS THAN 10 KTS 
 WILL PREVAIL INTO WEDNESDAY MORNING. AVIATION DISCUSSION NOT UPDATED 
 FOR TAF AMENDMENTS.
 
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 .FIRE WEATHER...NO FIRE WEATHER CONCERNS THROUGH FRIDAY. A PACIFIC 
 WEATHER SYSTEM WILL MOVE FROM THE NORTH ACROSS SOUTHEAST ARIZONA 
 THIS WEEKEND. THE SYSTEM MAY BRING SOME BREEZES PARTICULARLY ACROSS 
 THE HIGHER TERRAIN EAST OF TUCSON ON SATURDAY. CRITICAL FIRE WEATHER 
 THRESHOLDS ARE NOT EXPECTED TO BE MET AT THIS TIME. OTHERWISE... 
 COOLER TEMPERATURES ARE FORECAST THIS WEEKEND...AS WELL AS A SLIGHT 
 CHANCE OF SHOWERS ACROSS FIRE ZONE 146 ON SUNDAY. DRY CONDITIONS 
 AREAWIDE NEXT MONDAY AND TUESDAY WITH A GRADUAL WARMING TREND.
 
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 .PREV DISCUSSION...HIGH PRESSURE ALOFT WILL BUILD EWD OVER THE AREA 
 THRU THANKSGIVING DAY AS WEAK LOW PRESSURE DEVELOPS OVER THE BAJA 
 CALIFORNIA REGION. DRY CONDITIONS TO PREVAIL TONIGHT-THUR ALONG WITH 
 ABOVE NORMAL DAYTIME TEMPS. SURFACE PRESSURE GRADIENT TO TIGHTEN 
 SUFFICIENTLY TO SUPPORT LOCAL ELY BREEZES THUR MORNING. STILL 
 CONTINUED WARM AND DRY FRI AS THE UPPER RIDGE SHIFTS EWD AND 
 SHORTWAVE TROUGH MOVES ACROSS THE PACIFIC NW. THEREAFTER...UPPER 
 TROUGH TO MOVE ACROSS THE SWRN CONUS THIS WEEKEND. THERE WERE STILL 
 DIFFERENCES BETWEEN THE 24/12Z GFS/ECMWF SOLUTIONS REGARDING THE 
 EVOLUTION OF THIS SYSTEM...WITH THE ECMWF DEEPER AND SLOWER VERSUS 
 THE GFS. THE 24/12Z GFS ENSEMBLES SUPPORT A MORE-PROGRESSIVE TROUGH 
 SCENARIO AND THUS HAVE OPTED TO REDUCE INHERITED POPS THIS WEEKEND. 
 WILL STILL MAINTAIN A SLIGHT CHANCE OF RAIN/SNOW SHOWERS ACROSS THE 
 WHITE MOUNTAINS SUN. AT ANY RATE...THE MAIN IMPACT FROM THIS SYSTEM 
 APPEARS TO BE COOLER TEMPS SAT...AND QUITE COOL SUN WITH HIGH TEMPS 
 ABOUT 10 DEGS OR SO BELOW NORMAL. DRY CONDITIONS WITH A GRADUAL 
 WARMING TREND NEXT MON-TUE AS THE UPPER LOW MOVES EWD AND RIDGE 
 BUILDS ALONG THE WEST COAST.
 
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 .TWC WATCHES/WARNINGS/ADVISORIES...NONE.
 
 

 
 WEATHER.GOV/TUCSON