Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 310408
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
905 PM MST SUN AUG 30 2015

.SYNOPSIS...
DRIER WESTERLY FLOW WILL SLOWLY PUSH THE MOISTURE TO THE EAST BY
TUESDAY...LIMITING STORM CHANCES PRIMARILY TO HIGHER TERRAIN AREAS
TO THE EAST OF PHOENIX. THERE WILL ALSO BE A GRADUAL COOLING TREND
THIS WEEK WITH CENTRAL DESERTS HIGH TEMPERATURES DROPPING TO AROUND
SEASONAL NORMALS BY THE MIDDLE OR LATTER PORTION OF THE WEEK.

&&

.DISCUSSION...
ALTHOUGH ANTI-CYCLONIC FLOW HAD SHIFTED EAST EARLIER TODAY BRINGING
DEEPER LAYER WESTERLY TRAJECTORIES INTO THE FORECAST AREA (USUALLY
UNFAVORABLE FOR ORGANIZED STORMS IN THE PHOENIX METRO)...RESIDUAL
BOUNDARY LAYER MOISTURE HELD TIGHT OVER CNTRL AND ERN ARIZONA
(MIXING RATIOS AOA 10 G/KG). 00Z KPSR SOUNDING DATA INDICATED A
RATHER NOTABLE CAPPING INHIBITION AT THE H7 LEVEL (CINH NEAR 50
J/KG)...THOUGH INCREASING UPPER LEVEL DIVERGENCE AND ASCENT SUPPORTED
DEEP CONVECTION THROUGH PIMA AND PINAL COUNTIES. WITH DCAPE VALUES
IN EXCESS OF 1500 J/KG...NUMEROUS OUTFLOWS WERE COMMON HELPING ERODE
THE CAPPING INVERSION AND MIX MOISTURE TO THE TOP OF THE BOUNDARY
LAYER.

SHOWERS AND STORMS WILL CONTINUE THROUGH NRN PINAL AND POSSIBLY
PARTS OF SRN GILA COUNTY THROUGH THE EVENING...WITH MUCH OF MARICOPA
COUNTY WORKED OVER BY OUTFLOWS AND CONVECTION. IN GENERAL...POPS
WERE CONSOLIDATED TO MATCH RADAR TRENDS AND CONCEPTUALLY ADJUSTED
HIGH RESOLUTION ENSEMBLE BLENDS. OTHERWISE...ONLY COSMETIC CHANGES
TO ACCOUNT FOR PRECIPITATION EFFECTS WERE NEEDED FOR OTHER
METEOROLOGICAL FIELDS.

&&

.PREVIOUS DISCUSSION...
/236 PM MST SUN AUG 30 2015/
STARTING ON MONDAY...OPERATIONAL RUNS OF THE GFS AND ECMWF AS WELL
AS ENSEMBLE GUIDANCE CONTINUE TO CALL FOR THE START OF A GRADUAL
DRYING AND COOLING TREND AS TROUGHING SETTLES FURTHER ALONG THE WEST
COAST AND GIVES A DEEP SOUTHWESTERLY FLOW ALOFT TO SERN CA AND
ARIZONA. WHERE EARLIER FORECASTS HAVE CALLED FOR THIS FLOW TO SCOUR
OUT AND SWEEP THE DEEPER MOISTURE SURFACE TO OUR EAST AT A FAIRLY
QUICK RATE...DETERMINISTIC AND ENSEMBLE FCST GUIDANCE STILL POINT TO
A SOUTHERLY 850MB FLOW INTO THE REGION...MAINTAINING SOME SEMBLANCE
OF ELEVATED DEWPOINTS AND LL TO ML MIXING RATIOS THRU MIDWEEK.
CONFLUENT FLOW THROUGH THE ML AND UL WON`T BE OVERLY SUPPORTIVE OF
STORMS...BUT CANNOT RULE OUT AT LEAST SLIGHT CHANCES FOR THE LIMITED
AREAS OF HIGHER TERRAIN ACROSS SOUTH-CENTRAL AZ. OTHERWISE...BEST
LOCALES FOR STORMS WILL BE PRIMARILY CONFINED TO HIGHER TERRAIN
AREAS EAST OF PHOENIX. EXCEPT FOR SOME HIGH CLOUDS AT TIMES MOVING
THROUGH THE SOUTHWEST FLOW ALOFT SKIES WILL BE MOSTLY SUNNY OVER THE
LOWER DESERTS THROUGH MOST OF THE WORK WEEK. AS HEIGHTS SLOWLY
LOWER...HIGH TEMPERATURES WILL DROP OFF DAY BY DAY. MONDAY WILL
STILL SEE HIGH TEMPS WELL ABOVE NORMAL WITH HIGHS AROUND 107
EXPECTED AT PHOENIX BUT BY WEDNESDAY THE CENTRAL DESERTS SHOULD
LOWER TO AROUND 104 DEGREES...AND MUCH CLOSER TO SEASONAL
NORMALS...WITH LITTLE CHANGE THEN EXPECTED INTO THE WEEKEND.

