Flash Flood Warning 8, NWS Phoenix, AZ

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
250 PM MST WED JUL 28 1999

.SYNOPSIS...
A MOIST SOUTH TO SOUTHEAST FLOW WILL CONTINUE OVER THE DESERT
SOUTHWEST THROUGH THURSDAY. AN UPPER LEVEL DISTURBANCE WILL APPROACH
THE FORECAST AREA AND INCREASE THE CHANCE FOR SHOWERS AND
THUNDERSTORMS TONIGHT THROUGH MIDDAY THURSDAY. LOCALLY HEAVY RAINFALL
CAN BE EXPECTED WITH THE MORE INTENSE STORMS. OTHERWISE...EXPECT
VARIABLY CLOUDY SKIES WITH HUMID CONDITIONS TO PERSIST RIGHT ON
THROUGH THE UPCOMING WEEKEND...ALONG WITH A CHANCE FOR MAINLY
AFTERNOON THUNDERSTORMS OVER THE HIGHER TERRAIN AND NIGHTTIME STORMS
OVER THE DESERTS.

.DISCUSSION...
PROBLEM OF THE DAY IS OBVIOUS...POTENTIAL FOR HEAVY RAINFALL AND
LOCALIZED FLASH FLOODING OVER PORTIONS OF OUR CWA. PRECIPITABLE WATER
AMOUNTS STILL WELL ABOVE CLIMATOLOGY (GREATER THAN 1.75)...AND EVEN
WITH HIGH TEMPS THIS AFTERNOON HELD DOWN BY MORNING CLOUD COVER AND
SHOWERS...INSTABILITY FAR FROM NON-EXISTENT. TWO MID-UPPER LEVEL
DISTURBANCES AFFECTING CWA PROMISE TO MAKE THIS FORECAST QUITE
CHALLENGING AND LOADED WITH UNCERTAINTY. DISTURBANCE NUMBER 1 IS
CURRENTLY SUPPORTING DEEP CONVECTION OVER FAR SOUTHEAST CALIFORNIA...
WHILE DISTURBANCE NUMBER 2 (D2) MOVING TOWARD SOUTHEAST AZ IS
SUPPORTING CONVECTION AT AND SOUTH OF TUCSON. ATTM...STILL FEEL THAT
WIDESPREAD SHOWERS AND THUNDERSTORMS ARE A GOOD BET OVER SOUTH-
CENTRAL AZ TONIGHT THANKS TO D2 DYNAMICS. WILL HILITE POTENTIAL FOR
HEAVY RAINFALL SOUTH-CENTRAL AZ IN HWO. PER COORDINATION CALL WITH
TUCSON...HAVE OPTED NOT TO ISSUE FFA FOR AREA AT THIS TIME...AS
CONVECTION TO OUR SOUTH NOT OVERLY IMPRESSIVE. IF UPPER DISTURBANCE
DOES WHAT I EXPECT...SHOULD SEE MORNING SHOWERS OVER MUCH OF SW AND
S-CNTRL AZ THURSDAY...FOLLOWED BY PARTLY CLOUDY SKIES WITH ISOLATED
THUNDERSTORMS MAINLY OVER HIGHER TERRAIN THURSDAY AFTN/EVENING.
STORMS WILL CERTAINLY EXIST AND BE VIGOROUS OVER HIGHER TERRAIN GIVEN
GREATER CAPE DUE TO SLIGHTLY WARMER MAX TEMPS NEXT TWO DAYS. WILL GO
WITH AT LEAST MODERATELY WET MONSOON FORECAST IN EXTENDED AS UPPER
HIGH OVER FOUR CORNERS + MOISTURE RICH ATMOSPHERE = ACTIVE CONVECTIVE
AFTERNOONS AND NIGHTS. DG

AZZ020>028-CAZ030>033-291200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
333 PM MST (333 PM PDT) WED JUL 28 1999

...LOCALLY HEAVY RAINFALL POSSIBLE ESPECIALLY OVER SOUTH CENTRAL
ARIZONA TONIGHT...

THUNDERSTORMS ARE POSSIBLE OVER ALL OF THE FORECAST AREA LATE
THIS AFTERNOON AND TONIGHT. THE AIRMASS IS EXTEMELY MOIST...SO ANY
STORMS THAT FORM WILL BE CAPABLE OF PRODUCING LOCALLY HEAVY RAIN. AT
THIS TIME...THE BEST CHANCE FOR LOCALLY HEAVY RAINFALL WILL BE OVER
SOUTH CENTRAL ARIZONA TONIGHT.

THIS OUTLOOK WILL BE ISSUED ONLY ON DAYS WHEN SOME FORM OF HAZARDOUS
WEATHER IS EXPECTED SOMEWHERE OVER THE PHOENIX AREA OF WARNING
RESPONSIBILITY...WHICH INCLUDES SOUTH CENTRAL AND SOUTHWEST ARIZONA
AS WELL AS FAR SOUTHEAST CALIFORNIA.

FOR PURPOSES OF THIS OUTLOOK HAZARDOUS WEATHER REFERS TO ANY OF THE
FOLLOWING...LOCALLY HEAVY RAINFALL WHICH RESULTS IN FLOODING AND
RUNNING WASHES...SAND OR DUST STORM WHICH REDUCES VISIBILITY TO ONE
QUARTER MILE OR LESS...DAMAGING WINDS IN EXCESS OF 57 MPH...AND HAIL
AT LEAST THREE QUARTERS OF AN INCH IN DIAMETER.

WHEN HAZARDOUS WEATHER IS IMMINENT OR OCCURRING...THE PHOENIX
NATIONAL WEATHER SERVICE FORECAST OFFICE WILL PROVIDE IMPORTANT LIFE-
SAVING INFORMATION IN THE FORM OF WARNINGS...FOLLOW UP STATEMENTS...
AND SHORT TERM FORECASTS.

STORM SPOTTER ACTIVATION MAY BE NECESSARY LATER TODAY.

DG