367
FXUS65 KPSR 300957
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
257 AM MST FRI MAY 30 2025
KEY MESSAGES
- NEAR TO ABOVE NORMAL TEMPERATURES THROUGH SATURDAY WITH HIGHS
AS HIGH AS 105 DEGREES ACROSS PORTIONS OF THE LOWER DESERTS.
- AN INFLUX OF TROPICAL MOISTURE OVER THE WEEKEND WILL AID IN
WIDESPREAD CHANCES FOR SHOWERS AND SCATTERED THUNDERSTORMS, WITH
THE BEST CHANCES FOCUSED ON SUNDAY INTO SUNDAY NIGHT.
- BELOW NORMAL TEMPERATURES WITH HIGHS IN THE NINETIES ACROSS THE
LOWER DESERTS ARE EXPECTED FROM SUNDAY INTO THE MIDDLE PART OF
NEXT WEEK.
DISCUSSION
AN ATYPICAL WEATHER SCENARIO IS ALREADY STARTING TO TAKE SHAPE
ACROSS THE SOUTHWESTERN U.S. WITH A CUT-OFF LOW THAT HAS DEVELOPED
OVER THE PAST COUPLE OF DAYS AND IS NOW POSITIONED OVER AND JUST
WEST OF NORTHERN BAJA. YESTERDAY BROUGHT CONSIDERABLE MID AND
UPPER LEVEL CLOUDS INTO THE DESERT SOUTHWEST, BUT DRIER AIR
TEMPORARILY GETTING ENTRAINED INTO THE LOW FROM THE SOUTHWEST
WILL HELP TO BRING MOSTLY SUNNY SKIES FOR MUCH OF TODAY. THE WARM
AIR MASS STILL IN PLACE ALONG WITH H5 HEIGHTS HOVERING AROUND
586-588DM WILL HELP TO PUSH DAYTIME HIGHS TO BETWEEN 100-105
DEGREES ACROSS THE LOWER DESERTS TODAY.
MUCH FARTHER TO THE SOUTH, OFF THE COAST OF SOUTHWEST MEXICO,
TROPICAL STORM ALVIN DEVELOPED YESTERDAY AND IS FORECAST TO SLOWLY
DRIFT NORTHWARD TOWARD THE SOUTHERN TIP OF BAJA OVER THE NEXT
COUPLE OF DAYS. THIS TS WILL NOT HAVE ANY DIRECT IMPACTS ON OUR
WEATHER ACROSS THE DESERT SOUTHWEST, BUT IT WILL HELP TO STEER
TROPICAL MOISTURE NORTHWARD, EVENTUALLY GETTING PULLED INTO
SOUTHERN CALIFORNIA AND SOUTHERN ARIZONA STARTING LATE SATURDAY.
AS THE CUT-OFF LOW SITS NEARLY STATIONARY TO OUR SOUTHWEST THROUGH
SATURDAY NIGHT, IT WILL CONTINUE TO RESULT IN SOUTH SOUTHEASTERLY
MID-LEVEL FLOW INTO THE DESERT SOUTHWEST AND EVENTUALLY IN THE
LOWER LEVELS ON SUNDAY. MODEL FORECAST MOISTURE HAS INCREASED OVER
THE PAST SEVERAL RUNS WITH PWATS NOW SEEN REACHING 300% OF NORMAL
ON SUNDAY, OR BETWEEN 1.3-1.5" ACROSS OUR AREA. GIVEN THE EVEN
HIGHER EXPECTED MOISTURE LEVELS NOW, THE THREAT FOR THUNDERSTORMS
AND LOCALIZED HEAVY RAINFALL IS BECOMING A BIT MORE OF FORECAST
CONCERN.
