209  
FXUS65 KPSR 141144  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
444 AM MST SAT DEC 14 2019  
   
UPDATE
 
UPDATED AVIATION AND FIRE WEATHER DISCUSSION.  
 

 
   
SYNOPSIS
 
 
HIGH PRESSURE WILL RESULT IN NEAR TO SLIGHTLY ABOVE NORMAL  
TEMPERATURES FOR THE BEGINNING OF THE WEEKEND. SKIES WILL REMAIN  
MOSTLY SUNNY WITH OCCASIONAL INCREASES IN HIGH CLOUDS. A MOSTLY  
DRY WEATHER SYSTEM WILL ARRIVE SUNDAY BRINGING COOLER TEMPERATURES  
ACROSS THE AREA WITH CHILLY MORNING LOW TEMPERATURES MONDAY AND  
TUESDAY. TEMPERATURES WILL REBOUND VERY SLOWLY THROUGH THE FIRST  
HALF OF NEXT WEEK AS ANOTHER DRY WEATHER SYSTEM PASSES THROUGH THE  
AREA.  
 

 
   
DISCUSSION
 
 
EARLY THIS MORNING, A RATHER FLAT UPPER LEVEL HIGH PRESSURE RIDGE  
WAS IN PLACE ACROSS ARIZONA AND FAR SOUTHEAST CALIFORNIA. 500MB  
HEIGHTS OVER THE SOUTHERN DESERTS WERE IN THE 582-585DM BALLPARK,  
SUFFICIENT TO KEEP HIGH TEMPERATURES RUNNING NEAR OR SLIGHTLY ABOVE  
SEASONAL NORMALS. 2 AM IR IMAGERY SHOWED JUST A BIT OF LARGELY THIN  
HIGH CLOUDS STREAMING THROUGH THE FLOW WITH SKIES GENERALLY MOSTLY  
CLEAR. WE CAN EXPECT ANOTHER DAY TODAY SIMILAR TO THE PAST FEW DAYS,  
WITH HIGHS IN THE WARMER LOWER DESERTS STAYING ABOVE NORMAL AND IN  
THE UPPER 60S TO LOW 70S FOR THE MOST PART AS THE FLAT UPPER RIDGE  
STAYS OVERHEAD.  
 
VERY LITTLE HAS CHANGED WITH RESPECT TO THE FORECAST FOR SUNDAY INTO  
EARLY NEXT WEEK. A FAST MOVING, PROGRESSIVE UPPER TROF IS STILL  
EXPECTED TO RACE ACROSS ARIZONA, DROPPING SOUTHEAST WITH MOST OF THE  
ENERGY/MOISTURE MOVING THROUGH NORTHERN ARIZONA/FOUR CORNERS AREA  
AND SIGNIFICANTLY LIMITING ANY CHANCE OF PRECIPITATION ACROSS OUR  
AREA. POP TRENDS CONTINUE TO FALL OFF AND WE SHOULD ONLY SEE JUST A  
FEW LIGHT RAIN OR HIGHER ELEVATION SNOW SHOWERS MOVE THROUGH  
SOUTHERN GILA COUNTY SUNDAY INTO SUNDAY EVENING. MOST OF THE POPS  
ARE NOW LESS THAN 15 PERCENT, AND THIS IS SUPPORTED BY MOS, NBM AND  
NAEFS FORECAST POPS. THE MAIN IMPACT OF THE PASSING SYSTEM WILL BE  
TO USHER IN A COOLING TREND; HIGHS FALL TO AROUND NORMAL SUNDAY WITH  
PHOENIX TO LOWER TO A SEASONAL NORMAL 65 DEGREES, AND THEN TEMPS  
FALL OFF ANOTHER FEW DEGREES AND TO BELOW NORMAL LEVELS ON MONDAY.  
PHOENIX SHOULD SEE A HIGH IN THE LOW 60S MONDAY WITH SKY HARBOR ONE  
OF THE WARMER READINGS AT 63 DEGREES. COOLEST MORNING LOW OF THE  
NEXT WEEK LIKELY TO BE TUESDAY MORNING, WITH LOWS DROPPING TO NEAR  
FREEZING OVER SOME OF THE HIGHER TERRAIN ZONES TO THE EAST OF  
PHOENIX.  
 
