031
FXUS65 KPSR 030521
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1021 PM MST WED SEP 2 2026
UPDATE
06Z AVIATION DISCUSSION
KEY MESSAGES
- SLIGHT CHANCES FOR ISOLATED SHOWERS AND THUNDERSTORMS ARE
POSSIBLE ACROSS SOUTH CENTRAL ARIZONA THROUGH THURSDAY
AFTERNOON.
- TROPICAL MOISTURE WILL ARRIVE INTO THE REGION LATE THURSDAY
INTO FRIDAY, FURTHER INCREASING RAIN CHANCES ACROSS THE
SOUTHEASTERN THIRD OF ARIZONA BEFORE CHANCES SHIFT INTO
SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA THIS WEEKEND.
- TEMPERATURES SHOULD REMAIN IN A NEAR TO BELOW NORMAL CATEGORY
FOR THE FIRST WEEK OF SEPTEMBER, RESULTING IN WIDESPREAD MINOR
HEAT RISK AND LOCALIZED AREAS OF MODERATE HEAT RISK.
SHORT TERM /TODAY THROUGH FRIDAY/
A SOMEWHAT COMPLEX AND RAPIDLY SHIFTING FORECAST CONTINUES TO
EVOLVE DUE TO SEVERAL LARGE-SCALE WEATHER FEATURES EVIDENT IN
EARLY AFTERNOON WATER VAPOR IMAGERY: 1) BROAD PACIFIC TROUGHING
POSITIONED ALONG THE WEST COAST, 2) BROAD ANTICYCLONIC FLOW AND
MID/UPPER LEVEL HIGH PRESSURE DOWNSTREAM, CENTERED OVER THE
SOUTHEAST US, AND 3) TROPICAL STORM MARIE THAT IS CURRENTLY WELL
OFFSHORE, SOUTH OF BAJA CALIFORNIA. OBJECTIVE ANALYSIS SHOWS THE
INFLUENCE OF THE FIRST TWO OF THESE FEATURES EXTENDING INTO THE
DESERT SOUTHWEST, RESULTING IN CONFLUENT/CONVERGENT FLOW ALOFT.
ADDITIONALLY, A SHORTWAVE IS APPARENT EJECTING NORTHEASTWARD
AROUND THE WEST COAST TROUGH. REGARDLESS OF WHICH IS MORE
RESPONSIBLE, THE 12Z PSR SOUNDING ONCE AGAIN SHOWS A FAIRLY STRONG
MIDLEVEL TEMPERATURE INVERSION, INDICATIVE OF CONTINUED
SUBSIDENCE OVER THE FORECAST AREA. THE SHARP DECLINE IN MOISTURE
ABOVE THE RESIDUAL BOUNDARY LAYER IS ALSO APPARENT, WHICH WILL
ONCE AGAIN BEGIN TO MIX DOWN AND HELP FURTHER DRY THE MIXED LAYER
LATER THIS AFTERNOON. ACROSS THE FORECAST AREA, YET ANOTHER SHARP
DEWPOINT TEMPERATURE GRADIENT HAD FORMED THIS MORNING, THIS TIME
FOCUSED CLOSER TO THE N-S BORDER BETWEEN MARICOPA AND LA PAZ/YUMA
COUNTIES, INDICATING THAT BETTER LOW LEVEL MOISTURE STILL LIES
OVER THE EASTERN CWA. THIS WILL BE SUFFICIENT TO SUPPORT ISOLATED
SHOWERS AND THUNDERSTORMS ACROSS SOUTH-CENTRAL AZ THIS AFTERNOON,
WITH BETTER CHANCES FOCUSED TOWARDS THE SOUTH/EAST OF PHOENIX.
WITH MLCAPE VALUES UP TO AROUND 500 J/KG AND GFS BUFR SOUNDINGS
INDICATING DCAPES INCREASING TO UPWARDS OF 1000-1500+ J/KG,
UPDRAFTS WILL NOT BE PARTICULARLY ROBUST, BUT ANY STORMS THAT DO
FORM COULD PRODUCE LOCALIZED GUSTS OF 40+ MPH. WITH HIGHER HREF
NEIGHBORHOOD PROBABILITIES OF 35+ MPH GUSTS NEAR STORMS (~30%)
OVER THE DUST PRONE CORRIDOR IN PINAL COUNTY, IT WOULD NOT BE
SURPRISING TO SEE THESE STORMS PRODUCE LOCALLY DENSE BLOWING DUST.
