168  
FXUS65 KPSR 280538 AAA  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
1035 PM MST THU APR 27 2017  
   
UPDATE
 
UPDATED AVIATION DISCUSSION.  
   
SYNOPSIS
 
 
DEEPENING LOW PRESSURE SYSTEM IS EXPECTED OVER THE FOUR CORNERS AREA  
FRIDAY, AND WILL BRING WINDY CONDITIONS ACROSS ARIZONA FRIDAY  
AFTERNOON AND EVENING, INCLUDING HIGH FIRE DANGER. THERE IS ALSO A  
CHANCE OF AFTERNOON SHOWERS AND THUNDERSTORMS OVER THE MOUNTAINS  
EAST OF PHOENIX. MOSTLY CLEAR SKIES AND COOLER TEMPERATURES ARE  
FORECAST THIS WEEKEND, WITH A SIGNIFICANT WARMING TREND NEXT WEEK.  
 

 
   
DISCUSSION
 
 
A RATHER QUIET EVENING, UNDER DRY NORTHWESTERLY FLOW ALOFT AHEAD OF  
A RATHER STRONG UPPER LOW THAT IS EXPECTED TO DIG SOUTHWARD INTO THE  
4-CORNERS REGION ON FRIDAY AFTERNOON/EVENING. THE LATEST NAM3KM AND  
GFS MODEL RUNS CONTINUE TO BRING VERY STRONG WINDS INTO THE REGION  
ON FRIDAY AFTERNOON/EVENING, AS A VERY STRONG, BUT (MAINLY) DRY COLD  
FRONT PUSHES SOUTHWARD INTO OUR CWA. THE 00Z NAM3KM IS FORECASTING  
35 KT WINDS AT 850MB WITH THE 00Z GFS SHOWING 40 KTS AT 900MB OVER  
THE PHOENIX AREA FOR A BRIEF PERIOD JUST AHEAD OF THE FRONT. THE  
COMBINATION OF THESE WINDS AND VERY DRY AIR MOVING IN BEHIND THE  
FRONT WILL RESULT IN VERY HIGH FIRE DANGER LEVELS ON FRIDAY  
AFTERNOON/EVENING. ALTHOUGH OVERALL AVAILABLE MOISTURE WILL BE QUITE  
LIMITED, A BRIEF SHOT OF MOISTURE BEING DRAWN NORTHWARD AHEAD OF THE  
COLD FRONT (PWATS RISING TO AROUND 0.75 INCH), STRONG FRONTAL  
LIFTING, AND OROGRAPHIC LIFTING WILL LIKELY RESULT IN THE  
DEVELOPMENT OF SCATTERED SHOWERS AND THUNDERSTORMS FRIDAY AFTERNOON  
OVER THE HIGHER TERRAIN OF SOUTHERN GILA COUNTY. GIVEN THE FACT THAT  
CURRENT FORECASTS DO ALREADY REFLECT THESE UPDATED FORECAST TRENDS,  
NO FURTHER UPDATES ARE PLANNED AT THIS TIME.  
 

 
   
PREVIOUS DISCUSSION
 
 
TONIGHT THROUGH FRIDAY NIGHT...  
 
DRY NORTHWEST FLOW ALOFT REPLETE WITH VARIABLE HIGH CLOUDS ARE  
FORECAST TONIGHT AND EARLY FRIDAY, AHEAD OF ANOTHER STRONG COLD  
FRONT FORECAST TO SWEEP SOUTH THROUGH ARIZONA FRIDAY AFTERNOON AND  
EVENING. STRONG ATMOSPHERIC HEIGHT FALLS OVER CENTRAL AZ FRIDAY  
AFTERNOON, WITH COLD AIR PACKING ALONG/BEHIND THE FRONT PORTEND  
STRONG GUSTY WINDS. THIS UPCOMING WIND EPISODE MAY BE SLIGHTLY  
STRONGER THAN TUESDAYS WIND EVENT, AND PEAKING BETWEEN 6 PM AND 9 PM  
ON THE DESERTS AND MOUNTAINS SURROUNDING THE PHOENIX AREA.  
 
A RED FLAG WARNING FOR HIGH FIRE DANGER IS POSTED FOR A LARGE  
PORTION OF CENTRAL AND SOUTHERN AZ FRIDAY AFTERNOON AND EVENING.  
 
ADDITIONALLY, THERE IS A CHANCE OF AFTERNOON SHOWERS AND  
THUNDERSTORMS OVER THE MOUNTAINS OF SOUTHERN GILA COUNTY JUST EAST  
OF PHOENIX FRIDAY AFTERNOON.  
 
CLEARING SKIES WITH DIMINISHING WIND ARE EXPECTED FRIDAY NIGHT.  
 
SATURDAY AND SATURDAY NIGHT...  
 
SATURDAY WILL BE THE COOLEST DAY AFTER FRIDAYS FRONTAL PASSAGE.  
BREEZY TO WINDY CONDITIONS ARE ALSO FORECAST, BUT NOT AS STRONG AS  
THOSE EXPECTED BY FRIDAY EVENING. THE WINDIEST AREAS SATURDAY  
AFTERNOON WILL OCCUR DOWN THE COLORADO RIVER VALLEY.  
 
