Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 282128
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
228 PM MST TUE JUL 28 2015

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

&&

.SYNOPSIS...
A RETURN TO SOUTHEASTERLY FLOW WILL BRING A GRADUAL INCREASE IN
MOISTURE...ALLOWING SHOWER AND THUNDERSTORM CHANCES TO SLOWLY
INCREASE THROUGH THURSDAY. HIGH PRESSURE BUILDING OVER THE REGION
WILL THEN REDUCE RAIN CHANCES SOMEWHAT INTO THE UPCOMING
WEEKEND...BUT AT LEAST SLIGHT CHANCES WILL REMAIN OVER SOUTH-CENTRAL
ARIZONA. TEMPERATURES WILL REMAIN NEAR NORMALS OVERALL WITH A SLIGHT
DIP BELOW NORMAL FOR WEDNESDAY AND THURSDAY DUE TO WIDESPREAD CLOUD
COVERAGE.

&&

.DISCUSSION...
UNDER SOUTHEASTERLY FLOW ALOFT...MOISTURE CONTINUES TO SPREAD INTO
SOUTHEAST AND SOUTH-CENTRAL ARIZONA WITH SATELLITE ESTIMATED PWATS
BETWEEN 1.25 AND 1.50 INCHES. QUITE A BIT OF DRY AIR REMAINS BELOW
650MB WITH SURFACE DEW POINTS EARLY THIS AFTERNOON STILL HOVERING IN
THE MIDDLE 50S IN MOST LOCATIONS. SHOULD EXPECT SURFACE DEW POINTS TO
LOWER THROUGH THIS AFTERNOON DUE TO MIXING WITH VALUES DIPPING TO
BETWEEN 50-55. AM SEEING SOME SHOWERS AND THUNDERSTORMS FORMING OVER
HIGHER TERRAIN AREAS OF SOUTHEAST ARIZONA AND EXPECT THIS ACTIVITY TO
INCREASE IN COVERAGE...BUT STAY OVER HIGHER TERRAIN AT LEAST THROUGH
EARLY EVENING. CURRENT STEERING FLOW IS VERY LIGHT AND OUT OF THE
SOUTH...SO MOST STORMS TODAY WILL REMAIN FAIRLY STATIONARY. THE
BIGGEST CONCERN THROUGH THE REST OF TODAY WILL BE THE POTENTIAL FOR
SOME STORM OUTFLOWS AND BLOWING DUST ACROSS SOUTHERN MARICOPA AND
NORTHERN PINAL COUNTIES.

ATTENTION AFTER THIS EVENING THEN TURNS TOWARD AN INVERTED TROUGH
BOTH THE GFS AND EUROPEAN HAVE BEEN ADVERTISING OVER THE PAST COUPLE
MODEL RUNS. AS THE INVERTED TROUGH MOVES INTO SOUTHERN ARIZONA BY
12Z WEDNESDAY...THE BULK OF THE DEEP MOISTURE WILL BE ACCOMPANYING
THE TROUGH. HI-RES MODELS...ESPECIALLY THE HRRR...ARE CURRENTLY
SHOWING SOME LIGHT CONVECTIVE ACTIVITY MOVING INTO SOUTH-CENTRAL
ARIZONA LATE TONIGHT. HAVE SPREAD SLIGHT CHANCE POPS FURTHER TO THE
WEST AND NORTH FOR THIS TIME PERIOD...BUT THINK ANY RAIN ACTIVITY
WILL BE ON THE LIGHT SIDE.

