590  
FXUS65 KPSR 281252  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
552 AM MST TUE MAR 28 2017  
   
UPDATE
 
UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.  
 

 
   
SYNOPSIS
 
 
A PACIFIC TROUGH WILL AFFECT THE REGION THROUGH TUESDAY WITH  
GUSTY WINDS AND PATCHY BLOWING DUST. THE STRONGEST WINDS WILL  
CONTINUE OVER PORTIONS OF SOUTHWEST ARIZONA AND SOUTHEAST  
CALIFORNIA BEFORE DYING DOWN TUESDAY EVENING. A FEW SHOWERS AND  
THUNDERSTORMS ARE ALSO POSSIBLE ACROSS HIGH TERRAIN AREAS OF  
CENTRAL ARIZONA. OTHERWISE, HIGH PRESSURE WILL REDEVELOP ACROSS  
THE REGION WEDNESDAY AND THURSDAY AHEAD OF ANOTHER WEATHER SYSTEM  
MOVING INTO THE DESERT SOUTHWEST OVER THE WEEKEND.  
 

 
   
DISCUSSION
 
 
 
A POSITIVELY TILTED UPPER LEVEL TROUGH CONTINUES TO DIG SOUTH AND  
EAST ACROSS OUR AREA THIS MORNING CREATING A BROAD AREA OF ASCENT  
OVER SOUTHEAST ARIZONA. STRONG POSITIVE VORTICITY ADVECTION  
COMBINED WITH COOLER AIR RUSHING IN AT 500MB HAS CREATED  
CONVECTIVE SHOWERS THIS MORNING JUST BEHIND THE LEADING EDGE OF  
THE TROUGH. MOST OF THESE SHOWERS HAVE BEEN LIGHT GIVEN THE DRY  
ATMOSPHERE BELOW THEM AND RELATIVELY HIGH BASED (~10 KFT). A FEW  
OF THE SHOWERS ACROSS THE PHOENIX METRO AND IN SE ARIZONA THIS  
MORNING HAVE BEEN STRONG ENOUGH TO GENERATE IN CLOUD LIGHTNING  
WITH JUST A FEW CLOUD TO GROUND STRIKES BEING OBSERVED.  
 
AS THIS SYSTEM DIGS FURTHER SOUTH AND EAST, THE BACKSIDE OF THE  
TROUGH WILL BE POSITIONED NEARLY SQUARE OVER THE LOWER COLORADO  
RIVER BASIN. THIS WILL ACT TO ENHANCE 850MB WINDS TO ROUGHLY 40  
KTS OVER THE AREA DURING THE EARLY MORNING HOURS (15Z) ON TUESDAY.  
AS SURFACE HEATING TAKES PLACE, HIGHER MOMENTUM AIR WILL  
UNDOUBTEDLY MIX TO THE SURFACE BRINGING GUSTS UP TO 40 MPH.  
BLOWING DUST AND SAND ARE EXPECTED TO ACCOMPANY THESE GUSTY WINDS  
WHICH COULD RESULT IN BRIEFLY LOWERED VISIBILITIES.  
 
CLOSER TO PHOENIX, WINDS WILL BE MUCH LIGHTER WITH GUSTS FORECAST  
TO BE BELOW 25 MPH ON TUESDAY. MODELS INDICATE THE HIGHEST  
AMOUNTS OF LOW LEVEL MOISTURE, AND SUBSEQUENTLY INSTABILITY, WILL  
REMAIN TO OUR EAST TODAY IN GILA COUNTY. MOST MODELS HAVE A FEW  
HUNDRED J/KG OF CAPE MATERIALIZING THERE THIS AFTERNOON, WHICH IN  
COMBINATION WITH THE WESTERLY UPSLOPE FLOW, SHOULD BE ENOUGH TO  
INITIATE CONVECTIVE SHOWER ACTIVITY WITH A CHANCE OF A WEAK  
THUNDERSTORM. SOME MODEL SOLUTIONS INDICATE LIGHT PRECIPITATION  
COULD FORM OVER FAR EASTERN PORTIONS OF MARICOPA COUNTY TODAY AS  
WELL.  
 
THE TROUGH SHIFTS OFF TO OUR EAST LATE IN THE DAY ON TUESDAY WHICH  
SHOULD HELP WEAKEN WINDS DRAMATICALLY TUESDAY EVENING AND DIMINISH  
ANY CHANCE OF PRECIPITATION IN GILA COUNTY BY EARLY WEDNESDAY  
MORNING. BEYOND THIS, A TRANSIENT RIDGE BUILDS IN WHICH WILL HELP  
WARM TEMPERATURES ACROSS OUR ENTIRE CWA WITH HIGHS REACHING THE  
UPPER 80S BY THURSDAY.  
 
