Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 042121 AAA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
220 PM MST FRI SEP 4 2015

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

&&

.SYNOPSIS...
SUFFICIENT MOISTURE WILL REMAIN OVER MUCH OF ARIZONA TODAY PROVIDING
GOOD SHOWER AND THUNDERSTORM CHANCES...PARTICULARLY ACROSS THE
EASTERN HALF OF THE STATE. SOMEWHAT DRIER AIR WILL MOVE INTO THE
REGION OVER THE WEEKEND...REDUCING RAINFALL CHANCES VERY SLIGHTLY.
WHILE SOME THUNDERSTORM CHANCES WILL PERSIST DURING THE FIRST HALF
OF NEXT WEEK...A SUBSTANTIALLY WARMER AND DRIER AIRMASS WILL SPREAD
INTO THE AREA FOR THE LATTER HALF OF THE WEEK.

&&

.DISCUSSION... RELATIVELY STRONG UPPER LEVEL TROF REMAINS SITUATED
ALONG THE PAC NORTHWEST COAST EARLY THIS AFTERNOON PUTTING ARIZONA
UNDER SOUTHWEST FLOW ALOFT. IR IMAGERY AT 1 PM SHOWED TS KEVIN OFF
THE SOUTHWEST TIP OF BAJA CA...AND THE SOUTHWEST FLOW WAS TAPPING
INTO THE MID/HIGH LEVEL MOISTURE BEING SHED OFF OF KEVIN. MUCH OF
THIS MOISTURE HAS OVERSPREAD THE EASTERN HALF OF AZ. MORNING
SOUNDINGS SHOWED A MOIST BUT NOT ESPECIALLY UNSTABLE AIRMASS ACROSS
SOUTH CENTRAL AZ WITH PWAT VALUES NEAR 1.5 INCHES BUT RATHER SKINNY
AND MEAGER CAPE. LOW CAPE VALUES WERE DUE TO THE MODEST LAPSE RATES
AND RATHER MOIST ADIABATIC PROFILES AS SEEN IN THE 12Z RAOBS.
STEERING FLOW THIS AFTERNOON AND EVENING WILL BE SOUTHWESTERLY...AND
THE UPPER STREAMLINES DEPICT A LAMINAR AND SLIGHTLY CONFLUENT
FLOW...NOT CONDUCIVE TO STRONG STORM DEVELOPMENT. DYNAMICALLY
SPEAKING...THERE WILL BE WEAK RIPPLES MOVING IN THE SOUTHWESTERLY
FLOW BUT NO STRONG SHORT WAVES APPEAR READY TO MOVE ACROSS ARIZONA
LATER TODAY. HOWEVER THERE IS A JET STREAK RACING ACROSS CENTRAL
AZ...PUTTING THE CENTRAL DESERTS UNDER THE FAVORABLE RIGHT REAR
QUADRANT LATER THIS AFTERNOON.

AT 1 PM SURFACE DEW POINTS OVER THE CENTRAL DESERTS WERE ELEVATED AND
MOSTLY RANGED FROM THE UPPER 50S TO LOW 60S. WITH MOISTURE ELEVATED
AND INSTABILITY LIMITED...AND DYNAMICS BEING A MIXED BAG...IT IS
TOUGH TO SAY JUST HOW THE CONVECTION WILL PLAY OUT TODAY. SOME
MESOSCALE HI RES MODELS SUCH AS THE HRRR AND WRF4KM SUGGEST WE WILL
SEE STORMS IN THE PHOENIX AREA TONIGHT. AS SUCH WE WILL KEEP ABOUT A
30 PERCENT CHANCE FOR SHOWERS AND THUNDERSTORMS ACROSS SOUTH CENTRAL
ARIZONA LATER THIS AFTERNOON AND OVERNIGHT TONIGHT.

FOR THIS WEEKEND...UPPER TROFFING REMAINS SITUATED ALONG THE WEST
COAST AND ARIZONA WILL STAY UNDER A SOUTHWEST FLOW ALOFT.
HOWEVER...LATEST GUIDANCE DOES NOT REALLY DRY OUT THE EASTERN HALF
OF THE STATE...ESPECIALLY IN THE LOWER LEVELS. PWAT VALUES ARE
FORECAST TO REMAIN NEAR OR ABOVE 1.5 INCHES OVER SOUTH CENTRAL
ARIZONA THROUGH SUNDAY...EVEN THOUGH MUCH OF THE MOISTURE FROM KEVIN
WILL HAVE ALREADY LIFTED OUT TO THE NORTHEAST BY SATURDAY EVENING.
AGAIN...DYNAMICS NOT ESPECIALLY IMPRESSIVE EITHER DAY BUT THERE WILL
LIKELY BE WEAK DISTURBANCES MOVING THROUGH THE SOUTHWEST FLOW FROM
TIME TO TIME...INCREASING THE THREAT FOR SHOWERS OR STORMS.
STREAMLINES REMAIN RATHER LAMINAR AND SOUTHWESTERLY...SIMILAR TO
WHAT IS SEEN TODAY. WE FEEL IT IS A BIT OPTIMISTIC TO REMOVE THE
THREAT FOR CONVECTION FROM THE FORECAST THIS WEEKEND...SO WE WILL
RAISE POPS SLIGHTLY AND KEEP SOUTH CENTRAL AZ UNDER AT LEAST A
SLIGHT CHANCE FOR AFTERNOON/EVENING STORMS BOTH SATURDAY AND SUNDAY.

