796  
FXUS65 KPSR 271555  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
855 AM MST SAT MAY 27 2017  
   
SYNOPSIS
 
 
VERY TYPICAL MEMORIAL DAY HOLIDAY WEATHER WILL PERSIST THROUGH THE  
WEEKEND WITH AFTERNOON HIGH TEMPERATURES CLIMBING INTO THE 90S AND  
LOWER 100S. TEMPERATURES WILL PEAK ON MONDAY AND TUESDAY BEFORE  
MINOR COOLING STARTS BEYOND THE MIDDLE OF NEXT WEEK. SOME SCATTERED  
MOUNTAIN STORMS WILL ALSO BE POSSIBLE BY THE MIDDLE OF THE WEEK.  
 

 
   
DISCUSSION
 
 
VERY TYPICAL WEATHER FOR ARIZONA THIS MORNING AS A DRY WESTERLY FLOW  
ALOFT WAS IN PLACE ACROSS THE AREA, EASILY SEEN IN THE MORNING PLOT  
AND RAOB DATA. IR IMAGERY AT 9 AM SHOWED SUNNY SKIES AREA WIDE. THE  
12Z 500MB PLOT DATA DEPICTED VERY LITTLE CHANGE IN THE HEIGHT FIELD  
AND AS SUCH WE DO NOT EXPECT MUCH CHANGE IN THE HIGH TEMPERATURES  
FOR TODAY. HIGHS WILL REMAIN SLIGHTLY BELOW SEASONAL NORMALS AND IN  
THE MID TO UPPER 90S ACROSS THE CENTRAL DESERTS. PHOENIX SHOULD TOP  
OUT A DEGREE OR SO HIGHER THAN YESTERDAY AND AT ABOUT 97 DEGREES.  
OTHERWISE WE CAN EXPECT SUNNY SKIES AND RELATIVELY LIGHT WINDS FOR  
THE REST OF TODAY. CURRENT FORECASTS LOOK TO BE IN FINE SHAPE AND NO  
UPDATES ARE NEEDED.  
   
PREVIOUS DISCUSSION
 
 
LOWER THAN NORMAL HEIGHTS ALOFT PERSIST THIS MORNING FROM SOUTHERN  
CANADA INTO THE ROCKIES AS A TROUGH AXIS SHIFTS INTO THE PLAINS AND  
THE OVERALL PATTERN TEMPORARILY BECOMES PROGRESSIVE. INTO EARLY NEXT  
WEEK, A SPLIT FLOW TYPE OF PATTERN WILL MATERIALIZE OVER THE WESTERN  
CONUS AS HIGH AMPLITUDE RIDGING EXTENDS INTO WESTERN CANADA WHILE AN  
ACTIVE SUBTROPICAL JET UNDERCUTS THIS RIDGE INTO THE SOUTHWEST. THE  
INITIAL INFLUENCE OF THIS RIDGE WILL BE A RAPIDLY WARMING OF THE  
ATMOSPHERIC COLUMN, HOWEVER THE INTRODUCTION OF SUBTROPICAL WAVES  
WILL ALLOW MOISTURE AND CLOUDS TO RESTRICT ANY ADDITIONAL WARMTH  
WHILE ALSO CREATING AN ENVIRONMENT SUPPORTIVE OF MOUNTAIN STORMS  
OVER EASTERN ARIZONA.  
 
LOW LEVEL THERMAL PROFILES WILL REBOUND BEGINNING TODAY AS NEARLY  
STEADY STATE H5 HEIGHTS NEAR 579DM THIS MORNING SLOWLY INCREASE TO  
NEAR 585DM BY MONDAY. TEMPERATURE GUIDANCE SPREADS ARE VERY NARROW  
THROUGH THE WEEKEND PROVIDING VERY GOOD CONFIDENCE 100F TEMPERATURES  
WILL BE BREACHED SUNDAY FOLLOWED BY THE WARMEST DAY OF THE WEEK ON  
MONDAY. WHILE CERTAINLY NO WHERE NEAR RECORD BREAKING, HIGHS SOME 5F  
ABOVE NORMAL APPEAR VERY LIKELY MONDAY AND A DAY TYPICALLY FILLED  
WITH MORE OUTDOOR ACTIVITIES AND SUN/HEAT EXPOSURE.  
 
THROUGH AT LEAST THE FIRST HALF OF NEXT WEEK, AN ACTIVE SUBTROPICAL  
JET WILL BRING SEVERAL LOWER AMPLITUDE DISTURBANCE INTO THE  
SOUTHWEST DOMAIN. THE DETAILS REGARDING DEPTH/INTENSITY AND MOISTURE  
AVAILABILITY REMAIN VARIED AMONG OPERATIONAL AND ENSEMBLE MEMBER  
OUTPUT. THE 00Z OPERATIONAL GFS REMAINS ON THE MORE AGGRESSIVE SIDE  
BRINGING LOWER HEIGHTS AND SOMEWHAT STRONGER FORCING MECHANISMS  
FURTHER SOUTH. ENSEMBLE MEANS MORE CLOSELY RESEMBLE THE 00Z ECMWF  
AND CMC THOUGH IMPACTS ON END RESULT SENSIBLE WEATHER FORECASTS ARE  
MINIMAL AND LIMITED.  
 
