494
FXUS65 KPSR 291007
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
307 AM MST SAT AUG 29 2026
UPDATE
12Z AVIATION DISCUSSION
KEY MESSAGES
- EXTREME HEAT WARNINGS REMAIN IN EFFECT THROUGH SATURDAY WITH
AREAS OF MAJOR TO EXTREME HEAT RISK, DESPITE TEMPERATURES SLOWLY
DECREASING.
- TODAY WILL BRING LOW END CHANCES FOR SHOWERS AND ISOLATED
THUNDERSTORMS, WITH A LOW PROBABILITY FOR STRONG TO SEVERE
OUTFLOW WINDS AND BLOWING DUST FOCUSED IN SOUTHEAST CALIFORNIA.
- AN APPROACHING LOW PRESSURE SYSTEM WILL BRING MUCH BETTER
CHANCES FOR RAIN, INCLUDING A CHANCE OF STRONG TO SEVERE STORMS
ACROSS SOUTHERN ARIZONA MAINLY ON SUNDAY AND MONDAY.
SHORT TERM /TODAY THROUGH SATURDAY/
ANALYSIS OF MIDLEVEL WV IMAGERY REVEALS THAT THE FLOW ALOFT IS IN
THE PROCESS OF SHIFTING FROM SOUTHEASTERLY TO
SOUTHERLY/SOUTHWESTERLY AS PACIFIC TROUGHING IMPINGES ON THE
FORECAST AREA FROM THE NORTHWEST. THE UPSTREAM TROUGHING HAS BEGUN
TO IMPACT THE SUBTROPICAL RIDGE MORE NOTICEABLY, DISPLACING THE
HIGH EASTWARD WITH SOME SIGNS OF WEAKENING EARLY THIS AFTERNOON
COMPARED TO PREVIOUS DAYS. THIS WILL BECOME MUCH MORE APPARENT
TONIGHT INTO SATURDAY, AS ENSEMBLES CONTINUE TO BE IN EXCELLENT
AGREEMENT THAT H5 HEIGHTS WILL DROP FROM THE CURRENT 594-597 DAM
CLOSER TO 591-594 DAM TOMORROW. MIDLEVEL MOISTURE TRANSPORT FROM
OVER SONORA IS NOTED IN THE WATER VAPOR IMAGERY AS WELL AND HAS
BECOME APPARENT IN THE 12Z PSR SOUNDING WITH PWAT ANALYZED AT
1.57", UP FROM 1.26" YESTERDAY. LOW LEVEL MOISTURE, HOWEVER,
REMAINS GENERALLY UNSUPPORTIVE (MARGINALLY SUPPORTIVE AT BEST) FOR
THE FORMATION/MAINTENANCE OF LOWER DESERT THUNDERSTORMS, WITH
1000-700 MB MEAN MIXING RATIOS STILL BELOW 10 G/KG, BUT HOVERING
CLOSE TO 9 G/KG ACROSS MUCH OF THE AREA.
THROUGH THE REST OF TODAY, MOISTURE LOOKS TO REMAIN FAIRLY
CONSTANT, WITH MIDLEVEL SUBSIDENCE STILL EVIDENT IN AREA GFS BUFR
SOUNDINGS, WHICH MAKES SENSE GIVEN ANTICYCLONIC FLOW ALOFT.
