Flash Flood in Arizona, July 21, 2002

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
1030 AM MST SUN JUL 21 2002

.SYNOPSIS...AN UPSWING IN THUNDERSTORMS WILL OCCUR THIS WEEK AS HIGH
PRESSURE STRENGTHENS OVER THE FOUR CORNERS. AN UPPER LEVEL SYSTEM
MOVING WEST FROM NEW MEXICO WILL ENHANCE THUNDERSTORM DEVELOPMENT THIS
AFTERNOON AND EVENING. CONSIDERABLE MOISTURE IS EXPECTED TO REMAIN
OVER SOUTHEAST ARIZONA THIS WEEK.

.DISCUSSION...VISIBLE SATELLITE IMAGERY INDICATES MOSTLY CLOUDY
SKIES ACROSS SE AZ AT THIS TIME. KEMX WSR-88D DETECTS ISOLATED 25-30
DBZ ECHOES OVER GREENLEE COUNTY MOVING WWD. DEWPOINTS WERE IN THE
LOWER-MID 60S F WHICH WERE NEARLY INDENTICAL TO THIS TIME SUN.
22/12Z TUS SOUNDING SHOWED AN INCREASE IN MOISTURE VERSUS 24 HOURS
AGO WITH PRECIP WATER VALUE NEAR 1.5 INCH. HOWEVER HAVE NOTED THAT
SOUNDING NOT QUITE AS UNSTABLE AS 24 HOURS AGO WITH LIFTED INDEX
NEAR MINUS 3 AND SURFACE-BASED CAPE NEAR 1560 J/KG. MID-LEVEL
STEERING FLOW HAS ALSO INCREASED WITH 30-35 KT H7-H5 FLOW DEPICTED.
SHOWERS/THUNDERSTORMS CONTINUE TO DEVELOP OVER THE SW NM MOUNTAINS
AND SATELLITE IMAGERY INDICATES SOME EROSION TO CLOUD COVER ACROSS
SRN NM/FAR SE AZ. 17Z MSAS SURFACE COMPUTED LI/S HAS MINUS 4-6
VALUES E OF TUS WITH MORE STABLE ENVIRONMENT ACROSS WRN LOCALES.
STILL BELIEVE THAT THUNDERSTORMS WILL DEVELOP DURING THE NEXT FEW
HOURS OVER THE WHITE MOUNTAINS/RIM AND SUBSEQUENTLY MOVE EWD AT AN
INCREASED RATE VERSUS SUN. THUS EXPECT SCATTERED SHOWERS/TSTMS THIS
AFTERNOON MAINLY ERN SECTIONS WHICH IS ALREADY IN REFLECTED IN GOING
FORECAST. WILL MAINTAIN INHERITED FLASH FLOOD WATCH FOR NOW WITH
EXPECTATION THAT SOME STORMS WILL PRODUCE LOCALLY HEAVY RAINS. NO
CHANGES TO CURRENT FORECAST.  BF

.TWC...FLASH FLOOD WATCH FOR BURN AREAS NOON-9PM ZONES 29/33/34/35.

AZZ019-029>035-220700-
SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1200 PM MST SUN JUL 21 2002

.SYNOPSIS...THE PROBABILITY FOR PRECIPITATION IN EXCESS OF ONE INCH
AND SEVERE THUNDERSTORM WILL BE NEAR CLIMATOLOGY SOUTH AND EAST OF A
LINE FROM SAN MIGUEL TO TUCSON TO SAFFORD...BUT BELOW CLIMATOLOGY
ELSEWHERE.

.DISCUSSION...THE FAVORED AREA FOR THUNDERSTORM ACTIVITY TODAY IS
ACROSS THE FAR SOUTHEAST CORNER OF ARIZONA...MAINLY SOUTH AND EAST
OF A LINE FROM SAN MIGUEL TO TUCSON TO SAFFORD. NOT ONLY DOES THE
GOES-10 PRECIPITABLE WATER IMAGERY INDICATE THIS IS WHERE THE
DEEPER LOW AND MID-LEVEL MOISTURE RESIDES...BUT A WEAK MID-LEVEL
DISTURBANCE IN NORTHWEST CHIHUAHUA WILL SLOWLY PUSH NORTHWEST INTO
THE FAR SOUTHEAST CORNER OF THE FORECAST AREA BY THIS AFTERNOON. THE
TUCSON MORNING UPPER AIR SOUNDING INDICATED A SLIGHTLY MORE UNSTABLE
ATMOSPHERE COMPARED TO YESTERDAY WITH A STABLE CAPPING INVERSION
ALOFT. ALTHOUGH STORMS WILL STRUGGLE TO DEVELOP EARLY THIS
AFTERNOON...A FEW STORMS WILL EVENTUALLY BREAK THROUGH THIS CAPPING
INVERSION BY LATE THIS AFTERNOON RESULTING IN STRONGER STORMS.

THE THREAT FOR PRECIPITATION IN EXCESS OF ONE INCH WILL BE MINIMIZED
TODAY DUE TO A MORE PRONOUNCED STORM MOTION THAN PREVIOUS DAYS.
STORMS WILL INITIALLY DEVELOP OVER THE HIGHER TERRAIN TO THE EAST OF
TUCSON...THEN PUSH SOUTHWEST AT 10 TO 15 MPH INTO THE VALLEYS.

ALTHOUGH MID-LEVELS WERE SLIGHTLY DRIER THAN YESTERDAY...THE LOW
LEVELS HAVE MOISTENED UP A BIT. THIS IS SEEN NOT ONLY IN THE GOES-10
PRECIPITABLE WATER IMAGERY BUT IS ALSO REFLECTED IN THE SURFACE DEW
POINTS IN THE LOWER 60S. THE OVERALL RESULT IS A SLIGHT INCREASE IN
MOISTURE...WHICH WILL DECREASE THE THREAT FOR STRONG THUNDERSTORM
OUTFLOWS. THEREFORE...THE THREAT OF A SEVERE THUNDERSTORM WILL BE
BELOW CLIMATOLOGY ACROSS ALL OF SOUTHEAST ARIZONA. ALTHOUGH THESE
OUTFLOWS WILL BE WEAKER THAN SEVERE LEVEL WINDS...GUSTS TO 40 MPH
WILL ACCOMPANY THE STRONGER STORMS ACROSS THE FAR SOUTHEAST CORNER
OF THE STATE.