ISOLATED LIGHT SHOWERS MAY BEGIN TO DEVELOP AS EARLY AS
SATURDAY AFTERNOON, LIKELY FOCUSED ACROSS SOUTHWEST ARIZONA INTO
SOUTHEAST CALIFORNIA. AS MOISTURE LEVELS REALLY START TO RAMP UP
SATURDAY NIGHT INTO SUNDAY MORNING, THE CUT-OFF LOW WILL ALSO
BEGIN TO TRACK CLOSER TO OUR AREA RESULTING IN INCREASING FORCED
ASCENT. INSTABILITY IS ALSO EXPECTED TO INCREASE BEGINNING SUNDAY
MORNING BEFORE PEAKING AROUND 1000 J/KG DURING THE AFTERNOON
HOURS ACROSS SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA. IF MODEL
FORECAST MOISTURE AND INSTABILITY STAYS NEAR THE CURRENT EXPECTED
LEVELS, THE THREAT FOR THUNDERSTORMS SHOULD BE FAIRLY WIDESPREAD
OVER THE AREA, PEAKING ACROSS SOUTHEAST CALIFORNIA AND SOUTHWEST
ARIZONA SUNDAY AFTERNOON AND ACROSS SOUTH-CENTRAL ARIZONA SUNDAY
EVENING. THIS SHOULD ALSO RESULT IN A FEW STRONG TO SEVERE STORMS
WITH WINDS BEING THE MAIN THREAT. SCATTERED TO WIDESPREAD SHOWER
ACTIVITY IS ALSO LIKELY TO DEVELOP ACROSS THE REST OF THE AREA BY
SUNDAY AFTERNOON WITH CHANCES LASTING WELL INTO THE OVERNIGHT
HOURS SUNDAY NIGHT.
FORECAST QPF AMOUNTS ARE A LITTLE HIGHER THAN WHAT WE SAW 24 HOURS
AGO, PARTICULARLY ACROSS SOUTHWEST ARIZONA WHERE THERE NOW SEEMS
TO BE A BETTER THUNDERSTORM THREAT. THE LATEST AMOUNTS SHOW
0.1-0.25" ACROSS SOUTHEAST CALIFORNIA TO 0.3-0.5" ACROSS SOUTHERN
AND CENTRAL ARIZONA WITH LOCALIZED HIGHER AMOUNTS NEAR 0.75"
ACROSS LA PAZ COUNTY AND OVER THE ARIZONA HIGHER TERRAIN. DUE TO
THE INCREASED LIKELIHOOD OF THUNDERSTORMS AND HIGHER MOISTURE,
THERE VERY WELL COULD END UP BEING SOME LOCALIZED HEAVY RAINFALL
WITH AMOUNTS EXCEEDING 1". THIS COULD CAUSE SOME VERY LOCALIZED
MINOR FLOODING ISSUES WITHIN AREA WASHES OR LOW-LYING AREAS.
AS A REMINDER, THE TIMING OF THIS EVENT IS QUITE UNUSUAL AS WE ARE
WITHIN OUR CLIMATOLOGICAL DRIEST TIME OF YEAR. FOR SOME
PERSPECTIVE, PHOENIX SKY HARBOR HAS ONLY SEEN MEASURABLE RAINFALL
ON 38 SEPARATE DAYS DURING THE LAST WEEK OF MAY AND THE FIRST WEEK
OF JUNE SINCE 1896. THE LAST FEW TIMES PHOENIX RECORDED
MEASURABLE RAINFALL DURING THIS PERIOD WAS IN 2015, 2008, 1994,
AND 1992. THE HIGHEST AMOUNT RECORDED DURING THIS PERIOD WAS 0.41"
ON JUNE 3, 1915. FOR JUNE 1ST, PHOENIX HAS ONLY SEEN MEASURABLE
RAINFALL ONE TIME (1914). IT IS EVEN MORE UNUSUAL FOR YUMA TO SEE
ANY RAINFALL IN THE LAST WEEK OF MAY OR IN THE FIRST WEEK OF JUNE
AS IT HAS ONLY OCCURRED ON 11 SEPARATE DAYS.
THE TIMING OF THE CUT-OFF LOW EXITING THE AREA IS A LITTLE SLOWER
IN THE LATEST MODEL RUN, BUT OVERALL IT SHOULD TRACK OUT OF OUR
AREA MONDAY MORNING. LINGERING CHANCES FOR SHOWERS ARE LIKELY TO
BE PRESENT THROUGH MONDAY MORNING FOR SOUTH-CENTRAL ARIZONA AND
MAYBE THROUGH MONDAY AFTERNOON FOR THE HIGHER TERRAIN NORTH AND
EAST OF PHOENIX. DRYING CONDITIONS WILL THEN SPREAD OVER THE
REGION LATER MONDAY, BUT GUIDANCE IS STILL INDICATING A SECOND
POTENTIAL DISTURBANCE MOVING THROUGH OR NEAR OUR REGION TUESDAY
INTO EARLY WEDNESDAY. THE NBM HAS INTRODUCED SOME LOW END (10-15%)
POPS OVER THE ARIZONA HIGHER TERRAIN ON TUESDAY, BUT GIVEN THE
LIKELY DRY NATURE OF THE SYSTEM THE BULK OF THE AREA IS NOT
EXPECTED TO SEE ANY ADDITIONAL RAINFALL.
