AREA FORECAST DISCUSSION

 
 FXUS65 KPSR 231242 AAA
 AFDPSR
 
 AREA FORECAST DISCUSSION...UPDATED
 NATIONAL WEATHER SERVICE PHOENIX AZ
 540 AM MST MON NOV 23 2009
 
 .UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS
 
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 .SYNOPSIS...
 MOSTLY CLEAR NIGHTS AND SUNNY DAYS ARE EXPECTED TO CONTINUE THROUGH 
 AT LEAST FRIDAY. A RIDGE OF HIGH PRESSURE WILL SLOWLY BUILD OVER THE 
 WESTERN STATES THIS WEEK LEADING TO A GRADUAL WARMING TREND.  
 TEMPERATURES WILL RISE TO WELL ABOVE AVERAGE FOR LATE NOVEMBER BY 
 THANKSGIVING DAY...IN THE UPPER 70S TO NEAR 80 DEGREES ON THE LOW 
 DESERTS INCLUDING PHOENIX...YUMA...AND EL CENTRO. A LARGE COOLING 
 TREND IS ANTICIPATED SATURDAY AND SUNDAY AS A LOW PRESSURE SYSTEM 
 DEVELOPS OVER THE DESERT SOUTHWEST. 
 
 &&
 
 .DISCUSSION...
 WATER VAPOR IMAGERY SHOWS A LOW PRESSURE SYSTEM MOVING THROUGH THE 
 WESTERN STATES...THE SOUTHERN END OF WHICH IS BRUSHING ARIZONA AND 
 SOUTHEAST CALIFORNIA. THIS SYSTEM WILL HAVE LITTLE EFFECT ON OUR 
 WEATHER EXCEPT FOR SOME MORE NOTICEABLE WINDS...WITH LOCALLY BREEZY 
 CONDITIONS THIS AFTERNOON OVER THE LOWER COLORADO RIVER VALLEY. A 
 RIDGE OF HIGH PRESSURE WILL SLOWLY BUILD IN FROM THE PACIFIC LEADING 
 TO A GRADUAL WARMING TREND. ANTICIPATE TEMPERATURES TO PEAK ON 
 THURSDAY. A STRONG NORTH AND NORTHEASTERLY ORIENTED PRESSURE 
 GRADIENT WILL DEVELOP LEADING TO LOCALLY BREEZY CONDITIONS AT TIMES 
 WEDNESDAY AND THURSDAY. 
 
 THE MODELS DEPICT THE RIDGE BEGINNING TO SHIFT EASTWARD FRIDAY AS A 
 TROUGH MOVES IN. THE GFS AND THE CANADIAN ARE FASTER WITH IT THAN 
 THE ECMWF. WITH TIME...THE ECMWF AND GFS SHOW THE FLOW PATTERN 
 AMPLIFYING LEADING TO A TROUGH DIGGING SOUTHWARD OVER THE INTERIOR 
 WEST SATURDAY...WITH THE GFS FASTER THAN THE ECMWF. THE OPERATIONAL 
 CANADIAN SHOWS A MORE PROGRESSIVE PATTERN HOWEVER THE CANADIAN 
 ENSEMBLE MEAN SUPPORTS THE IDEA OF AMPLIFICATION AND A DIGGING 
 TROUGH. ON THE OTHER HAND...THE OPERATIONAL GFS IS MORE AGGRESSIVE 
 WITH THE TROUGHING OVER ARIZONA AND SOUTHEAST CALIFORNIA THAN MOST 
 OF THE GFS ENSEMBLE MEMBERS. THOUGH ECMWF HAS A SLOWER ARRIVAL OF A 
 DIGGING TROUGH OVER OUR FORECAST AREA IT MAKES UP FOR IT BY RAPIDLY 
 INTENSIFYING THE UPPER TROUGH INTO A CLOSED LOW OVER ARIZONA ON 
 SUNDAY. THE ECMWF HAS BEEN SHOWING SHOWING A DEEP CLOSED LOW OVER 
 ARIZONA FOR THIS WEEKEND FOR AT LEAST 6 RUNS NOW BUT IT HAS HAD RUN 
 TO RUN INCONSISTENCIES IN THE EVOLUTION/TRACK. SO THE GFS IS NOW 
 COMING AROUND TO A SOLUTION MORE LIKE THE ECMWF. 
 
