000 
FXUS65 KPSR 300455
AFDPSR
AZZ020>028-CAZ030>033-301200-

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
945 PM MST SUN JUL 29 2007

SOUTH-CENTRAL AND SOUTHWEST ARIZONA...AND SOUTHEAST CALIFORNIA 
FORECAST DISCUSSION

.SYNOPSIS...
A LOW PRESSURE SYSTEM APPROACHING FROM TEXAS AND NEW MEXICO WILL 
MOVE INTO PARTS OF SOUTHEAST ARIZONA MONDAY...AND OVER CENTRAL 
ARIZONA TUESDAY AND WEDNESDAY. THIS WILL INCREASE THE CHANCE OF 
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS OVER ARIZONA THROUGH 
MID WEEK. A STRONG HIGH PRESSURE SYSTEM WILL REBUILD OVER THE REGION 
THURSDAY INTO THE WEEKEND...AND WILL RESULT IN A DECREASING CHANCE 
FOR SHOWERS AND THUNDERSTORMS. 

&&

.SHORT TERM...
TONIGHT THROUGH WEDNESDAY...
IR SATELLITE INDICATES ONLY A COUPLE CLUSTERS OF STORMS OVER NRN 
AZ...THESE ARE QUICKLY FALLING APART OVER THE MOUNTAINS AND NOT 
PROPAGATING INTO THE DESERTS THIS EVENING. A LITTLE INVESTIGATION 
WITH GOES TPW SHOWS THAT SOME SIGNIFICANT MID-LEVEL DRYING TOOK 
PLACE TODAY OVER SRN PORTIONS OF THE STATE AND ALSO FAR SWRN 
CA...ALSO PWATER DROPPED ABOUT .50 INCHES ON THE 00Z KTUS/KPSR RAOBS 
COMPARED TO THIS TIME YESTERDAY. ADD TO THE DRYING SOME CONVECTIVE 
INHIBITION AND CONVERGENT FLOW AT THE 300-250MB LEVEL OVER OUR 
AREA...AND VOILA...NO STORMS OVER THE DESERTS OR THE PHOENIX METRO 
AREA. AS SUCH...REDUCED POPS CWA-WIDE TO LESS THAN 10 PERCENT FROM 
MARICOPA COUNTY WEST...KEEPING THE BEST CHANCES OVER SOUTHERN GILA 
COUNTY FOR TONIGHT. 

THE CURRENT GFS KEYED IN ON THE DRY AIR WITH A 700 MB DEW POINT 
BULLSEYE OF LESS THAN 3C RIGHT OVER OUR CWA. THE MODEL ALSO SUGGESTS 
THAT THE DRY AIR MASS WILL MOVES WEST TOMORROW AS SOME MOISTURE 
ADVECTS BACK INTO THE REGION AHEAD OF THE INVERTED TROF CURRENTLY 
PUSHING THROUGH NM. MODELS ALSO PROG THIS TROF TO WEAKEN AND CENTER 
NEAR THE SOUTHEAST CORNER OF AZ MONDAY EVENING...THUS ALLOWING THE 
UPPER LEVEL HIGH TO REPOSITION...AND THE FLOW TO BECOME MORE 
CONVERGENT AGAIN OVER OUR AREA. WITH LIGHT STEERING FLOW...THIS 
COULD LESSEN THE CHANCES FOR STORMS TO FORM OVER THE HIGHER TERRAIN 
AND PROPAGATE INTO THE LOWER DESERTS. INTERESTINGLY ENOUGH...OVER 
THE LAST COUPLE OF DAYS...THE NAM HAS BEEN DOING WELL AT CAPTURING 
THE PLACEMENT/SPATIAL EXTENT OF POPS. 00Z RUN SHOWS LITTLE 
ACCUMULATED PRECIP OVER MOST OF SOUTHERN AZ FOR 00Z-06Z TUESDAY TIME 
FRAME (MONDAY AFTN/EVE). WILL LET THE NEXT SHIFT ASSESS THE MODEL 
RUNS AND ADJUST POPS ACCORDINGLY FOR MONDAY AFTERNOON AND EVENING. 
NO OTHER EDITS TO THE GRIDS/FORECAST AT THIS TIME. 

