Flash Flood Warning 41, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-122200-

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
930 AM MST FRI AUG 12 2005

SOUTHWEST AND SOUTH-CENTRAL ARIZONA...AND SOUTHEAST CALIFORNIA
FORECAST DISCUSSION

.SYNOPSIS...
LOW PRESSURE SYSTEMS OVER NORTHERN ARIZONA AND NORTHERN BAJA
CALIFORNIA...AND VERY HUMID TROPICAL AIR OVER OUR AREA WILL CONTINUE
AT LEAST THROUGH SATURDAY. THIS MEANS A CONTINUATION OF SOME
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS WITH LOCALLY VERY
HEAVY RAIN AND POSSIBLE FLASH FLOODING. HOWEVER...ANOTHER LOW
PRESSURE SYSTEM FROM THE NORTHWEST WILL DEVELOP OVER SOUTHERN
CALIFORNIA AND BRING SOMEWHAT DRIER AIR TO SOUTHEAST CALIFORNIA THIS
WEEKEND...SPREADING EAST ACROSS SOUTHWEST AND SOUTH-CENTRAL ARIZONA
BY THE MIDDLE OF NEXT WEEK WITH SOMEWHAT WARMER WEATHER.

&&

.DISCUSSION...
JUST WHEN WE THOUGHT WE COULD RELAX THIS MORNING AND SAVOR A GOOD
CUP OF COFFEE...ONE LOOK AT THE UPPER AIR DATA GAVE US THE HEE BEE
JEE BEES. LET US EXPLAIN.

MONSOON MOISTURE OVER THE FORECAST AREA HAS BEEN SLIGHTLY HIGHER
THAN NORMAL FOR A COUPLE OF WEEKS NOW. UP THIS THIS MORNING...WEVE
HAD TO CONTEND WITH LIGHT AND PERSISTENT UPPER LEVEL DEFORMATION
ZONES THAT HAD BEEN CONTINUALLY SHIFTING AROUND THE STATE...ENOUGH
TO ENABLE CONVECTION TO REACH GREAT HEIGHTS (55 TO 60 THSD FEET)
WITH SOME RESULTANT SEVERE WEATHER.

HOWEVER THE PATTERN WAS SHIFTING THIS MORNING TOWARD A TRANSITIONAL
EVENT...MEANING STRONGER WESTERLIES...MORE UPPER LEVEL WIND SHEAR...
...AND BOOKOO MOISTURE.

PLOTS THIS MORNING SHOWED AN UPPER LEVEL CUTOFF LOW OVER NORTHERN
AND CENTRAL BAJA CA (BEST SEEN IN THE VAPOR IMAGERY). AND WHILE YOUR
THERE...CHECK OUT THE LITTLE VORT MAX OVER THE CENTRAL GULF OF CA
(AT 15Z)...MOVING TOWARD THE SOUTHERN AZ BORDER.  BECAUSE OF THE
UPPER LEVEL CUTOFF LOW...AND A PASSING GREAT BASIN SHORTWAVE...
300/250 MB HEIGHT FALLS OVER AZ AND SOUTHERN CA ARE STRONGER THAN
NORMAL... N THE 40 TO 50 METER RANGE...SUGGESTING VERTICAL MOTION
/UPPER LEVEL COOLING.   HORIZONTAL STRETCHING/DEFORMATION MOTIONS
WERE ALSO SEEN OVER SOUTHWEST/SOUTH CENTRAL AZ IN THE NORTHEAST
QUADRANT OF THE UPPER LOW.

MOISTURE WISE...ITS WET. 850/700 MB DEWPOINTS ON THE PHOENIX AND
TUCSON SOUNDINGS WERE HIGHER THAN NORMAL (WITH PHOENIX NEAR
EXTREME). THE FLAGSTAFF SOUNDING WAS MUCH DRIER TODAY...INDICATING A
STEEP EAST TO WEST MONSOON MOISTURE BOUNDARY GRADIENT EXISTS BETWEEN
PHOENIX AND FLAGSTAFF. THIS MOISTURE GRADIENT IS SUGGESTIVE OF
BACKBUILDING STORMS...FROM THE CENTRAL MOUNTAINS TOWARD SOUTHERN
DESERTS TO AREAS LIKE WICKENBURG...CAVE CREEK...PHOENIX...AND
SURROUNDINGS AREAS.

THEREFORE GIVEN SOME UPPER LEVEL DYNAMICS ACROSS THE STATE TODAY...
ALONG WITH PLENTY OF SUNSHINE AND A TROPICAL LIKE AIRMASS...IT COULD
BE VERY CONVECTIVELY ACTIVE WITH A MAJOR THREAT OF FLASH FLOODING. A
FLASH FLOOD WATCH MAY HAVE TO BE ISSUED THIS AFTERNOON AFTER WE SEE
HOW THE CHARACTER OF THE STORMS DEVELOP.  WE WILL MAINTAIN A VIGIL
TODAY AND TAKE QUICK ACTION WHEN NECESSARY.

