Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 300508
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1005 PM MST SAT AUG 29 2015

.SYNOPSIS...
THERE WILL CONTINUE TO BE SUFFICIENT MOISTURE EAST OF THE LOWER
COLORADO RIVER TO SUPPORT ISOLATED AFTERNOON AND EVENING
THUNDERSTORMS THROUGH SUNDAY. 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 NEXT WEEK WITH CENTRAL DESERTS HIGH
TEMPERATURES DROPPING TO AROUND SEASONAL NORMALS BY THE MIDDLE OF
NEXT WEEK.

&&

.DISCUSSION...
UPPER LEVEL ANTI-CYCLONE REMAINS PARKED OVER CNTRL ARIZONA THIS
EVENING WITH SUFFICIENT DIVERGENT FLOW AND BOUNDARY LAYER MOISTURE
TO SUPPORT SEMI-ORGANIZED CONVECTION. DESPITE THE 00Z ANALYZED
MEAGER 9 G/KG MIXING RATIOS...COOLER AIR ALOFT AND STEEPER THAN
TYPICAL LAPSE RATES COMPENSATED TO YIELD MLCAPES IN EXCESS OF 1000
J/KG. VERY WEAK STEERING FLOW...VERY WARM SFC TEMPERATURES...AND
DCAPE VALUES OVER 1500 J/KG SUPPORTED DEEP LONG TRAVELING OUTFLOW
BOUNDARIES. AT ONE POINT...5 TO 6 DISTINCT OUTFLOW BOUNDARIES WERE
COLLIDING THROUGH PINAL COUNTY PROVIDING EVEN MORE IMPETUS ASCENT
AND MOISTENING AT THE TOP OF THE BOUNDARY LAYER.

OBJECTIVE ANALYSIS SHOWS MOST INSTABILITY EXHAUSTED WITH GROWING
INHIBITION ACROSS THE FORECAST AREA. CORRESPONDINGLY...STORMS HAVE
BECOME FAR MORE ISOLATED AND MUCH WEAKER THAN EARLIER IN THE
EVENING. MADE SOME MINOR SALIENT ADJUSTMENTS TO POPS FOR THE
REMAINDER OF THE NIGHT ALONG WITH MODIFYING TRENDS IN TEMPERATURES
IN DEWPOINTS.

&&

.PREVIOUS DISCUSSION...
/152 PM MST SAT AUG 29 2015/
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...AND KSDL...
THUNDERSTORMS HAVE DISSIPATED ACROSS THE PHOENIX METRO THIS
EVENING...AND WINDS WILL MAINTAIN AN EASTERLY TRAJECTORY WITH CIGS
ABOVE 12K FT THROUGH SUNDAY MORNING. PROSPECTS FOR STORMS DIRECTLY
IMPACTING PHOENIX TERMINALS SUNDAY AFTERNOON ARE REMOTE AT
BEST...WITH ONLY TYPICAL WEST SFC WINDS DEVELOPING AFTER NOON.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
NO AVIATION IMPACTS WITH ONLY PERIODIC HIGH CIRRUS CLOUDS THROUGH
SUNDAY EVENING. SFC WINDS WILL FAVOR A S/SW DIRECTION THROUGH THE
PERIOD...THOUGH PERIODS OF VARIABLE WINDS WILL BE COMMON SUNDAY
MORNING.

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


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