482
FXUS65 KPSR 090948
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
248 AM MST WED SEP 9 2026
KEY MESSAGES
- ABOVE NORMAL TEMPERATURES WILL PREVAIL THROUGH THE REST OF THE
WEEK, RESULTING IN WIDESPREAD MODERATE HEAT RISK AND AREAS OF
MAJOR HEAT RISK.
- EXTREME HEAT WARNINGS WILL REMAIN IN EFFECT FOR PORTIONS OF THE
LOWER DESERTS THROUGH THE END OF THE WEEK.
- THUNDERSTORMS CHANCES WILL CONTINUE TO FOCUS OVER SOUTHEASTERN
ARIZONA AND THE EASTERN ARIZONA HIGH TERRAIN, WITH LOW CHANCES
FOR LOWER DESERT STORMS BEGINNING THURSDAY AND SLIGHTLY BETTER
FRIDAY.
- A PATTERN SHIFT BY THE WEEKEND WILL RESULT IN DECREASING
TEMPERATURES AND EVENTUALLY DRYING CONDITIONS FROM WEST TO EAST
ACROSS THE FORECAST AREA.
SHORT TERM /TODAY THROUGH THURSDAY/
MIDLEVEL WATER VAPOR IMAGERY AND 500 MB RAP ANALYSIS CONFIRM THAT
SOUTHEASTERLY FLOW ALOFT HAS ESTABLISHED ACROSS THE REGION, AS
SUBTROPICAL HIGH PRESSURE QUICKLY RETROGRADES FROM THE SOUTHERN
PLAINS INTO THE DESERT SOUTHWEST. ABUNDANT MIDLEVEL MOISTURE IS
STILL APPARENT IN THE WV IMAGERY, WITH SOME LINGERING ELEVATED
SHOWERS/SPRINKLES MOVING THROUGH SOUTHWEST AZ INTO SOUTHEAST CA
AHEAD OF A REMNANT MESOSCALE VORTEX. ADDITIONALLY, A GULF SURGE
MOVED THROUGH YESTERDAY EVENING, RESULTING IN DEWPOINTS ACROSS A
GOOD CHUNK OF THE AREA SURGING INTO THE 60S AND EVEN LOWER 70S FOR
LOCATIONS CLOSER TO THE GULF OF CALIFORNIA. THE MAIN QUESTION FOR
THE REMAINDER OF THE WEEK WILL BE WHETHER THE COMBINATION OF
BETTER MOISTURE PROFILES AND INSTABILITY WILL HELP BRING
THUNDERSTORM CHANCES TO THE LOWER DESERTS. MOISTURE AND
INSTABILITY WILL BE SUFFICIENT, BUT WILL THERE BE A SUFFICIENT
LIFTING MECHANISM TO TRIGGER LOWER DESERT STORMS? LATEST GUIDANCE
IS NOT OPTIMISTIC FOR THE NEXT FEW DAYS (THROUGH THURSDAY). UNDER
ANTICYCLONIC SUBSIDENCE WITH THE SUBTROPICAL HIGH SHIFTING ALMOST
DIRECTLY OVERHEAD LATER TODAY, INHIBITION WILL LIKELY BE TOO
STRONG (CIN AROUND -70 TO -100 J/KG OR LOWER) FOR THUNDERSTORMS
TO DEVELOP ANYWHERE BUT OVER HIGHER TERRAIN OF SOUTHERN
GILA/NORTHERN PINAL/FAR NORTHEASTERN MARICOPA COUNTIES.
ADDITIONALLY, LOW LEVEL MIXING RATIOS LOOK TO DROP INTO A 9-10
G/KG RANGE DUE TO THE SHALLOW GULF SURGE MOISTURE MIXING THROUGH
THE PBL. HOWEVER, DISTANT OUTFLOWS MAKING THEIR WAY INTO SOUTH-
CENTRAL AZ LOWER DESERTS FROM THE EAST AND/OR SOUTHEAST LOOKS
LIKELY. THIS, COMBINED WITH ANOTHER GULF SURGE MAY HELP TO FURTHER
MOISTEN THE LOWER LEVELS TONIGHT, SETTING THE STAGE FOR SLIGHTLY
BETTER CHANCES/COVERAGE OF STORMS THURSDAY. CAMS DO ALSO SHOW THE
POTENTIAL FOR SCATTERED ALTOCUMULUS SHOWERS TO DEVELOP TONIGHT IF
A SUFFICIENTLY STRONG GRAVITY WAVE PROPAGATES THROUGH THE FORECAST
AREA FROM EARLIER CONVECTION OVER SONORA/SOUTHEAST AZ. LATEST NBM
CAME IN WITH <10% CHANCES ACROSS ALL BUT THE HIGH TERRAIN OF S
GILA COUNTY THURSDAY, WHICH SEEMED A BIT TOO LOW GIVEN THE WEAKER
INHIBITION UNDER A DIMINISHING SUBTROPICAL HIGH. THUS, INCREASED
CHANCES SLIGHTLY FOR THURSDAY LATE AFTERNOON/EVENING.
