803  
FXUS65 KPSR 151729  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
1029 AM MST MON JUL 15 2019  
   
UPDATE
 
UPDATED AVIATION DISCUSSION.  
 

 
   
SYNOPSIS
 
 
STRONG HIGH PRESSURE WILL REMAIN PARKED OVER THE REGION THROUGH  
TOMORROW AND PROVIDE AN EXTENDED PERIOD OF HOT WEATHER. AN  
EXCESSIVE HEAT WARNING IS IN EFFECT TODAY THROUGH TUESDAY EVENING  
FOR MANY LOWER DESERT LOCATIONS. DRIER AIR WILL MOVE INTO THE  
REGION THROUGH TUESDAY AND LIMIT THE THREAT OF THUNDERSTORMS TO  
HIGH TERRAIN AREAS IN NORTH/EAST/SOUTHEAST ARIZONA. AN UPTICK IN  
MONSOON ACTIVITY LOOKS POSSIBLE WEDNESDAY THROUGH EARLY NEXT WEEK,  
WITH THE GREATEST CHANCES THIS WEEKEND INTO EARLY NEXT WEEK.  
 

 
   
DISCUSSION
 
 
THE SUBTROPICAL HIGH HAS NUDGED A LITTLE FURTHER SOUTH AND IS  
SITUATED OVER THE ARIZONA/NEW MEXICO BORDER. THE CENTER OF THIS  
HIGH WILL SLOWLY SHIFT TO THE EAST TODAY AS A PACIFIC TROUGH DIGS  
SOUTH ALONG THE WESTERN CONUS. THIS WILL GRADUALLY SHIFT THE WINDS  
ALOFT TO THE SOUTHWEST AND ADVECT DRIER MID-LEVEL AIR INTO THE  
REGION. SKIES TODAY WILL REMAIN MOSTLY SUNNY WITH A FEW MID-LEVEL  
CLOUDS FROM TIME TO TIME. WITH MOISTURE SLOWLY BEING PUSHED NORTH  
AND EAST, THE GREATEST THUNDERSTORM CHANCES WILL BE ACROSS HIGH  
TERRAIN AREAS IN NORTH/EAST/SOUTHEAST ARIZONA. WITH THUNDERSTORMS  
DEVELOPING AROUND OUR EASTERN FORECAST AREA TODAY, IT IS POSSIBLE  
THAT WE COULD SEE AN OUTFLOW BOUNDARY MAKE IT'S WAY INTO THE LOWER  
DESERTS, HOWEVER INSTABILITY WILL BE LIMITED AND REGENERATION OF  
STORMS IN THE LOWER DESERTS REMAINS VERY UNLIKELY. THE MAIN STORY  
TODAY WILL BE THE HEAT. WITH 592-594 DM HEIGHTS OVERHEAD AND A  
DRIER ATMOSPHERE IN PLACE, TEMPERATURES WILL HAVE NO TROUBLE  
SOARING INTO THE 110-115 DEGREE RANGE THIS AFTERNOON. DUE TO THIS,  
AN EXCESSIVE HEAT WARNING IS IN EFFECT FOR MANY LOWER DESERT  
LOCATIONS (GO TO THE PSR WATCHES/WARNINGS/ADVISORIES SECTION BELOW  
FOR MORE INFORMATION).  
 
ON TUESDAY, THE AFOREMENTIONED PACIFIC TROUGH DIGS FURTHER SOUTH  
AND EAST, PUSHING THE SUBTROPICAL RIDGE AND ASSOCIATED MONSOON  
MOISTURE A LITTLE FURTHER SOUTHEAST. THIS WILL RESULT IN EVEN  
LOWER PRECIPITATION CHANCES WITH THE BEST COVERAGE IN SOUTHEAST  
ARIZONA. WITH SIMILAR HEIGHTS IN PLACE ON TUESDAY AND AN EVEN  
DRIER ATMOSPHERE, EXPECT TEMPERATURES TO BE THE SAME OR MAYBE A  
DEGREE WARMER. THIS WILL KEEP THE EXCESSIVE HEAT WARNING IN  
EFFECT THROUGH TUESDAY EVENING FOR SIMILAR LOCATIONS. TUESDAY  
NIGHT, GUIDANCE CONTINUES TO SHOW A DECENT GULF SURGE FROM STORMS  
IN NORTHERN MEXICO. THIS WILL ADVECT MOISTURE INTO THE LOWER  
DESERTS ON WEDNESDAY AND POSSIBLY LEAD TO AN UPTICK IN MONSOON  
ACTIVITY WEDNESDAY EVENING. THIS INCREASE IN ATMOSPHERIC MOISTURE  
WILL ALSO LEAD TO A DECREASE IN HIGH TEMPERATURES (AROUND 5  
DEGREES) WEDNESDAY AFTERNOON.  
 