THERE IS A BIT OF A WRINKLE IN THE FORECAST OUT AT THE END OF THE
EXTENDED PERIOD...OVER THE COMING WEEKEND...AS MEDIUM RANGE MODELS
CONTINUE TO CALL FOR SOME TROPICAL MOISTURE TO BE DRAWN NORTHWARD BY
THE BROAD TROF OVER THE WESTERN CONUS...AND THEN SPREAD INTO THE
LOWER ARIZONA DESERTS LEADING TO AT LEAST A SLIGHT CHANCE OF
AFTERNOON AND EVENING SHOWERS OR THUNDERSTORMS BY SATURDAY. POPS
HAVE BEEN RAISED OVER THE WEEKEND ACCORDINGLY...AND WILL BE SLIGHTLY
GREATER THAN CLIMO VALUES FOR NOW.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
SHRA AND TSRA WILL GENERALLY SLIDE SOUTH OF TERMINAL LOCATIONS
THROUGH THIS EVENING AND OVERNIGHT. TIMING OF WIND SHIFTS IS LOW
GIVEN MULTIPLE OUTFLOW BOUNDARIES...HOWEVER SHOULD OBTAIN THE
TRADITIONAL EASTERLY FLOW AFTER MIDNIGHT. MODERATE CONFIDENCE THAT
STORM ACTIVITY WILL REMAIN EAST OF THE PHOENIX METRO MONDAY
AFTERNOON.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
NO AVIATION IMPACTS THROUGH MONDAY AFTERNOON WITH ONLY OCCASIONAL
HIGH CIRRUS. SFC WINDS WILL PERIODICALLY BECOME GUSTY...SOUTH AT
KBLH AND WEST AT KIPL...UP TO 25 KTS IN THE AFTERNOON AND
EVENING...WITH TENDENCY FOR LIGHT AND VARIABLE WINDS DURING THE MID
MORNING HOURS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
A LOW PRESSURE SYSTEM ACROSS THE PACIFIC NORTHWEST WILL DISPLACE THE
MONSOON HIGH TO THE SOUTH AND EAST THROUGH THE WEEK. THE TREND WILL
BE TOWARDS COOLER AND DRIER CONDITIONS ACROSS THE DESERT SOUTHWEST.
HOWEVER...ENOUGH MOISTURE WILL LINGER ACROSS EASTERN ARIZONA FOR
ISOLATED AFTERNOON THUNDERSTORMS. FOR THE WEEKEND...LATEST GUIDANCE
IS HINTING AT A RETURN TO DEEPER MOISTURE AND BETTER RAIN
CHANCES...PARTICULARLY SOUTH AND EAST OF PHOENIX.

&&

.SPOTTER INFORMATION STATEMENT...
SPOTTERS ARE ENCOURAGED TO REPORT CONDITIONS ACCORDING TO STANDARD
OPERATING PROCEDURES.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...MO/NOLTE/CB
AVIATION...MO
FIRE WEATHER...HIRSCH


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