621
FXUS65 KPSR 211204
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
504 AM MST WED OCT 21 2026
UPDATE
UPDATED 12Z AVIATION DISCUSSION.
KEY MESSAGES
- A STRONG LOW PRESSURE SYSTEM IS EXPECTED TO BRING MULTIPLE
ROUNDS OF SHOWERS AND THUNDERSTORMS THROUGH THURSDAY ACROSS
MUCH OF CENTRAL AND EASTERN ARIZONA.
- MODERATE TO HEAVY RAINFALL ACTIVITY LEADING TO AREAS OF FLASH FLOODING
AS WELL AS ISOLATED TO WIDELY SCATTERED STRONG TO SEVERE
THUNDERSTORMS LEADING TO DAMAGING WIND GUSTS, LARGE HAIL, AND
EVEN A FEW ISOLATED TORNADOES ARE ALL POSSIBLE.
- DRIER AIR FILTERING INTO THE REGION BY THE END OF THE WEEK WILL LEAD
TO MORE BENIGN WEATHER CONDITIONS DURING THE WEEKEND THROUGH AT
LEAST EARLY NEXT WEEK.
- NEAR NORMAL TEMPERATURES TODAY WILL COOL TO BELOW NORMAL LEVELS
BY THE LATTER HALF OF THE WEEK AND LAST THROUGH THE WEEKEND.
SHORT TERM /TODAY THROUGH THURSDAY/
A HIGHLY IMPACTFUL WEATHER EVENT IS LIKELY TO UNFOLD ACROSS MUCH
OF CENTRAL AND EASTERN AZ THROUGH THURSDAY AS A POTENT LOW
PRESSURE SYSTEM CURRENTLY JUST OFF THE SOUTHERN CA COAST IMPACTS
THE DESERT SOUTHWEST. LATE LAST EVENING, A FEW ROBUST THUNDERSTORMS,
LIKELY INSTIGATED FROM A LEADING SHORTWAVE, MATERIALIZED ACROSS
PORTIONS OF SOUTH-CENTRAL AZ. THIS INCLUDED A SUPERCELL STORM
THAT TRAVERSED PORTIONS OF THE PHOENIX EAST VALLEY FROM CHANDLER
NORTHEASTWARD THROUGH MESA WITH SEVERAL REPORTS OF LARGE HAIL.
THIS ACTIVITY WAS JUST AN APPETIZER OF WHAT IS LIKELY TO TRANSPIRE
DURING THE NEXT COUPLE OF DAYS.
LATEST SPC MESOANALYSIS SHOWS ROBUST MOISTURE ADVECTION WELL
UNDERWAY AS PWATS ACROSS SOUTH-CENTRAL AZ WERE ALREADY APPROACHING
1.3-1.5" AND WILL LIKELY GO A BIT HIGHER, PEAKING AT 1.6-1.7" BY
THIS AFTERNOON. THIS MOISTURE COMBINED WITH STEEP MID-LEVEL LAPSE
RATES WILL RESULT IN MLCAPE VALUES PEAKING UPWARDS OF 1000 J/KG BY
THIS AFTERNOON. THIS AMOUNT OF INSTABILITY COMBINED WITH ABUNDANT
MOISTURE WILL YIELD A FAVORABLE ENVIRONMENT FOR THUNDERSTORMS
CAPABLE OF PRODUCING HEAVY RAINFALL RATES IN EXCESS OF 1-2"/HR WITH
A GOOD POTENTIAL FOR TRAINING OF ACTIVITY AND THUS HEIGHTENING THE
POTENTIAL FOR FLASH FLOODING. IN ADDITION TO THE FLASH FLOOD THREAT,
ANOTHER MAJOR THREAT IS SEVERE WEATHER. GIVEN THE AMPLE AMOUNT OF
INSTABILITY EXPECTED TO BE IN PLACE COMBINED WITH VERY STRONG 0-6 KM
SHEAR VALUES IN EXCESS OF 50 KTS, THE THUNDERSTORMS THAT DEVELOP
WILL LIKELY HAVE SOME ORGANIZATION TO THEM WITH THE POTENTIAL TO
ACQUIRE SUPERCELLULAR CHARACTERISTICS. AS A RESULT, DAMAGING WIND
GUSTS IN EXCESS OF 60-70 MPH, LARGE HAIL IN EXCESS OF 1-2" IN
DIAMETER AND EVEN AN ISOLATED TORNADO OR TWO WILL BE THREATS WITH
ANY GIVEN SEVERE THUNDERSTORM. IN FACT, GIVEN THE HIGHLY UNUSUAL
FAVORABLE SEVERE WEATHER SETUP FOR THIS PART OF THE COUNTRY, THE
STORM PREDICTION CENTER HAS HIGHLIGHTED A PORTION OF NORTH-CENTRAL
AZ, JUST NORTH OF PHOENIX IN AN ENHANCED RISK OF SEVERE WEATHER
FOR LATER TODAY, MAINLY FOR VERY LARGE HAIL. EVEN AREAS OUTSIDE OF
THE ENHANCED RISK COULD SEE SIGNIFICANT SEVERE WEATHER.