REGARDLESS, AHEAD OF THESE SERIES OF WAVES, SUBSTANTIAL BACKING OF  
WINDS IN THE H9-H7 LAYER WILL OCCUR THROUGH THE RIO GRANDE VALLEY  
AND FOUR CORNERS. ALMOST ALL MODEL OUTPUT SUGGESTS NOTABLE MOISTURE  
ADVECTION UP THE RIO GRANDE VALLEY AND JUXTAPOSED WITH WEAKLY FORCED  
ASCENT ASSOCIATED WITH THE SHORTWAVES, ISOLD/SCT THUNDERSTORMS WILL  
BE POSSIBLE ALONG THE RIM, WHITE MOUNTAINS, AND PORTIONS OF SOUTHERN  
GILA COUNTY. THE LARGEST UNCERTAINTY LIES WITH THE AREAL EXTENT AND  
WESTWARD PUSH OF THE BEST QUALITY MOISTURE PLUME. INITIAL LOOK AT  
SREF PROBABILITIES SUGGEST GOOD CHANCES OF STORMS, HOWEVER  
DETERMINISTIC MODEL QPF IS QUITE UNDERWHELMING. THIS MAY BE A CASE  
OF MORE ELEVATED ECHOES AND LIGHTNING VERSUS ACCUMULATING RAINFALL.  
 
THE FORECAST FOR THE LATTER HALF OF NEXT WEEK STILL REMAINS QUITE  
UNCERTAIN WITH MODEL SPREAD GROWING IN A PARTIALLY BLOCKED FLOW  
PATTERN. THE OPERATIONAL 00Z GFS STILL REMAINS A MORE AGGRESSIVE  
OUTLIER THOUGH HAS BACKED OFF THE MOST UNLIKELY OUTCOME OF A DEEP  
CLOSED LOW. THE 00Z ECMWF AND GEM CONTINUE TO LOOK FAR MORE  
AGREEABLE WHEN COMPARED TO OTHER MEDIUM RANGE GUIDANCE KEEPING AN  
ILL DEFINED HEIGHT WEAKNESS AND TROUGHING SIGNATURE LINGERING  
THROUGH THE SW CONUS. MOISTURE WILL MOSTLY BE RELEGATED TO NEW  
MEXICO IN PERSISTENT WESTERLY FLOW (I.E. LITTLE TO NO CHANCE OF  
RAIN), THOUGH THE GENERAL WEAK CYCLONIC FLOW PATTERN WILL FAVOR  
TEMPERATURES HOVERING CLOSE TO CLIMATOLOGY.  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, AND KSDL,  
AND SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
 
FEW AVIATION WEATHER CONCERNS FOR SATURDAY. THE WINDS WILL REMAIN  
LIGHT AT 5 TO 10 KNOTS AND FOLLOW TYPICAL DIURNAL DIRECTIONAL  
SHIFTS. SKIES WILL REMAIN CLEAR WITH NO OTHER MAJOR CONCERNS.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
MONDAY THROUGH FRIDAY:  
GENERALLY WARM WITH MOSTLY DRY CONDITIONS FOR THE PERIOD. HOWEVER,  
A WEATHER SYSTEM WILL BRING A SLIGHT CHANCE FOR ISOLATED  
THUNDERSTORMS TUESDAY AND WEDNESDAY IN THE HIGHER ELEVATIONS TO  
THE NORTH AND EAST OF PHOENIX. RAINFALL AMOUNTS WITH ANY STORMS  
LOOKS MINIMAL BUT A THREAT OF DRY LIGHTNING WILL EXIST FOR BOTH  
DAYS. OUTSIDE OF THUNDERSTORMS, THE WINDS WILL BE THE BREEZY  
WEDNESDAY AND THURSDAY WITH GUSTS UP TO 20-25 MPH. OTHERWISE,  
MINIMUM RELATIVE HUMIDITIES WILL BOTTOM AT 10 TO 20 PERCENT WITH  
FAIR OVERNIGHT RECOVERIES.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
SPOTTER REPORTS WILL NOT BE NEEDED THROUGH THE MIDDLE OF NEXT WEEK.  
 

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

 
 

 
 
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DISCUSSION...CB  
PREVIOUS DISCUSSION...MO  
AVIATION...DEEMER  
FIRE WEATHER...DEEMER  
 
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