561  
FXUS65 KPSR 232226  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
326 PM MST SUN SEP 23 2018  
   
SYNOPSIS
 
 
HIGH TEMPERATURES WILL CONTINUE AT OR JUST ABOVE 100 DEGREES THROUGH  
THE WEEK WITH ONLY MODEST DAY TO DAY CHANGES ANTICIPATED. EXPECT A  
SLIGHT TO MODERATE INCREASE IN MOISTURE ALOFT THROUGH THE EARLY  
PART OF THE WEEK FOLLOWED BY DRIER AIR AGAIN BY WEDNESDAY.  
PRECIPITATION AND STORM CHANCES WILL REMAIN VERY LOW AND ARE  
GENERALLY NOT EXPECTED THROUGH THE FORECAST PERIOD WITH THE  
OCCASIONAL SLIGHT POSSIBILITY OF VERY ISOLATED, SHORT-LIVED  
POP-UP MORNING SHOWERS OR AFTERNOON STORMS.  
 

 
   
DISCUSSION
 
 
A FLAT HIGH PRESSURE RIDGE ALOFT REMAINS IN CONTROL OF SOUTH-CENTRAL  
AZ TODAY TO BRING YET ANOTHER DAY OF HOT, ABOVE NORMAL TEMPERATURES  
ACROSS THE REGION. EARLY AFTERNOON TEMPERATURES RANGED FROM THE LOW  
TO MID 100S OUT WEST TO THE UPPER 90S TO LOW 100S ACROSS THE LOWER  
DESERTS. IT'S ALSO DRIER TODAY WITH SURFACE DEWPOINTS TWO DAYS INTO  
A DRYING TREND REGISTERING 12 TO 19 DEGREES LOWER THAN YESTERDAY  
AFTERNOON WITH READINGS IN THE MID 30S TO MID 40S. AFTERNOON  
SATELLITE IMAGERY DEPICTED PATCHY MIDDLE CLOUDS DRIFTING  
NORTHEASTWARD OVER SOUTHERN TO SOUTHWEST AZ WITH MOSTLY CLEAR SKIES  
ACROSS OTHER LOWER DESERT AREAS.  
 
LITTLE CHANGE IS EXPECTED IN THE SENSIBLE WEATHER THIS WEEK WITH  
HIGH TEMPERATURES NEAR OR JUST ABOVE 100 DEGREES INTO NEXT WEEKEND  
AMIDST VERY LOW STORM CHANCES. THE HIGH PRESSURE ALOFT IS FORECAST  
TO FLATTEN AND REPOSITION MORE TO THE SOUTHWEST OF THE REGION AS  
BROAD, SAGGY CYCLONIC TROUGHING AND STRONGER WESTERLY FLOW TAKES ITS  
PLACE OVER ARIZONA. IN ADDITION A SLIGHT TO MODERATE INCREASE IN  
MOISTURE PARAMETERS IS ALSO EXPECTED FROM NOW THROUGH MONDAY AS PW  
NEAR 0.75 IN. INCREASE TO NEAR 1.4 IN. DUE TO LIGHT TO MODERATE  
MIDLEVEL AND SOME BL MOISTURE ADVECTION FROM NW MEXICO. AS A RESULT  
SEVERAL OF THE HIGH-RES MODELS SUCH AS THE HREF SHOW VERY ISOLATED  
AND SMALL POP-UP STORMS AND SHOWERS OVER PORTIONS OF THE LOWER  
DESERTS THROUGH MONDAY, THUS THE NON-ZERO POPS ACROSS THE LOWER  
DESERTS ARE INCLUDED IN THE FORECAST.  
 
ON TUESDAY AND WEDNESDAY A RELATIVELY DRY, SHALLOW AND WEAK FOUR-  
CORNERS TROUGH AXIS WILL MOVE ACROSS THE REGION AND TRY TO DRAW UP  
SOME MOISTURE FROM NW MEXICO INTO FAR SE, E AND NE AZ, ALTHOUGH  
DURING A SIMULTANEOUS DRYING TREND FURTHER WEST IN THE LOWER  
DESERTS. MODELS REMAIN IN AGREEMENT THAT THE ISOLATED STORM ACTIVITY  
ASSOCIATED WITH THIS FEATURE WILL LIKELY BE CONFINED TO FAR SE, E  
AND NORTH-CENTRAL AZ.  
 
FOR THE SECOND HALF OF THE WEEK DRY NORTHWESTERLY FLOW WILL BE IN  
CONTROL FOLLOWED BY A RIDGE OF HIGH PRESSURE MOVING INTO THE  
INTERMOUNTAIN WEST WHICH WILL INCREASE H5 HEIGHTS OVER SOUTH-CENTRAL  
DESERTS TO NEAR 588-590DAM BY THURSDAY AND FRIDAY. BY SATURDAY THE  
RIDGE AXIS SHIFTS EAST OF THE REGION AND IS REPLACED BY  
SOUTHWESTERLY FLOW ALOFT AS WELL AS INCREASING MOISTURE OUT AHEAD  
OF A CLOSED LOW PRESSURE STORM SYSTEM MOVING EAST INTO NORTHERN  
CA.  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, AND KSDL:  
ONLY MINIMAL AVIATION IMPACTS THROUGH MONDAY AFTERNOON WITH ONLY  
SOME OCCASIONAL CIGS AROUND 10K FT AND VIRGA DEVELOPING OVERNIGHT.  
GUSTY SOUTHEAST WINDS THIS AFTERNOON WILL RELAX AND EVENTUALLY SHIFT  
TOWARDS A SOUTHWEST HEADING PRIOR TO SUNSET THOUGH TIMING IS MORE  
UNCERTAIN THAN USUAL. A SHIFT BACK TO AN EASTERLY DIRECTION SHOULD  
OCCUR AFTER MIDNIGHT AND MAY BE MORE DELAYED THAN USUAL.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
LITTLE TO NO AVIATION CONCERNS THROUGH MONDAY AFTERNOON WITH JUST  
SOME OCCASIONAL MID/HIGH CLOUDS. WINDS WILL FAVOR A SOUTHERLY OR  
SOUTHWEST DIRECTION DURING AFTERNOON/EVENING HOURS, AND MORE  
VARIABLE OR NORTHERLY DURING THE MORNING.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
WEDNESDAY THROUGH SUNDAY:  
TEMPERATURES WILL REMAIN SEVERAL DEGREES ABOVE SEASONAL NORMALS  
THROUGH THE WEEKEND WITH DRY WEATHER FOR ALL DISTRICTS. MINIMUM  
AFTERNOON HUMIDITY LEVELS WILL RANGE FROM THE TEENS IN LOWER  
ELEVATIONS TO AROUND 25% AT HIGHER TERRAIN NORTH AND EAST OF  
PHOENIX. OVERNIGHT RECOVERY WILL BE FAIR TO GOOD. WIND SPEEDS SHOULD  
REMAIN TYPICALLY LIGHT FOR EARLY AUTUMN WITH ONLY THE USUAL  
AFTERNOON UPSLOPE GUSTINESS.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
SPOTTERS SHOULD FOLLOW STANDARD REPORTING PROCEDURES.  
 

 
   
PSR WATCHES/WARNINGS/ADVISORIES
 
 
AZ...NONE.  
CA...NONE.  

 
 

 
 
DISCUSSION...SAWTELLE  
AVIATION...MO  
FIRE WEATHER...MO  
 
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