LATEST HI-RES GUIDANCE HIGHLIGHTS ACTIVITY BEGINNING TO DEVELOP
ACROSS THE HIGHER TERRAIN AREAS NORTH AND EAST OF PHOENIX AND ACROSS
MUCH OF THE AZ HIGH COUNTRY BY THE LATE MORNING/EARLY AFTERNOON
HOURS BEFORE ACTIVITY POTENTIALLY EXPANDS INTO THE LOWER DESERTS OF
SOUTH-CENTRAL AZ SHORTLY AFTER. THE MOST WIDESPREAD ACTIVITY AND
LIKELY THE GREATEST THREAT FOR FLASH FLOODING IS FORECAST TO
OCCUR FROM LATER THIS EVENING THROUGH THE OVERNIGHT AND MORNING
HOURS OF THURSDAY AS THE MAIN UPPER-LEVEL JET STREAK ASSOCIATED
WITH THE LOW PRESSURE SYSTEM MOVES OVER THE GREAT BASIN AREA,
PUTTING MUCH OF THE REGION IN A FAVORABLE LOCATION FOR UPPER-LEVEL
DIVERGENCE. THE THREAT FOR SEVERE WEATHER WILL ALSO CONTINUE INTO
THURSDAY AS INSTABILITY AND SHEAR PARAMETERS WILL STILL REMAIN
MORE THAN SUFFICIENT. LATEST QPF FROM WPC CONTINUES TO HIGHLIGHT
AVERAGE TOTAL RAINFALL AMOUNTS OF 1-2" ACROSS THE HIGHER TERRAIN
AREAS NORTH AND EAST OF PHOENIX, WHILE LOWER AMOUNTS OF 0.25-
0.75" ARE FORECAST FOR THE LOWER DESERTS. HOWEVER, LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE IN AREAS THAT SEE TRAINING OF ACTIVITY.
AS THE UPPER TROUGH GRADUALLY PUSHES INLAND THROUGH THE SOUTHERN
GREAT BASIN DURING THE DAY ON THURSDAY, STRONG DRY AIR ADVECTION
WILL GRADUALLY SPREAD FROM WEST TO EAST WITH RAIN CHANCES FIRST
ENDING ACROSS THE SOUTH-CENTRAL AZ LOWER DESERTS BY THE MID TO
LATE AFTERNOON AND WILL LIKELY TAKE UNTIL LATE THURSDAY NIGHT INTO
EARLY FRIDAY MORNING FOR RAIN CHANCES TO END ACROSS THE HIGHER
TERRAIN AREAS.
WITH THE MAIN TROUGH AXIS STILL TO THE WEST OF THE REGION, AFTERNOON
TEMPERATURES WILL STILL WARM UP WELL INTO THE 80S ACROSS MUCH OF THE
LOWER DESERTS WITH SOME AREAS ACROSS THE WESTERN DESERTS TOUCHING 90
DEGREES. AS HEIGHTS ALOFT DECREASE WITH THE TROUGH AXIS PUSHING
INLAND THROUGH THE GREAT BASIN ON THURSDAY, TEMPERATURES WILL
NOTICEABLY COOL WITH MANY AREAS ONLY TOPPING OUT IN THE LOW 80S.
HOWEVER, DEPENDING ON THE AMOUNT OF RAIN AND CLOUD COVER, IT IS
POSSIBLE THAT AREAS IN SOUTH-CENTRAL AZ REMAIN COOLER THAN
CURRENTLY FORECASTED.
LONG TERM /FRIDAY THROUGH TUESDAY/
WITH STRONG DRY AIR ADVECTION IN PLACE BEHIND THE DEPARTING
TROUGH, WEATHER CONDITIONS WILL TURN MUCH QUIETER BEGINNING ON
FRIDAY. A PIECE OF ENERGY LEFT BEHIND FROM DEPARTING TROUGH IS
CURRENTLY BEING DEPICTED BY THE MODEL GUIDANCE TO SEPARATE ITSELF
FROM THE MAIN JET ENERGY AND BRIEFLY MORPH INTO A CUT-OFF LOW OVER
AZ DURING THE WEEKEND. THIS FEATURE FOR THE MOST PART SHOULD BE
INCONSEQUENTIAL, ALTHOUGH ENOUGH MOISTURE COULD BE PRESENT FOR
SOME SHOWERS TO MATERIALIZE OVER THE AZ HIGH TERRAIN ON SATURDAY
BUT FOR THE MOST PART SHOULD REMAIN ON THE LIGHT SIDE GIVEN THE
OVERALL LACK OF INSTABILITY THAT WILL BE PRESENT. THE LOWER
DESERTS SHOULD REMAIN RAIN-FREE AS THERE WILL BE TOO MUCH DRY AIR
IN PLACE. UNDER THE PRESENCE OF THE LOW, TEMPERATURES WILL BE
SEVERAL DEGREES BELOW NORMAL DURING THE WEEKEND WITH AFTERNOON
HIGHS STRUGGLING TO REACH 80 DEGREES ACROSS THE LOWER DESERTS. AS
THE UPPER-LEVEL LOW EXITS THE REGION AND WEAK RIDGING BUILDS
OVERHEAD EARLY NEXT WEEK, TEMPERATURES WILL REBOUND TO MORE
SEASONAL LEVELS.
