769  
FXUS65 KPSR 231012 AAA  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
310 AM MST SAT JUN 23 2018  
   
UPDATE
 
UPDATED AVIATION DISCUSSION.  
   
SYNOPSIS
 
 
TEMPERATURES CLOSER TO SEASONAL NORMALS CAN BE EXPECTED THROUGH  
MONDAY AS HIGH PRESSURE WEAKENS ACROSS THE SOUTHWEST. ANOTHER  
WARMUP IS EXPECTED TUESDAY AND WEDNESDAY, WITH HIGH TEMPERATURES  
FORECAST TO BE NEAR 110 DEGREES ACROSS THE LOWER DESERTS. A DRY  
WEATHER PATTERN WILL CONTINUE THROUGH LATE NEXT WEEK AS RICHER  
MOISTURE REMAINS FIXED OVER NORTHERN MEXICO.  
 

 
   
DISCUSSION
 
 
QUIESCENT WEATHER CONDITIONS CONTINUE ACROSS THE SOUTHWEST AMIDST  
A BENIGN LARGE-SCALE WEATHER PATTERN. BROAD WEST-NORTHWESTERLY  
FLOW IS POSITIONED ACROSS THE GREAT BASIN, WITH ARIZONA POSITIONED  
ALONG THE SOUTHERN FRINGE OF THE STRONGER FLOW ALOFT. A SHORTWAVE  
IMPULSE OVER THE NORTHERN ROCKIES WILL DIG SOUTHEASTWARD TOWARDS  
THE CENTRAL HIGH PLAINS, PROMPTING A WEAKENING OF MIDLEVEL HEIGHT  
FIELDS ACROSS ARIZONA THIS WEEKEND. AS A RESULT, A MINOR COOLING  
TREND CLOSER TO SEASONAL NORMALS WILL COMMENCE TODAY, WITH HIGH  
TEMPERATURES GENERALLY WITHIN A COUPLE DEGREES OF 105 THIS  
AFTERNOON ACROSS THE LOWER DESERTS. THE MINOR PATTERN CHANGE WILL  
ALSO SUPPORT AN INCREASE IN WINDS THIS AFTERNOON, AS SOUTHERLY TO  
SOUTHWESTERLY WINDS GUST TO 20 MPH THIS AFTERNOON ACROSS SOUTH-  
CENTRAL ARIZONA, TO 30 MPH ACROSS SOUTHWEST ARIZONA AND THE LOWER  
COLORADO RIVER VALLEY. ALSO OF INTEREST, A VERY SHALLOW LAYER OF  
RICHER MOISTURE FROM THE GULF OF CALIFORNIA IS ADVECTING NORTHWARD  
THIS MORNING, WITH 60S DEWPOINTS FUNNELING THROUGH THE LOWER  
COLORADO RIVER VALLEY AND IMPERIAL VALLEY, AND LOW 50S INTO SOUTH-  
CENTRAL ARIZONA. WHILE THIS WILL HAVE VIRTUALLY NO IMPACT ON  
SENSIBLE WEATHER CONDITIONS OTHER THAN TO FACILITATE A SLIGHT  
INCREASE IN BOUNDARY-LAYER RH, IT IS AT LEAST EVIDENCE THAT LOW-  
LEVEL MOISTURE WILL MORE EASILY BE ABLE TO SPREAD NORTHWARD ONCE  
A MORE TYPICAL MONSOONAL PATTERN TAKES HOLD AGAIN.  
 
INTO NEXT WEEK, A MID-LEVEL ANTICYCLONE WILL QUICKLY REBUILD IN  
THE WAKE OF THE AFOREMENTIONED SHORTWAVE TROUGH, LEADING TO  
ANOTHER MINOR WARMING TREND. THE HOTTEST TEMPERATURES OF THE WEEK  
(AND PERHAPS THE YEAR, SO FAR) WILL OCCUR ON TUESDAY AND  
WEDNESDAY, WITH PHOENIX FORECAST TO REACH 111 DEGREES ON TUESDAY.  
WHILE CURRENT HEATRISK OUTPUT SUGGESTS THIS WILL REMAIN JUST SHY  
OF EXCESSIVE HEAT THRESHOLDS, THESE TEMPERATURES WILL STILL RESULT  
IN HEAT-RELATED IMPACTS ACROSS THE LOWER DESERTS.  
 
