AREA FORECAST DISCUSSION

 
 FXUS65 KPSR 221720
 AFDPSR
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE PHOENIX AZ
 1020 AM MST SUN NOV 22 2009
 
 .SYNOPSIS...
 MOSTLY CLEAR NIGHTS AND SUNNY DAYS ARE EXPECTED TO CONTINUE AT LEAST 
 THROUGH THANKSGIVING. HIGH PRESSURE ALOFT BETWEEN HAWAII AND BAJA 
 CALIFORNIA IS EXPECTED TO BUILD NORTHEAST OVER OUR AREA WITH WARMER 
 WEATHER WEDNESDAY AND THANKSGIVING DAY. TEMPERATURES WILL RISE TO 
 WELL ABOVE AVERAGE FOR LATE NOVEMBER BY THANKSGIVING DAY...IN THE 
 UPPER 70S TO NEAR 80 DEGREES IN THE DESERT AREAS INCLUDING PHOENIX...
 YUMA AND EL CENTRO.
 
 &&
 
 .DISCUSSION...
 UNDER SUNNY SKIES WITH SOME HIGH THIN CIRRUS CLOUDS...TEMPERATURES 
 WERE GENERALLY CLOSE TO THE SAME OR A COUPLE OF DEGREES COOLER LATE 
 THIS MORNING COMPARED WITH THE SAME TIME YESTERDAY. WINDS WERE 
 GENERALLY CALM OR LIGHT...MOSTLY FROM FROM THE NORTH AND EAST IN 
 SOUTH-CENTRAL AND SOUTHWEST ARIZONA INCLUDING THE GREATER PHOENIX 
 AND YUMA AREAS.
 
 FORECAST LOOKS AS IF IT IS ON THE RIGHT TRACK...NO UPDATES.
 
 PREVIOUS DISCUSSION...
 AS OF 1 AM THIS MORNING SKIES WERE CLEAR ACROSS THE CWA...AND THE 
 AIRMASS WAS QUITE DRY WITH PWAT BELOW ONE QUARTER INCH. SURFACE 
 DEWPOINTS OVER THE DESERTS WERE LOW...RANGING FROM THE UPPER TEENS 
 TO AROUND 30. FOR TODAY INTO MONDAY...PROGS AGREE THAT THE STORM 
 TRACK WILL REMAIN WELL TO OUR NORTH...WITH A DRY NWLY FLOW IN PLACE 
 ACROSS THE CWA. A SERIES OF DISTURBANCES WILL PASS BY TO OUR 
 NORTH...KEEPING TEMPERATURES NEARLY FLAT LINED...AND SLIGHTLY ABOVE 
 SEASONAL NORMALS. A FEW HIGH CLOUDS WILL MOVE THROUGH THE FLOW...BUT 
 THEY WILL BE ON THE THIN SIDE...FOR MOSTLY SUNNY DAYS AND CLEAR 
 NIGHTS.
 
 TUESDAY INTO THE MIDDLE PORTION OF THE WEEK...BOTH THE GFS AND ECMWF 
 AGREE THAT HIGH PRESSURE WILL BUILD OVER THE WESTERN STATES...BUT 
 THERE WILL BE A SPLIT IN THE FLOW WITH A WEAK SRN BRANCH AND A BAGGY 
 TROF OR POSSIBLY CLOSED UPPER LOW SITUATED TO OUR SOUTH. LATEST GFS 
 IS A BIT MORE AGGRESSIVE IN DEVELOPING THIS LOW OVER BAJA...AND 
 ATTEMPTS TO WRAP MID AND HIGH CLOUDS INTO OUR CWA FROM THE SOUTHEAST 
 WED NIGHT THROUGH THURSDAY NIGHT. FEEL THIS IS OVERDONE...AND ANY 
 HIGH CLOUDINESS THAT ENTERS OUR CWA WILL BE ABOVE 500MB AND ON THE 
 THIN SIDE. THUS SKIES WILL STILL BE MOSTLY SUNNY. OF COURSE...THE 
 PROXIMITY OF THE LOW TO OUR SOUTH WILL KEEP HEIGHTS/THICKNESSES FROM 
 RISING TOO MUCH AND AS SUCH THE WARMING TREND DURING THIS PERIOD 
 WILL BE MINIMAL. STILL...EXPECT HIGHS ABOVE CLIMO AND IN THE MID TO 
 UPPER 70S EACH DAY OVER OUR WARMER DESERTS.
 