 THE SHORT OF ALL OF THIS IS MUCH COOLER AND BREEZY TO WINDY 
 CONDITIONS FOR THIS COMING WEEKEND. CONSERVATIVELY...THE MAX TEMPS 
 OVER THE LOW DESERTS SUNDAY WILL BE IN THE MID 60S...AFTER PEAKING 
 NEAR 80 THURSDAY AND FRIDAY. SOME ADDITIONAL COOLING IS ANTICIPATED 
 MONDAY OVER THE SOUTH-CENTRAL DESERTS WHILE OUR WESTERN AREAS 
 ACTUALLY START TO WARM UP. WINDS LOOK LIKE THEY WILL BE CONSIDERABLY 
 STRONGER SUNDAY THAN SATURDAY...MAINLY OVER SOUTHEAST CALIFORNIA AND 
 THE LOWER COLORADO RIVER VALLEY. GIVEN THE OVERLAND TRAJECTORY...THE 
 SYSTEM LOOKS TO BE MOISTURE STARVED AND THUS HAVE HELD OFF 
 INTRODUCING ANY MENTION OF PRECIP...BEST CHANCES LOOK TO BE OUTSIDE 
 OF OUR FORECAST AREA OVER THE WHITE MOUNTAINS. 
 
 &&
 
 .AVIATION...
 SOUTHEAST CA...SOUTHWEST AND SOUTH CENTRAL AZ...INCLUDING KIPL... 
 KBLH...KPHX...AND KIWA.
 
 EXCEPT FOR OCCASIONAL THIN HI CIRRUS...AOA 20K FEET...SKIES TO BE 
 MOSTLY CLEAR NEXT 24 HOURS ALL AIRFIELDS. FOR THE MOST PART WINDS 
 WILL BE RATHER LIGHT AND DIURNAL...EXCEPT DOWN THE LOWER CO RIVER 
 VALLEY TODAY. SURFACE HIGH DEVELOPING TO OUR NORTH WILL TIGHTEN 
 GRADIENT DOWN THE RIVER...AND CAUSE BREEZY NORTH WINDS TO DEVELOP AT 
 KBLH AFTER ABOUT 18Z. EXPECT OCNL GUSTS BETWEEN 20-25KT STARTING 
 EARLY THIS AFTERNOON AND THEN TAPERING OFF SHORTLY AFTER SUNSET. 
 OTHERWISE NO AVIATION CONCERNS. VFR CONDITIONS EXPECTED ALL 
 AIRFIELDS NEXT 24 HOURS.
 
 AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
 
 &&
 
 .FIRE WEATHER...
 WEDNESDAY THROUGH SUNDAY...
 HIGH PRESSURE ALOFT WILL DOMINATE THE WEATHER PATTERN WEDNESDAY AND 
 THURSDAY...WITH MOSTLY CLEAR OR CLEAR SKIES EXPECTED EACH DAY...AND 
 RELATIVELY LIGHT WINDS. HIGH TEMPERATURES WILL CONTINUE WELL ABOVE 
 SEASONAL NORMALS...ALONG WITH VERY DRY AIR OVER THE DESERTS. MANY 
 LOCALES WILL SEE MINIMUM RH VALUES IN THE SINGLE DIGITS...WITH 
 MODEST RECOVERY AT NIGHT. FORECAST MODELS IN BETTER AGREEMENT 
 REGARDING A CHANGE IN THE WEATHER DEVELOPING OVER THE WEEKEND. A LOW 
 PRESSURE SYSTEM WILL BE SETTLING IN OVER THE DESERT SOUTHWEST... 
 LEADING TO A SUBSTANTIAL COOLING TREND FRIDAY THROUGH SUNDAY. HIGH 
 TEMPERATURES MAY FALL AROUND 15 DEGREES OVER THIS TIME FRAME WITH 
 HIGHS SUNDAY EXPECTED IN THE MID 60S OVER MOST OF THE LOWER DESERTS. 
 THIS WILL BE RATHER DRY SYSTEM FOR OUR AREA WITH NO PRECIPITATION IN 
 THE FORECAST AT THIS TIME. HOWEVER HUMIDITIES WILL BE ON THE 
 INCREASE...PARTLY DUE TO INCREASING LOW LEVEL MOISTURE AND ALSO 
 COOLING TEMPERATURES. BREEZY OR LOCALLY WINDY WEATHER IS LIKELY OVER 
 THE WEEKEND AS WELL.
 
 &&
 
 .PSR WATCHES/WARNINGS/ADVISORIES...
 
 AZ...NONE.
 
 CA...NONE.
 
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 NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
 
 WEATHER.GOV/PHOENIX
 
 DISCUSSION...AJ
 AVIATION...CB
 FIRE WEATHER...CB
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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