AREA FORECAST DISCUSSION

 
 FXUS65 KPSR 251429
 AFDPSR
 
 AREA FORECAST DISCUSSION...UPDATED
 NATIONAL WEATHER SERVICE PHOENIX AZ
 729 AM MST WED NOV 25 2009
 
 .UPDATE...ADDED SNOW TO THE WEATHER GRIDS AND ZONE FORECAST PACKAGE 
 FOR ZONE 24 SATURDAY NIGHT AND SUNDAY.
 
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 .SYNOPSIS...
 HIGH PRESSURE ALOFT WILL KEEP CONDITIONS DRY AND WARM THROUGH FRIDAY.
 A LOW PRESSURE SYSTEM WILL BRING COOLER AND BREEZY CONDITIONS TO THE 
 AREA THIS WEEKEND...WITH BELOW NORMAL TEMPERATURES LIKELY BY SUNDAY.
 
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 .DISCUSSION...
 RIDGE OF HIGH PRESSURE OVER THE WESTERN STATES WILL CONTINUE WELL 
 ABOVE NORMAL TEMPERATURES THROUGH FRIDAY...UNDER CLEAR SKIES.  
 TEMPERATURES ACROSS THE LOWER DESERTS THANKSGIVING DAY ARE EXPECTED 
 TO TOP OUT IN THE UPPER 70S TO NEAR 80...BEFORE A COUPLE DEG OF 
 COOLING FRIDAY. 
 
 MODELS IN GOOD AGREEMENT THAT A STRONG PACIFIC LOW PRESSURE SYSTEM 
 WILL MOVE THROUGH THE REGION THIS WEEKEND...WITH THE LATEST 
 GFS/ECMWF INDICATING THE BEST CHANCE FOR MOUNTAIN SNOW AND LOWER 
 ELEVATION RAIN SATURDAY NIGHT INTO SUNDAY. EVEN STILL...MOISTURE IS 
 LIMITED WITH THIS SYSTEM GIVEN THE INLAND TRAJECTORY...AND THE MAIN 
 IMPACT WILL BE SIGNIFICANTLY COOLER WEATHER. MODELS ARE INDICATING 
 A STRONG JET ON THE BACKSIDE OF THE TROUGH WILL AID IN BRINGING MUCH 
 COLDER AIR FROM THE NORTHERN STATES ALL THE WAY SOUTHWARD INTO 
 ARIZONA. BETWEEN TODAY AND SUNDAY...BOTH THE GFS AND ECMWF ARE 
 INDICATING 700MB TEMPS WILL DROP FROM AROUND 3.5C TO -6C...WITH 
 HIGHS AROUND 60 SUNDAY ACROSS THE WARMEST DESERTS. WINDS WILL ALSO 
 INCREASE RATHER DRAMATICALLY OVER THE WEEKEND...PARTICULARLY ALONG 
 THE CO RIVER VALLEY WESTWARD. THE ELEVATED WIND SPEEDS OVERNIGHT 
 SATURDAY INTO SUNDAY SHOULD KEEP TEMPS OVER THE WESTERN DESERTS 
 RATHER MILD SUNDAY MORNING...IN THE MID 40S TO NEAR 50. LESS WIND IS 
 EXPECTED OVER THE CENTRAL ARIZONA ZONES...WITH OVERNIGHT LOWS 
 DROPPING SEVERAL DEG...INTO THE LOW 40S /AND EVEN THIS MIGHT BE TOO 
 WARM/. BY MONDAY MORNING...LESS WIND AND CLEAR SKIES WILL LEAD TO 
 MAXIMUM RADIATIONAL COOLING...WITH OVERNIGHT LOWS DIPPING INTO THE 
 UPPER 30S ACROSS THE COOLER DESERT LOCALES. 
 
 TUESDAY/WEDNESDAY...UPPER RIDGING IS EXPECTED TO BUILD AGAIN OVER 
 THE WESTERN CONUS...WITH MOST OF THE SOUTHWEST UNITED STATES UNDER 
 DRY NORTHERLY FLOW ALOFT...WITH TEMPERATURES RETURNING TO NEAR 
 NORMAL FOR THIS TIME OF YEAR. 
 