CONVECTIVE POTENTIAL FOR EARLY NEXT WEEK MAY BE SOMEWHAT MORE MUTED
THAN RECENT DAYS AS DEEP LAYER WINDS VEER SOMEWHAT MORE WESTERLY AS
TROUGHING TRANSLATES INTO THE GREAT BASIN AND NRN ROCKIES.
STILL...BOUNDARY LAYER MOISTURE WILL BE DIFFICULT TO COMPLETELY
SCOUR OUT AND SOME MODEST INFUSION OF MIDLEVEL MOISTURE PEELING OFF
THE REMNANTS OF KEVIN MAY BE POSSIBLE. HOWEVER...THERE REMAINS SOME
DISCONNECT WITH THE MORE QUALITY TROPICAL MOISTURE TO THE
SOUTH...AND THE BEST WV TRANSPORT MAY BE DEFLECTED AROUND THE
FORECAST AREA. IN ADDITION...WITH MID LATITUDE TROUGHING LIFTING TO
THE NORTH AND HEIGHTS ALOFT RISING AHEAD OF THE REMNANT TROPICAL
SYSTEM...MODELS DEPICT SUBSTANTIAL MIDLEVEL WARMING AND INCREASED
CONVECTIVE INHIBITION. KEPT SOME MODEST NEAR CLIMATOLOGY POPS
THROUGH TUESDAY...HOWEVER MEASURABLE RAINFALL AT LOWER DESERT
ELEVATIONS MAY BE DIFFICULT TO COME BY.

SOME MINOR UNCERTAINTY STILL EXISTS FOR THE LATTER HALF OF NEXT WEEK
AS SUBTLE DIFFERENCES IN THE SUBTROPICAL RIDGE POSITION WILL DICTATE
IF AND HOW QUICKLY MOISTURE IS COMPLETELY SCOURED SOUTH OF THE
FORECAST AREA. MESOSCALE PROCESSES AND OUTFLOW FROM SONORAN MCS/S
MAY ALLOW FOR GULF SURGES AND BOUNDARY LAYER MOISTURE
ADVECTION...BUT DEFINITIVELY FORECASTING AND TIMING SUCH EVENTS
WOULD PROVE FRUITLESS AT THIS TIME. REGARDLESS...H5 HEIGHT RISES AOA
590DM WILL RESULT IN TEMPERATURES PEAKING BACK ABOVE NORMAL UNDER
GRADUALLY MORE COMPRESSIONAL SUBSIDENT FLOW.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
SCT-BKN MID CLOUDS AOA 10KFT CAN BE EXPECTED THIS THIS EVENING AND
OVERNIGHT...WITH SOME PARTIAL CLEARING OF DEBRIS CLOUDS BY SATURDAY
MORNING. UPPER LEVEL DISTURBANCE WILL KEEP POTENTIAL FOR ISOLATED TO
WIDELY SCATTERED THUNDERSTORMS UNTIL ABOUT 08Z TONIGHT. WITH THE
STORMS COMES THE THREAT FOR GUSTY OUTFLOWS AND LOCAL BLOWING DUST TO
IMPACT TERMINALS ALTHOUGH CONFIDENCE TOO LOW TO INTRODUCE WIND SHIFTS
OR REDUCTIONS IN VISIBILITY IN THE TAFS AT THIS TIME.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
SURFACE WINDS WILL CONTINUE TO FAVOR SOUTH AT KBLH...BECOMING
WESTERLY AT KIPL SOMETIME AFTER 03Z THIS EVENING. SKIES GENERALLY
CLEAR WITH A FEW MID-HIGH CLOUDS DURING PERIOD. ANTICIPATE STORM
ACTIVITY WILL BE ISOLATED AND CONFINED TO AREAS EAST OF THE LOWER
COLORADO RIVER VALLEY.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
STORM CHANCES WILL CONTINUE OVER SOUTH-CENTRAL ARIZONA BEFORE
TRENDING DOWN SIGNIFICANTLY WEDNESDAY. HUMIDITIES WILL ALSO BEGIN TO
TREND DOWN FROM WEST TO EAST ACROSS THE ENTIRE FORECAST AREA NEXT
WEEK...BEGINNING AS EARLY AS MONDAY. A GRADUAL WARMING TREND WILL
ENSUE DURING THE PERIOD CLIMBING TO SEVERAL DEGREES ABOVE NORMAL BY
NEXT THURSDAY.

&&

.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/MO
AVIATION...MEYERS
FIRE WEATHER...MEYERS



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