546
FXUS65 KPSR 262109
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
ISSUED BY NATIONAL WEATHER SERVICE TUCSON AZ
209 PM MST MON OCT 26 2026
KEY MESSAGES
- DRY AND TRANQUIL WEATHER CONDITIONS WILL CONTINUE THROUGH THE
MIDDLE OF THE WEEK WITH TEMPERATURES WITHIN A FEW DEGREES OF
DAILY NORMALS.
- AN UNSETTLED WEATHER PATTERN WILL RETURN TO THE REGION LATE IN
THE WEEK AND PERSIST THROUGH THIS WEEKEND RESULTING IN MUCH
COOLER TEMPERATURES AND CHANCES FOR WIDESPREAD RAINFALL.
- THERE WILL ALSO BE A POSSIBILITY OF EMBEDDED THUNDERSTORMS WITH
HEAVIER RAINFALL WHICH COULD LEAD TO LOCALIZED FLASH FLOODING
FRIDAY AND SUNDAY.
SHORT TERM /TODAY THROUGH WEDNESDAY/
LATEST MID-LVL WV IMAGERY AND 500 MB STREAMLINE ANALYSIS REVEALS
A TROUGH OF LOW PRESSURE LOCATED OVER THE PAC NW ALONG WITH A
WEAK SHORTWAVE PROGRESSING THROUGH THE INTERMOUNTAIN WEST. THIS
DISTURBANCE WILL RESULT IN A FEW HIGH CLOUDS PASSING THROUGH N AZ
THIS AFTERNOON, OTHERWISE DRY AND TRANQUIL WEATHER CONDITIONS ARE
ANTICIPATED ACROSS OUR FORECAST AREA DURING THE NEXT 24 HRS. UNDER
MOSTLY CLEAR SKIES, TEMPERATURES WILL REMAIN WITHIN A DEGREE OR
TWO OF SEASONAL NORMALS WITH HIGHS REACHING THE MID 80S ACROSS THE
LOWER DESERTS AND THE MID TO UPPER 70S FOR THE HIGHER ELEVATIONS.
DUE TO CALM WINDS AND DRY CONDITIONS OVERNIGHT, COOL OVERNIGHT
LOW TEMPERATURES IN THE MID 50S TO AROUND 60 DEGREES CAN BE
EXPECTED TUESDAY MORNING.
QUIET WEATHER CONDITIONS WILL CONTINUE INTO THE MIDDLE OF THE WEEK
UNDER QUASI-ZONAL WESTERLY FLOW ALOFT. DRY AIR ALOFT WILL HELP
KEEP SKIES CLEAR TO MOSTLY CLEAR THROUGH TUESDAY BEFORE A SLIGHT
SHIFT IN THE UPPER LEVEL WINDS OUT OF THE SOUTHWEST HELPS TO DRAW
MORE ABUNDANT HIGH CLOUDS INTO OUR REGION. OVERALL THERE WILL BE
VERY LITTLE VARIATION IN 500 MB HEIGHTS WHICH WILL RESULT IN
DAYTIME HIGHS TOPPING OUT IN THE MID 80S ACROSS THE LOWER DESERTS.
OVERNIGHT LOWS WILL ALSO FALL WITHIN A NORMAL RANGE IN THE MID
50S TO LOWER 60S THROUGH WEDNESDAY.
LONG TERM /THURSDAY THROUGH SUNDAY/
THE WEATHER PATTERN IS EXPECTED TO SHIFT LATE THIS WEEK WITH A DEEP
TROUGH GETTING CARVED OUT OVER THE PACIFIC NORTHWEST AND SOUTHWEST
TO OFF THE COAST OF CALIFORNIA BY THURSDAY. THE POLAR JET ASSOCIATED
WITH THE NORTHERN STREAM SYSTEM IS EXPECTED TO DIP FARTHER SOUTHWARD
OFF THE WEST COAST, WHILE A STRONGER SUBTROPICAL JET ACROSS THE
CENTRAL PACIFIC SHIFTS EASTWARD TOWARD BAJA. ALTHOUGH THESE JET
BRANCHES ARE NOT EXPECTED TO PHASE TOGETHER GOING INTO FRIDAY, THERE
IS LIKELY TO BE SOME COMBINED ENERGY REACHING THE WESTERN U.S.