THURSDAY THROUGH MONDAY, THE SUBTROPICAL HIGH EXPANDS INTO THE  
EASTERN CONUS AND GRADUALLY SHIFTS WINDS ALOFT TO THE SOUTH AND  
THEN SOUTHEAST. THIS WILL CONTINUE TO ADVECT MONSOON MOISTURE  
INTO THE REGION. IN ADDITION, MODELS CONTINUE TO DEPICT A SERIES  
OF WAVES PROPAGATING AROUND THE SUBTROPICAL HIGH AND ACROSS THE  
REGION, ESPECIALLY THIS WEEKEND INTO MONDAY. THESE WAVES COULD  
SERVE AS AN EXTRA MECHANISM FOR STORM DEVELOPMENT IN THE LOWER  
DESERTS. UNFORTUNATELY, CONFIDENCE STILL REMAINS LOW ON EXACT  
TIMING, SO IT'S HARD TO SAY WHICH DAYS WILL BE MORE ACTIVE THAN  
OTHERS, BUT RIGHT NOW IT LOOKS LIKE THE BEST CHANCES ARE THIS  
WEEKEND AND EARLY NEXT WEEK. THE GOOD NEWS IS, THE GRADUAL  
INCREASE IN MOISTURE THROUGH EARLY NEXT WEEK WILL CAUSE A  
DOWNWARD TREND IN TEMPERATURES, WITH HIGHS FALLING AROUND OR JUST  
BELOW AVERAGE SUNDAY AND NEXT MONDAY.  
 

 
   
AVIATION
 
UPDATED AT 1730 UTC  
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:  
 
WINDS WILL FOLLOW THE TYPICAL DIURNAL DIRECTIONAL TENDENCIES WITH  
THE WESTWARD SHIFT OCCURRING WITHIN THE NEXT HOUR OR SO. THERE IS  
NO CHANCE FOR THUNDERSTORMS IN THE TERMINAL AREA AND THE CHANCE  
FOR ANY OUTFLOWS IS LOW. OTHERWISE, EXPECT OCCASIONAL AFTERNOON  
BREEZES.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
 
WINDS WILL BECOME PREDOMINANTLY WESTERLY-SOUTHWESTERLY AT BOTH  
SITES WITH OCCASIONAL AFTERNOON GUSTS. THE WINDS WILL BECOME VERY  
LIGHT AND VARIABLE IN DIRECTION LATE TONIGHT. NO STORMS OR  
OUTFLOWS ARE EXPECTED ANYWHERE NEAR THE TERMINAL AREA.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
WEDNESDAY THROUGH SUNDAY:  
TEMPERATURES WILL BECOME MORE SEASONAL, ALTHOUGH STILL HOT DURING  
THE DAYTIME. MINIMUM RH VALUES WILL STRUGGLE TO STAY ABOVE 15%  
THROUGH SATURDAY (THOUGH HIGHER TERRAIN EASTERN DISTRICTS WILL  
LIKELY BE A LITTLE MORE SATURATED). ON SUNDAY, MINIMUM RH VALUES  
INCREASE INTO THE UPPER TEENS/LOW 20S. OVERNIGHT RECOVERIES  
THROUGH SATURDAY WILL RANGE FROM 25-40% AT LOWER ELEVATIONS AND  
SUBSTANTIALLY HIGHER IN EASTERN DISTRICTS. SATURDAY NIGHT INTO  
SUNDAY MORNING, MINIMUM RH VALUES WILL INCREASE INTO THE 40S AND  
50S. WINDS WILL REMAIN FAIRLY LIGHT WITH SOME AFTERNOON BREEZES  
FAVORING TYPICAL DIURNAL TENDENCIES. THERE WILL BE SLIGHT CHANCES  
FOR STORMS, MAINLY ALONG THE HIGHER TERRAIN NORTH/EAST/SOUTHEAST  
OF PHOENIX. HOWEVER, PERIODIC OUTFLOW BOUNDARIES WITH ERRATIC  
SHIFTING WINDS WILL BE POSSIBLE. THE BEST STORM CHANCES IN THE  
LOWER DESERTS LOOK TO BE THIS WEEKEND.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
SPOTTERS SHOULD FOLLOW STANDARD REPORTING PROCEDURES.  
 

 
   
PSR WATCHES/WARNINGS/ADVISORIES
 
 
AZ...EXCESSIVE HEAT WARNING UNTIL 8 PM MST TUESDAY FOR AZZ532-534-  
536>544-546-548>551-553>556-559.  
 
CA...EXCESSIVE HEAT WARNING UNTIL 8 PM PDT TUESDAY FOR CAZ566>568.  
 

 
 

 
 
DISCUSSION...HERNANDEZ  
AVIATION...DEEMS  
FIRE WEATHER...HERNANDEZ  
 
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