 
SUNDAY THROUGH THURSDAY  
 
DRY NORTHWEST FLOW ALOFT, ALONG WITH WARMER TEMPERATURES ARE  
FORECAST THIS PERIOD. STRONG WARMING WILL OCCUR NEXT WEDNESDAY AND  
THURSDAY WITH HIGH TEMPERATURES APPROACHING THE 100 DEGREE MARK.  
 

 
   
AVIATION
 
 
 
IT NOW APPEARS, AS WINDS ALOFT INCREASE AHEAD OF A RATHER STRONG  
WEATHER SYSTEM AND ASSOCIATED STRONG COLD FRONT MOVING TOWARDS THE  
REGION, THAT LIGHT WESTERLY WINDS WILL PERSIST THROUGH THE NIGHT.  
THESE WESTERLY WINDS ARE EXPECTED TO BEGIN TO PICK UP BY MID-MORNING  
FRIDAY AS THE SYSTEM APPROACHES FROM THE NORTH. VERY STRONG WESTERLY  
WINDS, WITH SUSTAINED SPEEDS AS HIGH AS 35 MPH AND GUSTS TO 45 MPH  
ARE NOW EXPECTED AS THE VERY SHARP, BUT DRY COLD FRONT MOVES INTO  
SOUTH-CENTRAL AZ. THESE WINDS, ALONG WITH AREAS OF BLOWING DUST WILL  
LIKELY AFFECT ARRIVAL/DEPARTURE RATES. ALONG WITH SOME HIGH CIRRUS,  
A FEW LOWER CLOUDS IN THE 5-6K FOOT RANGE ARE EXPECTED TO DEVELOP  
ALONG/AHEAD OF THE FRONT, BUT WITH ANY SHOWERS/THUNDERSTORMS  
REMAINING WELL OFF TO THE EAST. WINDS ARE THEN EXPECTED TO GRADUALLY  
DIMINISH FRIDAY EVENING ONCE THE SFC FRONT MOVES THRU.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
 
PERIODS OF STRONG GUSTY WINDS AND A COUPLE DISTINCT WIND SHIFTS WILL  
BE THE PRIMARY AVIATION PROBLEMS THROUGH FRIDAY MORNING UNDER ONLY  
HIGHER CIRRUS CIGS. A NORTHERLY COMPONENT THIS AFTERNOON WILL BECOME  
WESTERLY THIS EVENING WITH SOME TIME OF VARIABLE DIRECTION POSSIBLE  
OVERNIGHT. A FRONTAL PASSAGE WILL CAUSE WINDS TO SWITCH BACK TO  
NORTHERLY FRIDAY MORNING WITH VERY STRONG GUSTS BEGINNING DURING THE  
LATE MORNING HOURS. WINDS WILL GRADUALLY DIMINISH FRIDAY  
AFTERNOON/EVENING AS WINDS ALOFT WEAKEN. PATCHY CIRRUS IN THE 20-25K  
FOOT RANGE TO PRETTY MUCH CLEAR OUT COMPLETELY IN FRIDAY AS VERY DRY  
AIR MOVES INTO THE REGION.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
SUNDAY THROUGH THURSDAY: STRONG HIGH PRESSURE WILL BUILD ACROSS THE  
DISTRICTS NEXT WEEK RESULTING IN A STEADY WARMING TREND, DRY  
CONDITIONS, AND WEAKER WIND SPEEDS THAN EXPERIENCED THIS WEEK.  
MINIMUM AFTERNOON HUMIDITY VALUES WILL FALL TO NEAR 10 PERCENT OVER  
MOST OF THE AREA WHILE HIGH TEMPERATURES RISE INTO A RANGE OF 5-10  
DEGREES ABOVE AVERAGE. OVERNIGHT RECOVERY WILL ONLY BE POOR TO FAIR.  
AFTERNOON AND EARLY EVENING WINDS WILL FAVOR A WEST TO NORTHWEST  
DIRECTION WITH THE TYPICAL LATE APRIL/EARLY MAY UPSLOPE GUSTINESS.  
WINDS OVERNIGHT WILL MOSTLY TREND TOWARDS A DRAINAGE DIRECTION.  
 

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

 
   
PSR WATCHES/WARNINGS/ADVISORIES
 
 
AZ...RED FLAG WARNING FROM 11 AM TO 9 PM MST FRIDAY FOR AZZ132.  
 
RED FLAG WARNING FROM 3 PM TO 9 PM MST FRIDAY FOR AZZ133.  
 
RED FLAG WARNING FROM 9 AM TO 4 PM MST FRIDAY FOR AZZ131.  
 
WIND ADVISORY FROM 2 PM TO 8 PM MST FRIDAY FOR AZZ552-557-  
558-560>563.  
 
CA...RED FLAG WARNING FROM 9 AM TO 4 PM PDT FRIDAY FOR CAZ231.  
 

 
 

 
 
VISIT US ON FACEBOOK, TWITTER, AND AT WEATHER.GOV/PHOENIX  
 
DISCUSSION...PERCHA/VASQUEZ  
AVIATION...PERCHA/MO  
FIRE WEATHER...MO  
 
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