Severe Thunderstorm Warning 43, NWS Phoenix, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
435 PM MST WED AUG 29 2012

.UPDATE...TO AVIATION DISCUSSION...

.SYNOPSIS...
HIGH PRESSURE ACROSS THE SOUTHERN ROCKIES WILL WEAKEN...RESULTING IN
NEAR NORMAL TEMPERATURES THROUGH THE END OF THE WEEK. ABOVE NORMAL
TEMPERATURES WILL RETURN BY SUNDAY AND LAST INTO EARLY NEXT WEEK AS
STRONG HIGH PRESSURE BECOMES REESTABLISHED ACROSS THE DESERT
SOUTHWEST. RAIN CHANCES WILL GENERALLY REMAIN AT OR BELOW NORMAL FOR
ANY GIVEN LOCATION FOR THE NEXT WEEK...HOWEVER ISOLATED TO SCATTERED
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE
SPREADING FROM SOUTHEAST CALIFORNIA INTO ARIZONA HEADING INTO THE
WEEKEND.

&&

.DISCUSSION...
HIGH PRESSURE WAS BEGINNING TO RETREAT NORTHEAST FROM THE FOUR
CORNERS REGION...WITH THE RIDGE AXIS AND DRY AIR ALOFT BECOMING
PINCHED OFF. SEVERAL DISTINCT INVERTED TROUGHS/SHORTWAVES CAN BE
NOTED ON WV IMAGERY ACROSS THE GULF OF CALIFORNIA/BAJA PENINSULA
RIDING NORTHWEST TOWARDS THE WRN PERIPHERY OF THE SOUTHWEST CONUS
RIDGE AXIS. AN OVERNIGHT GULF SURGE HAD TRANSPORTED SHALLOW 70F+
DEWPOINTS THROUGHOUT SOUTHEAST CALIFORNIA AND LOWER COLORADO RIVER
VALLEY...THOUGH MECHANICAL MIXING OF DRY AIR ALOFT HAS PARTIALLY
AMELIORATED THE OPPRESSIVE CONDITIONS OVER THE WESTERN CWA FOR THE
TIME BEING. HOWEVER...WOULD EXPECT THICKER SFC MOISTURE TO RESUME
ITS NORTHWARD TREK TONIGHT.

THE DEEPER MOISTURE GRADIENT ACROSS THE REGION IS QUITE STEEP...WITH
13Z/12Z YUMA AND TUCSON SOUNDING DATA DEPICTING A SIGNIFICANT
DIFFERENCE IN THE H8-H7 MOISTURE PROFILE (ESSENTIALLY HALF THE WATER
CONTENT AT KTWC IN THIS COMPARABLE LAYER). ALTHOUGH MOISTURE HAS
BEEN CREEPING NORTH ACROSS THE INTERNATIONAL BORDER...EASTERLY FLOW
OVER SOUTHEAST/CENTRAL ARIZONA HAS REINFORCED THE DRIER ATMOSPHERIC
COLUMN WITH CONVECTIVE ELEMENTS STRUGGLING EVEN OVER THE PREFERRED
HIGHER TERRAIN LOCATIONS. ON THE OTHER HAND...FLOW OVER SOUTHEAST
CALIFORNIA/FAR WESTERN ARIZONA HAS BECOME MORE SOUTHERLY THROUGH THE
MID/UPPER LEVELS AS INSTABILITY HAS GROWN SIGNIFICANTLY (ALBEIT IN A
LARGELY CAPPED ENVIRONMENT). AS A RESULT...ISOLATED SHOWERS WERE
RAPIDLY BLOSSOMING OVER LA PAZ COUNTY...AND GIVEN THE PRESENCE OF
STRONGER DIFLUENCE APPROACHING FROM NWRN MEXICO...INCREASING
INSTABILITY...AND MULTIPLE BOUNDARIES/FORCING MECHANISMS...WOULD
EXPECT AT LEAST CONTINUED ISOLATED CONVECTIVE DEVELOPMENT INTO THE
EVENING HOURS THROUGHOUT THE SOUTHEAST CALIFORNIA AND THE LOWER
COLORADO RIVER VALLEY.