FOLLOWING A VERY FAST MOVING SHORT WAVE ON TUESDAY (WHICH WILL HAVE  
NO EFFECT ON HIGH TEMPERATURES DUE TO ITS VERY TRANSITORY NATURE),  
ANOTHER RATHER PROGRESSIVE UPPER TROF PUSHES EAST AND ACROSS THE  
AREA WEDNESDAY INTO THURSDAY. AS WITH THE WEEKEND SYSTEM, LATEST  
TRENDS CONTINUE TO SHOW A DRIER SYSTEM FOR US WITH VERY LITTLE  
CHANCES FOR PRECIPITATION. MOST PRECIP WITH THE MID WEEK SYSTEM WILL  
STAY NORTH AND OVER THE HIGHER TERRAIN OF NORTHERN ARIZONA. NAEFS  
POPS SHOW SOME SINGLE DIGIT NUMBER FOR THE SOUTHERN DESERTS, AND  
GEFS PLUMES FOR PHOENIX ARE BASICALLY FLAT-LINED AT ZERO FOR THE  
NEXT 7 DAYS. GEFS QPF ENSEMBLE MEMBERS ALSO SHOW VIRTUALLY NO QPF  
ANYWHERE IN OUR AREA FROM ANY MEMBER WITH THIS SYSTEM. ABOUT THE  
ONLY THING THAT THE MID WEEK SYSTEM WILL DO IS USHER IN SOME  
INCREASE IN CLOUD COVER, AND KEEP TEMPERATURES HOVERING NEAR OR  
SLIGHTLY BELOW SEASONAL NORMAL THROUGH THURSDAY. AFTER THAT,  
STRONGER RIDGING ALOFT RETURNS FOR FRIDAY INTO SATURDAY ALLOWING FOR  
A WARMING TREND THAT WILL PUSH HIGHS ABOVE NORMAL. ON FRIDAY THE  
FORECAST HIGH FOR PHOENIX IS 68 DEGREES, 3 DEGREES ABOVE NORMAL.  
 

 
   
AVIATION
 
UPDATED AT 1145Z.  
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:  
 
NO MAJOR AVIATION WEATHER CONCERNS THROUGH AT LEAST SATURDAY  
EVENING. THE WINDS WILL REMAIN FAIRLY LIGHT, MOSTLY AT OR BELOW 8  
KTS, WITH DIRECTIONS FOLLOWING TYPICAL DIURNAL TENDENCIES. THE  
WINDS WILL BECOME WESTERLY BETWEEN 20Z-22Z ALTHOUGH THERE MAY  
BE A SHORT PERIOD OF SOUTHERLY WINDS DURING THAT TIME UNTIL THE  
WINDS BECOME PREDOMINANTLY WESTERLY. WIND DIRECTIONS WILL SHIFT  
EASTERLY AGAIN THIS EVENING BUT WILL MAINTAIN A SLIGHT SOUTHERLY  
DIRECTIONAL COMPONENT. CEILINGS SHOULD NOT BE A MAJOR PROBLEM  
REMAINING AOA 8K FEET.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
 
THE PRIMARY AVIATION CONCERN WILL BE THE STRENGTHENING OF THE  
WESTERLY WINDS LATE THIS AFTERNOON. GUSTS UPWARDS OF 25 KTS ARE  
VERY LIKELY, PARTICULARLY AT KIPL, ALTHOUGH STRONG GUSTS AT KBLH  
ARE ALSO POSSIBLE.  
 

 
   
FIRE WEATHER
 
 
MONDAY THROUGH FRIDAY:  
A WEATHER SYSTEM WILL PASS THROUGH THE AREA EARLY NEXT WEEK. THE  
PRIMARY CHANGE WILL BE COOLER TEMPERATURES, PARTICULARLY DURING  
THE OVERNIGHT AND EARLY MORNING HOURS. THIS SYSTEM WILL BE FAIRLY  
DRY WITH HARDLY ANY RAIN CHANCES. MIN RH VALUES WILL BE THE LOWEST  
TUESDAY AFTERNOON, 15-25%, WITH MOST DAYS IN THE 20-35% RANGE. MAX  
RH VALUES WILL ALSO BE THE LOWEST ON TUESDAY IN THE 40-50% RANGE  
WITH SLIGHTLY HIGHER VALUES ON ALL OTHER DAYS. WINDS WILL REMAIN  
FAIRLY LIGHT OUTSIDE OF AN OCCASIONAL BREEZE OR TWO, WITH  
DIRECTIONS MOSTLY FOLLOWING DIURNAL TENDENCIES. EXPECT NIGHTTIME  
INVERSION LAYERS TO DEVELOP EACH NIGHT AND SLOWLY LIFT BY LATE  
MORNING.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
SPOTTERS SHOULD FOLLOW STANDARD REPORTING PROCEDURES.  
 

 
   
PSR WATCHES/WARNINGS/ADVISORIES
 
 
AZ...NONE.  
CA...WIND ADVISORY FROM 1 PM THIS AFTERNOON TO 10 AM PST SUNDAY FOR  
CAZ562.  
 

 
 

 
 
DISCUSSION...CB  
AVIATION...DEEMS  
FIRE WEATHER...DEEMS  
 
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