Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 291623
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
923 AM MST WED JUL 29 2015

.SYNOPSIS... THE COMBINATION OF AMPLE MOISTURE AND A WEATHER
DISTURBANCE MOVING NORTHWARD ACROSS THE REGION IS EXPECTED TO
TRIGGER WIDESPREAD SHOWER AND THUNDERSTORM ACTIVITY TODAY AND
TONIGHT...WITH STRONG WINDS...AREAS OF BLOWING DUST...HEAVY
DOWNPOURS...AND LOCAL FLASH FLOODING POSSIBLE FROM THE HEAVIER
STORMS. HIGH PRESSURE BUILDING OVER THE REGION WILL THEN GRADUALLY
REDUCE RAIN CHANCES FROM THURSDAY ONWARD INTO THE UPCOMING
WEEKEND...AND INTO EARLY NEXT WEEK...BUT AT LEAST SLIGHT CHANCES
WILL REMAIN OVER SOUTH-CENTRAL ARIZONA. TEMPERATURES WILL TAKE A
SLIGHT DIP BELOW NORMAL FOR TODAY AND THURSDAY DUE TO WIDESPREAD
CLOUD COVERAGE...BEFORE SLOWING WARMING BACK UP FROM FRIDAY INTO
EARLY NEXT WEEK AS THE ATMOSPHERE SLOWLY DRIES OUT.

&&

.DISCUSSION...
AN UPPER LEVEL DISTURBANCE IS EVIDENT IN THE WATER VAPOR IMAGERY ON
THE NORTHERN END OF AN UPPER LOW CENTERED OFF THE SOUTHERN BAJA
COAST. IT IS MOVING INTO A DEFORMATION ZONE THAT EXITS BETWEEN THE
UPPER LOW...A RIDGE CENTERED OVER THE SOUTH-CENTRAL STATES...AND
WESTERLY FLOW TO THE NORTH. THERE ALSO APPEARS TO BE AN MCV OVER
SOUTHERN ARIZONA EVIDENT IN RADAR IMAGERY WHICH IS ROUGHLY LOCATED
ON THE NORTHERN SIDE OF THE PRE-EXISTING SYNOPTIC DISTURBANCE. 12Z
MODELS DEPICT VARYING AMOUNTS OF UPPER LEVEL DIVERGENCE AND OMEGA
MOVING ACROSS ARIZONA AND INTO SOUTHEAST CALIFORNIA TODAY. WITH
FAIRLY THICK CLOUD COVER NEAR AND EAST OF THE LOWER COLORADO RIVER
VALLEY...THERE MAY BE A LACK OF SURFACE HEATING TO REALIZE THE FULL
POTENTIAL OF THE MOIST AIRMASS. SPEAKING OF WHICH...THE 12Z PSR
SOUNDING WAS CLOSE TO 1.9 INCHES WHICH IS WELL ABOVE CLIMO. BEST
STORM ACTIVITY FOR OUR AREA PRIOR TO 00Z LOOKS TO SOUTHWEST ARIZONA
AND SOUTHEAST CALIFORNIA WHERE SURFACE HEATING AND SOME FORCING WILL
BE BETTER. WITH AN EASTERLY COMPONENT TO THE STEERING FLOW...MOUNTAIN
STORMS WILL HAVE A GOOD CHANCE OF SURVIVING OVER THE LOWER DESERTS OF
SOUTH-CENTRAL ARIZONA...INCLUDING THE PHOENIX AREA. ANTICIPATE THAT
SCENARIO TO DEVELOP LATER TODAY WITH MORE ISOLATED NUISANCE TYPE
SHOWERS PRIOR TO THAT. MAY NEED TO MAKE SOME FURTHER ADJUSTMENTS TO
FORECASTS LATER ON. STAY TUNED.

&&

.PREVIOUS DISCUSSION ISSUED AT 300 AM MST/PDT...
TODAY AND TONIGHT... IT NOW APPEARS THAT TODAY AND TONIGHT WILL BE A
RATHER ACTIVE PERIOD FOR CONVECTIVE ACTIVITY ACROSS THE REGION...WITH
GRIDDED POPS NOW BOASTED INTO THE LIKELY RANGE ACROSS SOUTH-CENTRAL
AZ. ALTHOUGH CONSIDERABLE DEBRIS CLOUDS ACROSS THE REGION THIS
MORNING WILL LIKELY DELAY THE ONSET OF ACTIVITY SOMEWHAT...THE
COMBINATION OF AMPLE MOISTURE (PWATS IN THE 1.6-2.0 INCH RANGE)
DIFFLUENT FLOW ALOFT...AND A RATHER VIGOROUS INVERTED TROF THAT IS
MOVING INTO THE REGION FROM THE SOUTH IS EXPECTED TO PRODUCE
WIDESPREAD SHOWER/THUNDERSTORM ACTIVITY ACROSS SOUTH-CENTRAL ARIZONA
THIS EVENING...WITH THE ACTIVITY MOVING INTO SW AZ AND SE CA LATER
TONIGHT. GIVEN THE FACT THAT THE FORECAST SOUNDING FOR PHOENIX IS
SHOWING RATHER STRONG SE-LY WINDS (30-40KT) THROUGH THE MID- LEVELS
OF THE ATMOSPHERE...MLCAPES APPROACHING/EXCEEDING 1000J/KG...AND LI`S
IN THE -4 TO -5 RANGE...IT APPEARS THAT ISOLATED SEVERE STORMS ARE
LIKELY...WITH VERY STRONG WINDS AND HEAVY RAINS THAT COULD PRODUCE
LOCAL FLASH FLOODING...WITH THE TIMING FOR THE STRONGEST ACTIVITY
BEING BETWEEN 02Z AND 06Z THIS EVENING. ALTHOUGH BLOWING DUST IS VERY
LIKELY THIS EVENING AS THE STORM ACTIVITY MOVES THOUGH...AT THIS
POINT WE ARE NOT EXPECTING WIDESPREAD DENSE BLOWING DUST...SINCE IT
APPEARS THAT THE ATMOSPHERE WILL BE UNSTABLE ENOUGH TO ALLOW THE DUST
TO BE MIXED THROUGH A RATHER DEEP/BROAD LAYER/AREA...LIKE WHAT
HAPPENED LAST EVENING. THE HIGH-RES MODELS THEN INDICATE THAT THE
STORMS WILL MOVE WESTWARD INTO SW AZ AND SE CA LATER TONIGHT AND
EARLY THU MORNING...PERHAPS AS AN ORGANIZED AREA...BRINGING LOCALLY
HEAVY RAINS AND GUSTY WINDS TO THAT REGION AS WELL.