MODELS SHOW YET ANOTHER TROUGH DIVING DOWN FROM THE PACIFIC  
NORTHWEST AND INTO OUR AREA ON FRIDAY. THIS WILL CAUSE A RATHER  
SHARP COOLING TREND FRIDAY WITH HIGHS AT LEAST 10 DEGREES COOLER  
THAN THURSDAY. THIS TRANSITION TO A COOLER AIRMASS WILL  
SUBSEQUENTLY INCREASE PRESSURE GRADIENTS AND DRIVE ANOTHER ROUND  
OF WINDY CONDITIONS, ESPECIALLY OUT IN SE CALIFORNIA AND THE  
COLORADO RIVER BASIN. ALTHOUGH AT THIS POINT, THEY DO NOT LOOK AS  
STRONG AS WHAT WE WILL BE EXPERIENCING ON TUESDAY. AS WITH OUR  
CURRENT TROUGH, THE BEST CHANCE OF PRECIPITATION WILL REMAIN IN  
GILA COUNTY WITH AMOUNTS REMAINING RATHER LIGHT.  
 
ALL MAJOR GLOBAL CIRCULATION MODELS AGREE THAT THIS TROUGH WILL  
LINGER THROUGH SATURDAY BUT MAJOR DIFFERENCES ARISE BEYOND THAT.  
BECAUSE OF THIS, THERE IS VERY LOW CONFIDENCE IN THE FORECAST FOR  
EARLY NEXT WEEK AS EACH ONE OF THE MODELS HAS THEIR OWN UNIQUE  
SOLUTION. FOR NOW, HAVE GONE WITH A BLENDED APPROACH AND HAVE KEPT  
TEMPERATURES NEAR SEASONAL NORMALS.  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, AND KSDL:  
WEST-NORTHWESTERLY FLOW WILL STRENGTHEN THIS AFTERNOON WITH GUSTS  
REACHING 20 TO 25 KT. MEANWHILE, LATEST GUIDANCE INDICATES THAT  
ISOLATED SHOWERS WILL DEVELOP ACROSS THE HIGHER TERRAIN, BUT WILL  
REMAIN WELL NORTH AND EAST OF PHOENIX. THIS EVENING, WINDS WILL  
SUBSIDE WITH A SHIFT TO DOWNSLOPE EASTERLY MORE LIKELY AT KIWA  
THAN AT KPHX.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
WINDS WILL REMAIN THE PRIMARY AVIATION WEATHER IMPACT. GUSTS TO  
30-35 KT WILL BE POSSIBLE AT KBLH BUT SOMEWHAT WEAKER AT KIPL.  
IMPROVING CONDITIONS ARE EXPECTED THIS EVENING AT BOTH SITES AS  
HIGH PRESSURE BUILDS IN AND THE STRONGER WINDS ABATE.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
THURSDAY THROUGH MONDAY: THE WEATHER PATTERN WILL REMAIN  
RELATIVELY ACTIVE ACROSS THE DESERT SOUTHWEST THROUGH EARLY NEXT  
WEEK, THOUGH IN GENERAL PRECIPITATION IS NOT EXPECTED. ONLY  
EXCEPTION WILL BE IN THE HIGHER TERRAIN WELL NORTH AND EAST OF  
PHOENIX. MAIN WEATHER IMPACT WILL BE BREEZY TO WINDY CONDITIONS,  
WHICH ARE EXPECTED TO REDEVELOP THURSDAY AND FRIDAY AS THE NEXT  
LOW PRESSURE SYSTEM MOVES THROUGH THE REGION. WITH RHS GENERALLY  
REMAINING BELOW 15 PERCENT, ELEVATED FIRE DANGER WILL AGAIN BE A  
POSSIBILITY FOR A FEW HOURS ACROSS SOUTHEASTERN CALIFORNIA,  
PARTICULARLY THURSDAY AFTERNOON. THEREAFTER, THE LOW PRESSURE  
SYSTEM WILL LIKELY MOVE THROUGH ARIZONA SATURDAY, BRINGING BELOW  
NORMAL TEMPERATURES ALONG WITH A GENERAL DECREASE IN WIND AND AN  
INCREASE IN MOISTURE. HIGH PRESSURE WILL FOLLOW FOR SUNDAY AND  
MONDAY, RESULTING IN A WARMING TREND AND A RETURN TO ABOVE NORMAL  
TEMPERATURES.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
 
SPOTTERS SHOULD FOLLOW REPORTING PROCEDURES WITH CRITERIA REPORTS  
THIS WEEK.  
 

 
   
PSR WATCHES/WARNINGS/ADVISORIES
 
 
AZ...RED FLAG WARNING FROM NOON TODAY TO 7 PM MST THIS EVENING FOR  
AZZ131-132.  
 
WIND ADVISORY UNTIL 7 PM MST THIS EVENING FOR AZZ020-021-026.  
 
CA...RED FLAG WARNING FROM NOON TODAY TO 7 PM PDT THIS EVENING FOR  
CAZ231.  
 
WIND ADVISORY UNTIL 7 PM PDT THIS EVENING FOR CAZ031.  
 
WIND ADVISORY UNTIL 4 PM PDT THIS AFTERNOON FOR CAZ030-032-033.  
 

 
 

 
 
VISIT US ON FACEBOOK, TWITTER, AND AT WEATHER.GOV/PHOENIX  
 
DISCUSSION...WILSON  
AVIATION...HIRSCH  
FIRE WEATHER...HIRSCH  
 
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