AVIATION
UPDATED AT 1203Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
ROUNDS OF ISOLATED TO SCATTERED STRONG THUNDERSTORMS WITH HEAVY
RAIN LEADING TO SUB-VFR VIS, BRIEF STRONG AND ERRATIC WIND GUSTS,
ISOLATED LARGE HAIL, AND LOW CIGS WILL BE POSSIBLE TODAY THROUGH
AT LEAST THURSDAY MORNING. CONFIDENCE IN TIMING OUT BEST CHANCES
RA/TS IS MODERATE, AS ISOLATED RA/TS MAY DEVELOP AT ANY TIME. AN
INCREASE IN ACTIVITY IS EXPECTED GOING INTO THIS AFTERNOON AND
THEN THERE MAY BE A BREAK THIS EVENING/EARLY TONIGHT BEFORE
ANOTHER ROUND DEVELOPS LATER TONIGHT-THURSDAY MORNING. A DOWNTREND
IN ACTIVITY IS EXPECTED BY THURSDAY EVENING. WINDS WILL FAVOR A
LIGHT EASTERLY COMPONENT THROUGH MOST OF THE TAF PERIOD, WITH
PERIODS OF SOUTHERLY WINDS DURING SHOWERS AND STORMS. LOWEST CIGS
TODAY ARE EXPECTED AROUND 5-7K FT AGL AND THEN MAY DIP TO 3-5K FT
THURSDAY MORNING WITH SHOWERS AND STORMS.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO MAJOR AVIATION CONCERNS ARE EXPECTED DURING THE TAF PERIOD.
OUTSIDE OF EXTENDED PERIODS OF VRB CONDITIONS, S'RLY FLOW WILL BE
FAVORED AT KBLH, WITH SOME GUSTS UPWARDS OF 20-25 KT DURING THE
AFTERNOON HOURS, WHILE WINDS AT KIPL WILL TAKE ON FAMILIAR DIURNAL
TRENDS, FLIPPING BETWEEN SE AND W. FEW-SCT SKIES WILL BE COMMON
THROUGH WEDNESDAY EVENING, WITH THE LOWEST BASES AROUND 6-7 KFT.
FIRE WEATHER
A LOW PRESSURE SYSTEM WILL BRING VERY ACTIVE WEATHER CONDITIONS
ACROSS MUCH OF CENTRAL AND EASTERN AZ THROUGH THURSDAY AS MULTIPLE
ROUNDS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED. SIGNIFICANT
RAINFALL ACTIVITY IS LIKELY IN SOME AREAS, PARTICULARLY ACROSS
THE HIGHER TERRAIN AREAS OF THE EASTERN DISTRICTS WHERE RAINFALL
AMOUNTS IN EXCESS OF 1-2" ARE POSSIBLE. MINRHS THROUGH THURSDAY
WILL RANGE BETWEEN 30-40% ACROSS THE WESTERN DISTRICTS AND
BETWEEN 40-70% ACROSS THE EASTERN DISTRICTS ALONG WITH GOOD TO
EXCELLENT OVERNIGHT RECOVERIES. SOME GUSTY WINDS WITH PEAK GUSTS
UPWARDS OF 25-30 MPH ARE LIKELY THIS AFTERNOON AND ONCE AGAIN ON
THURSDAY ACROSS THE WESTERN DISTRICTS. MUCH QUIETER CONDITIONS
ARE EXPECTED STARTING FRIDAY ALONG WITH A DECREASE IN HUMIDITY
VALUES. NEAR NORMAL TEMPERATURES TODAY WILL COOL INTO A BELOW
NORMAL CATEGORY STARTING THURSDAY AND LASTING THROUGH THE WEEKEND.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...FLOOD WATCH FROM 11 AM MST THIS MORNING THROUGH THURSDAY EVENING
FOR AZZ545-547-552-556>558-560>563.
FLOOD WATCH FROM 2 PM MST THIS AFTERNOON THROUGH THURSDAY
AFTERNOON FOR AZZ534-537-538-540>544-546-548>551-553>555.
CA...NONE.
SHORT TERM...LOJERO
LONG TERM...LOJERO
AVIATION...BENEDICT/RW
FIRE WEATHER...LOJERO
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