998
FXUS65 KPSR 142018
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
118 PM MST MON SEP 14 2026
KEY MESSAGES
- ABUNDANT MOISTURE WILL REMAIN SITUATED ACROSS THE EASTERN HALF
OF ARIZONA PROVIDING ENHANCED CHANCES FOR SHOWERS AND
THUNDERSTORMS THROUGH THE MIDDLE PORTION OF THE WEEK, ESPECIALLY
OVER THE MOUNTAIN LOCATIONS.
- THERE WILL BE THE POTENTIAL FOR SOME STORMS TO PRODUCE STRONG WINDS,
BUT THE BIGGER THREAT WILL BE HEAVY RAINFALL LEADING TO
LOCALIZED FLASH FLOODING OVER THE NEXT FEW DAYS.
- SHOWER AND THUNDERSTORM CHANCES WILL DIMINISH BY THE END OF THE
WEEK THROUGH THE UPCOMING WEEKEND AS DRIER AIR FILTERS IN.
- NEAR TO SLIGHTLY ABOVE NORMAL TEMPERATURES ARE EXPECTED THROUGHOUT
THE ENTIRE WEEK.
SHORT TERM /TODAY THROUGH WEDNESDAY/
LATEST OBJECTIVE ANALYSIS INDICATES THE SUBTROPICAL RIDGE OF HIGH
PRESSURE CENTERED OVER THE SOUTHEASTERN STATES WHILE BROAD UPPER-
LEVEL TROUGHING REMAINS SITUATED OVER THE NORTHWESTERN STATES. THIS
OVERALL PATTERN CONFIGURATION CONTINUES TO SUPPORT MORE OF A SOUTH
TO SOUTHWEST FLOW ACROSS MUCH AZ WHILE MORE WESTERLY FLOW, BRINGING
DRIER AIR, IS OCCURRING FROM THE LOWER COLORADO RIVER VALLEY
WESTWARD. THE SOUTH TO SOUTHWEST FLOW ENTRENCHED ACROSS MUCH OF AZ
IS EXPECTED TO REMAIN IN PLACE THROUGH THE MIDDLE OF THE WEEK,
AIDING WITH PERIODIC MOISTURE INFLUXES AS PWAT VALUES PEAK ABOVE
1.5" ALONG WITH LOW-LEVEL MIXING RATIOS OF 12-14 G/KG. THEREFORE,
AN ELEVATED POTENTIAL FOR SHOWER AND THUNDERSTORM ACTIVITY WILL
REMAIN IN PLACE, ESPECIALLY FROM PHOENIX EASTWARD THROUGH THE
MIDDLE OF THE WEEK BEFORE CHANCES DIMINISH TOWARDS THE END OF THE
WEEK ONCE THE DRIER AIR FILTERS IN.
THE COMBINATION OF PLENTIFUL MOISTURE AND STRONG DAYTIME HEATING
SHOULD RESULT IN GOOD INSTABILITY ONCE AGAIN AS MUCAPE VALUES ARE
EXPECTED TO PEAK AT 1000-1500 J/KG. THE LATEST HREF MEMBERSHIP SHOWS
SOUTHEAST AZ BECOMING CONVECTIVELY ACTIVE DURING THE AFTERNOON HOURS
WITH SOME OF THIS ACTIVITY DRIFTING INTO THE HIGHER TERRAIN AREAS TO
THE EAST AND SOUTHEAST OF PHOENIX WITH MORE ISOLATED ACTIVITY ACROSS
THE SOUTH-CENTRAL AZ LOWER DESERTS. SIMILAR TO THE LAST COUPLE OF
DAYS, DESPITE THE VERY FAVORABLE THERMODYNAMIC PARAMETERS IN
PLACE, THE LACK OF GOOD UPPER-LEVEL FORCING FOR ASCENT CONTINUES
TO BE A LIMITING FACTOR FOR MORE WIDESPREAD ACTIVITY. WITH THESE
STORMS, HEAVY RAINFALL LEADING TO LOCALIZED FLASH FLOODING WILL BE
THE PRIMARY THREAT WITH STRONG DOWNBURST WIND GUSTS A SECONDARY
THREAT GIVEN THAT DCAPE VALUES WILL STILL BE SUFFICIENTLY HIGH,
RANGING BETWEEN 1000-1200 J/KG. QUIETER CONDITIONS CAN BE
EXPECTED THIS EVENING INTO AT LEAST THE FIRST PART OF THE
OVERNIGHT PERIOD, BEFORE POTENTIALLY ANOTHER ROUND OF ELEVATED
SHOWERS AND STORMS DEVELOPS, MOST LIKELY AFTER 3 AM MST. THE
LATEST HI-RES GUIDANCE IS INDICATING THE BEST POTENTIAL OVER THE
FOOTHILLS AND HIGHER TERRAIN TO NORTH AND EAST OF PHOENIX.
