521
FXUS65 KPSR 010911
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
211 AM MST TUE SEP 1 2026
KEY MESSAGES
- DRY AND TRANQUIL WEATHER UNDER MOSTLY CLEAR SKIES CAN BE
EXPECTED MID-WEEK BEFORE POTENTIALLY ANOTHER PERIOD OF WET
WEATHER MATERIALIZES BY THE END OF THE WEEK INTO THE WEEKEND.
- NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES ARE EXPECTED
THROUGHOUT MUCH OF THE WEEK.
SHORT TERM /TODAY THROUGH WEDNESDAY/
LATEST GOES IR IMAGERY SHOWS A BATCH OF HIGH CLOUDS ASSOCIATED WITH
SHOWERS AND STORMS FROM YESTERDAY IS NOW PROGRESSING INTO NM AS MUCH
DRIER AIR IS ADVECTING INTO AZ UNDER W-SW FLOW ALOFT. ALTHOUGH UPPER-
LVL MOISTURE HAS BEEN SCOURED OUT, THERE IS STILL PLENTY OF RESIDUAL
MOISTURE IN THE LOWER LEVELS WITH DEW POINTS STILL HOVERING IN THE
LOW TO MID 60S ACROSS MUCH OF THE REGION WITH THE EXCEPTION OF SE
CALIFORNIA WHERE DEW POINTS ARE IN THE 50S. WE WILL CONTINUE TO HOLD
ONTO THIS MOISTURE THROUGH THE AFTERNOON WHICH COULD LEAD TO AN
ISOLATED STORM OR TWO DEVELOPING OVER THE TYPICAL TERRAIN FEATURES
INCLUDING THE HARQUAHALA MOUNTAINS IN LA PAZ COUNTY AND THE TABLE
TOP WILDERNESS IN WESTERN MARICOPA COUNTY. HIGH-RES MODELS ARE
INDICATING THIS SCENARIO UNFOLDING FOR A FEW HOURS THIS AFTERNOON,
BUT ACTIVITY SHOULD WANE EARLY THIS EVENING WITH THE LOSS OF DAYTIME
HEATING. FURTHER DRYING OF THE BOUNDARY LAYER CAN BE ANTICIPATED ON
WEDNESDAY WITH MIXING RATIOS FALLING TO AROUND 8 G/KG. THIS WILL
LEAD TO ANOTHER QUIET DAY ACROSS OUR FORECAST AREA WITH ANY ISOLATED
CONVECTION RELEGATED TO THE HIGHER TERRAIN OF NORTHERN AND
SOUTHEASTERN AZ.
A LARGE TROUGH OF LOW PRESSURE WILL REMAIN SITUATED OVER THE WEST
COAST THROUGH THE MIDDLE OF THIS WEEK WITH THE SUBTROPICAL RIDGE
DISPLACED WELL EAST OF THE REGION. THIS PATTERN WILL RESULT IN 500
MB HGHTS REMAINING IN A SEASONABLE 587-590 DAM RANGE. IN RESPONSE,
TEMPERATURES ARE NOT EXPECTED TO FLUCTUATE MUCH AT ALL WITH LOWER
DESERT HIGHS TOPPING OUT IN THE UPPER 90S TO LOWER 100S AND LOWS
IN THE UPPER 70S TO MID 80S. DUE TO A SLIGHT ENHANCEMENT OF THE
MID-LVL JET, WINDS WILL BECOME GUSTIER EACH AFTERNOON, ESPECIALLY
ACROSS SE CALIFORNIA AND THE LOWER COLORADO RIVER VALLEY.
LONG TERM /THURSDAY THROUGH SUNDAY/
THE FORECAST BECOMES A BIT MORE MUDDY HEADING INTO THE END OF THIS
WEEK AND THROUGH THE WEEKEND. CURRENTLY THE NHC SHOWS A TC LIKELY
FORMING OVER THE E PACIFIC, SOUTH OF THE TIP OF THE BAJA DEL NORTE
WITHIN THE NEXT 24-48 HRS. MOST FORECAST MODELS SHOW THE STORM
ITSELF CURVING OUT INTO OPEN WATERS, HOWEVER THERE IS GOOD EVIDENCE
THAT AT LEAST SOME TROPICAL MOISTURE WILL GET PULLED UP INTO MEXICO
AND MAKING IT AS FAR NORTH AS SOUTHERN AZ AS EARLY AS THURSDAY.
