000 
FXUS65 KPSR 160347
AFDPSR

AREA FORECAST DISCUSSION 
NATIONAL WEATHER SERVICE PHOENIX AZ
845 PM MST WED APR 15 2009

.SYNOPSIS...
A STRONG UPPER LEVEL LOW PRESSURE SYSTEM WILL REMAIN OVER THE AREA 
THROUGH FRIDAY BEFORE MOVING OFF TO THE EAST BY THE WEEKEND AND 
BEING REPLACED BY HIGHER PRESSURE ALOFT. THE PRESENCE OF THE UPPER 
LOW WILL RESULT IN COOLER-THAN-NORMAL TEMPERATURES THROUGH FRIDAY 
BEFORE A STRONG WARMING TREND TAKES HOLD OF THE AREA OVER THE 
WEEKEND. THERE WILL ALSO BE A SLIGHT CHANCE OF SHOWERS OVER THE 
HIGHER TERRAIN WELL TO THE EAST OF PHOENIX BEFORE THE UPPER LOW 
EXITS THE REGION ON FRIDAY. 

&&

.DISCUSSION...
A LARGE LOW PRESSURE SYSTEM MOVED INTO AZ WEDNESDAY AFTERNOON...AND 
A MUCH COLDER AIRMASS IS SETTLING OVER THE REGION. ITS GOING TO BE A 
COLD ONE TONIGHT...EVERYWHERE...AND ANOTHER COOL AFTERNOON THURSDAY. 
SKIES WERE MOSTLY CLEAR ACROSS OUR FORECAST AREA (SOUTHEAST CA...AND 
SOUTHWEST AND SOUTH CENTRAL AZ)...SO NO PROBLEMS EXPECTED TONIGHT 
AND THURSDAY MORNING.  

HOWEVER...SINCE THE LOW PRESSURE SYSTEM WILL BASICALLY REMAIN QUASI- 
STATIONARY OVER AZ THROUGH EARLY FRIDAY...THERE APPEARS TO BE A 
SMALL DISTURBANCE FOR LATE THURSDAY/THURSDAY EVENING ROTATING IN 
FROM THE NORTH...AND ACROSS PORTIONS OF SOUTH CENTRAL AZ. ALTHOUGH A 
VERY DRY LOWER ATMOSPHERE IS EXPECTED OVER SOUTH CENTRAL AZ THURSDAY 
EVENING...THERE APPEARS TO BE SOME CLOUDINESS WITH THIS DISTURBANCE 
...AROUND 8000 FEET DEEP...BETWEEN 12 AND 20 THSD FEET...WITH 
SATURATED CONDITIONS BELOW MINUS 10 DEGREES C.  ANY CLOUDS COLDER 
THAN MINUS 10 C ARE CONDUCIVE TO ICE XTAL AND PRECIP FORMATION.  
THEREFORE...WE ARE A LITTLE CONCERNED THERE COULD BE EXTENSIVE VIRGA 
OVER PORTIONS OF SOUTH CENTRAL AZ...FROM PHOENIX EASTWARD...RESULTING
IN A FEW SHOWERS OVER THE HIGHEST ELEVATIONS OF ZONE 24...SOUTHERN 
GILA COUNTY EARLY THURSDAY EVENING. FORECASTS ALREADY REFLECT THIS 
POSSIBILITY. THERE MAY EVEN BE VIRGA SHOWERS OVER THE NORTH AND EAST 
PORTIONS OF THE GREATER PHOENIX AREA...RESULTING IN LOCALLY GUSTY 
WINDS...AND A FEW SPRINKLES.  THIS POSSIBILITY WILL BE ASCERTAINED
WITH NEW MODEL DATA ARRIVING SHORTLY.

OTHERWISE...A FEW UPDATES WERE MADE TO TONIGHTS FORECAST FOR 
DIMINISHING WIND...AND IN ZONE 24 WE HAVE UPGRADED THE PROBABILITY 
OF PRECIP SLIGHTLY FOR LATE THURSDAY AND THURSDAY EVENING.

NO ADDITIONAL UPDATES EXPECTED. PORTIONS OF PREVIOUS DISCUSSION
BELOW STILL APPLY.