BOTH WEDNESDAY AND THURSDAY STILL LOOK LIKE THE BEST POTENTIAL FOR
SHOWERS AND THUNDERSTORMS...BUT CONFIDENCE IN HOW WIDESPREAD RAINFALL
WILL BE IS STILL ON THE LOW SIDE. DURING THE DAY WEDNESDAY...SHOWERS
AND THUNDERSTORMS WILL LIKELY BE FOCUSED NEAR THE INVERTED TROUGH
THAT MOVES THROUGH SOUTHERN ARIZONA DURING THE DAY WEDNESDAY AND INTO
SOUTHEAST CALIFORNIA WEDNESDAY EVENING INTO WEDNESDAY NIGHT. TYPICAL
HIGH TERRAIN MONSOON ACTIVITY MAY BE SOMEWHAT LIMITED DUE TO THE
POTENTIAL FOR EXTENSIVE CLOUDINESS...BUT WITH EXPECTED CAPE VALUES
NEAR 500 J/KG AND SOME BREAKS IN THE CLOUDS...WE SHOULD STILL SEE AT
LEAST ISOLATED TO SCATTERED THUNDERSTORMS WEDNESDAY AFTERNOON AND
EVENING. THREATS OF BLOWING DUST AND LOCALIZED FLOODING WILL BE
POSSIBLE DURING THIS EVENT. CONDITIONS THURSDAY WILL BE SIMILAR TO
WEDNESDAY LIKELY MINUS THE INVERTED TROUGH. INSTABILITY WILL BE
SOMEWHAT LIMITED DUE TO CLOUD COVER AND WARMER MID-LEVELS...BUT
MOISTURE WILL BE PLENTIFUL WITH PWATS REMAINING NEAR 1.5-1.7 INCHES.
POPS FOR THURSDAY ARE MORE BROAD-BRUSHED DUE TO A LACK OF A TRIGGER
BUT FAVORING HIGHER TERRAIN AREAS. HIGH TEMPERATURES BOTH WEDNESDAY
AND THURSDAY WILL LIKELY FALL A BIT BELOW NORMAL DUE TO THE INCREASED
MOISTURE AND CLOUD COVER.

BEYOND FRIDAY...ALTHOUGH THERE WILL STILL BE ENOUGH MONSOON
MOISTURE TO KEEP UP SOME ACTIVITY THROUGH THE WEEKEND AND INTO EARLY
NEXT WEEK ...THE COMBINATION OF LESS AVAILABLE MOISTURE (PWATS ONLY
IN THE 1.3-1.4 INCH RANGE ACROSS SOUTH-CENTRAL AZ) AND WARMER MID-
LEVEL TEMPERATURES...AS THE MAIN THE UPPER HIGH POSITIONS ITSELF
PRETTY MUCH OVERHEAD DURING THIS ENTIRE PERIOD...WILL LIKELY LIMIT
THUNDERSTORM ACTIVITY...WITH PRETTY MUCH NEAR-CLIMO POPS LOADED INTO
THE GRIDS AT THIS TIME.

&&

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

LATEST GUIDANCE CONTINUES TO INDICATE THAT CONVECTION WILL GENERALLY
REMAIN MOST CONCENTRATED SOUTH OF THE PHOENIX AREA LATE THIS
AFTERNOON AND THIS EVENING. HOWEVER...THERE IS A HIGH PROBABILITY OF
AN OUTFLOW BOUNDARY REACHING KIWA/KPHX BETWEEN 04Z AND 07Z...LIKELY
BRINGING AN ABRUPT INCREASE IN WIND WITH PERHAPS SOME REDUCTION IN
VSBY DUE TO BLOWING DUST. LOOKING AHEAD...A HIGHER LIKELIHOOD OF
THUNDERSTORM RELATED IMPACTS IS ANTICIPATED WEDNESDAY.

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

WINDS WILL GENERALLY REMAIN LIGHT AND SOMEWHAT VARIABLE THROUGH
TONIGHT. AN OUTFLOW BOUNDARY MAY BRING AN INCREASE IN WIND AND
MOISTURE LATE TONIGHT...BRINGING HIGHER CHANCES OF THUNDERSTORMS
WEDNESDAY.

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...KUHLMAN/PERCHA
AVIATION...HIRSCH
FIRE WEATHER...HIRSCH


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