ROUGHLY 90% OF THE GEFS AND EPS MEMBERS SHOW PWATS INCREASING FROM
1.5" ON THURSDAY TO AROUND 1.8-2.0" OVER PORTIONS OF SOUTHCENTRAL
AND SOUTHWEST AZ BY FRIDAY OR SATURDAY. GIVEN THIS LIKELY INCREASE
IN MOISTURE, NBM POPS HAVE INCREASED TO AROUND 40-50% WITH THE
INITIAL MOISTURE PUSH LATE THURSDAY INTO FRIDAY. THEREAFTER, POPS
REMAIN QUITE LOW IN A 20-30% RANGE THROUGH THE WEEKEND WHICH IS
MOST LIKELY DUE TO UNCERTAINTY IN TIMING AND COVERAGE OF RAINFALL
WITHIN THE DETERMINISTIC MODEL OUTPUT.
ALTHOUGH THERE WILL BE ADEQUATE MOISTURE RETURN, THE POSITIONING
OF THE RIDGE/TROUGH FEATURES OVER THE WEST WILL PLAY A KEY ROLE IN
HOW MUCH RAINFALL MAY ACTUALLY MATERIALIZE. IF THE RIDGE
STRENGTHENS TOO MUCH AND RETROGRADES WWD, THEN THE FOCUS FOR
HEAVIER RAINFALL MAY BE MUCH FURTHER WEST INTO SOCAL AND NORTH
INTO UT AND CO AS INDICATED BY THE LATEST ECMWF AND GFS RUNS. IT
WILL LIKELY BE AT LEAST 2 OR 3 MORE DAYS UNTIL WE HAVE A GOOD IDEA
ON WHAT WILL HAPPEN LATE THIS WEEK, AND ANY FORECAST THAT DOES
NOT SHOW A RANGE OF POSSIBLE OUTCOMES SHOULD BE DISREGARDED AT
THIS TIME.
UNCERTAINTY IN THE TEMPERATURE FORECAST BY THIS WEEKEND IS ALSO
APPARENT AS INDICATED BY LARGE (8-10 DEGREE) SPREADS WITHIN THE
NBM INTERQUARTILE RANGE. ONCE OUR REGION DOES BEGIN TO DRAW IN THE
PACIFIC MOISTURE, TEMPERATURES WILL LIKELY DIP DOWN TO AROUND 3-5
DEGREES BELOW NORMAL BY THE END OF THIS WEEK. HOWEVER, AS RIDGING
ALOFT ATTEMPTS TO BUILD OVER THE AREA THIS WEEKEND, TEMPERATURES
MAY WARM CLOSER TO NORMAL BY SUNDAY OR MONDAY.
AVIATION
UPDATED AT 0515Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION CONCERNS ARE EXPECTED DURING THE TAF PERIOD.
WINDS WILL RETURN TO FOLLOWING LIGHT AND DIURNAL TRENDS WITH
VARIABILITY DURING DIRECTIONAL SHIFTS. THERE ARE HINTS OF AN
ISOLATED AFTERNOON VCTS AND LATER EVENING OUTFLOW, BUT CURRENT
CHANCES FOR EITHER OF THESE EVENTS IS AROUND 10% OR LESS AND
THEREFORE HAVE BEEN EXCLUDED FROM THE TAFS. OTHER THAN A FEW LOW-
LEVEL BASES AROUND 7-10 KFT, SKIES WILL BE MOSTLY CLEAR.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO MAJOR AVIATION CONCERNS ARE EXPECTED DURING THE TAF PERIOD.
WINDS WILL FOLLOW FAMILIAR DIURNAL TRENDS WITH PERHAPS SOME
VARIABILITY OCCURRING DURING DIRECTIONAL SWITCHES. OTHER THAN A
FEW BASES AROUND 10 KFT, SKIES WILL BE MOSTLY CLEAR.
FIRE WEATHER
AFTER ABUNDANT WETTING RAINFALL OCCURRED ACROSS SOUTH-CENTRAL AZ
YESTERDAY, DRIER CONDITIONS WILL SETTLE INTO THE REGION TODAY
WITH RAIN CHANCES FALLING TO AROUND 10% OR LESS THROUGH THE MIDDLE
OF THIS WEEK. BETTER AREA-WIDE RAIN CHANCES WILL RETURN BY LATE
WEEK AND INTO THIS WEEKEND. EXPECT MINRHS OF 15-25% ACROSS THE
WESTERN DISTRICTS TO 30- 50% OVER THE NEXT FEW AFTERNOONS.
OVERNIGHT RECOVERY WILL RANGE FROM POOR ACROSS SE CALIFORNIA TO
GOOD ACROSS SOUTH-CENTRAL AZ. TEMPERATURES WILL RANGE FROM NEAR TO
SLIGHTLY BELOW NORMAL OVER THE NEXT SEVERAL DAYS WITH LOWER
DESERT HIGHS IN THE UPPER 90S TO LOW 100S.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...SALERNO
LONG TERM...SALERNO
AVIATION...RW
FIRE WEATHER...SALERNO
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