 LATE IN THE FORECAST PERIOD...FRIDAY INTO SATURDAY...MED RANGE PROGS 
 START TO DIVERGE...AS IS OFTEN THE CASE. BOTH GFS AND ECMWF 
 ADVERTISE A RATHER PROGRESSIVE SHORT WAVE TO MOVE INTO THE WESTERN 
 STATES...AND ACROSS ARIZONA. HOWEVER...GFS IS MORE PROGRESSIVE AND 
 KEEPS THE SYSTEM WELL TO OUR NORTH WITH A DRY WLY FLOW IN PLACE BOTH 
 DAYS. EUROPEAN DIGS THE SYSTEM MORE TO THE SOUTHEAST...AND BRINGS A 
 MUCH COOLER AIRMASS INTO ARIZONA BY SATURDAY. HPC EXTENDED PERIOD 
 GUIDANCE SUGGESTS A MODEL BLEND SOLUTION FOR SATURDAY...AND THE 
 TRACK RECORD OF THE EUROPEAN OVER THE GFS WOULD SUGGEST THAT IT 
 MIGHT END UP BEING THE SUPERIOR MODEL. AS SUCH HAVE LOWERED TEMPS A 
 FEW DEGREES ON SATURDAY TO REFLECT THE COOLER ECMWF SOLUTION...AND 
 ADDED SOME CLIMO SINGLE DIGIT POPS INTO THE FORECAST AS WELL. 
 
 &&
 
 .AVIATION...
 SOUTHEAST CA...SOUTHWEST AND SOUTH CENTRAL AZ...INCLUDING KIPL... 
 KBLH...KPHX...AND KIWA.
 
 A WEATHER SYSTEM PASSING WELL TO THE NORTH TODAY AND TONIGHT WILL 
 HAVE NO APPRECIABLE EFFECT ON SURFACE WINDS. THUS LIGHT WINDS WILL 
 CONTINUE TODAY...EVEN A BIT LIGHTER THAN YESTERDAY. SOMEWHAT 
 STRONGER WINDS CAN BE EXPECTED MONDAY AFTERNOON...PERHAPS GETTING 
 ABOVE 10 KTS FROM THE NORTH DOWN THE LOWER COLORADO RIVER VALLEY 
 INCLUDING KBLH. SKIES WILL BE CLEAR EXCEPT FOR MINOR AMOUNTS OF HIGH 
 CIRRUS CLOUDS ABOVE 20 THOUSAND FEET ASL.
 
 AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
 
 &&
 
 .FIRE WEATHER...
 TUESDAY THROUGH SATURDAY...
 HIGH PRESSURE WILL BE IN PLACE OVER THE SOUTHWEST TUESDAY THROUGH 
 FRIDAY FOR SLIGHTLY WARMER TEMPERATURES...LOW DAYTIME HUMIDITY AND 
 MODEST OVERNIGHT RECOVERY. WINDS WILL FAVOR NORTH AND NORTHEAST 
 DIRECTIONS THROUGH THANKSGIVING DAY...LOCALLY WINDY AT TIMES AT THE 
 RIDGETOPS...WITH LIGHT WINDS FRIDAY. THERE ARE CONFLICTING SIGNALS 
 AS TO WHAT THE WEATHER WILL DO AFTER FRIDAY. A COOLING TREND IS 
 ANTICIPATED ALONG WITH STRONGER WINDS. GIVEN THE 
 UNCERTAINTY...FORECASTS REFLECT CONSERVATIVE TRENDS. 
 
 
 &&
 
 .PSR WATCHES/WARNINGS/ADVISORIES...
 
 AZ...NONE.
 
 CA...NONE.
 
 &&
 
 $$
 
 NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
 
 WEATHER.GOV/PHOENIX
 
 DISCUSSION...ELLIS/CB
 AVIATION...ELLIS/AJ
 FIRE WEATHER...AJ
 
 
 

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