Severe Thunderstorm Warning 49, NWS Phoenix, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
920 AM MST SAT AUG 31 2013

.SYNOPSIS...
DEEP MONSOON MOISTURE WILL CONTINUE TO COVER THE REGION THROUGH THE
WEEKEND...RESULTING IN A CHANCE OF AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS AREA-WIDE. NEXT WEEK...MONSOON MOISTURE WILL DECREASE
SOMEWHAT...WITH WARMER AFTERNOONS EXPECTED. A SLIGHT CHANCE OF
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS ARE FORECAST...WITH
DAY TO DAY VARIABILITY IN STORM COVERAGE.

&&

.DISCUSSION...
VERY MOIST AND SOMEWHAT UNSTABLE AIRMASS REMAINS IN PLACE ACROSS
ARIZONA AND SOUTHEAST CA THIS MORNING...WITH PWAT VALUES IN EXCESS
OF 2 INCHES OVER MUCH OF THE AREA. SAN DIEGO SOUNDING CAME IN WITH
2.22 INCHES PWAT...AND 2.1 AT PHOENIX. IR IMAGERY SHOWED MOSTLY
CLOUDY SKIES ACROSS THE AREA...AND RADAR INDICATED POCKETS OF VIRGA
OR LIGHT SHOWERS HERE AND THERE ACROSS THE LOWER DESERT AT 8 AM. 8
AM SURFACE DEWPOINTS ACROSS THE LOWER DESERTS...FROM THE GREATER
PHOENIX AREA WESTWARD INTO SERN CA...WERE ALMOST UNIFORMLY 73
DEGREES. DESPITE THE COOL SURFACE TEMPS...AT 8 AM MOST OF THE LOWER
DESERTS WERE RUNNING IN THE LOW 80S...THERE IS SUFFICIENT LOW LEVEL
MOISTURE TO SUPPORT MLCAPE VALUES BETWEEN 500 AND 1500 J/KG OVER THE
LOWER DESERTS AS SHOWN IN THE LATEST SPC MESOANALYSIS GRAPHIC.

ONE THING THAT IS LACKING TODAY IS DYNAMICS...INVERTED TROF HAS
ROTATED AROUND THE HIGH AND IS NOW MOVING ACROSS PORTIONS OF NWRN AZ
AND SRN NEVADA. WIND FIELDS ALOFT ARE VERY WEAK AS SEEN IN THE
MORNING SOUNDINGS...AND STEERING WINDS THIS AFTERNOON ARE LIGHT
VARIABLE TO SOUTHWEST AT LESS THAN 10KT. UPPER LEVEL DEFORMATION
ZONE SHOWN IN THE STREAMLINES IS ALSO ACROSS NORTHERN ARIZONA...SO
BETTER FORCING IS NORTH OF OUR AREA. SO FOR TODAY WE ARE LOOKING AT
A VERY MOIST AND RATHER UNSTABLE ATMOSPHERE WITH WEAK DYNAMICS AND
FORCING. THIS ADDS UP TO A MODERATE GRADE MONSOON DAY...AND WE
RAISED POPS IN THE PHOENIX AREA TO ABOUT 15 PERCENT. SINGLE DIGIT
POPS THAT HAD BEEN IN PLACE SEEM TOO LOW GIVEN THE CURRENT
CONDITIONS. SHOULD THUNDERSTORMS DEVELOP TODAY...HEAVY RAIN WILL BE
THE MAIN THREAT...GIVEN PWAT OVER 2 INCHES AND THE SLOW MOVING
NATURE OF THE STORMS WILL ALLOW THEM TO DUMP COPIOUS RAINFALL
AMOUNTS BEFORE THEY DISSIPATE. CURRENT FORECASTS HAVE BEEN UPDATED
FOR CURRENT WEATHER TRENDS AND APPEAR TO BE IN GOOD SHAPE.

.PREVIOUS DISCUSSION...
TODAY AND SUNDAY...
CONSIDERABLE CONVECTIVE DEBRIS CLOUDS COVERED A LARGE PART OF
CENTRAL AND SOUTHWEST AZ AT 09Z SAT...ALONG WITH ISOLATED SPRINKLES.

