Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 292052
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
152 PM MST SAT AUG 29 2015

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.SYNOPSIS...
STRONG HIGH PRESSURE ALOFT WILL KEEP HIGH TEMPERATURES WELL ABOVE
SEASONAL NORMALS TODAY WITH HOTTER LOWER DESERTS REACHING OR
EXCEEDING 110. THERE WILL BE SUFFICIENT MOISTURE EAST OF THE LOWER
COLORADO RIVER TO SUPPORT ISOLATED TO SCATTERED AFTERNOON AND
EVENING THUNDERSTORMS THROUGH SUNDAY. STARTING TUESDAY DRIER
WESTERLY FLOW ALOFT WILL SLOWLY PUSH THE MOISTURE OFF TO THE EAST
LIMITING STORM CHANCES PRIMARILY TO HIGHER TERRAIN AREAS TO THE EAST
OF PHOENIX. THERE WILL ALSO BE A GRADUAL COOLING TREND STARTING
SUNDAY WITH CENTRAL DESERTS HIGH TEMPERATURES DROPPING TO AROUND
SEASONAL NORMALS BY THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
WITH THE CLEAR MORNING START TO SUPPLY AMPLE HEATING TO THE MOUNTAIN
AND DESERT SURFACES THROUGH MIDDAY...CONVECTIVE ACTIVITY REALLY TOOK
DURING THE 12 PM MST HOUR. FAIRLY ISOLATED STORMS WERE FIRING ACROSS
SOUTHWEST AND WESTERN AZ WITH MORE SCATTERED ACTIVITY OVER
THE EASTERN WHITE MTNS...THE INTL BORDER IN SE AZ AND ACROSS NW AZ
FROM KINGMAN DOWN THROUGH PRESCOTT. BROAD...BUT
SUBTLE...ANTICYCLONIC CIRCULATION NOTED IN THE STORM ACTIVITY SO FAR
ON REGIONAL IR LOOPS...INDICATIVE OF THE ML CIRC CENTER MODEL
STREAMLINE FCSTS PEGGED EARLIER THIS MORNING THROUGH THE 700-400MB
OR SO LAYER. GIVEN THE LIGHT STEERING FLOW AND WINDS IN THE CIRC
CENTER...STORM MOTION WILL BE ON THE SLOW SIDE TODAY. SOME LOCALIZED
FLOODING IMPACTS COULD OCCUR...BUT CURRENT AIRCRAFT AND MODEL
SOUNDINGS AS WELL AS ALREADY WARM SFC TEMPERATURES POINT TO DEEP
MIXING AND AN INVERTED V PROFILE MAKING STRONG WINDS A THREAT FROM
STORMS TODAY. IT IS THAT POTENTIAL FOR WIND THAT COULD HELP
PROPAGATE SOME BOUNDARIES...AND ASSOCIATED BLOWING DUST...ACROSS THE
AREA THAT COULD HELP TRIGGER ISO TO WIDELY SCT THUNDERSTORM
DEVELOPMENT ACROSS PORTIONS OF THE SOUTH-CENTRAL DESERTS...INCLUDING
THE PHX METRO...LATER THIS AFTN AND EVENING. GIVEN THE GENERALLY
LIGHT WINDS ALOFT...ANY DEBRIS CLOUDINESS WILL BE SLOW TO CLEAR THE
AREA. LINGERING CLOUDS COULD HELP KEEP OVERNIGHT LOWS ON THE MILD
SIDE FOR SUNDAY AM.