FORECAST FOR THURSDAY AND FRIDAY BECOMES HIGHLY UNCERTAIN AS
OPERATIONAL MODELS SEEMINGLY HAVE GROSSLY UNDERESTIMATED THE
MOISTURE PROFILES AND TRAJECTORIES/FLUXES AIMED TOWARDS SOUTHERN
CALIFORNIA. HIGHER RESOLUTION MODELS DO NOT APPEAR TO CORRECTLY
IDENTIFY THE LOCATION OF SMALL PERTURBATION CURRENTLY SUPPORTING
THUNDERSTORMS...EITHER SPURIOUSLY ERUPTING WIDESPREAD ORGANIZED
CONVECTION OR HAVING A COMPLETE DEARTH OF SIMULATED REFLECTIVITY
RETURNS. CONCEPTUALLY...WOULD EXPECT THURSDAY TO BE CHARACTERIZED AS
A TRANSITIONAL DAY WITH DEEPER MOISTURE BEGINNING TO SURGE
NORTHEAST...AWAITING BETTER ASCENT AND THERMODYNAMIC PROFILES. HAVE
RAMPED UP POPS EVER SO SLIGHTLY FEELING MODELS ARE UNDERESTIMATING
MOISTURE/UVV INTERACTION. EVEN SREF PRECIPITATION PROBABILITIES GROW
SUBSTANTIALLY JUST OUTSIDE THE FORECAST AREA BOUNDARY...HINTING THAT
OUTFLOWS WILL BECOME MORE PREVALENT AND POTENTIAL FOCUSING
MECHANISMS INTO LOWER ELEVATION DESERT LOCATIONS.

MODELS DO AGREE THAT INCREASING JET ENERGY AND SOUTHERLY FLOW
THROUGHOUT THE ATMOSPHERIC COLUMN WILL ENVELOP MUCH OF THE FORECAST
AREA BY FRIDAY...AND CONTINUE THROUGH SATURDAY AS HIGH PRESSURE
CONTINUES TO SLIDE NORTHEASTWARD. WITH SEVERAL WAVES APPARENTLY
READY TO PROPAGATE INTO THE RIGHT ENTRANCE REGION OF THE
JET...CONVECTION MAY BECOME SOMEWHAT MORE NUMEROUS FRIDAY AFTERNOON
AND EVENING...WITH SREF PROBABILITIES INCREASING ACROSS THE BOARD.
THE EXTENT OF FORCING AND FAVORABLE FLOW BECOME A LARGE QUESTION
MARK ON SATURDAY...NOT EVEN CONSIDERING THE POSSIBLE RAMIFICATIONS
OF ERSTWHILE THUNDERSTORM ACTIVITY ON ATMOSPHERIC OVERTURNING AND
CONTAMINATION.

GFS/ECMWF HAVE COME INTO GOOD AGREEMENT THAT THE RIDGE WILL
RETROGRADE BACK OVER THE DESERT SOUTHWEST...AND REMAIN THE
PREDOMINANT WEATHER FEATURE INTO AT LEAST EARLY NEXT WEEK. HAVE KEPT
THE TRENDS OF INCREASED FORECAST TEMPERATURES LATE IN THE WEEKEND
THROUGH NEXT WEEK...AND FUTURE SHIFTS MAY NEED TO EXTEND THIS TREND
TEMPORALLY LATER THROUGH THE FORECAST PERIOD. DRIER CONDITIONS WILL
ALSO YIELD GENERALLY BELOW NORMAL RAIN CHANCES...WITH CONVECTION
PRIMARILY CONFINED TO THE CLIMATOLOGICALLY FAVORED HIGHER TERRAIN
AREAS.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA...AND KSDL...
FEW-SCT CLOUD DECKS AOA 12KFT AND LIGHT WINDS PERSISTING ACROSS THE
AREA THROUGH THE EVENING INTO THURSDAY. THERE IS A SLIGHT CHANCE OF
CONVECTIVE DEVELOPMENT OVER THE HIGHER TERRAIN WELL NORTH AND EAST
OF THE TERMINALS THIS EVENING...BUT NOT EXPECTING ANY IMPACTS AT THE
TERMINALS.

SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH...
THUNDERSTORMS THAT DEVELOPED OVER LA PAZ COUNTY TO THE EAST OF
BLYTHE THIS AFTERNOON ARE NOW DISSIPATING...AND THEY ARE NOT
EXPECTED TO AFFECT THE WEATHER AT KBLH. FEW-SCT CLOUD DECKS AOA
12KFT WITH LIGHT SOUTH-SOUTHEASTERLY WINDS THIS EVENING/OVERNIGHT
INTO THURSDAY. ISOLATED THUNDERSTORM ARE POSSIBLE THROUGH THE TAF
PERIOD...BUT CONFIDENCE IS TOO LOW TO INCLUDE IN TAFS...AT THIS TIME.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
MOISTURE LEVELS REMAIN ELEVATED ACROSS THE REGION THROUGH THE
WEEKEND...AND WILL GRADUALLY TREND DOWN INTO THE MIDDLE OF NEXT
WEEK. THIS WILL KEEP A SLIGHT CHANCE OF AFTERNOON AND EVENING
THUNDERSTORMS IN THE FORECAST THROUGH WEDNESDAY...THE BEST CHANCES
WILL BE MAINLY CONFINED EAST OF THE LOWER COLORADO RIVER VALLEY AND
THE HIGHER TERRAIN AREAS OF SOUTH-CENTRAL ARIZONA. WINDS WILL BE
PREDOMINATELY SOUTH-SOUTHWESTERLY AND LOCALLY GUSTY ALONG THE LOWER
COLORADO RIVER VALLEY THIS WEEKEND...BECOMING LIGHT WEST-SOUTHWEST
AS CONDITIONS SLOWLY DRY OUT AND TEMPERATURES WARM UP BY MIDWEEK.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

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

DISCUSSION...HIRSCH/MO
AVIATION...PERCHA/MEYERS
FIRE WEATHER...MEYERS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
538 AM MST WED AUG 29 2012

AZZ020>028-CAZ030>033-301245-
LOWER COLORADO RIVER VALLEY AZ-WEST CENTRAL DESERTS-
NORTHWEST MARICOPA COUNTY-GREATER PHOENIX AREA-
SOUTHERN GILA COUNTY/TONTO NATIONAL FOREST FOOTHILLS-
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-
538 AM MST WED AUG 29 2012 /538 AM PDT WED AUG 29 2012/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST-CENTRAL
ARIZONA...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 SHOWERS AND THUNDERSTORMS WILL DEVELOP LATE THIS AFTERNOON
AND THIS EVENING. THE STRONGEST STORMS WILL BE CAPABLE OF PRODUCING
BRIEF HEAVY RAIN...WIND GUSTS UP TO 45 MPH AND OCCASIONAL LIGHTNING.

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

ISOLATED AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS WILL REMAIN
A THREAT THROUGH 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

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PHOENIX AZ
342 PM MST WED AUG 29 2012

AZZ020-021-292330-
LA PAZ AZ-
342 PM MST WED AUG 29 2012

...SIGNIFICANT WEATHER ADVISORY...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A

SIGNIFICANT WEATHER ADVISORY FOR...
  CENTRAL LA PAZ COUNTY IN WEST CENTRAL ARIZONA

UNTIL 430 PM MST

AT 334 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
STRONG THUNDERSTORM 11 MILES WEST OF BOUSE...MOVING NORTHWEST AT 10
MPH.

WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM...ALONG WITH
HEAVY RAIN AND FREQUENT DANGEROUS LIGHTNING. THIS WILL MAINLY AFFECT
PORTIONS OF HIGHWAY 95 AND HIGHWAY 72.

MOTORISTS ARE ADVISED TO AVOID THE ADVISORY AREA AND BE PREPARED TO
PULL OFF THE ROADWAY. IF YOU ARE IN THE ADVISORY AREA AND STORMS
APPROACH...TAKE SHELTER IN A STURDY BUILDING.

LAT...LON 3398 11435 3414 11417 3395 11401 3380 11419
TIME...MOT...LOC 2239Z 146DEG 10KT 3396 11419

AJ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
520 PM MST WED AUG 29 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0430 PM     TSTM WND DMG     13 ESE POSTON           33.87N 114.22W
08/29/2012                   LA PAZ             AZ   LAW ENFORCEMENT

            POWER POLLS DOWN BETWEEN MIKE POSTS 127 AND 129 ON U.S.
            HIGHWAY 95.

&&

EVENT NUMBER PSR1200295

MB