HOWEVER, THE CONVECTIVE THREAT LATE IN THE OVERNIGHT HOURS INTO
EARLY TUESDAY MORNING WILL BE HIGHLY CONDITIONAL OF WHETHER OR NOT
A GRAVITY WAVE/OUTFLOW WILL BE A SUFFICIENT TRIGGERING MECHANISM
FOR DEVELOPMENT AS THE OVERALL LARGER SCALE FORCING FOR ASCENT
WILL STILL BE LACKING.
BETTER UPPER-LEVEL SUPPORT IS MORE LIKELY TO MATERIALIZE, ESPECIALLY
HEADING INTO LATE TUESDAY THROUGH WEDNESDAY, AS A WEAK MID-LEVEL
LOW CURRENTLY LOCATED OVER THE SOUTHERN TIP OF THE BAJA PENINSULA
IN CONJUNCTION WITH ANOTHER WEAK UPPER-LEVEL LOW OFF THE WEST
COAST OF THE BAJA PENINSULA MOVE INTO THE REGION. THEREFORE, THESE
FEATURES ARE LIKELY TO PAIR UP AND BE SUFFICIENT TO TRIGGER MORE
WIDESPREAD SHOWER AND THUNDERSTORM ACTIVITY ACROSS MUCH OF CENTRAL
AND EASTERN AZ. LATEST NBM IS HONING IN ON THIS INCREASING
COVERAGE AS IT SHOWS POPS INCREASING TO 50-80% FROM PHOENIX
EASTWARD FROM TUESDAY EVENING THROUGH WEDNESDAY. THE MAIN CONCERN
WILL BE AN INCREASING THREAT FOR FLASH FLOODING GIVEN THE ABUNDANT
MOISTURE IN PLACE WITH BOTH THE ECMWF AND GFS INDICATING PWATS
EXCEEDING 1.8" ALONG WITH LOW-LEVEL MIXING RATIOS AS HIGH AS 14
G/KG. IN ADDITION, MLCAPE VALUES ARE LIKELY TO RANGE BETWEEN
1000-1500 J/KG PROVIDING PLENTY OF INSTABILITY. THEREFORE, THE
ENVIRONMENT IS LIKELY TO BECOME FAVORABLE FOR THESE THUNDERSTORMS
TO PRODUCE HIGH RAINFALL RATES IN EXCESS OF 1-2"/HR, LEADING TO
THAT ENHANCED FLASH FLOOD POTENTIAL. A FLOOD WATCH WILL LIKELY BE
NEEDED FOR PORTIONS OF THE AREA FROM LATE TUESDAY THROUGH
WEDNESDAY.
TEMPERATURES THROUGH THE MIDDLE OF THE WEEK WILL CONTINUE TO RUN
SLIGHTLY ABOVE NORMAL ACROSS THE WESTERN DESERTS AS HIGH TOP OUT
AROUND 105 DEGREES, WHILE MORE CLOUDS AND POTENTIAL RAINFALL WILL
KEEP HIGHS CLOSER TO 100 DEGREES ACROSS THE SOUTH-CENTRAL AZ LOWER
DESERTS. IN FACT, WITH THE GREATER LIKELIHOOD OF MORE ABUNDANT
CLOUD COVER AS WELL AS HIGHER RAINFALL POTENTIAL, AFTERNOON HIGHS
ON WEDNESDAY ACROSS MUCH OF THE SOUTH-CENTRAL AZ LOWER DESERTS
ARE NOW FORECAST TO TOP OUT IN THE 90S.
LONG TERM /THURSDAY THROUGH SUNDAY/
GUIDANCE IS STARTING TO AGREE ON A QUICKER DRYING TREND LATER THIS
WEEK AS THE PACIFIC TROUGH IS FAVORED TO MOVE FARTHER INTO THE
GREAT BASIN AND AT LEAST INTO NORTHERN AND WESTERN PORTIONS OF THE
DESERT SOUTHWEST. THIS IS LIKELY TO PUSH DRIER AIR EASTWARD
THROUGH MOST IF NOT ALL OF ARIZONA AS EARLY AS THURSDAY BUT MORE
SO FRIDAY INTO SATURDAY. THURSDAY IS STILL A BIT OF AN UNCERTAIN
DAY AS RAIN CHANCES MAY STILL LINGER ACROSS THE SOUTH-CENTRAL
LOWER DESERTS AND DEFINITELY OVER EASTERN ARIZONA. HOWEVER, BY
FRIDAY, ENOUGH DRY AIR MOVING IN SHOULD END CHANCES OVER THE
LOWER DESERTS AND REALLY LIMIT CHANCES OVER THE HIGH TERRAIN. IT
IS DOUBTFUL WE WILL COMPLETELY SCOUR OUT ALL OF THE MOISTURE
ACROSS THE HIGHER TERRAIN, SO 10-20% POPS REMAIN EACH DAY ACROSS
EASTERN GILA COUNTY THROUGH THE WEEKEND.