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 .AVIATION...
 SOUTHEAST CA...SOUTHWEST AND SOUTH CENTRAL AZ...INCLUDING KIPL... 
 KBLH...KPHX...AND KIWA.
 
 HIGH PRESSURE ALOFT WILL AGAIN LEAD TO MOSTLY CLEAR OR CLEAR SKIES 
 FOR THE NEXT 24 HOURS...THE ONLY CLOUDINESS BEING HIGH THIN CIRRUS. 
 OTHERWISE WINDS WILL BE GENERALLY ON THE LIGHT SIDE...AND FAVOR THE 
 NORTH THROUGH EAST. WINDS WILL BE MOSTLY FROM THE NORTH DOWN THE 
 LOWER CO RIVER VALLEY THROUGH THURSDAY MORNING...WITH SOME GUSTS TO 
 20KT OR SO FROM 18Z WED THROUGH 01Z THU. OCCASIONAL BREEZES FROM THE 
 NORTHEAST ARE LIKELY ACROSS PORTIONS OF SOUTH-CENTRAL ARIZONA...WITH 
 A FEW GUSTS TO 18KT POSSIBLE MAINLY DURING THE MORNING HOURS TODAY. 
 VFR CONDITIONS EXPECTED ALL AIRFIELDS NEXT 24 HOURS.
 
 AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
 
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 .FIRE WEATHER...
 FRIDAY THROUGH TUESDAY...
 HIGH PRESSURE ALOFT WILL BEGING TO WEAKEN FRIDAY AS AN UPPER LEVEL 
 LOW PRESSURE SYSTEM BEGINS TO TAKE SHAPE OVER THE WESTERN UNITED 
 STATES. HIGH TEMPERATURES WILL REMAIN WELL ABOVE SEASONAL NORMALS 
 WITH THE WARMEST DESERTS REACHING TO NEAR 80 DEGREES. WINDS WILL BE 
 ON THE LIGHT SIDE...AND MINUMUM RH VALUES WILL BE BELOW 15 PERCENT 
 OVER MUCH OF THE LOWER DESERTS. OVER THE WEEKEND A VIGOROUS AND 
 RATHER COLD LOW PRESSURE SYSTEM WILL DEVELOP OVER ARIZONA...LEADING 
 TO SUBSTANTIAL COOL DOWN ALONG WITH INCREASING WIND. AS THE LOW 
 DROPS SOUTH INTO ARIZONA SATURDAY NIGHT INTO SUNDAY...WINDY 
 CONDITIONS WILL DEVELOP OVER SOUTHEAST CALIFORNIA AND SOUTHWEST 
 ARIZONA...WITH PEAK GUSTS BETWEEN 25KT AND 35KT FROM THE NORTH 
 EXPECTED. THIS WILL BE A RATHER DRY SYSTEM FOR OUR AREA...WITH JUST 
 A SLIGHT CHANCE FOR SHOWERS EXPECTED OVER THE HIGHER TERRAIN EAST OF 
 PHOENIX...MAINLY DURING THE DAY SUNDAY.
 
 OTHERWISE MUCH COOLER AND DRIER AIR WILL BE USHERED INTO THE STATE 
 WITH THIS SYSTEM. HIGH TEMPERATURES SUNDAY WILL LOWER INTO LOWER 60S 
 OVER MOST OF THE DESERTS...AND THIS WILL BE 10 DEGREES OR SO BELOW 
 SEASONAL NORMALS. BY MONDAY MINIMUM RH VALUES WILL DROP BELOW 15 
 PERCENT OVER MOST OF THE DESERTS...BEHIND THE EXITING LOW. LESS WIND 
 ALONG WITH A WARMING TREND IS EXPECTED EARLY NEXT WEEK AS HIGHER 
 PRESSURE RETURNS ...ALTHOUGH THE AIRMASS WILL REMAIN QUITE DRY.
 
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 .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...MCLANE/WANEK
 AVIATION...CB
 FIRE WEATHER...CB