HOWEVER, WITH THIS AMOUNT OF MOISTURE, ONLY ONE OUTFLOW BOUNDARY
PASSING THROUGH AN AREA MAY BE ENOUGH TO MOISTEN THE LOW LEVELS
SUFFICIENTLY TO SUPPORT DEEP MOIST CONVECTION IF FOLLOWED BY
ANOTHER LIFTING MECHANISM (SECOND OUTFLOW BOUNDARY). INVERTED-V
SOUNDINGS AND DCAPES AROUND 1000-1500+ J/KG AREAWIDE WILL MEAN
THAT DISTANT THUNDERSTORMS OVER AZ HIGH TERRAIN AND PORTIONS OF
SOUTHEAST AZ ARE LIKELY TO FORM LONG- LIVED OUTFLOWS, PUSHING INTO
SOUTH-CENTRAL AZ LOWER DESERTS DURING THE EVENING. THE MOST
LIKELY OUTCOME FOR THE GREATER PHOENIX AREA THIS EVENING WOULD BE
ANOTHER ROUND OF ISOLATED-SCATTERED ELEVATED SHOWERS AND STORMS
FORMING LATER IN THE EVENING OR OVERNIGHT FROM EARLIER OUTFLOWS OR
DISTANT GRAVITY WAVES. AS STEERING FLOW TRANSITIONS OUT OF THE
SOUTHWEST, PARTICULARLY ACROSS THE WESTERN CWA, THERE WILL BE
BETTER CHANCES FOR DECAYING THUNDERSTORMS TO MOVE OFF THE BAJA
SPINE INTO IMPERIAL COUNTY MID TO LATE THIS AFTERNOON. HREF
PROBABILITIES INDICATE A POTENTIAL FOR ADDITIONAL DEVELOPMENT OF
THUNDERSTORMS OVER THE SOUTHEAST CA DESERTS AND EVEN 10-30%
NEIGHBORHOOD PROBABILITIES OF 58+ MPH WIND GUSTS NEAR STORMS, BUT
THESE STORMS WILL BE FEEDING OFF A DECAYING SOURCE OF INSTABILITY
AS SOUTHWESTERLY FLOW RAPIDLY DRIES THE LOWER LEVELS. A 10%
NEIGHBORHOOD PROBABILITY FOR SEVERE GUSTS IS ALSO INDICATED OVER
PROMINENT TERRAIN OF CENTRAL/NORTHEASTERN LA PAZ COUNTY LATE THIS
AFTERNOON INTO THE EVENING. IF THIS COMES TO FRUITION, EXPECT
AREAS OF BLOWING DUST TO CAUSE REDUCTIONS IN VISIBILITY THAT COULD
BECOME HAZARDOUS TO MOTORISTS/AVIATION USERS ACROSS PORTIONS OF
SOUTHEAST CA AND SOUTHWEST AZ (MAINLY LA PAZ COUNTY).
WHAT OCCURS SATURDAY AFTERNOON/EVENING IS STILL QUITE UNCERTAIN
AS IT WILL BE MORE OF A CONDITIONAL TYPE ENVIRONMENT FOR STORM
DEVELOPMENT. MOISTURE IS EXPECTED TO HAVE INCREASED ENOUGH TO
BRING MUCAPES UP TO AROUND 1000 J/KG INTO SOUTH-CENTRAL ARIZONA,
BUT NOT ENOUGH TO ERASE ALL OF THE CIN. THE QUESTION IS WHERE
EXACTLY WILL SHOWERS AND STORMS DEVELOP SATURDAY AFTERNOON AND IF
A LARGE ENOUGH CLUSTER CAN DEVELOP TO FORCE A STRONG OR MULTIPLE
OUTFLOWS INTO THE LOWER DESERTS. IT IS LOOKING MORE ENCOURAGING
FOR STORM POTENTIAL AS THE AMOUNT OF CIN DOES NOT LOOK TOO HIGH
AND ANY DECENT OUTFLOW SHOULD OVERCOME IT. WE WILL ALSO START TO
SEE SOME UPPER LEVEL SUPPORT FROM THE INCOMING TROUGH. LATEST HREF
CONSENSUS IS FOR STORMS TO EVENTUALLY CONGEAL OVER CENTRAL PIMA
COUNTY THEN TREND NORTHWARDS OVER THE TABLETOP WILDERNESS AND
SOUTHERN PINAL COUNTY, SENDING OUTFLOWS NORTHWARD TOWARDS THE
GREATER PHOENIX AREA DURING THE EARLY EVENING, WITH ISOLATED-
SCATTERED DEVELOPMENT OF ELEVATED SHOWERS/STORMS BEHIND THOSE
OUTFLOWS. SATURDAY SHOULD ALSO BE THE LAST OF THE EXTREME HEAT
WITH FORECAST HIGHS DROPPING TO 107-111 DEGREES BEFORE A MUCH MORE
NOTICEABLE COOL DOWN BEGINS SUNDAY.
