410  
FXUS65 KPSR 192148 CCA  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
250 PM MST SAT AUG 19 2017  
   
..UPDATED AVIATION DISCUSSION
 
 
   
SYNOPSIS
 
 
AN INCREASE IN MONSOON MOISTURE OVER THE NEXT COUPLE DAYS WILL  
LEAD TO RAIN CHANCES MOVING BACK INTO THE AREA, ESPECIALLY ACROSS  
SOUTHEAST AND SOUTH-CENTRAL ARIZONA. RAIN CHANCES WILL LAST INTO  
THE MIDDLE OF THE WEEK BEFORE ANOTHER DRYING TREND LOWERS CHANCES  
BY THURSDAY OR FRIDAY. TEMPERATURES OVER THE NEXT WEEK WILL  
REMAIN NEAR NORMAL.  
 

 
   
DISCUSSION
 
 
MODEST MID LEVEL MOISTURE ADVECTION OCCURRED DURING THE OVERNIGHT  
HOURS ACROSS SOUTH-CENTRAL AND SOUTHEAST ARIZONA AS SOUTHERLY  
FLOW INCREASED EAST OF A DEVELOPING CUT-OFF LOW JUST OFF THE  
CALIFORNIA COAST. THIS LED TO THE 12Z PHOENIX SOUNDING SHOWING A  
PWAT OF 0.96", A DECENT IMPROVEMENT OVER THE PAST COUPLE DAYS. A  
GULF SURGE ALSO MOVED INTO SOUTHWEST ARIZONA NEAR SUNRISE THIS  
MORNING RAISING SURFACE DEW POINTS INTO THE 70S IN YUMA. EVEN WITH  
THIS MOISTURE ADVECTION INTO THE AREA, WE ARE ONLY EXPECTING  
SHOWERS AND THUNDERSTORMS ACROSS FAR EASTERN GILA COUNTY THIS  
AFTERNOON.  
 
WATER VAPOR IMAGERY CURRENTLY SHOWS A MODEST SHORTWAVE TROUGH  
ACROSS SONORA MEXICO WHICH IS VERY SLOWLY MOVING TO THE NORTH  
NORTHEAST. MODELS ARE FORECASTING THIS TROUGH TO MOVE INTO  
SOUTHEAST ARIZONA DURING THE OVERNIGHT HOURS TONIGHT AS WELL AS A  
DECAYING MCS. MOISTURE WILL CONTINUE TO SPREAD NORTH AND WEST INTO  
THE AREA TONIGHT AS PWATS INCH CLOSER TO 1.25". AT LEAST A COUPLE  
HI-RES CAMS SHOW SOME LIGHT SHOWER/SPRINKLE ACTIVITY MOVE INTO  
THE PHOENIX AREA LATE TONIGHT, LIKELY INFLUENCED BY THE DECAYING  
MCS.  
 
THE CUT-OFF LOW WILL CONTINUE TO SIT JUST OFF THE SOUTHERN  
CALIFORNIA COAST INTO EARLY NEXT WEEK ALLOWING FOR AT LEAST SOME  
SORT OF SOUTHERLY WIND COMPONENT AND MOISTURE FEED. UPPER LEVEL  
SUPPORT FOR STORM ACTIVITY WILL MOSTLY STAY WEST OF OUR AREA AND A  
SOUTH TO SOUTHWESTERLY STEERING FLOW IS NOT FAVORABLE FOR  
WIDESPREAD STORM ACTIVITY ACROSS SOUTHWEST AND SOUTH-CENTRAL  
ARIZONA. POPS FOR SUNDAY THROUGH WEDNESDAY REMAIN MAINLY IN THE  
SLIGHT CHANCE CATEGORY AS PWATS HOVER AROUND LOW GRADE MONSOON  
LEVELS. TEMPERATURES THROUGH THE PERIOD SHOULD END UP NEAR OR  
SLIGHTLY BELOW NORMAL DUE TO THE INFLUENCE OF THE LOW TO OUR WEST.  
 