THURSDAY AND THURSDAY NIGHT... ALTHOUGH THERE WILL STILL BE PLENTY
OF MOISTURE ACROSS THE REGION ON THURSDAY...IT APPEARS LIKELY THAT
IT WILL BE A BIT OF A DOWN-DAY DUE TO THE FACT THAT TODAY/S ROUND OF
ACTIVITY WILL LEAVE THE ATMOSPHERE PRETTY WORKED-OVER...WITH A LOT
OF LEFT-OVER DEBRIS CLOUDS AROUND. STILL...SOME CONVECTIVE ACTIVITY
CAN STILL BE EXPECTED...WITH THE BEST CHANCES FOR IT BEING OVER THE
HIGHER TERRAIN OF SOUTH-CENTRAL AZ AND OVER SE CA. THE PRIMARY
THREATS ON THURSDAY WILL BE LOCALLY HEAVY RAINS AND LOCALIZED FLASH
FLOODING. HIGH TEMPERATURES ON THURSDAY WILL LIKELY END UP BEING
BELOW NORMAL...HELD DOWN BY CLOUDINESS AND A RATHER MOIST BOUNDARY
LAYER.

FRIDAY AND BEYOND...ALTHOUGH THERE WILL STILL BE ENOUGH MONSOON
MOISTURE TO KEEP UP SOME ACTIVITY DURING THIS PERIOD...A GRADUAL
DOWNTREND IN CONVECTIVE ACTIVITY AND A SLOW WARMING TREND APPEARS TO
BE IN THE CARDS AS THE MAIN UPPER HIGH CENTER GRADUALLY BUILDS
OVERHEAD AND THE ATMOSPHERE SLOWLY DRIES OUT...WITH PWATS FALLING
INTO THE 1.30 TO 1.50 RANGE BY EARLY NEXT WEEK.

&&

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

SHOWER AND THUNDERSTORM ACTIVITY WILL INCREASE THROUGH THE DAY TODAY
IN AREAL COVERAGE AFTER 15Z. OUTFLOW WINDS FROM NEARBY STORMS WILL
BE TRICKY TO PIN DOWN A TIME AND A DIRECTION ONCE CONVECTION BEGINS.
THE THREAT FOR HEAVY RAINS NEAR TERMINALS IN THE AFTERNOON AND
EVENING HOURS EXISTS ALONG WITH A SLIGHT CHANCE FOR BLOWING DUST AND
REDUCED VISIBILITIES. CONFIDENCE IS LOW AT THIS TIME TO INCLUDE
REDUCED VIS IN THE TAFS.

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

SCATTERED CLOUD DECKS AOA 10KFT WILL CONTINUE TO OVERSPREAD THE
AREA...AND INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS WILL BE
IN PLACE AFTER 21Z TODAY. GUSTY SOUTHERLY WINDS LATE THIS MORNING
WILL PERSIST THROUGH THIS AFTERNOON.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...FRIDAY THROUGH TUESDAY... LOW-LEVEL MOISTURE SHOULD
DECLINE SOMEWHAT THROUGH THE WEEKEND...THOUGH CONDITIONS WILL REMAIN
FAVORABLE FOR AT LEAST ISOLATED THUNDERSTORM ACTIVITY ACROSS MUCH OF
THE REGION. LESS ACTIVITY IS THEN ANTICIPATED EARLY NEXT WEEK AS THE
MONSOON HIGH SHIFTS WESTWARD OVER AZ. WINDS WILL REMAIN FAIRLY LIGHT
EACH DAY ASIDE FROM AFTERNOON BREEZINESS AND THE POTENTIAL FOR
STRONGER THUNDERSTORM OUTFLOW WINDS.

&&

.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...AJ
PREVIOUS DISCUSSION...PERCHA
AVIATION...DEWEY
FIRE WEATHER...HIRSCH


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