IN WHAT HAS REMAINED THE THEME THUS FAR IN JUNE, THE  
CLIMATOLOGICALLY FAVORED ANTICYCLONE NEAR THE FOUR CORNERS THAT  
TYPICALLY SUPPORTS PROLONGED PERIODS OF EXCESSIVE HEAT, WILL  
INSTEAD BE SHORT-LIVED AS ANOTHER UPPER TROUGH DEVELOPS OVER THE  
WESTERN CONUS. THIS WILL ACT TO WEAKEN THE ANTICYCLONE, AND BRING  
TEMPERATURES BACK CLOSER TO SEASONAL NORMALS BY LATE NEXT WEEK,  
WHILE AMPLIFIED RIDGING (AND ASSOCIATED HEAT) IS FOCUSED EAST OF  
THE ROCKIES. WHILE MONSOONAL MOISTURE WILL STRUGGLE TO MAKE IT  
INTO SOUTH-CENTRAL ARIZONA WITH THIS PATTERN GIVEN THE SLIGHTLY  
WEST OF SOUTH COMPONENT TO THE FLOW ALOFT, IT WILL BE MORE LIKELY  
TO REACH NEW MEXICO AND FAR EASTERN ARIZONA BY LATE NEXT WEEK.  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, AND KSDL:  
 
HIGH PRESSURE AND DRY NORTHWESTERLY FLOW ALOFT TO KEEP SKIES MAINLY  
CLEAR THROUGH THE TAF PERIOD. WINDS TO MAINLY FOLLOW NORMAL DIURNAL  
PATTERNS, WITH SOME GUSTINESS (UP TO 15-20 KT GUSTS) DURING THE  
AFTERNOON/EARLY EVENING HOURS ON SATURDAY. MINIMAL AVIATION CONCERNS  
THROUGH THE TAF PERIOD.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
 
HIGH PRESSURE AND DRY NORTHWESTERLY FLOW ALOFT TO KEEP SKIES MAINLY  
CLEAR THROUGH THE TAF PERIOD. WINDS TO REMAIN SOUTHERLY AT KBLH AND  
SOUTHEASTERLY AT KIPL THROUGH THE TAF PERIOD. AT KIPL, WIND GUSTS UP  
TO 15 TO 25 KTS WILL BE POSSIBLE AND AT KBLH WIND GUSTS UP TO 20 TO  
30 KTS WILL BE POSSIBLE DURING THE DAY ON SATURDAY.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
MONDAY THROUGH FRIDAY:  
A RAPID WARMING TREND WILL SPREAD INTO THE DISTRICTS EARLY NEXT  
WEEK WITH TEMPERATURES EASILY CLIMBING ABOVE SEASONAL NORMALS BY  
TUESDAY. BY THE MIDDLE OF THE WEEK, HOT AND DRY CONDITIONS WILL  
RETURN WITH HIGHS NEAR OR JUST ABOVE 110 DEGREES ACROSS THE LOWER  
DESERTS. MINIMUM AFTERNOON HUMIDITY VALUES WILL FALL BACK MOSTLY  
INTO THE SINGLE DIGITS WITH A RETURN OF POOR TO FAIR OVERNIGHT  
RECOVERY. NO STRONG WINDS ARE EXPECTED NEXT WEEK, ALTHOUGH TYPICAL  
AFTERNOON UPSLOPE GUSTINESS WILL BE COMMON AROUND TERRAIN  
FEATURES. THERE ARE STILL NO SIGNS OF RAIN THROUGH LATE NEXT  
WEEK.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
SPOTTER ACTIVATION WILL NOT BE NEEDED THROUGH AT LEAST THE MIDDLE OF  
NEXT WEEK.  
 

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

 
 

 
 
DISCUSSION...ROGERS  
AVIATION...PERCHA  
FIRE WEATHER...ROGERS/MO  
 
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