874  
FXUS65 KPSR 200444  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
944 PM MST SUN NOV 19 2017  
   
UPDATE
 
UPDATED AVIATION DISCUSSION.  
 

 
   
SYNOPSIS
 
 
THE STREAK OF DRIER WEATHER AND ABOVE NORMAL TEMPERATURES WILL  
PERSIST THROUGH THE WEEK WITH UNSEASONABLE WARMTH QUICKLY RETURNING  
THE NEXT SEVERAL DAYS. IN FACT, RECORD HIGHS WILL BE LIKELY BY THE  
MIDDLE OF THE WEEK AND INTO THE LONG HOLIDAY WEEKEND.  
 

 
   
DISCUSSION
 
 
A FAST MOVING, LOW AMPLITUDE SHORTWAVE WAS PROGRESSING INTO SOUTHERN  
NEW MEXICO THIS AFTERNOON HELPING REINFORCE DRY ADVECTION AND  
SUBSIDENT FLOW IN ITS WAKE. AFTER THE COOLEST MORNING SINCE THE VERY  
BEGINNING OF APRIL, TEMPERATURES HAVE RESPONDED QUICKLY THIS  
AFTERNOON BREAKING A SHALLOW, STEEP INVERSION. WITH AMBIENT  
TEMPERATURES, DEWPOINTS, AND THE SYNOPTIC SETUP NEARLY IDENTICAL TO  
YESTERDAY, AN OVERNIGHT FORECAST OF NEAR PERSISTENCE LOOKS VERY  
APPLICABLE. THIS WILL YIELD ANOTHER CRISP, REFRESHING MORNING WITH  
WIDESPREAD 40S AND 50S.  
 
MODELS REMAIN IN EXCELLENT AGREEMENT THROUGH THE WEEKEND,  
DEPICTING GRADUAL HEIGHT/THICKNESS RISES ASSOCIATED WITH A BUILDING  
RIDGE ACROSS THE INTERMOUNTAIN WEST. THE ECMWF ENSEMBLES, IN  
PARTICULAR, ARE EXHIBITING REMARKABLY LOW VARIABILITY (NAEFS MEMBERS  
ALSO DISPLAY A SIMILAR LOW VARIANCE). THIS WILL EQUATE TO A  
PRONOUNCED WARMING TREND THROUGH LATE IN THE WEEK WITH NAEFS 500MB  
HEIGHTS IN EXCESS OF 590DM LIKELY SETTING RECORDS TUESDAY-THURSDAY,  
PARTICULARLY IN THE YUMA VICINITY (H5 RECORDS NEAR 588DM PER KTWC  
HISTORICAL SOUNDING DATA). SIMILARLY, MIDTROPOSPHERIC H7  
TEMPERATURES WILL PROBABLY TOUCH RECORD LEVELS AS WELL (+11C VS  
RECORDS +8-10C). SOME SUBTLE COOLING WILL SPREAD INTO THE REGION  
DURING THE WEEKEND THOUGH TEMPERATURES WILL REMAIN WELL ABOVE NORMAL  
AS THE RIDGE SLIDES EASTWARD INTO THE PLAINS.  
 
LATEST BLENDED GUIDANCE CONTINUES TO STRONGLY SUGGEST THAT  
TEMPERATURES WILL EXCEED DAILY RECORDS BY WEDNESDAY AND THANKSGIVING  
(SEE CLIMATE SECTION BELOW). GIVEN THE EXCEPTIONALLY LOW STANDARD  
DEVIATIONS EVIDENT IN THE ECMWF TEMPERATURE GUIDANCE, THE OFFICIAL  
FORECAST WAS ADJUSTED ABOVE THE MEDIAN OF ALL AVAILABLE GUIDANCE  
RESULTING IN A FORECAST HIGH OF 89 DEGREES FOR PHOENIX THANKSGIVING  
DAY. IT'S NOT TOTALLY OUT OF THE QUESTION THAT PHOENIX COULD FLIRT  
WITH 90 DEGREES WEDNESDAY/THURSDAY, WHICH WOULD SET A RECORD FOR THE  
LATEST 90 AT KPHX (RECORD IS 90 DEG ON NOV 15 1999). POPS ALSO  
REMAIN AT 0 PERCENT AND IT IS VERY LIKELY THE LONG DRY STRETCH WILL  
CONTINUE INTO AT LEAST THE END OF NOVEMBER, WHICH WOULD RESULT IN A  
METEOROLOGICAL FALL (SEPT-OCT-NOV) WITHOUT ANY MEASURABLE RAINFALL  
AT SKY HARBOR AIRPORT (LAST OCCURRED IN 1938).  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, AND KSDL:  
A LIGHT WESTERLY COMPONENT HAS DEVELOPED AT KPHX THIS EVENING,  
WHILE WEAK NORTHERLY WINDS HAVE DEVELOPED ELSEWHERE. ALL IN ALL,  
THE GRADIENT REMAINS WEAK, AND EASTERLY WINDS ARE FORECAST TO  
RETURN AT MOST LOCATION AFTER BY 06Z. HIGH CLOUDINESS WILL  
INCREASE OVERNIGHT AS WELL FROM THE NORTHWEST, ENOUGH FOR A SCT  
LAYER ABOVE 20 THOUSAND FEET THROUGH TOMORROW. AVIATION CONCERNS  
ARE EXPECTED TO BE MINIMAL.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
NO AVIATION CONCERNS THROUGH MONDAY MORNING AS WINDS FAVOR THE  
NORTH AND WEST DIRECTIONS AT BOTH KIPL AND KBLH. SCT HIGH CLOUDS  
EXPECTED WITH NO OTHER AVIATION CONCERNS.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
TUESDAY THROUGH SATURDAY:  
UNSEASONABLY STRONG HIGH PRESSURE ALOFT WILL BRING WARMING  
CONDITIONS THROUGH THE MIDDLE OF THE WEEK WITH TEMPERATURES  
REACHING INTO THE MIDDLE TO UPPER 80S ACROSS THE DESERTS STARTING  
WEDNESDAY. UNUSUALLY DRY AIR WILL ALSO AFFECT THE AREA THROUGH THE  
MIDDLE OF THE WEEK BEFORE THERE IS A SLIGHT BOOST IN MOISTURE BY  
LATE IN THE PERIOD. MINIMUM RH VALUES WILL FALL BETWEEN 10-15%  
THROUGH WEDNESDAY AND 15-20% FOR LATE IN THE WEEK. LIGHT WINDS  
WILL DOMINATE FOR THE DURATION OF THE FORECAST.  
 

 
   
CLIMATE
 
 
RECORD HIGHS FOR SELECTED DATES THIS WEEK:  
 
DATE PHOENIX YUMA  
---- ------- ----  
NOV 22 89 IN 1950 91 IN 1950  
NOV 23 87 IN 1950 87 IN 1950  
NOV 24 88 IN 1950 89 IN 1950  
 
THE PHOENIX RECORD HIGH FOR ANY THANKSGIVING IS 87 ON NOV 23 1950  
AND NOV 27 2014.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
SPOTTERS SHOULD FOLLOW STANDARD REPORTING PROCEDURES.  
 

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

 
 

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