FOR THE PAST COUPLE MORNINGS, 12Z PSR SOUNDINGS HAVE INDICATED
SEVERAL NEAR-SATURATED LAYERS IN THE MIDDLE AND UPPER PORTIONS OF
THE PROFILE, CONSISTENT WITH THE PATCHY MID AND HIGH CLOUD DECKS
THAT HAVE BEEN DRAPED ACROSS THE FORECAST AREA. THIS MOISTURE HAD
BEEN IMPORTED FROM A PERIOD SOUTHWESTERLY FLOW, BUT NOW, DEBRIS
CLOUDS FROM UPSTREAM CONVECTIVE ACTIVITY TO THE EAST/SOUTHEAST
WILL LIKELY PROVIDE AT LEAST PARTIAL CLOUD COVER FOR THE NEXT FEW
NIGHTS. WITH HIGHER SURFACE DEWPOINTS AND CONTINUED PERIODS OF
OVERNIGHT CLOUD COVER THROUGH THE NEXT FEW DAYS, INEFFICIENT
RADIATIVE COOLING WILL RESULT IN VERY WARM OVERNIGHT LOWS IN THE
MIDDLE TO UPPER 80S ACROSS THE LOWER DESERTS, AROUND 7F-10F ABOVE
NORMALS. DAYTIME HIGHS WILL COMMONLY REACH A 4F-7F ABOVE NORMAL
RANGE UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE, PEAKING
BETWEEN 105F-111F ACROSS THE TYPICALLY HOTTER LOWER DESERT
LOCALES. THESE TEMPERATURES TRANSLATE TO WIDESPREAD MODERATE
HEATRISK WITH POCKETS OF MAJOR HEATRISK, PRIMARILY DRIVEN BY THE
VERY WARM OVERNIGHT LOWS. IT IS ALSO IMPORTANT TO NOTE THAT THE
HIGHER HUMIDITY NOW IN PLACE WILL MAKE THE HEAT LESS TOLERABLE AND
POTENTIALLY MORE DANGEROUS, WITH HEAT INDICES PEAKING UPWARDS OF
108F-118F DURING THE LATTER HALF OF THE WORK WEEK. AS A RESULT,
EXTREME HEAT WARNINGS WILL REMAIN IN EFFECT FOR PORTIONS OF THE
LOWER DESERTS THROUGH THE END OF THE WEEK.
LONG TERM /FRIDAY THROUGH TUESDAY/
THE UPPER LEVEL PATTERN WILL BEGIN TO SHIFT FRIDAY, AS TROUGHING
ENTERS THE NORTHWEST US AND DISPLACES THE SUBTROPICAL HIGH EAST OF
THE REGION THIS WEEKEND. FLOW ALOFT WILL TRANSITION BACK OUT OF
THE SOUTHWEST, ENDING THE BRIEF, MORE TYPICAL MONSOON FLOW PATTERN
EXPERIENCED DURING THE MIDDLE OF THE WORK WEEK TO SOMETHING MORE
AKIN TO A TRANSITION SEASON SETUP. HOWEVER, BEFORE MORE PRONOUNCED
SOUTHWESTERLY DRYING BEGINS IN EARNEST THIS WEEKEND, WEAKER FLOW
ALOFT AND PERHAPS THE BEST MOISTURE PROFILES OF THE WEEK OVER
SOUTH- CENTRAL AZ (NEAR-SURFACE MIXING RATIOS 11-12 G/KG) WILL
PRESENT AN OPPORTUNITY FOR AT LEAST ONE ACTIVE MONSOON
THUNDERSTORM DAY ACROSS THE LOWER DESERTS (IF THE HIGHLY
CONDITIONAL THREAT IS NOT REALIZED ON THURSDAY). KPHX GFS BUFR
SOUNDINGS, WHICH ADMITTEDLY HAVE BEEN VERY SENSITIVE TO SUBTLE
CHANGES IN LOW LEVEL MOISTURE, INDICATE A BALANCE OF CAPE/DCAPE
AROUND 1500 J/KG LATE FRIDAY AFTERNOON INTO THE EARLY EVENING,
WITH WEAK (GREATER THAN -50 J/KG) CIN FOR SEVERAL HOURS. ON
SATURDAY, THERMODYNAMICS ALSO LOOK SIMILARLY FAVORABLE, WITH THE
CAP ALMOST COMPLETELY DISAPPEARING. BOTH DAYS, THE THREAT IS ONCE
AGAIN HIGHLY CONDITIONAL, AS THERE IS NO OBVIOUS UPPER LEVEL
ASCENT MECHANISM.