BY SUNDAY...TROUGHING OFF THE PACIFIC NORTHWEST WILL MOVE INLAND AND
THE AMPLIFIED UPPER RIDGE OVER THE INTERMOUNTAIN WEST WILL BEGIN TO
TRANSITION TO THE EAST. RESULTING FLOW ALOFT OVER OUR REGION WILL
BECOME MORE SOUTHWESTERLY WHILE 1000-500MB THICKNESSES BEGIN TO
DECREASE. TEMPS SHOULD COOL A FEW DEGREES BUT THEY WILL REMAIN WELL
ABOVE NORMAL. THE FLOW WILL START TO SHIFT THE DEEPER MOISTURE
FURTHER TO THE EAST...BUT THERE WILL BE SUFFICIENT MOISTURE AND
INSTABILITY TO KEEP THE THREAT GOING FOR AFTN/EVE STORMS ACROSS
SOUTH CENTRAL ARIZONA. ABOVE CLIMO POPS WILL REMAIN FROM MARICOPA
CTY EASTWARD...WITH DRY CONDITIONS ACROSS SE CA AND THE CO RIVER
VALLEY.

GFS AND ECMWF OPERATIONAL RUNS AS WELL AS ENSEMBLE GUIDANCE CONTINUE
TO CALL FOR A GRADUAL DRYING AND COOLING TREND TO OCCUR OVER THE
ENTIRE WORK WEEK NEXT WEEK...AS TROFFING ALOFT INITIALLY DEVELOPS
ALONG THE WEST COAST AND PLACES A DRYING SOUTHWEST FLOW ALOFT ACROSS
SERN CALIFORNIA AND ARIZONA. AS THE WEEK PROGRESSES THE TROFFING
STARTS TO PUSH INLAND AND AS THIS HAPPENS TEMPERATURES WILL COOL
DOWN TO NEAR SEASONAL NORMALS. MONDAY INTO TUESDAY THE TROF AXIS
REMAINS ALONG THE WEST COAST...AND FLOW IS NOT SUFFICIENT TO
COMPLETELY SCOUR OUT THE MOISTURE OVER ALL OF SOUTH CENTRAL AZ. FOR
THE MOST PART THE THREAT OF AFTERNOON AND EVENING STORMS WILL BE
CONFINED TO THE HIGHER TERRAIN EAST OF PHOENIX BUT CHANCES IN THE
GREATER PHOENIX AREA WILL CERTAINLY NOT BE ZERO...THEY WILL HOVER IN
THE 5 TO 10 PERCENT BALLPARK. FOR THE LATTER HALF OF THE WORKWEEK AS
THE TROF AXIS SHIFTS INLAND AND SOUTHWEST FLOW ALOFT BECOMES
STRONGER...MOISTURE WILL BE PUSHED OFF TO THE EAST AND EVENTUALLY
ANY THREAT FOR STORMS WILL FOCUS OVER HIGHER TERRAIN AREAS TO THE
EAST OF GLOBE WITH SKIES IN THE GREATER PHOENIX AREA MOSTLY SUNNY
EACH DAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...KSDL...

SUFFICIENT INSTABILITY FOR SCATTERED SHOWERS AND THUNDERSTORMS WILL
PERSIST ACROSS SOUTH-CENTRAL AZ THROUGH THE EARLY EVENING. STEERING
FLOW REMAINS QUITE WEAK...SO ANY DEVELOPMENT IN THE PHOENIX METRO
AREA WILL LIKELY NOT OCCUR UNTIL AT LEAST 01-02Z. KPHX/KIWA TAFS HAVE
BEEN AMENDED TO INCLUDE THE MENTION OF VCTS. COVERAGE OF STORMS IN
THE VALLEY IS EXPECTED TO BE AT LEAST ISOLATED...THOUGH THE GREATER
LIKELIHOOD IS FOR AN OUTFLOW BOUNDARY TO MOVE THROUGH AROUND
03Z...BRINGING AN ABRUPT WIND SHIFT FROM THE EAST OR SOUTHEAST. ENVIRONMENT
IS FAVORABLE FOR GUSTY WINDS ALONG WITH AREAS OF BLOWING DUST.
CONDITIONS ARE THEN EXPECTED TO IMPROVE AFTER 04-06Z.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

TYPICAL DIURNAL WIND PATTERNS WITH LITTLE CLOUD COVER EXPECTED. FEW
STORMS BETWEEN KBLH-KPHX-KNYL BETWEEN 19Z-01Z.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
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.

&&

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



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