TEMPERATURES WILL COOL DOWN A GOOD DEAL FOR SUNDAY WITH HIGHS
MOSTLY IN THE LOWER 90S WITH A GRADUAL WARMING OF TEMPERATURES
THROUGH THE MIDDLE OF NEXT WEEK. THERE REMAINS A GOOD DEAL OF
UNCERTAINTY WITH THE TEMPERATURE FORECAST DUE TO THE TWO WEATHER
SYSTEMS, BUT FOR NOW IT SEEMS LIKELY TEMPERATURES WILL REMAIN AT
LEAST A FEW DEGREES BELOW NORMAL INTO THE MIDDLE OF NEXT WEEK.
UNFORTUNATELY, ENSEMBLES ARE STARTING TO POINT TOWARD A STRONG
SUB-TROPICAL RIDGE NUDGING ITS WAY INTO OUR AREA BY NEXT WEEKEND
OR EARLY INTO THE FOLLOWING WEEK. IF THIS WERE TO HAPPEN, WE COULD
END UP SEEING OUR FIRST 110 DEGREE DAYS DURING THE SECOND WEEK OF
JUNE.
AVIATION
UPDATED AT 0547Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, KDVT:
NO AVIATION WEATHER CONCERNS ARE EXPECTED THROUGH THE TAF PERIOD.
WINDS WILL CONTINUE TO FOLLOW TYPICAL DIURNAL TENDENCIES, WITH
WIND SPEEDS MOSTLY STAYING UNDER 10 KTS. LIGHT AND VARIABLE WINDS
ARE EXPECTED AT TIMES AS WELL, PARTICULARLY DURING DIURNAL
TRANSITIONS. THERE WILL ALSO BE ANOTHER SURGE OF SOUTHWEST WIND
BETWEEN 03-10Z, WITH POTENTIAL FOR SUSTAINED SPEEDS UP TO 10-14
KTS AND GUSTS TO AROUND 20 KTS. SCT MID AND HIGH CLOUDS WILL
CONTINUE.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO AVIATION WEATHER CONCERNS ARE ANTICIPATED THROUGH THE NEXT 24
HOURS. WINDS AT KIPL WILL PREDOMINANTLY FAVOR THE E-SE, WHILE
DIRECTIONS AT KBLH WILL FAVOR THE S. PERIODS OF LIGHT AND VARIABLE
WINDS ARE ANTICIPATED DURING THE OVERNIGHT AND MORNING HOURS.
OTHERWISE, EXPECT CLEARING SKIES TONIGHT FOLLOWED BY A RETURN OF
SCT MID AND HIGH CLOUDS FRIDAY AFTERNOON.
FIRE WEATHER
AN UNSEASONABLY WET WEATHER SYSTEM WILL TRACK THROUGH THE AREA
SUNDAY, BRINGING 50-80% CHANCES FOR WETTING RAIN TO THE EASTERN
DISTRICTS OF SOUTH-CENTRAL ARIZONA AND 30-60% CHANCES OVER MUCH OF
THE WESTERN DISTRICTS. UNTIL THEN, SEASONABLY HOT AND DRY
CONDITIONS WILL PREVAIL. AFTERNOON MINRHS WILL INCREASE FROM 8-15%
TODAY TO 10-20% SATURDAY AND PEAK SUNDAY AT 25-30% AREAWIDE.
OVERNIGHT RECOVERIES WILL ALSO IMPROVE EACH NIGHT, FROM 20-40%
TONIGHT TO 60-80% AREAWIDE BY SUNDAY NIGHT. WINDS WILL FAVOR
TYPICAL DIURNAL TENDENCIES THROUGH SATURDAY WITH SOME BREEZINESS
THIS EVENING AND AGAIN SATURDAY AFTERNOON AND EVENING. AFTER
SUNDAY, EXPECT HUMIDITIES TO GRADUALLY DECREASE, RETURNING TO
MORE TYPICAL LEVELS BY THE LATTER HALF OF NEXT WEEK.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
DISCUSSION...KUHLMAN
AVIATION...BENEDICT/SMITH
FIRE WEATHER...KUHLMAN
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