AS CONDITIONS DRY OUT INTO THE WEEKEND, TEMPERATURES ARE LIKELY
TO FACE A BIT OF A WARMING TREND BUT AS OF NOW THE REGION IS
FAVORED TO STAY UNDER BROAD UPPER LEVEL TROUGHING INTO THE
WEEKEND. LOWER DESERT HIGHS ARE EXPECTED TO WARM TO ABOVE NORMAL
BY FRIDAY OR SATURDAY, BUT SO FAR THE NBM INDICATES A MOST LIKELY
RANGE OF 103-107 DEGREES.
AVIATION
UPDATED AT 1735Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
THE MAIN IMPACT WILL BE PERIODS OF VCSH/VCTS, AND SHRA/TSRA LATER
THIS AFTERNOON (00-04Z) AND ONCE AGAIN TOMORROW MORNING (10-14Z).
CONFIDENCE REMAINS LOW AS EARLY MORNING MODELS HAD A SIMILAR
OUTLOOK THIS MORNING, WITH NOTHING DEVELOPING AS EXPECTED. HOWEVER,
THE ENVIRONMENT LOOKS MORE FAVORABLE OVER THE NEXT COUPLE OF DAYS
BUT MONITORING AND UPDATES WILL NEED TO FOLLOW. SHRA/TSRA WILL BE
CAPABLE OF PRODUCING LOCALLY GUSTY WINDS WITH A LOW CHANCE
(10-20%) FOR GUSTS >30 KTS. A PERIOD OF SOUTHERLY CROSS WINDS WILL
GIVE WAY TO WESTERLY FLOW BY THIS AFTERNOON (21-22Z) THEN BACK
E/SE TONIGHT. WIND SPEEDS WILL MOSTLY STAY UNDER 10 KTS, OUTSIDE
OF SHOWER AND STORM INFLUENCES. SCT TO OCCASIONALLY BKN CLOUD
DECKS AROUND 8-10K FT AGL WILL BE COMMON THROUGH THE TAF PERIOD.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO AVIATION WEATHER CONCERNS WILL EXIST THROUGH THE TAF PERIOD
UNDER MOSTLY CLEAR SKIES. WINDS WILL CONTINUE TO BEHAVE SIMILAR
TO THE PAST 24 HOURS VARYING BETWEEN SOUTHEASTERLY AND WESTERLY AT
KIPL AND SOUTHERLY TO SOUTHWESTERLY AT KBLH WITH PERIODS GUSTS
BETWEEN 20-25 KTS THIS AFTERNOON.
FIRE WEATHER
PERIODS OF SCATTERED SHOWERS AND THUNDERSTORMS ARE LIKELY THROUGH
WEDNESDAY ACROSS THE EASTERN DISTRICTS SUPPORTING A LOCALIZED
HEAVY RAINFALL THREAT. MOISTURE LEVELS WILL REMAIN ELEVATED EXCEPT
FOR SOUTHEAST CALIFORNIA. EXPECT MINIMUM HUMIDITY LEVELS TO STILL
FALL INTO A 15-25% RANGE FOR THE WESTERN DISTRICTS WHILE THE
EASTERN DISTRICTS WILL ONLY DIP TO 30-45% THROUGH WEDNESDAY.
WINDS WILL GENERALLY FOLLOW DIURNAL PATTERNS ACROSS THE EASTERN
DISTRICTS, WHILE MUCH OF THE WESTERN DISTRICTS WILL HAVE ELEVATED
SOUTHERLY WINDS WITH OCCASIONAL GUSTS ABOVE 20 MPH. BY THURSDAY
INTO FRIDAY, MUCH DRIER AIR IS FORECAST TO SPREAD EASTWARD ACROSS
THE REGION, EVENTUALLY ENDING RAIN CHANCES FOR ALL BUT THE FAR
EASTERN ARIZONA HIGH TERRAIN AND LOWERING HUMIDITIES INTO THE
TEENS ACROSS THE LOWER DESERTS.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...LOJERO
LONG TERM...KUHLMAN
AVIATION...RYAN
FIRE WEATHER...KUHLMAN
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