EVENING WEATHER BALLOONS CONTINUED TO SHOW AN UNUSUALLY HIGH AMOUNT
OF MONSOON MOISTURE STREWN ACROSS MOST OF AZ AND SOUTHERN CA. THE
UPPER LEVEL DEFORMATION ZONE THAT STRETCHED FROM THE 4 CORNER TO
SOUTHWEST AZ...AND HELPED TO SUPPORT LARGE CONVECTIVE STORMS FRIDAY
AFTERNOON WILL SHIFT TOWARD NORTHWEST AZ THIS AFTERNOON. ACTUALLY
MOST OF SOUTHERN AZ IS ON THE BACKSIDE OF A WEAK INVERTED TROF
MOVING EAST TO WEST...AND THE ATMOSPHERE BECOMES QUASI-STABLE TODAY
AND SUNDAY. THEREFORE CONVECTIVE POTENTIAL IN SOUTHWEST AND SOUTH
CENTRAL AZ WILL NOT BE AS WIDESPREAD AS FRIDAY AFTERNOON...AND LOWER
PRECIP PROBABILITIES REFLECT THAT.

MONDAY AND TUESDAY...
THE CORE OR DEEPEST MONSOON MOISTURE SHIFTS WEST INTO SOUTHERN CA
AND COLORADO RIVER VALLEY MON AND TUE...WITH SOME DRYING IN EASTERN
AZ. THE BEST POTENTIAL FOR CONVECTIVE STORMS MON AND TUE WILL BE
OVER SOUTHEAST CA AND THE COLORADO RIVER...AS THAT AREA COMES UNDER
INCREASING ENTRANCE REGION JET DYNAMICS. IN OTHER WORDS...
ACCELERATING UPPER LEVEL SOUTHERLY WINDS OVER SOUTHEAST CA AND THE
COLORADO RIVER VALLEY DYNAMICALLY SUPPORT THE POTENTIAL FOR A CHANCE
OF CONVECTIVE STORMS. THE REMAINDER OF THE FORECAST AREA...SOUTH
CENTRAL AND PARTS OF SOUTHWEST AZ WILL ONLY HAVE A SLIGHT CHANCE OF
AFTERNOON AND EVENING THUNDERSTORMS.

WEDNESDAY THROUGH SATURDAY...
A SLIGHT CHANCE OF AFTERNOON SHOWERS AND THUNDERSTORMS WILL CONTINUE
OVER SOUTHWEST AND SOUTH CENTRAL AZ THIS PERIOD. WARMER AFTERNOONS
AND A MARGINALLY MOIST AIRMASS WILL PROVIDE THE SLIGHT THREAT OF
STORMS.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA AND KSDL...
LIGHT AND VARIABLE MORNING WINDS WILL ATTEMPT EASTERLY HEADINGS
BEFORE BECOMING MORE PROMINENTLY WEST BY MIDDAY/EARLY AFTERNOON
REMAINING ONLY 12KTS OR LESS. SCT TO BKN MID LEVEL CIGS WILL PERSIST
THROUGH THE DAY. UNCERTAINTY ABOUT STORMS THROUGH THE PHOENIX AREA
THIS EVENING REMAINS HIGH...AS SUCH LEFT MENTION OF ANY WX OUT OF
12Z TAFS.

SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH...
SOUTHERLY WINDS ALONG THE COLORADO RIVER...INCLUDING KBLH AND
WESTERLY WINDS FOR KIPL EXPECTED TO DEVELOP MIDDAY. UNTIL
THEN...WINDS WILL REMAIN LIGHT AND VARIABLE. CLOUD COVER IN THE FORM
OF SCT TO BKN SKIES WILL PERSIST AOA 10KFT THROUGH THE DAY. THERE IS
AN ISOLATED CHANCE OF AFTERNOON SHOWER/STORM DEVELOP ACROSS
SOUTHEAST CALIFORNIA LATER TODAY SO INCLUDED VCSH FOR THE AFTERNOON
AND EVENING PERIOD FOR BOTH KIPL AND KBLH.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
SLIGHTLY DRIER CONDITIONS ARE EXPECTED FOR THE COMING WEEK WITH
DECREASING STORM CHANCES AND HUMIDITIES EXPECTED. MINIMUM HUMIDITIES
WILL BE IN THE TEENS OVER THE LOWER DESERTS OF ARIZONA...REMAINING
IN THE 20-30 PERCENT RANGE OVER SOUTHEAST CALIFORNIA AND HIGHER
TERRAIN WITH GOOD OVERNIGHT RECOVERIES. TEMPERATURES DURING THIS
PERIOD WILL WARM TO NORMAL VALUES BEFORE ABOVE NORMAL VALUES APPEAR
DURING THE LATE PERIOD. STORM CHANCES WILL RETREAT TO THE
EVER-FAVORED HIGHER TERRAIN WITH LESSER CHANCES OF STORMS DOWN INTO
THE LOWER ELEVATIONS BY THE LATE WEEK. WINDS THROUGH THE MIDWEEK
PERIOD WILL BE SLIGHTLY ELEVATED AND MORE PERSIST FROM THE
SOUTHEAST...OTHERWISE FOLLOW TYPICAL DIURNAL TRENDS AND SPEEDS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

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

DISCUSSION...CB
PREVIOUS DISCUSSION...VASQUEZ
AVIATION...NOLTE
FIRE WEATHER...NOLTE

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
559 AM MST SAT AUG 31 2013

AZZ020-025-CAZ030>033-011300-
LOWER COLORADO RIVER VALLEY AZ-YUMA/MARTINEZ LAKE AND VICINITY-
JOSHUA TREE NATIONAL PARK-LOWER COLORADO RIVER VALLEY CA-
RIVERSIDE COUNTY/EASTERN DESERTS-IMPERIAL COUNTY-
559 AM MST SAT AUG 31 2013 /559 AM PDT SAT AUG 31 2013/

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

.DAY ONE...TODAY AND TONIGHT.

THERE IS A SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS AS
EXCESSIVE AMOUNTS OF MONSOON MOISTURE STILL COVER THE AREA. THE
GREATEST THUNDERSTORM THREAT IS THE POTENTIAL FOR HEAVY RAIN AND
LOCALIZED FLOODING...IF THUNDERSTORMS DEVELOP. OTHER HAZARDS INCLUDE
STRONG THUNDERSTORM WINDS AND DANGEROUS LIGHTNING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.

SUNDAY THROUGH WEDNESDAY...A SLIGHT CHANCE OF THUNDERSTORMS ARE
FORECAST. HOWEVER THERE ARE SOME INDICATIONS THAT A GREATER THREAT OF
THUNDERSTORMS COULD DEVELOP MONDAY AND TUESDAY AFTERNOONS. THUNDER-
STORM HAZARDS INCLUDING STRONG WINDS...HEAVY RAIN...AND DEADLY
LIGHTNING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED.

AZZ021>024-026>028-011300-
WEST CENTRAL DESERTS-NORTHWEST MARICOPA COUNTY-GREATER PHOENIX AREA-
SOUTHERN GILA COUNTY/TONTO NATIONAL FOREST FOOTHILLS-
SOUTHWEST DESERTS-SOUTHWEST MARICOPA COUNTY-
NORTHWEST AND NORTH CENTRAL PINAL COUNTY-
559 AM MST SAT AUG 31 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST-CENTRAL ARIZONA...SOUTH-
CENTRAL ARIZONA...SOUTHWEST ARIZONA AND WEST-CENTRAL ARIZONA.

.DAY ONE...TODAY AND TONIGHT.

THERE IS A SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS AS
EXCESSIVE AMOUNTS OF MONSOON MOISTURE STILL COVER THE AREA. THE
GREATEST THUNDERSTORM THREAT IS THE POTENTIAL FOR HEAVY RAIN AND
LOCALIZED FLOODING...IF THUNDERSTORMS DEVELOP. OTHER HAZARDS INCLUDE
STRONG THUNDERSTORM WINDS AND DANGEROUS LIGHTNING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.

A SLIGHT CHANCE OF THUNDERSTORMS ARE FORECAST. THUNDERSTORM HAZARDS
INCLUDE STRONG WINDS AND DEADLY LIGHTNING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED.

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX