Flash Flood in Arizona, August 19, 2001

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
245 PM MST SUN AUG 19 2001

.SYNOPSIS...AN INCREASE IN MOISTURE IS EXPECTED THE NEXT FEW DAYS AS
HIGH PRESSURE ALLOWS A MORE SOUTHEAST WIND FLOW. THIS WILL INCREASE
THE THUNDERSTORM ACTIVITY ACROSS SOUTHEAST ARIZONA TONIGHT THROUGH
MONDAY. A TROUGH OFF THE WEST COAST WILL BRING SOME DRY AIR INTO
THE STATE WITH A DECREASE IN THE THUNDERSTORM ACTIVITY BY MIDWEEK.

.DISCUSSION...ISOLATED THUNDERSTORMS WERE DEVELOPING ACROSS THE AREA
THIS AFTERNOON...MAINLY IN THE MOUNTAINS. ALREADY HAD SOME REPORTS
OF HAIL WITH A STORM AROUND SONOITA. EXPECT THUNDERSTORMS TO BECOME
MORE NUMEROUS THIS EVENING...WITH SHOWERS AND ISOLATED STORMS
LINGERING OVERNIGHT. THE MAIN LARGE SCALE FEATURE HELPING TRIGGER
STORMS TODAY WAS A DISTURBANCE LIFTING NORTH FROM THE UPPER LOW OVER
BAJA. EVENTUALLY THE BAJA LOW MOVES INTO SOUTHERN CALIFORNIA TONIGHT
AND THEN ACROSS THE STATE MONDAY. ETA MODEL SHOWED SOME DECENT
DYNAMICS STILL OVER THE AREA AS THE UPPER LOW OPENS UP AND MOVES
THROUGH ARIZONA INTO LATE MONDAY. THUS...TOMORROW LOOKS FAVORABLE
FOR ANOTHER ACTIVE THUNDERSTORM DAY. THE ONLY LIMITING FACTOR WILL
BE THE AMOUNT OF DAYTIME HEATING WHICH IS EXPECTED TO BE CUT DOWN DUE
TO THE DEBRIS CLOUDINESS FROM TONIGHT STORMS. BY TUESDAY...ANOTHER
SHORTWAVE TROUGH IS FORECAST TO MOVE INTO NEVADA PROVIDING SOME
LIFTING OVER THE STATE TO SUPPORT SCATTERED THUNDERSTORMS. AVN AND
MRF CONTINUE TO DRY THE REGION OUT AS A MODERATE WESTERLY FLOW
DEVELOPS IN ASSOCIATION WITH A TROUGH ALONG THE WEST COAST. ALWAYS
HATE TO REMOVE THE MENTION OF STORMS TOTALLY FROM THE FORECAST THIS
TIME OF YEAR...BUT THE ODDS APPEAR TO BE TOO LOW AFTER THURSDAY.

.TWC...NONE.

AZZ019-029>035-200700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
12 NOON MST SUN AUG 19 2001

.SYNOPSIS...THE COMBINATION OF INCREASED SUNSHINE...A MOIST
ATMOSPHERE...AND DYNAMICS ASSOCIATED WITH AN UPPER LOW OFF THE BAJA
COAST WILL LEAD TO AN INCREASE IN THUNDERSTORM ACTIVITY LATER THIS
AFTERNOON AND THIS EVENING. A FEW STORMS MAY LINGER ON OVERNIGHT.

.DISCUSSION...A LOT MORE SUNSHINE THIS MORNING THAN THE PREVIOUS
MORNINGS WHICH WILL ALLOW THE LOWER PART OF THE ATMOSPHERE TO WARM
UP TO ITS POTENTIAL THIS AFTERNOON. AS OF 12 NOON...TEMPERATURES
WERE RUNNING 3 TO 6 DEGREES ABOVE SATURDAY READINGS. PRECIPITABLE
WATER VALUES ARE STILL A LITTLE ABOVE NORMAL AND RANGE FROM JUST
OVER AN INCH IN PARTS OF GRAHAM AND COCHISE COUNTIES TO OVER 1.50
WEST OF TUCSON.

UPPER AIR ANALYSIS AND SATELLITE IMAGERY THIS MORNING SHOWED AN
ELONGATED UPPER LOW EXTENDING FROM OFF THE BAJA COAST NORTHEAST INTO
SOUTHWEST ARIZONA. UPPER LEVEL HIGH PRESSURE EXTENDS FROM NORTHERN
ARIZONA SOUTHEAST INTO CHIHUAHUA MEXICO. SOUTHERN ARIZONA LIES IN
DIVERGENCE AREA BETWEEN THESE TWO FEATURES. MORNING MODELS SLOWLY
MOVE THE BAJA LOW SLOWLY TO THE NORTH-NORTHEAST AND INCREASE UPWARD
VERTICAL MOTION FIELDS TONIGHT.

