091  
FXUS65 KPSR 240538 AAA  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
1040 PM MST TUE JAN 23 2018  
   
UPDATE
 
UPDATED AVIATION DISCUSSION.  
   
SYNOPSIS
 
TEMPERATURES WILL WARM EACH DAY THROUGH THURSDAY. A WEAK  
COLD FRONT WILL THEN MOVE THROUGH, LEADING TO A FEW BREEZES IN SE  
CALIFORNIA THURSDAY, AND MODEST COOLING FRIDAY. A WARMING TREND IS  
THEN EXPECTED SUNDAY INTO EARLY NEXT WEEK AS A RIDGE GRADUALLY  
BUILDS BACK INTO THE REGION.  
 

 
   
DISCUSSION
 
THE UPPER WEATHER PATTERN THIS AFTERNOON IS DEFINED BY  
A WEAK TROUGH OF LOW PRESSURE SAGGING ACROSS EAST AND SOUTHEAST  
ARIZONA...A RIDGE OF HIGH PRESSURE CURRENTLY EXPANDING INTO THE  
DESERT SOUTHWEST AND A STRONG UPPER LOW SPINNING IN THE GULF OF  
ALASKA.  
 
SIGNIFICANT WARMING HAS ALREADY OCCURRED OVER THE PAST 24 HOURS  
THANKS TO THE UPPER RIDGE NUDGING IN. THIS WAS VERY EVIDENT ON THE  
12Z TUCSON(KTWC) UPPER SOUNDING, BETWEEN 900-600MB, WHERE 2-6C OF  
WARMING IS OBSERVED. THIS WARMER AIR HAS ALREADY STARTED TO MIX DOWN  
FOR A NOTICEABLE WARM-UP OF 6 TO 10 DEGREES F IN TEMPERATURES ACROSS  
THE PHOENIX METRO COMPARED TO YESTERDAY. EXPECT A FEW DEGREES OF  
WARMING OVER THE NEXT FEW DAYS AS THE UPPER RIDGE CONTINUES TO  
EXPAND AND FLOP INTO ARIZONA.  
 
THEREAFTER, THE UPPER LOW IN THE GULF OF ALASKA BEGINS TO MAKE ITS  
WAY INTO THE PACIFIC NORTHWEST AND THE GREAT BASIN, WITH THE  
SOUTHERN PERIPHERY OF THIS SYSTEM, AND ASSOCIATED BOUNDARY, TRACKING  
THROUGH SOUTHERN CALIFORNIA THURSDAY. THE ATMOSPHERE WILL REMAIN TOO  
DRY TO BRING ANY CHANCE OF PRECIPITATION WITH THIS FEATURE. IT WILL  
HOWEVER, INCREASE PRESSURE GRADIENTS ACROSS THE CALIFORNIA ZONES FOR  
SOME BREEZY SOUTHWEST TO WEST WINDS DURING THE DAY THURSDAY.  
 
AFTER A FEW DEGREES OF COOLING DUE TO THIS TROUGH PASSAGE ON FRIDAY  
AND SATURDAY, WE WILL SEE YET ANOTHER WARM-UP ACROSS THE ENTIRE  
FORECAST AREA AS A STRONGER RIDGE OF HIGH PRESSURE BUILDS INTO THE  
DESERT SOUTHWEST. THIS WILL LIKELY RESULT IN AFTERNOON TEMPERATURES  
NEAR 80 IN THE PHOENIX METRO SUNDAY AND MONDAY. THE 23/12Z GFS IS A  
FEW DEGREES WARMER THAN THE 23/12Z ECMWF. GIVEN THE WARMER TEMPS AS  
OF LATE, WILL LEAN MORE TOWARD THE GFS. IN GENERAL, AFTERNOON  
MAXIMUM TEMPERATURES WILL BE 8 TO 10 DEGREES ABOVE CLIMATOLOGICAL  
NORMAL.  
 
MODELS IN SOME DISAGREEMENT ON THE NEXT UPPER TROUGH TO IMPACT THE  
REGION LATE IN THE PERIOD TUESDAY/WEDNESDAY. THE GFS REMAINS  
PROGRESSIVE WITH THIS SYSTEM, KEEPING IT ACROSS THE ARIZONA/UTAH  
BORDER, WHILE THE ECMWF IS MORE AMPLIFIED AND STRONGER, BRINGING IT  
INTO CENTRAL ARIZONA WEDNESDAY. IN ANY EVENT, WE WILL HAVE TO KEEP  
AN EYE ON IT FOR NOW, BUT GIVEN HOW THE PATTERN HAS BEEN SET-UP FOR  
US SO FAR, THE PROGRESSIVE PATTERN IS THE MORE LIKELY SCENARIO.  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL AND SOUTHEAST  
CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
 
HIGH PRESSURE ALOFT AND A VERY DRY AIRMASS TO KEEP SKIES MAINLY  
CLEAR AT ALL OF THE TAF SITES THROUGH AT LEAST THE NEXT 24 HOURS.  
WINDS TO REMAIN MAINLY FROM AN EASTERLY DIRECTION AT ALL OF THE  
PHOENIX AREA TERMINALS THROUGH THE TAF PERIOD, WITH SOME GUSTINESS  
POSSIBLE DURING THE LATE MORNING/EARLY AFTERNOON HOURS ON WEDNESDAY,  
AS HIGH PRESSURE AT THE SFC BUILDS INTO THE 4-CORNERS REGION. WINDS  
AT KIPL TO REMAIN WESTERLY THROUGH THE TAF PERIOD, WITH SPEEDS  
REMAINING MAINLY AOB 5 KTS. WINDS AT KBLH TO BE PRIMARILY FROM A  
NORTHERLY TO NORTHEASTERLY DIRECTION, WITH A PERIOD OF NEAR-CALM  
CONDITIONS LIKELY FOR A TIME DURING THE MORNING HOURS ON WEDNESDAY.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
DRY CONDITIONS WITH ABOVE NORMAL TEMPERATURES CAN BE EXPECTED THE  
NEXT FEW DAYS, BEFORE A DRY COLD FRONT MOVES ACROSS THE REGION  
THURSDAY. THIS FEATURE WILL BRING BREEZY SOUTHWEST TO WEST WINDS TO  
SOUTHEAST CALIFORNIA THURSDAY, FOLLOWED BY A COOL DOWN IN  
TEMPERATURES ACROSS THE ENTIRE REGION FRIDAY.  
 
ANOTHER WARMING TREND WILL IMPACT THE AREA SUNDAY INTO EARLY NEXT  
WEEK, WITH THE LOWER DESERTS FLIRTING WITH 80 DEGREES SUNDAY AND  
MONDAY.  
 

 
   
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...NWS TUCSON  
AVIATION...PERCHA  
FIRE WEATHER...NWS TUCSON  
 
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