Severe Thunderstorm Warning 42, NWS Phoenix, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
220 PM MST WED AUG 28 2013

.SYNOPSIS...
AFTER A SHORT-LIVED REPRIEVE...STORM ACTIVITY WILL GET BACK INTO
FULL SWING STARTING TONIGHT AND LASTING INTO THE WEEKEND...AS A
COUPLE OF WEATHER DISTURBANCES...AND A VERY MOIST AIRMASS MOVES IN
FROM THE SOUTH. MUCH COOLER AND CLOUDY CONDITIONS ARE EXPECTED FOR
THURSDAY AND FRIDAY...WITH TEMPERATURES REMAINING BELOW NORMAL
THROUGH THE WEEKEND. A RETURN TO A MORE TYPICAL MONSOON PERIOD WITH
WARMER TEMPERATURES IS EXPECTED FROM SUNDAY INTO NEXT WEEK.

&&

.DISCUSSION...
ANOTHER ROUND OF THUNDERSTORMS HAS ALREADY BEGAN TO DEVELOP ACROSS
OUR CWA THIS AFTERNOON...WITH RADAR NOW SHOWING ISOLATED STORMS NOW
DEVELOPING ACROSS SOUTH-CENTRAL AND SOUTHWEST ARIZONA AS OF 1:30PM
THIS AFTERNOON. THIS ACTIVITY IS EXPECTED TO INCREASE SIGNIFICANTLY
THIS EVENING AND TONIGHT AS AN INVERTED TROF MOVES NORTHWARD INTO
SOUTHERN ARIZONA...WITH A MOISTURE-RICH AIRMASS (PWAT VALUES IN THE
1.75-2.00 INCH RANGE AND MIXING RADIOS AOA 12 G/KG) ASSOCIATED WITH
THIS TROF. LATEST NAM AND GFS OUTPUT SUGGESTS THAT...ALTHOUGH
WIDESPREAD WETTING RAINS WILL OCCUR FROM THIS EVENING ONWARD INTO
THURSDAY...THEY BOTH SHOW FAIRLY LIMITED INSTABILITY...WITH MLCAPE
VALUES MAINLY AT 500 J/KG OR LESS. THUS...ALTHOUGH SOME AREAS WILL
DEFINITELY SEE HEAVY RAIN AND LOCALIZED FLOODING...WIDESPREAD HEAVY
RAIN/FLASH FLOODING IS NOT EXPECTED AT THIS TIME. THE RAIN AND
WIDESPREAD THICK CLOUD COVER IS EXPECTED TO KEEP TEMPERATURES WELL
BELOW 100F AT MOST LOWER DESERT LOCATIONS ON THURSDAY...WITH SOME
AREAS LIKELY NOT GETTING OUT OF THE 80S.

FRIDAY MAY BE THE DAY WHEN WE SEE MORE WIDESPREAD HEAVY RAINS AND
STRONGER DOWNBURST WINDS. THE GFS...NAM...AND (TO A LESSER EXTENT)
THE ECMWF ARE ALL MOVING A SECOND DISTURBANCE NORTHWARD RIGHT INTO
SOUTH-CENTRAL ARIZONA...WITH GFS MLCAPE VALUES THAT DAY JUMPING
TO...OR ABOVE 1000 J/KG AND PWAT VALUES EXCEEDING 2.00 INCHES.
FORECAST SOUNDING ALSO INDICATE SOMEWHAT STRONGER WINDS
ALOFT/GREATER WIND SHEAR ON FRIDAY AS WELL. IN ADDITION...MOISTURE
FROM THE REMAINS OF TROPICAL STORM JULIETTE...WHICH HAS JUST
DEVELOPED OFF THE TIP OF BAJA WILL BE MOVING INTO THE REGION. IF
THIS SCENARIO VERIFIES...THEN WIDESPREAD HEAVY RAINS AND EVEN SEVERE
WX BECOMES A REAL POSSIBILITY ACROSS THE PHX AREA. A FLASH FLOOD
WATCH MAY HAVE TO BE ISSUED AS WELL IF FUTURE MODEL RUNS HANG ON TO
THIS IDEA.

