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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