AS THE TROUGH SETS UP TO OUR WEST ON WEDNESDAY INTO THURSDAY, HIGH
LEVEL MOISTURE WILL STREAM INTO OUR REGION, FOLLOWED BY INCREASING
SOUTHERLY MOIST FLOW IN THE LOWER LEVELS THURSDAY NIGHT INTO FRIDAY.
GUIDANCE IS IN VERY GOOD AGREEMENT SOUTHERLY LOW LEVEL MOIST
ADVECTION WILL COMBINE WITH SOME TOP-DOWN SATURATION IN THE UPPER
LEVELS ON FRIDAY ACROSS SOUTHERN AND CENTRAL ARIZONA. PWATS ARE
SHOWN TO QUICKLY RISE TO JUST ABOVE 200% OF NORMAL BY FRIDAY
MORNING, WHILE LOW LEVEL MIXING RATIOS RISE TO A RESPECTABLE 8-9
G/KG. THIS DECENT MOISTURE IS ALSO EXPECTED TO COINCIDE WITH MODEST
LOW LEVEL UPSLOPE FORCING AND QUITE STRONG MID AND UPPER LEVEL
ASCENT WITHIN THE LEFT EXIT REGION OF THE SUBTROPICAL JET. ALTHOUGH
WE ARE STILL FOUR DAYS OUT, CONFIDENCE IS QUITE GOOD IN SHOWER
ACTIVITY BLOSSOMING AT SOME POINT THURSDAY NIGHT/FRIDAY MORNING
ACROSS SOUTH-CENTRAL ARIZONA AND LASTING THROUGH MUCH OF FRIDAY.
GUIDANCE ALSO SHOWS MODEST MUCAPE OF 250-500 J/KG ON FRIDAY WHICH
SHOULD ALLOW FOR SOME ISOLATED TO SCATTERED WEAK THUNDERSTORMS.
SHEAR VALUES LOOK TO BE ON THE LOW SIDE, SO AT THIS POINT WE ARE NOT
ANTICIPATING ANY STRONG STORMS. FORECAST QPF FROM THURSDAY NIGHT
THROUGH FRIDAY NIGHT CURRENTLY AVERAGES AROUND 0.50" ACROSS THE
PHOENIX AREA TO UPWARDS OF 0.75-1.00" IN THE HIGHER TERRAIN NORTH OF
PHOENIX. THE HIGHER END OF GUIDANCE IS AT LEAST DOUBLE THAT, SO IT'S
NOT OUT OF THE QUESTION TO HAVE TO WORRY ABOUT SOME MINOR FLOODING
ISSUES FRIDAY. WPC HAS ALSO INCLUDED THIS AREA IN A SLIGHT RISK ON
THEIR DAY 5 ERO.