PORTIONS OF PREVIOUS DISCUSSION...
UPPER LOW IS NOT PROGGED BY ANY OF THE MODELS TO EXIT THE REGION 
VERY QUICKLY AS IT IS BLOCKED FROM DOING SO BY MS VALLEY HIGH 
AMPLITUDE RIDGE. SO...OUR FAR ERN CWA WILL BE VULNERABLE TO A COUPLE 
MORE SHORTWAVES ROTATING AROUND THE CIRCULATION OF THE LOW. EVEN 
THOUGH MOISTURE IS PRETTY SKIMPY...WILL LEAVE SLIGHT CHANCE POPS 
GOING IN HIGHER TERRAIN ZONE 24 THRU TOMORROW EVENING. TEMPS WILL BE 
SLOW TO RECOVER...ESPECIALLY ERN CWA...AS WE REMAIN IN THE CYCLONIC 
CIRCULATION TOMORROW. LOW FINALLY SHOULD BEGIN TO ACCELERATE SOME BY 
FRIDAY FOR RISING HEIGHTS AND WARMER TEMPS CWA-WIDE. 

EXTENDED STILL LOOKS VERY WARM AS STRONG RIDGING COMMENCES OVER THE 
WRN U.S. MEX MOS GIVING MAX TEMPS WELL INTO THE 90S BY THE MIDDLE OF 
NEXT WEEK...WITH EVEN A 100 FORECAST BY THE MOS FOR KBLH. NOT READY 
TO GO THAT WARM...YET. HOWEVER...RECORDS FOR NEXT WEEK ARE EASILY 
ABOVE THE CENTURY MARK MOST LOWER DESERTS...SO TEMPS NEAR 100 WOULD 
NOT BE UNPRECEDENTED. AS THE RIDGE BUILDS AND THE AMS WARMS...SOME 
MID LEVEL MOISTURE IS PROGGED TO ADVECT INTO THE REGION FROM THE SE 
BY ABOUT WED NEXT WEEK. WILL NEED TO WATCH OUT FOR THE POSSIBILITY 
OF SOME HIGH-BASED CONVECTION OVER ZONE 24. LATER SHIFTS WILL HAVE 
PLENTY OF TIME TO REACT TO THIS AND INCLUDE IT IN FORECAST. 

&&

.AVIATION...
SOUTH CENTRAL AZ INCLUDING KPHX AND KIWA AIRFIELDS... 
CLEAR SKIES AND LIGHT WIND ARE EXPECTED THROUGH 22Z THU. AFTER 22Z 
THU...INCREASING CLOUDS...SCT-BKN NEAR 12 THSD MSL...ARE EXPECTED 
THROUGH 03Z FRI. 


SOUTHEAST CA...INCLUDING KIPL AND KBLH AIRFIELDS... 
CLEAR SKIES AND STEADY WEST WIND IN THE 5 TO 15 KNOT RANGE IS 
EXPECTED THROUGH 03Z FRI.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
THE STRONG LOW PRESSURE SYSTEM IS EXPECTED TO MOVE EAST OF OUR 
AREA...WHICH WILL ALLOW HIGHER PRESSURE ALOFT FROM THE PACIFIC TO 
SLOWLY BUILD OVER THE REGION. THIS WILL BRING MOSTLY CLEAR 
SKIES...DRY CONDITIONS...AND A WARMING TREND TO OUR AREA THIS COMING 
WEEKEND. TEMPERATURES WILL REACH THE UPPER 80S BY SATURDAY AND ARE 
EXPECTED TO WARM INTO THE MID 90S BY THE BEGINNING OF NEXT WEEK. 
THIS DRY AIRMASS WILL BRING MINIMUM RH VALUES DROPPING INTO THE 
SINGLE DIGITS BY EARLY NEXT WEEK. OCCASIONAL BREEZINESS FROM THE 
NORTH IS EXPECTED IN THE HIGHER ELEVATIONS OF SOUTHEAST CALIFORNIA 
AND DOWN THE LOWER COLORADO RIVER VALLEY MAINLY SATURDAY AND FROM 
THE EAST IN SOUTH-CENTRAL ARIZONA EARLY NEXT WEEK. 
OTHERWISE...GENERALLY LIGHT WIND IS EXPECTED.
 
&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE. 

CA...NONE.


$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...VASQUEZ/ESTLE
AVIATION...VASQUEZ
FIRE WEATHER...PADDOCK