ENSEMBLES CONTINUE TO DISAGREE ON HOW FAR SOUTH THE JET WILL DIP
WITH THE INCOMING NORTHWEST US TROUGHING THIS WEEKEND, HOWEVER, IT
WILL LIKELY REMAIN FAR ENOUGH REMOVED THAT JET DYNAMICS DO NOT
COME INTO PLAY TO INFLUENCE THUNDERSTORM CHANCES LOCALLY.
REGARDLESS, MOISTURE WILL NOT BE ENTIRELY SCOURED OUT OF
EASTERN/SOUTHEASTERN AZ, AND DAILY MONSOON THUNDERSTORM ACTIVITY
WILL BE MAINTAINED OVER PROMINENT TERRAIN FEATURES OF EASTERN AZ,
SOUTHEASTERN AZ, AND SONORA INTO NEXT WEEK. EVENTUALLY, IF THE
SUBTROPICAL HIGH CAN REASSERT ITSELF EAST OF THE REGION AND/OR
TROUGHING WEAKENS AND RETREATS NORTH, DAILY CONVECTION TO OUR
SOUTH COULD PUSH BETTER MOISTURE INTO SOUTH-CENTRAL AZ AND ONCE
AGAIN GIVE OUR AREA A SHOT AT MORE WIDESPREAD THUNDERSTORM CHANCES
BY THE MIDDLE OF NEXT WEEK. ANTICIPATE TEMPERATURES TO DECREASE
BACK INTO A NEAR NORMAL RANGE OVER THE WEEKEND AS A RESULT OF THE
PATTERN SHIFT, AND POSSIBLY SLIGHTLY BELOW NORMAL NEXT WEEK.
AVIATION
UPDATED AT 0520Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR WEATHER CONCERNS WILL EXIST THROUGH WEDNESDAY NIGHT UNDER
OCCASIONAL MID/HIGH CIGS, PATCHY VIRGA, AND ISOLD SHRA. CONFIDENCE
IN WIND FORECAST ARE SOMEWHAT LOWERED TONIGHT AS A SW HEADING MAY
REDEVELOP DUE TO A GULF SURGE BEFORE WEAKENING AGAIN AND BECOMING
EAST/VARIABLE CLOSER TO SUNRISE. DIRECTIONS SHOULD SWITCH BACK TO
W/SW BY NOON WEDNESDAY WITH LIMITED AFTERNOON GUSTS.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO MAJOR WEATHER CONCERNS WILL EXIST THROUGH WEDNESDAY NIGHT UNDER
OCCASIONAL MID/HIGH CIGS AND PATCHY VIRGA/SHRA. CONFIDENCE IN WIND
TRENDS IS ONLY MODERATE WITH A TENDENCY FOR A NW DIRECTION TO BECOME
MORE SOUTHERLY DURING THE DAY WEDNESDAY. EXTENDED PERIODS OF NEARLY
CALM CONDITIONS MAY BE COMMON DURING THIS TRANSITION.
FIRE WEATHER
ABOVE NORMAL TEMPERATURES WILL PREVAIL THROUGH THE END OF THE WORK
WEEK, THEN TEMPERATURES ARE LIKELY TO DECREASE CLOSER TO NORMAL OVER
THE WEEKEND. AFTERNOON MINIMUM HUMIDITIES WILL GENERALLY RANGE
BETWEEN 18-30% AREAWIDE THROUGH MUCH OF THE WEEK FOLLOWING FAIR TO
GOOD OVERNIGHT RECOVERIES BETWEEN 35-70%. FAIRLY TYPICAL DIURNAL
WINDS WITH OCCASIONAL AFTERNOON UPSLOPE BREEZINESS CAN BE EXPECTED
THROUGH THURSDAY, FOLLOWED BY AN INCREASE IN SOUTHERLY TO
SOUTHWESTERLY WINDS FRIDAY INTO THIS WEEKEND. RAIN AND THUNDERSTORM
CHANCES WILL REMAIN LOW AND MOSTLY LIMITED TO THE EASTERN ARIZONA
HIGH TERRAIN THROUGH MIDWEEK BEFORE SLIGHT CHANCES BECOME INTRODUCED
TO THE LOWER DESERTS OF AT LEAST THE EASTERN DISTRICTS LATE WEEK.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...EXTREME HEAT WARNING UNTIL 8 PM MST FRIDAY FOR AZZ532.
EXTREME HEAT WARNING UNTIL 8 PM MST THURSDAY FOR AZZ531-535>544-
546-548>551-559.
EXTREME HEAT WARNING FROM 10 AM THIS MORNING TO 8 PM MST FRIDAY
FOR AZZ530-533.
CA...EXTREME HEAT WARNING UNTIL 8 PM PDT FRIDAY FOR CAZ562-566-567.
EXTREME HEAT WARNING FROM 10 AM THIS MORNING TO 8 PM PDT FRIDAY
FOR CAZ569-570.
SHORT TERM...WHITTOCK
LONG TERM...WHITTOCK
AVIATION...18
FIRE WEATHER...WHITTOCK
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