WITH THE INCREASED SUNSHINE THIS MORNING...TOWERING CUMULUS CLOUDS
ARE ALREADY DEVELOPING OVER THE HIGHER TERRAIN. THUNDERSTORMS THAT
DEVELOP EARLY THIS AFTERNOON WILL WILL NOT MOVE OFF THEM UNTIL LATER
THIS AFTERNOON. STORMS THAT DEVELOP LATER THIS AFTERNOON AND THIS
EVENING WILL HAVE THE POTENTIAL FOR STRONG DOWNBURST WINDS...
ESPECIALLY FROM TUCSON WEST...AS AFTERNOON SOUNDINGS WILL LIKELY
HAVE AN INVERTED-V LOOK TO THEM. THUS WILL GO ABOVE CLIMATOLOGY FROM
TUCSON WEST. ALTHOUGH THE STORMS WILL BE MOVING AROUND 15 TO 20 MPH
WHICH WILL REDUCE THE RISK FOR FLASH FLOODING...SOME OF THE STORMS
MAY BE BIG ENOUGH TO PRODUCE HEAVY RAINFALL. WILL SLIGHTLY GO ABOVE
CLIMATOLOGY FROM TUCSON WEST.

STORM MOVEMENT WILL BE GENERALLY TO THE WEST AT 15 TO 20 MPH.

AZZ019-029>035-200700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK...CORRECTION
NATIONAL WEATHER SERVICE TUCSON AZ
1205 PM MST SUN AUG 19 2001

.SYNOPSIS...THE COMBINATION OF INCREASED SUNSHINE...A MOIST
ATMOSPHERE...AND DYNAMICS ASSOCIATED WITH AN UPPER LOW OFF THE BAJA
COAST WILL LEAD TO AN INCREASE IN THUNDERSTORM ACTIVITY LATER THIS
AFTERNOON AND THIS EVENING. A FEW STORMS MAY LINGER ON OVERNIGHT.

.DISCUSSION...A LOT MORE SUNSHINE THIS MORNING THAN THE PREVIOUS
MORNINGS WHICH WILL ALLOW THE LOWER PART OF THE ATMOSPHERE TO WARM
UP TO ITS POTENTIAL THIS AFTERNOON. AS OF 12 NOON...TEMPERATURES
WERE RUNNING 3 TO 6 DEGREES ABOVE SATURDAY READINGS. PRECIPITABLE
WATER VALUES ARE STILL A LITTLE ABOVE NORMAL AND RANGE FROM JUST
OVER AN INCH IN PARTS OF GRAHAM AND COCHISE COUNTIES TO OVER 1.50
WEST OF TUCSON.

UPPER AIR ANALYSIS AND SATELLITE IMAGERY THIS MORNING SHOWED AN
ELONGATED UPPER LOW EXTENDING FROM OFF THE BAJA COAST NORTHEAST INTO
SOUTHWEST ARIZONA. UPPER LEVEL HIGH PRESSURE EXTENDS FROM NORTHERN
ARIZONA SOUTHEAST INTO CHIHUAHUA MEXICO. SOUTHERN ARIZONA LIES IN
DIVERGENCE AREA BETWEEN THESE TWO FEATURES. MORNING MODELS SLOWLY
MOVE THE BAJA LOW SLOWLY TO THE NORTH-NORTHEAST AND INCREASE UPWARD
VERTICAL MOTION FIELDS TONIGHT.

WITH THE INCREASED SUNSHINE THIS MORNING...TOWERING CUMULUS CLOUDS
ARE ALREADY DEVELOPING OVER THE HIGHER TERRAIN. THUNDERSTORMS THAT
DEVELOP EARLY THIS AFTERNOON WILL NOT MOVE OFF THE HIGHER TERRAIN
UNTIL LATER THIS AFTERNOON. STORMS THAT DEVELOP LATER THIS AFTERNOON
AND THIS EVENING WILL HAVE THE POTENTIAL FOR STRONG DOWNBURST
WINDS...ESPECIALLY FROM TUCSON WEST...AS AFTERNOON SOUNDINGS WILL
LIKELY HAVE AN INVERTED-V LOOK TO THEM. THUS WILL GO ABOVE
CLIMATOLOGY FROM TUCSON WEST. ALTHOUGH THE STORMS WILL BE MOVING
AROUND 15 TO 20 MPH WHICH WILL REDUCE THE RISK FOR FLASH
FLOODING...SOME OF THE STORMS MAY BE BIG ENOUGH TO PRODUCE HEAVY
RAINFALL. WILL SLIGHTLY GO ABOVE CLIMATOLOGY FROM TUCSON WEST.

STORM MOVEMENT WILL BE GENERALLY TO THE WEST AT 15 TO 20 MPH.