&&

.LONG TERM...
WEDNESDAY NIGHT THROUGH SUNDAY...
A STRONG UPPER LEVEL HIGH PRESSURE SYSTEM OR LARGE ANTICYCLONE IS 
FORECAST TO BUILD OVER THE REGION THURSDAY THROUGH SUNDAY.  THIS IS 
THE FIRST BREAK IN THE PERSISTENT UPPER LEVEL DEFORMATION FIELDS... 
REPLETE WITH EMBEDDED DISTURBANCES...THAT HAS PROMOTED WIDESPREAD 
THUNDERSTORM DEVELOPMENT ACROSS THE STATE FOR THE PAST WEEK OR SO 
(CONSIDERING THE RELATIVELY HIGH MONSOON MOISTURE FIELDS).  MORE 
ORGANIZED ANTI-CYCLONIC WINDS ALOFT THURSDAY THROUGH SUNDAY SHOULD 
THEREFORE PROMOTE A MORE CLIMATOLOGICAL AND DIMINISHED PATTERN TO 
THUNDERSTORM DEVELOPMENT DURING THE AFTERNOONS AND EVENINGS. 
THEREFORE WE WILL TRANSITION FORECASTS BACK TO A MORE STANDARD 
MONSOON... I.E. A CHANCE OF AFTERNOON THUNDERSTORMS IN THE 
MOUNTAINS...WITH A SLIGHT CHANCE OVER THE DESERTS DURING THE 
EVENINGS.

&&
 
.AVIATION...
JULY 30 0430 UTC (JULY 30 2130 MST)

ISOLATED THUNDERSTORM ACTIVITY EXPECTED TO REMAIN OVER THE HIGHER 
TERRAIN OF NORTHEASTERN AZ...AND SOUTH OF THE INTERNATIONAL BORDER 
TONIGHT. AN ISOLATED STORM COULD FORM ACROSS THE CENTRAL DESERTS 
OVERNIGHT...BUT CONFIDENCE IS LOW THAT IT WILL IMPACT KPHX/KIWA TAF 
SITES. DEBRIS CLOUDINESS...MOSTLY AT OR ABOVE 12 KFT...WILL PERSIST 
INTO THE MORNING HOURS.      

SEE TAFS PHXTAFPHX...PHXTAFIWA...PHXTAFYUM...LAXTAFBLH AND LAXTAFIPL 
FOR MORE DETAILED INFORMATION.

AVIATION DISCUSSION IS NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
JULY 29 2140 UTC (JULY 29 1440 MST)

THE THREAT FOR AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS WILL 
CONTINUE THROUGH AT LEAST WEDNESDAY. AMPLE MOISTURE COUPLED WITH 
WEAK DISTURBANCES ALOFT WILL AID IN CONVECTIVE DEVELOPMENT EACH DAY. 
THUNDERSTORM AERIAL COVERAGES WILL BE DIFFICULT TO FORECAST...BUT 
BEST PRECIPITATION CHANCES REMAIN ACROSS ARIZONA FIRE WEATHER ZONES 
132/133 AND LESS SO ACROSS THE LOWER COLORADO RIVER VALLEY AND 
SOUTHEAST CALIFORNIA. EXPECT ERRATIC GUSTY OUTFLOW WINDS...FREQUENT 
CLOUD TO GROUND LIGHTNING AND PERIODS OF HEAVY RAIN WITH ANY STORMS 
THAT DEVELOP.

LITTLE CHANGE IS EXPECTED WITH MAXIMUM DAYTIME TEMPERATURES THROUGH 
FRIDAY...REMAINING AT OR SLIGHTLY BELOW SEASONAL NORMALS. MINIMUM RH 
VALUES ACROSS THE ARIZONA DESERT FLOOR WILL DIP INTO THE MID TO 
UPPER TWENTIES WITH GOOD OVERNIGHT RECOVERY. MOISTURE VALUES ACROSS 
SOUTHEAST CALIFORNIA THE NEXT FEW DAYS...ESPECIALLY ACROSS WESTERN 
IMPERIAL COUNTY AND JOSHUA TREE NATIONAL PARK...WILL FLUCTUATE 
DEPENDING ON THE WIND DIRECTION WITH A STRONG MOISTURE GRADIENT 
ACROSS CENTRAL SOUTHERN CALIFORNIA. NON-THUNDERSTORM WINDS WILL 
GENERALLY BE LIGHT IN THE MORNINGS/EARLY AFTERNOONS...BECOMING GUSTY 
AT TIMES IN THE LATE AFTERNOON INTO THE EVENING HOURS.  

&&


.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

SHORT TERM...MEYERS
LONG TERM...VASQUEZ
AVIATION...MEYERS
FIRE WX...ROGERS