OVER THE NEXT FEW DAYS, TS MARIE WILL CONTINUE ITS (MOST LIKELY)
NORTHWESTWARD TRAJECTORY, EVENTUALLY SHIFTING FURTHER OUT INTO
OPEN WATERS. GLOBAL GUIDANCE STILL SHOWS EXCELLENT LOW LEVEL
MOISTURE FILTERING UP THE GULF OF CALIFORNIA AND OVER SONORA
THANKS TO THE DISTANT INFLUENCE OF TS MARIE, THEN THAT BETTER
MOISTURE PUSHES INTO SOUTHEASTERN AZ THURSDAY NIGHT INTO FRIDAY.
HOWEVER, ENSEMBLES NOW SHOW A DEEPER WEST COAST TROUGH AND
STRONGER SOUTHWESTERLY FLOW ALOFT, KEEPING MOISTURE CONFINED
FURTHER SOUTH AND EAST OF THE CWA DURING THIS TIMEFRAME. HIGHER
TERRAIN NORTH, EAST, AND SOUTHEAST OF THE GREATER PHOENIX AREA ARE
STILL LIKELY TO SEE SEVERAL ROUNDS OF SHOWERS AND STORMS WITH
SOME CAPABLE OF PRODUCING STRONG WIND GUSTS AND LOCALLY HEAVY
RAINFALL. BUT THE LATEST WPC ERO UPDATES FOR DAY 3 (FRIDAY) HAVE
SHIFTED CONSIDERABLY, WITH AREAS UNDER A SLIGHT RISK (AT LEAST 15%
PROBABILITY OF FLASH FLOOD GUIDANCE BEING MET WITHIN 25 MILES OF
A POINT) NOW ALMOST ENTIRELY TO THE SOUTH AND EAST OF THE FORECAST
AREA. ISOLATED INSTANCES OF FLASH FLOODING ACROSS SOUTH-CENTRAL
AZ REMAIN POSSIBLE, WITH SOME OF THE LONGER RANGE CAMS REVEALING
THE POTENTIAL FOR SCATTERED SHOWERS AND STORMS DEVELOPING
PRIMARILY DURING THE OVERNIGHT/MORNING HOURS THURSDAY NIGHT/FRIDAY
AND POSSIBLY AGAIN FOR FRIDAY NIGHT/SATURDAY.
DUE TO THE PRESENCE OF TROUGHING TO OUR WEST AND A SEASONABLE 500
MB HGHT FIELD AROUND 587-590 DAM, TEMPERATURES WILL REMAIN WITHIN
A DEGREE OR TWO OF DAILY NORMALS THROUGH THE END OF THIS WEEK.
LOWER DESERT HIGHS WILL GENERALLY RANGE FROM THE UPPER 90S TO
AROUND 105 DEGREES EACH AFTERNOON, FOLLOWING MORNING LOWS FROM THE
UPPER 70S TO MIDDLE 80S. THE WEST COAST TROUGH WILL ALSO INDUCE A
COMPACT 700-500 MB HGHT GRADIENT OVER SOUTHEAST CA AND WESTERN AZ
BEGINNING TODAY WHICH WILL LEAD TO BREEZY CONDITIONS ACROSS THE
IMPERIAL AND LOWER COLORADO RIVER VALLEYS. GUSTS COULD REACH
UPWARDS OF 25-30 MPH IN THE AFOREMENTIONED AREAS AND POTENTIALLY
AS HIGH AS 40 MPH IN FAR SW IMPERIAL COUNTY.
LONG TERM /SATURDAY THROUGH TUESDAY/
THE FORECAST BECOMES MORE UNCERTAIN HEADING INTO THIS WEEKEND,
BUT THE GENERAL MODEL CONSENSUS IS SHOWING THE SUBTROPICAL RIDGE
OVER THE SOUTHEAST U.S. RETROGRADING WEST INTO THE SOUTHERN
PLAINS. THE WESTERN PERIPHERY OF THE RIDGE WILL LIKELY NOSE INTO
EASTERN AZ ON SATURDAY. IF THIS OCCURS, THEN THE SUBTROPICAL JET
WILL LIKELY SHIFT FARTHER WEST, SETTING UP BETTER MOISTURE
ADVECTION OVER SOCAL AND WESTERN AZ. THIS SCENARIO IS CURRENTLY
BEING REFLECTED WITHIN THE NBM SHOWING A WESTWARD PROGRESSION OF
POPS FROM SOUTHCENTRAL AZ EARLY SATURDAY INTO SOUTHWEST AZ AND
SOUTHEAST CA LATE SATURDAY INTO SUNDAY. DUE TO AN OVERALL INCREASE
IN MOISTURE AND EXTENSIVE CLOUD COVER THIS WEEKEND, IT IS LIKELY
WE WILL SEE LOWER INSTABILITY WHICH COULD LIMIT CONVECTION AND
KEEP THE THREAT OF HEAVY RAINFALL AT A MINIMUM IN OUR FORECAST
REGION WITH BETTER PROSPECTS OF HEAVY RAIN AND FLASH FLOODING OVER
SOCAL AND S NV. THERE IS STILL PLENTY OF TIME FOR THINGS TO
CHANGE AND WE WILL LIKELY HAVE TO WAIT UNTIL WE ARE WITHIN THE
HIGH-RES WINDOW FOR THIS WEEKEND'S FORECAST TO BECOME MORE CLEAR.