CONSIDERABLE MOISTURE IS EXPECTED TO LINGER INTO SATURDAY AS
WELL...BUT IF THERE IS A LOT OF CONVECTIVE ACTIVITY ON FRIDAY...THE
WORKED-OVER ATMOSPHERE AND CONSIDERABLE DEBRIS CLOUDS COULD SERVE TO
REDUCE THUNDERSTORM ACTIVITY ON SATURDAY...WITH TEMPERATURES BEING
KEPT BELOW NORMAL FOR A 3RD DAY.

A SLOW DRYING TREND IS EXPECTED TO BEGIN ON SUNDAY...AND CONTINUE
INTO NEXT WEEK AS THE MAIN UPPER HIGH CENTER SHIFTS WESTWARD BACK
OVER THE DESERT SOUTHWEST...AND BEGINS TO CUT OFF THE MOISTURE FLOW
FROM THE SOUTH...WITH MORE OF A MID TO LOW-GRADE MONSOON EXPECTED
FROM SUNDAY INTO THE MIDDLE OF NEXT WEEK...AND POSSIBLY EVEN LESS
ACTIVITY FOR THE END OF NEXT WEEK AS WE MOVE FURTHER INTO
SEPTEMBER...WITH LESS CLOUD COVER AND WARMER TEMPERATURES ACROSS THE
LOWER DESERTS.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA AND KSDL...
WELL DEFINED WEATHER SYSTEM WILL BE APPROACHING FROM THE SOUTHEAST
LATER THIS AFTERNOON INTO THE DAY ON THURSDAY...FOR AN INCREASING
CLOUD AND WEATHER TREND. THUNDERSTORMS ARE POSSIBLE THIS EVENING BUT
CONFIDENCE A BIT TOO LOW TO MENTION IN THE TAFS ATTM. CONFIDENT WE
WILL SEE SHOWERS DEVELOPING AFTER 06Z AND CONTINUING INTO THE DAY
THURSDAY. MAY SEE AN EMBEDDED THUNDERSTORM LATE TONIGHT OR THURSDAY
BUT WILL STICK WITH VCSH FOR NOW DURING THE LATTER PORTION OF THE
TAF PERIOD. CIGS NEXT 24 HOURS SHOULD STAY AOA 10K FEET FOR THE MOST
PART BUT COULD LOWER TO 8K OR BELOW SHOULD A HEAVIER SHOWER OR TSTM
DEVELOP. WINDS TO FAVOR THE SOUTHEAST NEXT 24 HOURS BUT MAY BRIEFLY
SWING TO THE SOUTHWEST OR WEST BETWEEN 23Z AND 04Z OR SO.

SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH...M
ISOLATED AFTN/EVE THUNDERSTORMS POSSIBLE TODAY BUT BIGGER IMPACT
WILL BE WHEN A LARGE DISTURBANCE APPROACHES FROM THE SOUTHEAST LATER
TONIGHT BRINGS A SUBSTANTIAL INCREASE IN MOISTURE ALONG WITH A
GREATLY ELEVATED THREAT FOR SHOWERS AND EMBEDDED TSTMS. ATTM FEEL
THREAT FOR SHOWERS IS GREATER THAN STORMS THUS WILL GO WITH VCSH IN
THE TAFS FOR THE LATTER PORTION OF THE TAF PERIOD. CIGS WILL LOWER
TO AROUND 10K LATER TONIGHT...AND COULD GO LOWER SHOULD A HEAVIER
SHOWER OR THUNDERSTORM DEVELOP.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
TROPICAL MOISTURE LEFT OVER FROM FERNAND WILL GRADUALLY DIMINISH
SATURDAY THROUGH THE MIDDLE OF NEXT WEEK...AS MONSOON CONDITIONS
RETURN TO CLIMATIC NORMALS. BELOW SEASONAL NORMAL HIGH TEMPERATURES
SATURDAY WILL STEADILY CLIMB AND REACH TO NORMAL VALUES BY ABOUT
TUESDAY...AND ELEVATED HUMIDITIES SATURDAY WILL GRADUALL LOWER DAY
TO DAY...FINALLY FALLING INTO THE TEENS BY NEXT WEDNESDAY. WINDS
WILL GENERALLY FOLLOW NORMAL DIURNAL TENDENCIES WITH TYPICAL
AFTERNOON AND EARLY EVENING GUSTINESS...ESPECIALLY OVER FAVORED
HIGHER TERRAIN LOCATIONS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...PERCHA
AVIATION....CB
FIRE WEATHER...CB

