Flash Flood in Arizona, August 4, 2002

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
120 PM MST SUN AUG 4 2002

.SYNOPSIS...HIGH PRESSURE POSITIONED OVER THE CENTRAL PART OF THE
COUNTRY WILL EVENTUALLY SHIFT WESTWARD...AND STRENGTHEN OVER ARIZONA
BY THE END OF THE WEEK. THIS WILL RESULT IN A LITTLE WARMER
AFTERNOON TEMPERATURES WEDNESDAY INTO THE WEEKEND. UNTIL THEN...A
COUPLE OF WEATHER DISTURBANCES WILL IMPACT SOUTHEAST ARIZONA THROUGH
TUESDAY. THESE DISTURBANCES WILL CONTINUE TO BRING CONSIDERABLE
CLOUDINESS AND PERIODS OF RAIN WITH EMBEDDED THUNDERSTORMS. LOCALLY
HEAVY RAINFALL WILL BE A CONCERN...ESPECIALLY THIS EVENING AND
MONDAY.

.DISCUSSION...HEAVY DOWNPOURS WITH LOCAL RUNOFF PROBLEMS WILL BE THE
MAIN CONCERN THIS EVENING AND AGAIN MONDAY. A DISTURBANCE
APPROACHING THE BOOTHEEL OF NEW MEXICO WAS PROVIDING ENOUGH UPPER
LEVEL SUPPORT FOR THUNDERSTORMS ALREADY THIS AFTERNOON. LATEST ETA
MODEL SHOWED AN INCREASE IN THE DIFFLUENT FLOW ALOFT OVER MOST OF
THE EASTERN ONE-HALF OF ARIZONA THIS EVENING. THIS UPPER LEVEL
SUPPORT COMBINED WITH DIFFERENTIAL HEATING ALONG THE WESTERN AND
EASTERN EDGES OF THE CLOUD COVER WILL RESULT IN MORE THUNDERSTORMS
YET THIS AFTERNOON AND EARLY THIS EVENING. HAVE THOUGHT ABOUT
POSTING A FLASH FLOOD WATCH FOR LATER THIS AFTERNOON AND
EVENING...BUT NOT TOO SURE ABOUT WHERE TO PLACE IT SINCE MOST OF
SOUTHEASTERN ARIZONA COULD SEE LOCALLY HEAVY DOWNPOURS. HOWEVER...
BASED ON SATELLITE AND RADAR BOTH SANTA CRUZ AND COCHISE COUNTIES
WILL NEED TO BE WATCHED CLOSELY. OTHERWISE...MAY HAVE A SIMILAR
REPEAT OF YESTERDAY WITH SCATTERED SHOWERS AND THUNDERSTORMS
SWITCHING OVER TO MORE STRATIFORM TYPE RAINFALL THIS EVENING. THE
NEXT DISTURBANCE WAS JUST SOUTH OF BRO TEXAS THIS AFTERNOON. THIS
FEATURE IS FORECAST BY THE ETA MODEL TO TRACK NORTHWEST TONIGHT AND
START IMPACTING SOUTHEAST ARIZONA BY MONDAY AFTERNOON. CURRENT
THINKING IS THAT CONSIDERABLE CLOUDINESS WILL REMAIN OVER OUR CWA
THROUGH TUESDAY NIGHT WITH WELL ABOVE CLIMO POPS. THIS WOULD LEAD TO
COOLER THAN NORMAL AFTERNOON HIGH TEMPERATURES ACROSS THE AREA.
LATEST MEDIUM RANGE MODELS WERE NOW INDICATING THAT THE HIGH
CENTERED OVER THE CENTRAL UNITED STATES WILL FLATTEN AND SHIFT
WESTWARD OVER ARIZONA BY THE END OF THE WEEK. THIS SOLUTION IS
SOMEWHAT OF A CHANGE FROM PREVIOUS RUNS...SO FOR NOW WILL NOT MAKE
MAJOR ADJUSTMENTS TO THE EXTENDED FORECAST WE CURRENTLY HAVE ON THE
STREET. HOWEVER...WILL SHOW A GENERAL INCREASE IN DAYTIME HIGHS
STARTING WEDNESDAY WITH UNCERTAINTY TERMS RATHER THE AREAL COVERAGE
WORDING FOR THE SHOWERS AND THUNDERSTORMS THURSDAY INTO SUNDAY. THIS
IS MAINLY BECAUSE THE FLOW AND MOISTURE IMPORT BECOME LESS FAVORABLE
FOR T-STORMS WHEN HIGH PRESSURE IS PARKED RIGHT OVER US.

.TWC...NONE.

AZZ019-029>035-050700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1130 AM MST SUN AUG 4 2002

.SYNOPSIS...AIRMASS OVER SOUTHERN ARIZONA REMAINS VERY MOIST...WITH
ENOUGH INSTABILITY FOR SCATTERED...SLOW MOVING THUNDERSTORMS WITH
HEAVY RAINFALL THIS AFTERNOON.

.DISCUSSION...ISOLATED THUNDERSTORMS HAVE ALREADY DEVELOPED OVER
PORTIONS OF FAR SOUTHEAST ARIZONA AND NORTHERN MEXICO LATE THIS
MORNING. AN INCREASE IN THUNDERSTORM COVERAGE IS EXPECTED DURING THE
AFTERNOON AND EVENING HOURS...AS A DISTURBANCE OVER THE BOOTHEEL OF
NEW MEXICO MOVES INTO SOUTHERN ARIZONA LATE THIS AFTERNOON AND
EVENING.

WINDS ARE LIGHT IN THE LOWER AND MID LEVELS OF THE ATMOSPHERE...SO
EXPECT STORMS TO BE SLOW MOVING WITH THE PRIMARY THREAT OF EXCESSIVE
RAINFALL THIS AFTERNOON/EVENING. SATELLITE IMAGERY INDICATES DEEPER
MOISTURE HAS PUSHED WEST ACROSS ALL OF SOUTHERN ARIZONA TODAY...WITH
THE MORNING TUCSON SOUNDING INDICATING PRECIPITABLE WATER VALUES OF
1.80 INCHES. THE ACCOMPANYING GRAPHICS WILL SHOW THE THREAT FOR MORE
THAN ONE INCH OF RAINFALL TO INCLUDE ALL OF SOUTHERN ARIZONA...WITH
THE GREATEST THREAT IN COCHISE...SANTA CRUZ...EASTERN PIMA...AND
GRAHAM COUNTIES. ALTHOUGH THERE IS A POSSIBILITY FOR ISOLATED SEVERE
STORMS...THE HEAVY RAINFALL THREAT WILL BE MUCH MORE SIGNIFICANT
TODAY.

STORM MOTION WILL BE SLOW...AROUND 5 TO 10 MPH...AND GENERALLY TO
THE NORTHWEST.

ZELL