THE UPPER LEVEL CUTOFF LOW OVER OVER NORTHERN BAJA WILL APPROACH
SOUTHERN AZ SATURDAY...AND A STRONGER PACIFIC SHORTWAVE EXPECTED TO
MOVE INTO SOUTHERN CA SUNDAY AND MONDAY. THEREFORE THE FLOW IS
BECOMING MORE DYNAMICAL UNDER THESE TRANSITION EVENTS THIS WEEKEND.
DRIER AIR WILL LIKELY MOVE INTO SOUTHEAST CA OVER THE WEEKEND...
HOWEVER THE MOISTURE WILL BE POOLED AND CONVERGENT OVER ALL OF AZ.
THEREFORE OUR FLASH FLOOD AND SEVERE THUNDERSTORM CHANCES ARE
STATISTICALLY IMPROVED AS SEVERAL ATMOSPHERIC FEATURES COME TOGETHER
TODAY AND THIS WEEKEND.

CURRENT FORECASTS LOOK OK FOR NOW...HOWEVER WE MAY HAVE TO ISSUE
STATEMENTS LATER IN THE SHIFT AFTER WE SEE HOW THE CHARACTER OF THE
CONVECTION DEVELOPS.

&&

.AVIATION...
DISCUSSION FOR 18Z TAFS. ATMOSPHERE REMAINS VERY MOIST UNSTABLE THIS
MORNING. AS USUAL A BIT TRICKY TO TIME IF...OR WHEN STORMS WILL
EFFECT KPHX/KIWA. BEST GUESS AT THIS TIME IS LATE AFTERNOON THROUGH
THE EVENING HOURS...WHICH IS REPRESENTED IN THE TAFS.  THREATS WILL
BE LOW VISIBILITY...STRONG GUSTY WINDS...AND LOW CIGS. SOME DRIER
AIR HAS MOVED PUSHED INTO SERN CA AND WESTERN ARIZONA...SO EXPECTING
JUST SOME TOWERING CU OUT THERE. SEE TAFS
PHXTAFPHX...PHXTAFIWA...PHXTAFYUM...LAXTAFBLH...LAXTAFIPL FOR MORE
DETAILED INFORMATION.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.
CA...NONE.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

VASQUEZ

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
631 AM MST FRI AUG 12 2005

AZZ020>028-CAZ030>033-130100-
GREATER PHOENIX AREA-IMPERIAL COUNTY-JOSHUA TREE NATIONAL PARK/JTNP/-
LOWER COLORADO RIVER VALLEY AZ-LOWER COLORADO RIVER VALLEY CA-
NORTHWEST AND NORTH CENTRAL PINAL COUNTY-NORTHWEST MARICOPA COUNTY-
RIVERSIDE COUNTY/EASTERN DESERTS-
SOUTHERN GILA COUNTY/TONTO NATIONAL FOREST FOOTHILLS-
SOUTHWEST DESERTS-SOUTHWEST MARICOPA COUNTY-WEST CENTRAL DESERTS-
YUMA/MARTINEZ LAKE AND VICINITY-
631 AM MST (631 AM PDT) FRI AUG 12 2005

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

.DAY ONE...TODAY

VERY HUMID TROPICAL AIR STILL OVER THE AREA COMBINED WITH LOW
PRESSURE SYSTEMS OVER NORTHERN BAJA CALIFORNIA AND NORTHERN
ARIZONA WILL CAUSE SHOWERS AND THUNDERSTORMS TO DEVELOP AGAIN
THIS AFTERNOON AND THIS EVENING. SOME OF THESE STORMS WILL
PRODUCE LOCALLY VERY HEAVY RAIN WITH A POSSIBILITY OF FLASH
FLOODING ESPECIALLY IN UPSLOPE AREAS...AND THOSE AREAS BURNED BY
FIRES. STRONG GUSTY DAMAGING WINDS ARE ALSO POSSIBLE WITH THE
THUNDERSTORMS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

VERY HUMID TROPICAL AIR WILL STILL BE OVER SOUTHWEST AND SOUTH-
CENTRAL ARIZONA AT LEAST THROUGH SATURDAY. THIS WILL RESULT IN SOME
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS AGAIN. SOME OF THESE
STORMS WILL PRODUCE LOCALLY VERY HEAVY RAIN WITH A POSSIBILITY OF
FLASH FLOODING. STRONG GUSTY DAMAGING WINDS ARE ALSO POSSIBLE WITH
THE THUNDERSTORMS.

SOME DRIER AIR WILL MOVE INTO SOUTHEAST CALIFORNIA THIS WEEKEND AND
SPREAD EAST ACROSS SOUTHWEST AND SOUTH-CENTRAL ARIZONA BY THE
MIDDLE OF NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

ELLIS