LONG TERM /SUNDAY THROUGH THURSDAY/
SUNDAY AND/OR MONDAY ARE STILL LOOKING QUITE INTERESTING FOR
THUNDERSTORM POTENTIAL WITH THE ENVIRONMENT POTENTIALLY SUPPORTING
SOME SEVERE STORMS. SOME INGREDIENTS FOR STRONG TO SEVERE STORMS
ARE EXPECTED TO BE PRESENT, LIKE UPPER LEVEL SUPPORT AND
SUFFICIENT INSTABILITY, BUT WIND SHEAR WILL BE SOMEWHAT LACKING.
MOISTURE IS FORECAST TO IMPROVE ENOUGH TO SUPPORT A NEARLY
UNCAPPED ENVIRONMENT ACROSS SOUTH-CENTRAL ARIZONA SUNDAY AND
POTENTIALLY AGAIN MONDAY AFTERNOON WITH MUCAPES AS HIGH AS
1500-1800 J/KG. BOTH DAYS HAVE THE POTENTIAL TO BRING SCATTERED
TO NUMEROUS SHOWERS AND THUNDERSTORMS ACROSS SOUTH-CENTRAL AND
EASTERN ARIZONA. STRONG TO LOCALIZED SEVERE WIND GUSTS, BLOWING
DUST, HEAVY RAINFALL, AND FLOODING ALL LOOK POSSIBLE, BUT AS
STATED ABOVE THE THREAT MAY BE LOCALIZED DUE TO THE FAIRLY WEAK
SHEAR WHICH IS OFTENTIMES NEEDED TO SUSTAIN STRONG STORMS OR
CLUSTERS OF STORMS. WE SHOULD HAVE A BETTER IDEA ON HOW THIS
STRONG TO SEVERE STORM THREAT MAY EVOLVE BY SATURDAY/SATURDAY
NIGHT. GUIDANCE THEN SUGGESTS SOME DRYING WILL OCCUR BY TUESDAY
WHICH SHOULD DECREASE RAIN CHANCES SUBSTANTIALLY THROUGH THE
MIDDLE OF NEXT WEEK.
