Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 291120 AAA
AFDPSR

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PHOENIX AZ
420 AM MST SAT AUG 29 2015

.UPDATE...AVIATION AND FIRE WX SECTION.

&&

.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 MONDAY DRIER WESTERLY
FLOW ALOFT WILL PUSH THE MOISTURE OFF TO THE EAST LIMITING STORM
CHANCES PRIMARILY TO HIGHER TERRAIN AREAS TO THE EAST OF PHOENIX.
THERE WILL BE A GRADUAL COOLING TREND STARTING SUNDAY WITH CENTRAL
DESERTS HIGH TEMPERATURES DROPPING TO AROUND SEASONAL NORMALS BY THE
MIDDLE OF NEXT WEEK.

&&

.DISCUSSION... A STRONG UPPER LEVEL TROF CURRENTLY SPINNING OFF THE
PAC NW COAST HAS KEPT THE DOWNSTREAM UPPER RIDGE PUMPED UP OVER THE
DESERT SOUTHWEST...WITH H5 VALUES AROUND 593DM ACROSS ARIZONA PER
THE LATEST PLOT DATA. THE HIGH HEIGHTS ALOFT CONTINUED TO PRODUCE
HOT WEATHER ACROSS THE LOWER DESERTS WITH PHOENIX REACHING 109
YESTERDAY AND YUMA HITTING 111. LITTLE CHANGE IN THE PATTERN IS
EXPECTED TODAY AND CONTINUED HOT WEATHER IS ON TAP FOR THE LOWER
DESERTS...IN FACT PHOENIX IS EXPECTED TO REACH 110 TODAY WITH 110
PLUS READINGS OVER THE HOTTER WESTERN DESERTS. TEMPERATURES TODAY
WILL BE VERY CLOSE TO EXCESSIVE HEAT WARNING LEVELS.

WITH THE TROFFING SITTING OFF THE WEST COAST AND THE RIDGE PARKED
FIRMLY OVERHEAD...STEERING FLOW IS EITHER WEAK AND NONDESCRIPT OR
WEAK SOUTHERLY. PLENTY OF MOISTURE CONTINUES TO FLOW NORTH THRU
CENTRAL AND EASTERN ARIZONA WITH PWAT VALUES BETWEEN 1.25 AND 1.5
INCHES...AND SURFACE DEWPOINTS REMAIN HIGH AS WELL. AT 2 AM MOST OF
THE LOWER DESERTS RANGED FROM THE MID 50S TO THE MID 60S. EAST OF
THE LOWER COLORADO RIVER TODAY THERE WILL BE SUFFICIENT MOISTURE...
MLCAPE AND DAYTIME HEATING TO KEEP A THREAT GOING FOR AFTERNOON AND
EVENING STORMS...AND IN FACT SEVERAL LOCAL MESOSCALE MODELS
INCLUDING THE HRRR CALL FOR CONVECTION BREAKING OUT THIS AFTERNOON
OVER THE CENTRAL DESERTS...INCLUDING THE GREATER PHOENIX AREA...AND
PERSISTING INTO THE NIGHTTIME HOURS. POPS HAVE BEEN RAISED EAST OF
THE LOWER COLORADO RIVER INTO THE 15-20 PERCENT BALLPARK WITH
CHANCES FORECAST IN THE HIGHER TERRAIN EAST OF PHOENIX.

ON SUNDAY SIGNIFICANT SHORTWAVE ENERGY IS FORECAST TO MOVE INLAND
OVER THE PAC NORTHWEST AND IN RESPONSE FLOW OVER THE DESERT
SOUTHWEST AND ARIZONA BECOMES INCREASINGLY SOUTHWESTERLY. HEIGHTS
ALOFT FALL SLIGHTLY AND 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. POPS WILL BE SIMILAR TO TODAY...BUT
SLIGHTLY LOWER WEST OF MARICOPA COUNTY.

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...

EASTERLY FLOW ACROSS THE PHX AREA WILL CONTINUE INTO THE MID
AFTERNOON AS WESTERLY WINDS WILL BE A LITTLE SLOW TO
DEVELOP...LIKELY AFTER 22Z. ENOUGH MOISTURE REMAINS FOR SOME
SHOWERS/STORMS TO DEVELOP OVER THE MTNS OF ARIZONA...INCLUDING WEST
AND SOUTH OF PHX WHICH MAY IMPACT ARRIVAL/DEPARTURE ROUTES.
POSSIBLE...THOUGH NOT ENOUGH TO EXPLICITLY PUT IN TAFS...OF OUTFLOW
COMING IN THIS EVENING PRODUCING SOME BLDU AND PERHAPS A FEW
SHOWERS/STORMS IN THE PHX AREA ITSELF.

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... MONDAY THROUGH FRIDAY... OVERALL THE WEATHER
PATTERN WILL BE ON A GENTLE COOLING AND DRYING TREND. FOR MUCH OF
THE WEEK...ANY RAIN CHANCES WILL REMAIN OVER THE HIGHER ELEVATIONS
OF EASTERN ARIZONA. NO SIGNIFICANT WINDS THOUGH THE AFTERNOONS MAY
BE JUST A BIT BREEZIER THAN USUAL.

&&

.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...CB
AVIATION...INIGUEZ
FIRE WEATHER...INIGUEZ


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