Severe Thunderstorm Warning 54, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-241045-

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
WEATHER SERVICE PHOENIX AZ
925 PM MST SAT AUG 23 2003

.SYNOPSIS...
A FLOW ALOFT FROM THE EAST THEN SOUTH IS EXPECTED AT LEAST THROUGH
THE FIRST HALF OF THE COMING WEEK AS HIGH PRESSURE ALOFT REMAINS
CENTERED NORTH AND EAST OF ARIZONA. THIS MEANS AN INCREASING CHANCE
OF SHOWERS AND THUNDERSTORMS WITH LOCALLY HEAVY RAIN AND GUSTY WINDS
THROUGH TUESDAY AND TUESDAY NIGHT. THE REMAINS OF HURRICANE IGNACIO
ARE EXPECTED TO MOVE NORTH INTO THE SOUTHWESTERN UNITED STATES BY
TUESDAY AND TUESDAY NIGHT WITH AN INCREASING CHANCE OF HEAVY RAIN.

.DISCUSSION...
FROM THE PLOT DATA...ONE CAN REALLY SEE THE SUBTLE BUT SIGNIFICANT
INFLUENCE OF THE TEXAS/NORTH CENTRAL MEXICO INVERTED TROF AS IT
APPROACHES FAR SOUTHEAST AZ. 300/250 MB NORTHEAST WINDS ON THE FAR
WESTERN FLANK OF THIS INVERTED TROF...SUDDENLY FAN OUT OVER CENTRAL
AZ INTO A DIFLUENT PATTERN THAT HELPED SUPPORT SCATTERED VERY
TALL (55 THSD FOOT) THUNDERSTORMS ACROSS PARTS OF THE STATE SATURDAY
AFTERNOON AND EVENING. OF COURSE A RATHER HUMID MONSOON AIRMASS
WITH PLENTY OF AVAILABLE CONVECTIVE POTENTIAL ENERGY WAS IN PLACE.
IN FACT 850/700 MB PLOT DATA SHOWED A PLUME OF VERY DEEP MONSOON
MOISTURE GENERALLY EXTENDING FROM THE BAJA PENINSULA NORTH
THROUGH THE LOWER COLORADO RIVER VALLEY...THEN INTO NORTHWEST AZ
AND UTAH.

FOR THE REMAINDER OF TONIGHT (SATURDAY NIGHT)... NUMEROUS OUTFLOW
BOUNDARIES...SOME COLLIDING...ALONG WITH WEAK UPPER SUPPORT WILL
ENABLE SHOWERS AND THUNDERSTORMS TO CONTINUE INTO EARLY SUNDAY
MORNING. THEREFORE FORECASTS FOR SOUTHWEST AND SOUTH CENTRAL ARIZONA
WILL REFLECT THIS.

FOR SUNDAY...THE INVERTED TROF SHIFTS TOWARD NORTHWEST MEXICO...
WITH DIFLUENT 300/250 WINDS ACROSS NORTHWEST MEXICO...AND
ACCELERATING SOUTH TO SOUTHWESTERLY WINDS ACROSS SOUTHEAST
CA/WESTERN AZ...FLOWING INTO A WESTERLY SHORTWAVE TROF PASSING
THROUGH THE GREAT BASIN. AS A RESULT...MODELS SHIFT THE UPPER
SUPPORT INTO FAR SOUTHEAST CA AND SOUTHWEST AZ FOR INCREASING
CONVECTION SUNDAY AFTERNOON AND EVENING. THIS AREA MAY BE THE HOT
SPOT SUNDAY.

THE MEXICO INVERTED TROF IS FORECAST TO DAMPEN OUT QUICKLY AS IT
MOVES INTO FAR SOUTHWEST AZ MONDAY AFTERNOON AND EVENING...
CONTINUING THE THREAT FOR THUNDERSTORMS ACROSS THE FORECAST AREA.

WILL MAKE SOME MINOR MODIFICATIONS TO THE REMAINDER OF TONIGHTS
FORECAST...KEEPING A CHANCE FOR SHOWERS/TSTMS GOING IN SOUTHWEST AND
SOUTH CENTRAL AZ THROUGH SUNDAY MORNING.

WE WILL NOT UPGRADE THE CHANCE FOR CONVECTION IN SOUTHEAST CA AND
SOUTHWEST AZ FOR SUNDAY AFTERNOON/EVENING...BUT WILL PASS ALONG OUR
THOUGHTS TO THE MID SHIFT FOR THE NEXT REGULARLY SCHEDULED FORECAST
UPDATE.  VASQUEZ

.PSR...NONE.

AZZ020>028-CAZ030>033-240200-

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
430 PM MST SAT AUG 23 2003

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

.DAY ONE...TODAY

THE AIRMASS OVER ARIZONA AND SOUTHEAST CALIFORNIA IS QUITE MOIST AND
UNSTABLE. THUS...SCATTERED SHOWERS AND THUNDERSTORMS ARE FORECAST TO
DEVELOP FROM THE HIGHER TERRAIN OF SOUTH-CENTRAL ARIZONA WEST OVER
THE SOUTH-CENTRAL ARIZONA DESERT AREAS INCLUDING THE GREATER PHOENIX
AREA THROUGH THIS EVENING. ISOLATED STORMS ARE POSSIBLE ELSEWHERE.
WHERE STORMS DO FORM...THERE IS A POTENTIAL...ESPECIALLY IN
SOUTH-CENTRAL ARIZONA INCLUDING THE GREATER PHOENIX AREA...FOR
STRONG GUSTY DAMAGING WINDS AND LOCALLY HEAVY RAIN WHICH COULD LEAD
TO FLOODING OF WASHES AND LOW SPOTS INCLUDING DIPS IN THE ROADS.
STAY AWAY FROM FLOODED ROADS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THERE IS AN INCREASING POTENTIAL FOR SHOWERS AND THUNDERSTORMS WITH
HEAVY RAIN AND FLOODING THROUGH TUESDAY AND TUESDAY EVENING...AS THE
REMAINS OF HURRICANE IGNACIO MOVE NORTH INTO THE SOUTHWESTERN UNITED
STATES. STAY AWAY FROM FLOODED AREAS INCLUDING FLOODED ROADWAYS AND
BE READY TO MOVE TO HIGHER GROUND IF A WARNING IS ISSUED DURING THE
UPCOMING WEEK.

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

ELLIS