TEMPERATURES WILL DROP INTO OR EVEN JUST BELOW NORMAL EARLY NEXT
WEEK, BUT HIGHS ARE STILL FORECAST TO TOP 100 DEGREES EACH DAY
ACROSS THE LOWER DESERTS. ONCE THE DRIER AIR MOVES INTO THE REGION
BY THE MIDDLE OF NEXT WEEK, WE EXPECT TEMPERATURES TO QUICKLY WARM
TO A FEW DEGREES ABOVE NORMAL BUT WITH LITTLE CHANCE OF REACHING
110 DEGREES AGAIN.
AVIATION
UPDATED AT 1009Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
THE MAIN AVIATION CONCERN WILL BE THUNDERSTORMS AND GUSTY
OUTFLOWS, LATE THIS EVENING AND INTO THE OVERNIGHT PERIOD. BEFORE
THEN, TYPICAL DIURNAL TENDENCIES ARE EXPECTED. MODELS CONTINUE TO
POINT TOWARDS AN ACTIVE NIGHT WITH A SOUTHERLY TO SOUTHEASTERLY
GUSTY OUTFLOW WITH GUSTS BETWEEN 25-30KTS POSSIBLE. HI-RES
GUIDANCE SHOWS STORMS POPPING UP AS EARLY AS 22-23Z BUT NOT OVER
FULLY OVER THE TERMINALS UNTIL CLOSER TO 01-03Z. A PROB30 REMAINS
REFLECTED THE TAFS FOR IN ALL TERMINALS FOR THUNDERSTORMS HOWEVER
THE EXACT TIMING CONTINUES TO BE CHALLENGING AND MAY BE SUBJECT
TO CHANGE AS WE GET CLOSE TO THE EVENT TONIGHT. ANY OUTFLOWS FROM
THE S/SE WOULD ALSO BRING BLDU/HZ WITH THEM, MOSTLY EXPECTED TO
IMPACT KPHX AND KIWA. WINDS ARE CURRENTLY FORECASTED TO SETTLE
BACK OUT OF THE EAST FOR THE OVERNIGHT PERIOD, ONCE STORMS
SUBSIDE, BUT THEY COULD REMAIN HIGHLY VRB UNTIL MORNING. MOSTLY
SCT MID/HIGH CLOUD DECKS WILL BE COMMON THROUGH THE PERIOD, WITH
THE LOWEST CIGS FORECASTED AT 10KFT.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
THE MAIN AVIATION CONCERN IS A CHANCE FOR THUNDERSTORMS THIS
EVENING AT KIPL. BEFORE THEN WINDS WILL TEND TO FOLLOW THEIR
TYPICAL DIURNAL PATTERNS. OSCILLATING BETWEEN SOUTHERLY AND
SOUTHWESTERLY AT KBLH AND SOUTHEASTERLY TO WESTERLY AT KIPL,
FAVORING A WESTERLY COMPONENT FOR A MAJORITY OF THE PERIOD. WIND
SPEEDS WILL GENERALLY BE AOB 10 KT, WITH SOME GUSTS UP AROUND 20KT
EXPECTED TOMORROW AFTERNOON AT BOTH TERMINALS. A PROB30 IS
REFLECTED IN THE TAFS FOR KIPL FOR TS FROM 23-01Z TONIGHT, BUT THE
MAIN CONCERN WILL BE THE INCREASE IN GUST SPEEDS DURING THAT
TIMEFRAME. KIPL CAN EXPECT GUSTS BETWEEN 25-30KTS WITH SOME
OUTLIER HI-RES GUIDANCE SUGGESTING HIGHER AT TIMES, BUT BASED ON
LAST NIGHTS EVENS NOT IMPOSSIBLE TO SEE GUSTS UPWARDS OF 35KTS
ONCE MORE FOR A SHORT PERIOD. OTHERWISE, FEW- SCT MID/HIGH CLOUD
DECKS WILL BE COMMON THROUGHOUT THE PERIOD.
FIRE WEATHER
HOT AND RELATIVELY DRY CONDITIONS WILL CONTINUE INTO THIS WEEKEND,
BUT WITH SLIGHT CHANCES FOR ISOLATED SHOWERS AND THUNDERSTORMS.
CHANCES THEN INCREASE CONSIDERABLY BY SATURDAY NIGHT/SUNDAY,
ESPECIALLY ACROSS SOUTHERN AND CENTRAL ARIZONA. AFTERNOON MINIMUM
HUMIDITIES WILL RANGE BETWEEN 17-25% SATURDAY AND 15-30% AREAWIDE
SUNDAY FOLLOWING FAIR TO GOOD OVERNIGHT RECOVERIES. WINDS WILL BE
RELATIVELY LIGHT AND FOLLOW DIURNAL TENDENCIES THROUGH TONIGHT
BEFORE SOUTH TO SOUTHWESTERLY WINDS INCREASE THIS WEEKEND,
PARTICULARLY ACROSS THE WESTERN DESERTS, WHERE AFTERNOON GUSTS
INCREASE UP TO 20-30 MPH.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...EXTREME HEAT WARNING UNTIL 8 PM MST THIS EVENING FOR AZZ530>555-
559-560.
FLOOD WATCH FROM THIS AFTERNOON THROUGH LATE TONIGHT FOR AZZ534-
537-538-540>563.
CA...EXTREME HEAT WARNING UNTIL 8 PM PDT THIS EVENING FOR CAZ562-
565>567-569-570.
SHORT TERM...WHITTOCK/KUHLMAN
LONG TERM...KUHLMAN
AVIATION...RYAN
FIRE WEATHER...WHITTOCK/KUHLMAN
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