Flash Flood in Arizona, July 29, 2001

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
215 PM MST SUN JUL 29 2001

SYNOPSIS...CLOUDS FROM A THUNDERSTORM COMPLEX IN MEXICO COVERED
NEARLY ALL OF SOUTHERN ARIZONA DURING THE DAY SUNDAY KEEPING
TEMPERATURES DOWN. HIGH TEMPERATURES WERE KEPT MOSTLY IN THE 80S DUE
THE CLOUDS AND THESE LOW TEMPERATURES ARE ALSO KEEPING A LID ON
THUNDERSTORM DEVELOPMENT. SOUTHERN ARIZONA WILL SEE SCATTERED
THUNDERSTORMS DEVELOP DURING THE EVENING HOURS TODAY AND CONTINUE
INTO THE NIGHT DUE TO THE HIGH MOISTURE CONTENT OF THE AIR MASS.
LOOK FOR A DECREASE IN THUNDERSTORMS MONDAY AND TUESDAY AND ON
WEDNESDAY ANOTHER THUNDERSTORM COMPLEX WILL LIKELY INCREASE THE
MOISTURE IN SOUTHERN ARIZONA ONCE AGAIN.

DISCUSSION...HARD TO GET MUCH CONVECTION WITH ALL THE CLOUDS
OVERHEAD. BREAKS IN COCHISE COUNTY IN THE EARLY AFTERNOON WILL
SPREAD NORTHWEST INTO THE EVENING BUT TEMPERATURES CANNOT CLIMB MUCH
TO GET THE CONVECTION REALLY GOING. AIR MASS REMAINS VERY MOIST SO
WILL NOT RULE OUT POSSIBILITY OF KEEPING THUNDERSTORMS GOING INTO
THE NIGHT. DO NOT SEE ANY SPECIFIC FEATURE TO FORCE THE CONVECTION
SO BELIEVE RAIN AMOUNTS WILL NOT BE HEAVY. TROUGH OVER THE WEST
COAST DIGS AND MOVES INLAND NEXT FEW DAYS. THIS WILL PREVENT
MOISTURE FROM SPREADING FAR TO THE WEST. ANOTHER EASTERLY WAVE COMES
OUR WAY TUESDAY NIGHT INTO WEDNESDAY. WILL LET CONVECTION TRAIL OFF
MONDAY AND TUESDAY THEN PICK UP AGAIN AS EASTERLY WAVE COMES IN.
WITH TROUGH ALONG WEST COAST THIS NEXT WAVE WILL TEAR APART AS IT
MOVES INTO SOUTHERN ARIZONA JUST LIKE TODAYS WAVE DID. BOTTOM LINE
IS THAT PLENTY OF MOISTURE IS HERE AND WILL REMAIN BUT WITH DAYTIME 5
CLOUDS IT IS HARD TO GET CONVECTION GOING TO TAKE ADVANTAGE OF THE
MOISTURE.

PRF

.TWC...NONE.

AZZ019-029>035-300700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1125 AM MST SUN JUL 29 2001

.SYNOPSIS...A SIGNIFICANT INCREASE IN MOISTURE ACROSS SOUTHERN
ARIZONA WILL LEAD TO AN ABOVE CLIMATOLOGICAL THREAT OF FLASH
FLOODING ACROSS THE REGION...ESPECIALLY IN THE MOUNTAINS SOUTHEAST
OF TUCSON. ALTHOUGH SURFACE HEATING TODAY IS LIMITED DUE TO AN
ABUNDANCE OF CLOUD COVER...AN UPPER LEVEL DISTURBANCE PUSHING
NORTHWEST THROUGH THE AREA WILL HELP INITIATE THUNDERSTORM ACTIVITY.

.DISCUSSION...GOES SOUNDER IMAGERY THIS MORNING SHOWS THAT ALL OF
SOUTHERN ARIZONA HAS EXPERIENCED A SIGNIFICANT SURGE OF MOISTURE
DURING THE PAST 24 HOURS. IN FACT...THE TUCSON UPPER AIR SOUNDING
THIS MORNING GIVES A PRECIPITABLE WATER VALUE OF 1.74 INCHES WHICH
IS THE HIGHEST VALUE SEEN THIS SUMMER. IN ADDITION...AN UPPER LEVEL
DISTURBANCE ACROSS NORTHERN SONORA WHICH EXTENDS INTO FAR SOUTHEAST
ARIZONA WILL CONTINUE TO PUSH NORTHWEST THROUGH THE REGION TODAY...
RESULTING IN WEAK AREA OF LIFT ALOFT. ALTHOUGH CONDITIONS SEEM RIGHT
FOR AN UPSWING IN ACTIVITY...SOMETIMES YOU CAN HAVE TOO MUCH OF A
GOOD THING.

THE PROBLEM IS THAT A THUNDERSTORM COMPLEX IN NORTHERN SONORA HAS
SPREAD A SIGNIFICANT AMOUNT OF MID LEVEL CLOUD COVER OVER ALL OF
SOUTHERN ARIZONA...THUS SIGNIFICANTLY REDUCING AMOUNT OF SURFACE
HEATING. HOWEVER...BREAKS IN THE CLOUD COVER THIS AFTERNOON SHOULD
ALLOW TEMPERATURES TO WARM UP ENOUGH FOR INITIATE CONVECTION WHICH
WILL LAST WELL INTO THE EVENING. THE THREAT OF SEVERE STORMS WILL BE
MINIMAL ACROSS THE COUNTY WARNING AREA.

THE MAIN THREAT TODAY WILL BE FLASH FLOODING. THE ATMOSPHERE IS SO
MOIST THAT IF ANY THUNDERSTORMS STAY PUT OVER A SPECIFIC AREA...A
SIGNIFICANT AMOUNT OF RAIN WILL FALL. FORTUNATELY...THE STEERING
FLOW FOR STORMS TODAY WILL BE AROUND 10 MPH WHICH SHOULD PUSH THEM
OFF OF THE MOUNTAINS. ADDITIONAL RAuINFALL FROM WARM-TOPPED
CONVECTION TONIGHT WILL CONTINUE THE THREAT OF FLASH FLOODING. THE
GREATEST RISK WILL BE OVER THE HIGHER TERRAIN SOUTHEAST OF TUCSON.

STORM MOVEMENT WILL BE TO THE NORTHWEST AT 10 MPH.