BY THE MIDDLE PART OF THIS WEEK, THE LOW WILL START TO SPREAD  
DRIER AIR INTO SOUTHEAST CALIFORNIA AND FAR SOUTHWEST ARIZONA AS  
FLOW ALOFT TURNS SLIGHTLY SOUTHWESTERLY AND THIS WILL SERVE TO  
CONFINE STORM DEVELOPMENT TO AREAS EAST OF THE LOWER COLORADO  
RIVER VALLEY. ON THURSDAY THE LOW IS FORECAST TO OPEN UP AND MOVE  
INLAND, BRINGING MORE DRY AIR FURTHER EAST ACROSS THE LOWER  
DESERTS AND AS THIS OCCURS, STORM CHANCES FROM PHOENIX WEST FALL  
WITH POPS TO BE IN THE SINGLE DIGITS. SLIGHT CHANCES FOR STORMS  
WILL CONTINUE OVER THE HIGHER TERRAIN OF SOUTHERN GILA COUNTY INTO  
THE END OF THE WORK WEEK. HIGH TEMPS TUESDAY INTO THURSDAY WILL  
STAY A BIT BELOW NORMAL, ESPECIALLY OVER SOUTH- CENTRAL ARIZONA,  
UNDER THE INFLUENCE OF THE LOW AND ITS SLIGHTLY COOLER AIRMASS.  
TEMPERATURES SHOULD CLIMB SLIGHTLY FRIDAY AS LOW CONTINUES TO  
WEAKEN AND HIGH PRESSURE ALOFT BECOMES SLIGHTLY STRONGER.  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, AND KSDL:  
 
WESTERLY WINDS TO PERSIST AT THE PHOENIX AREA TAF SITES LATER THAN  
USUAL, WELL INTO TONIGHT, WITH STRONGER GUSTS POSSIBLE DURING THE  
LATE AFTERNOON/EARLY EVENING HOURS, WITH THE SWITCH TO EASTERLY NOT  
LIKELY TO OCCUR UNTIL SOMETIME AFTER MIDNIGHT AS WELL. A SIMILAR  
WIND PATTERN IS EXPECTED TO OCCUR ON SUNDAY AS WELL. MONSOON  
MOISTURE RETURNING BACK TO THE REGION WILL LIKELY PRODUCE ISOLATED  
SHOWERS AND THUNDERSTORMS SUNDAY AFTERNOON/EVENING, BUT CONFIDENCE  
IS FAR TOO LOW TO INCLUDE ANYTHING MORE THAN AN INCREASE IN MID/HIGH  
CLOUDINESS INN THE TAFS AT THIS TIME.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
 
WINDS TO REMAIN MAINLY SOUTHERLY AT KBLH THROUGH THE TAF PERIOD,  
UNDER MAINLY CLEAR SKIES. WESTERLY SUNDOWNER WINDS AT KIPL TO  
PERSIST THROUGH SUNDAY MORNING, THEN BECOMING LIGHT/VARIABLE FOR A  
TIME DURING THE MID/LATE MORNING HOURS. WESTERLY TO SOUTHWESTERLY  
WINDS WILL THEN RETURN TO KIPL ON SUNDAY AFTERNOON.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
MONDAY THROUGH FRIDAY: A MODERATE AMOUNT OF MONSOON MOISTURE WILL  
PERSIST THROUGH AT LEAST MID WEEK BRINGING A CHANCE OF STORMS (20-  
30%) TO THE HIGHER ELEVATIONS EACH DAY AND A SLIGHT CHANCE (~10%) FOR  
THE LOWER ELEVATIONS OF SOUTH-CENTRAL ARIZONA. SLIGHTLY DRIER AIR  
MOVING IN LATE WEEK WILL LIKELY CONFINE STORMS TO THE HIGH  
ELEVATIONS ON THURSDAY AND FRIDAY WHILE ALL AREAS WILL SEE NEAR  
SEASONAL TEMPS. MINIMUM HUMIDITIES WILL HOVER AROUND 20% FOR THE  
LOWER ELEVATIONS WHILE THE HIGHER ELEVATIONS OF GILA COUNTY WILL BE  
MUCH MORE FAVORABLE, AROUND 30-40%.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
SPOTTERS SHOULD FOLLOW STANDARD REPORTING PROCEDURES.  
 

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

 
 

 
 
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DISCUSSION...KUHLMAN  
PREVIOUS DISCUSSION...CB  
AVIATION...PERCHA  
FIRE WEATHER...WILSON  
 
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