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
422 AM MST WED AUG 28 2013

AZZ020>023-025>028-CAZ030>033-291300-
LOWER COLORADO RIVER VALLEY AZ-WEST CENTRAL DESERTS-
NORTHWEST MARICOPA COUNTY-GREATER PHOENIX AREA-
YUMA/MARTINEZ LAKE AND VICINITY-SOUTHWEST DESERTS-
SOUTHWEST MARICOPA COUNTY-NORTHWEST AND NORTH CENTRAL PINAL COUNTY-
JOSHUA TREE NATIONAL PARK-LOWER COLORADO RIVER VALLEY CA-
RIVERSIDE COUNTY/EASTERN DESERTS-IMPERIAL COUNTY-
422 AM MST WED AUG 28 2013 /422 AM PDT WED AUG 28 2013/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EXTREME SOUTHWEST
ARIZONA...EXTREME WEST-CENTRAL ARIZONA...SOUTH-CENTRAL
ARIZONA...SOUTHWEST ARIZONA...WEST-CENTRAL ARIZONA...EXTREME
SOUTHEAST CALIFORNIA AND SOUTHEAST CALIFORNIA.

.DAY ONE...TODAY AND TONIGHT.

ISOLATED THUNDERSTORMS ARE POSSIBLE LATE THIS AFTERNOON WITH
INCREASING CHANCES TONIGHT. THE PRIMARY HAZARDS THIS AFTERNOON ARE
BRIEF HEAVY DOWNPOURS...GUSTY WINDS...BLOWING DUST...AND DEADLY
LIGHTNING. AN INCREASING THREAT OF HEAVY RAINFALL AND LOCALIZED
FLOODING IS EXPECTED TONIGHT ALONG WITH A SMALL THREAT OF GUSTY
WINDS AND DEADLY LIGHTNING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

BETTER ORGANIZED AND MORE EXPANSIVE THUNDERSTORM CHANCES ARE
EXPECTED FOR THURSDAY THROUGH FRIDAY. THE PRIMARY WEATHER HAZARDS
WILL BE HEAVY RAINFALL AND ISOLATED AREAS OF FLOODING...ESPECIALLY
WASHES AND LOW LYING AREAS. ADDITIONAL THREATS INCLUDE...GUSTY WINDS
IN EXCESS OF 40 MPH AND DEADLY LIGHTNING. AREAS OF BLOWING DUST MAY
ALSO BE POSSIBLE WITH THUNDERSTORM OUTFLOWS. A SLIGHT CHANCE FOR
AFTERNOON AND EVENING THUNDERSTORMS WILL CONTINUE THROUGH THE WEEKEND
INTO EARLY NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

AZZ024-291300-
SOUTHERN GILA COUNTY/TONTO NATIONAL FOREST FOOTHILLS-
422 AM MST WED AUG 28 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST-CENTRAL ARIZONA.

.DAY ONE...TODAY AND TONIGHT.

ISOLATED TO SCATTERED THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON
AND EVENING. THE PRIMARY WEATHER HAZARD IS LOCALLY HEAVY RAIN AND
DEADLY LIGHTNING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

BETTER CHANCES FOR MORE EXPANSIVE THUNDERSTORM CHANCES ARE EXPECTED
FOR THURSDAY AND FRIDAY. THE PRIMARY WEATHER HAZARDS WILL BE GUSTY
WINDS IN EXCESS OF 40 MPH...DEADLY LIGHTNING...LOCALLY HEAVY RAIN
LEADING TO FLOODING OF WASHES AND LOW LYING AREAS. DAILY AFTERNOON
AND EVENING THUNDERSTORM CHANCES WILL CONTINUE THROUGH THE WEEKEND
INTO EARLY NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

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