THE FRIDAY WEATHER EVENT WILL NOT BE THE LAST PERIOD OF RAIN
EXPECTED OVER THE NEXT WEEK AS ANOTHER LIKELY EVEN STRONGER SYSTEM
IS FORECAST TO TRACK EAST NORTHEASTWARD TOWARD SOUTHERN CALIFORNIA
AND NORTHERN BAJA ON SATURDAY BEFORE MOVING THROUGH OUR REGION ON
SUNDAY. THERE IS MUCH MORE UNCERTAINTY WITH THIS SECOND WEATHER
SYSTEM COMPARED TO THE FIRST AS THERE ARE NOTABLE TIMING AND
EVOLUTION DIFFERENCES. THERE ARE ALSO SOME DIFFERENCES WITH THE
POTENTIAL PHASING OF THE POLAR AND SUBTROPICAL JET STREAMS WHICH IF
IT OCCURS WOULD LIKELY RESULT IN A DECENT LOW PRESSURE SYSTEM
DEVELOPING WITHIN THE BASE OF THE LARGE SCALE TROUGH. MODELS AT
LEAST AGREE THAT THERE WILL BE AS MUCH IF NOT BETTER MOISTURE THEN
THE FRIDAY SYSTEM AND STRONGER MID-LEVEL AND FRONTAL ASCENT. GIVEN
THE UNCERTAINTY, QPF AMOUNTS ARE STILL QUITE VOLATILE TO ANY BIG
CHANGES IN THE STRENGTH OF THE SYSTEM AND TRACK. HOWEVER, SO FAR
ENSEMBLE MEAN QPF AMOUNTS INDICATE OVERALL HIGHER AVERAGE AMOUNTS
COMPARED TO FRIDAY'S EVENT, AS WELL AS MORE WIDESPREAD COVERAGE.
RAIN CHANCES COULD ALSO EXTEND INTO MONDAY, ESPECIALLY ACROSS
EASTERN PORTIONS OF ARIZONA.
TEMPERATURES WILL TAKE A HIT LATER THIS WEEK AND THROUGH THE WEEKEND
WITH NBM FORECAST HIGHS DROPPING INTO A 75-80 DEGREE RANGE FRIDAY
AND SATURDAY AND EVEN LOWER STARTING SUNDAY. THE COOLEST AIR SO FAR
THIS FALL SHOULD MOVE IN WITH THE SUNDAY WEATHER SYSTEM AS HIGHS MAY
FALL TO AS THE UPPER 60S TO LOWER 70S FOR SUNDAY AND MONDAY.
AVIATION
UPDATED AT 1715Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO WEATHER ISSUES WILL EXIST THROUGH TUESDAY AFTERNOON UNDER A FEW
PASSING HIGH CIRRUS DECKS. CONFIDENCE IS EXCELLENT THAT A LIGHT
EAST, OR NEARLY CALM WIND WILL TRANSITION TO W/SW BY MID AFTERNOON,
THEN REVERT BACK TO EAST OVERNIGHT. EXTENDED PERIODS OF A LIGHT AND
VARIABLE COMPONENT WILL BE COMMON. A PERIOD OF SOUTHERLY CROSS
RUNWAY WINDS IS LIKELY TUESDAY AFTERNOON, ALBEIT WITH SPEEDS UNDER
8KT.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO WEATHER ISSUES WILL EXIST THROUGH TUESDAY AFTERNOON UNDER CLEAR
SKIES. WINDS WILL BE LIGHT AND VARIABLE FOR THE MAJORITY OF THE TIME
FRAME WITH A TREND FOR A LIGHT NOCTURNAL WEST COMPONENT AT KIPL AND
NORTH TRAJECTORY AT KBLH.
FIRE WEATHER
WARM AND DRY CONDITIONS WILL TRANSPIRE THROUGH MUCH OF THIS WEEK
BEFORE A MUCH COOLER AND WETTER PATTERN SETS UP FRIDAY INTO THIS
WEEKEND. MINIMUM HUMIDITY LEVELS WILL CONTINUE TO FALL, REACHING
20-35% TODAY AND 15-30% TUESDAY BEFORE GRADUAL MOISTURE
IMPROVEMENT ARRIVES MID-WEEK. OVERNIGHT RECOVERIES WILL REMAIN
GOOD AT 40-65%. WINDS WILL REMAIN LIGHT EACH DAY FAVORING TYPICAL
DIURNAL PATTERNS AND MINIMAL UPSLOPE BREEZINESS.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...SALERNO
LONG TERM...KUHLMAN
AVIATION...18
FIRE WEATHER...SALERNO
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