SIMILAR TO RAIN CHANCES, THERE IS ALSO A HIGH UNCERTAINTY IN THE
TEMPERATURE FORECAST BY THIS WEEKEND AS INDICATED BY LARGE (5-8
DEGREE) SPREADS WITHIN THE NBM INNER QUARTILE RANGE, ESPECIALLY ON
SATURDAY. THIS IS LIKELY DUE TO THE STRENGTH OF THE RIDGE AND HOW
MUCH CLOUD COVER WILL OCCUR OVER THE REGION. IT IS LIKELY THAT
SATURDAY WILL BE THE COOLEST DAY WITH HIGHS IN THE LOWER DESERTS
MAINLY IN THE MID TO UPPER 90S. HOWEVER, AS RIDGING ALOFT CAUSES
AN OVERALL INCREASE IN MID LVL HGHTS/THICKNESS, TEMPERATURES MAY
WARM TO NEAR OR EVEN SLIGHTLY ABOVE NORMAL FROM SUNDAY INTO EARLY
NEXT WEEK.
AVIATION
UPDATED AT 0520Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION CONCERNS ARE EXPECTED THROUGH THURSDAY EVENING
UNDER FEW-SCT CLOUD DECKS AROUND 8-12 KFT. WINDS WILL FAVOR
DIURNAL TRENDS WITH A SLOWER-THAN-USUSAL TURN TO WESTERLY FLOW,
RESULTING IN A WINDOW OF SOUTHERLY CROSSWINDS AT KPHX AND KDVT.
THERE ARE HINTS OF TS DEVELOPING IN THE SOUTHERN AND EASTERN
PORTIONS OF THE AIRSPACE BY THE AFTERNOON HOURS WITH PERHAPS SOME
CELLS MIGRATING TO WITHIN THE VICINITY OF THE TERMINALS. KIWA IS
THE MOST LIKELY (20-30% CHANCES) TO SEE VCTS, BUT NEARBY
CONVECTION CANNOT BE RULED OUT FOR THE OTHER SITES. HOWEVER,
CHANCES ARE TOO LOW (<20%) TO WARRANT INCLUSION OF EVEN VCTS AT
THIS TIME FOR KPHX, KDVT, AND KSDL.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
BREEZY CONDITIONS, ONCE AGAIN DURING THE AFTERNOON AND EVENING,
HOURS WILL BE THE MAIN AVIATION CONCERN. WINDS OVERNIGHT WILL BE
LIGHT, WITH PERHAPS SOME VARIABILITY BEING OBSERVED AT TIMES,
ESPECIALLY AT KBLH. FLOW WILL CONTAIN SOME DEGREE OF A WESTERLY
COMPONENT AT KIPL WHILE KBLH SWITCHES BETWEEN SOUTHERLY AND
SOUTHWESTERLY DIRECTIONS. MOSTLY CLEAR SKIES WILL BE COMMON OVER
THE REGION.
FIRE WEATHER
DRIER CONDITIONS WILL PREVAIL THROUGH THURSDAY WITH ONLY ISOLATED
CHANCES FOR SHOWERS AND THUNDERSTORMS MOSTLY RELEGATED TO THE HIGHER
TERRAIN OF SOUTHCENTRAL AND SOUTHEASTERN AZ. BETTER CHANCES FOR
WETTING RAINS RETURN TO THE REGION LATE THIS WEEK INTO THIS WEEKEND.
AFTERNOON MINIMUM HUMIDITIES WILL RANGE FROM 7-15% ACROSS SOUTHEAST
CA AND BETWEEN 15-35% FOR MUCH OF SOUTHERN AZ THROUGH THE NEXT FEW
DAYS AND WILL LIKELY INCREASE ABOVE 25% AREAWIDE THIS WEEKEND.
OVERNIGHT RECOVERIES WILL RANGE FROM POOR ACROSS THE WESTERN DESERTS
AND GOOD TO EXCELLENT ACROSS THE EASTERN DISTRICTS. DAYTIME WINDS
WILL REMAIN ELEVATED OUT OF THE SOUTH TO SOUTHWEST, WITH THE
STRONGEST GUSTS IN SOUTHEAST CA AND ALONG THE LOWER COLORADO RIVER
VALLEY PEAKING BETWEEN 20-30 MPH DURING THE AFTERNOON/EARLY EVENING.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...WHITTOCK
LONG TERM...SALERNO
AVIATION...RW
FIRE WEATHER...WHITTOCK/SALERNO
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