198  
FXUS65 KPSR 201132  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
432 AM MST TUE MAY 20 2025  
   
UPDATE  
UPDATED 12Z AVIATION DISCUSSION.  
 
 
   
KEY MESSAGES  
 
1) TEMPERATURES WILL CONTINUE TO WARM THROUGH MID WEEK WITH LOWER  
DESERT HIGHS TOPPING 100 DEGREES BY WEDNESDAY AND LIKELY PEAKING  
AT AROUND 105 DEGREES ON THURSDAY.  
 
2) THE UPCOMING HOT TEMPERATURES WILL RESULT IN WIDESPREAD  
MODERATE HEATRISK (LEVEL 2) FROM WEDNESDAY-FRIDAY, POSING RISK TO  
VULNERABLE POPULATIONS.  
 
 
   
DISCUSSION  
 
WEATHER PATTERN OVERVIEW:  
THE SYNOPTIC WAVE PATTERN OVER THE NEXT SEVERAL DAYS WILL STAY  
QUITE ZONAL WITH ANY DISTURBANCES PASSING ACROSS SOUTHWEST CANADA,  
THE NORTHERN ROCKIES, INTO THE NORTHERN PLAINS. A PACIFIC RIDGE  
WHICH HAS SET UP OFF THE CALIFORNIA COAST WILL BE THE DRIVER OF  
OUR WEATHER THROUGH THE END OF THE WEEK WITH THE RIDGE CENTER  
STAYING TO OUR WEST AND SOUTHWEST, BUT STILL PROVIDING ABOVE  
SEASONAL NORMAL HEIGHTS AND TEMPERATURES. H5 HEIGHTS CURRENTLY  
BETWEEN 581-583DM WILL GRADUALLY RISE INTO THURSDAY BEFORE PEAKING  
AT AROUND 586-588DM, OR JUST SHY OF THE 90TH PERCENTILE OF  
CLIMATOLOGY FOR THE PERIOD. UNDER THE DRY WESTERLY QUASI-ZONAL  
FLOW AND RISING HEIGHTS, TEMPERATURES WILL GRADUALLY WARM WITH  
READINGS NEARING 100 DEGREES TODAY, TO BETWEEN 100-105 DEGREES  
WEDNESDAY, BEFORE PEAKING BETWEEN 102-107 DEGREES ON THURSDAY.  
MODERATE HEATRISK WILL DEVELOP OVER A GOOD PORTION OF THE AREA  
WEDNESDAY WITH THE AREAL EXTENT OF MODERATE HEATRISK PEAKING AT  
AROUND 75% COVERAGE ON THURSDAY. THURSDAY'S HIGHS WILL FALL SHORT  
OF DAILY RECORDS BY AROUND 3-5 DEGREES, BUT THEY WILL BE NEARLY  
10 DEGREES ABOVE NORMAL.  
 
BY THURSDAY NIGHT INTO FRIDAY, A WEAK SHORTWAVE TROUGH IS SHOWN  
MOVING ACROSS NORTHERN CALIFORNIA BEFORE MOSTLY WASHING OUT OVER  
THE GREAT BASIN LATER FRIDAY INTO SATURDAY. DESPITE THIS FEATURE  
BASICALLY WASHING OUT BEFORE IT REACHES OUT REGION, IT IS STILL  
EXPECTED TO BRING SOME WEAK TROUGHING INTO OUR REGION BY SATURDAY  
ALLOWING FOR MODEST COOLING. NBM FORECAST HIGHS ON FRIDAY DROP  
CLOSER TO 100 DEGREES BEFORE DIPPING JUST BELOW 100 DEGREES ON  
SATURDAY, OR A FEW DEGREES ABOVE NORMALS. IN ADDITION TO THE  
ROUGHLY 5-8 DEGREES OF COOLING INTO SATURDAY, WE SHOULD ALSO SEE A  
RETURN OF SOME THIN HIGHER CLOUDS AND BREEZIER CONDITIONS STARTING  
FRIDAY. MODEL UNCERTAINTY IS STILL HIGHER FOR SUNDAY INTO  
MEMORIAL DAY AS A RIDGE IS LIKELY TO BUILD OVER THE GREAT BASIN  
INTO THE NORTHERN ROCKIES, BUT IT COULD GET UNDERCUT BY A WEAK  
SHORTWAVE TROUGH POTENTIALLY SHIFTING EAST NORTHEASTWARD INTO OUR  
REGION. THIS SHORTWAVE IS NOT LIKELY TO DO MUCH OF ANYTHING OTHER  
THEN KEEPING OUR TEMPERATURES FAIRLY STABLE THROUGH EARLY NEXT  
WEEK.  
 
FORECAST CONFIDENCE & DEVIATIONS:  
CONFIDENCE IN THE FORECAST GUIDANCE THROUGH THE LATTER HALF OF THE  
WEEK REMAINS VERY GOOD GIVEN THE SMALL ENSEMBLE VARIATION. AS  
ELUDED TO ABOVE, THE INCREASING MODEL UNCERTAINTY BY SUNDAY IS  
LEADING TO LOWER FORECAST CONFIDENCE, BUT OVERALL THIS STILL  
SHOULDN'T CHANGE THE POTENTIAL FORECAST TEMPERATURES BY MORE THAN  
A FEW DEGREES EITHER WAY. NO DEVIATIONS FROM THE NBM WERE MADE FOR  
THIS CURRENT PACKAGE.  
 
 
   
AVIATION  
UPDATED AT 1130Z.  
 
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, KDVT:  
WINDS WILL BE LIGHT, GENERALLY AOB 8 KT, AND WILL TEND TO FOLLOW  
THEIR TYPICAL DIURNAL TENDENCIES. SKIES WILL REMAIN CLEAR.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
AT BOTH TERMINALS WIND SPEEDS WILL BE LIGHT, GENERALLY AOB 7 KT.  
AT KIPL, CURRENT SOUTHERLY WINDS WILL GO SOUTHEASTERLY THIS  
AFTERNOON, THEN SOUTHWESTERLY THIS EVENING. AT KBLH, CURRENT LIGHT  
AND VARIABLE WINDS WILL GO SOUTHERLY/SOUTHEASTERLY THIS AFTERNOON  
AND THEN SOUTHWESTERLY LATE THIS EVENING. SKIES WILL REMAIN CLEAR.  
 
 
   
FIRE WEATHER  
 
HIGH PRESSURE WILL GRADUALLY BUILD OVER THE REGION THROUGH MID  
WEEK BRINGING WARMING CONDITIONS AND CONTINUED LOW HUMIDITIES.  
HIGH TEMPERATURES ARE EXPECTED TO REACH OR EVEN TOP 100 DEGREES  
OVER MUCH OF THE LOWER DESERTS BEGINNING WEDNESDAY AS MINRHS STAY  
BETWEEN 7-12%. LIGHTER WINDS WILL ALSO PREVAIL THROUGH MID WEEK,  
BUT WITH SOME PERIODIC AFTERNOON BREEZINESS IN THE TEENS. ABOVE  
NORMAL TEMPERATURES AND SEASONABLY DRY CONDITIONS WILL CONTINUE  
THROUGH THE REST OF THE WEEK WITH WINDS INCREASING BY THURSDAY  
INTO FRIDAY AS AFTERNOON GUSTS BETWEEN 20-25 MPH ARE MORE LIKELY.  
THIS COULD BRING ANOTHER PERIOD OF ELEVATED FIRE WEATHER  
CONDITIONS MOSTLY LIKELY OCCURRING ON FRIDAY.  
 
 
   
PSR WATCHES/WARNINGS/ADVISORIES  
 
AZ...NONE.  
CA...NONE.  
 
 
 
 
DISCUSSION...KUHLMAN  
AVIATION...BERISLAVICH  
FIRE WEATHER...KUHLMAN  
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