Flash Flood in Arizona, August 18, 2003

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
245 PM MST MON AUG 18 2003

.SYNOPSIS...INCREASING MOISTURE FROM THE SOUTH...COMBINED WITH A
IMPULSE LIFTING NORTH ACROSS THE REGION WILL BRING SCATTERED SHOWERS
AND THUNDERSTORMS TO MUCH OF SOUTHERN ARIZONA TONIGHT. HIGH PRESSURE
ALOFT OVER SOUTH CENTRAL CALIFORNIA WILL GRADUALLY SHIFT EAST INTO
THE FOUR CORNERS REGION BY THE MIDDLE OF THE WEEK. AS THE HIGH
SHIFTS EAST...FAVORABLE FLOW WILL CONTINUE ACROSS SOUTHERN ARIZONA
FOR THE CHANCE OF AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS
INTO THE UPCOMING WEEKEND.

.DISCUSSION...
SCATTERED SHOWERS AND THUNDERSTORMS...SOME WITH HEAVY RAIN...HAD
DEVELOPED TO THE SOUTH AND EAST OF THE TUCSON METRO AREA THIS
AFTERNOON. THESE STORMS DEVELOPED ALONG MOISTURE AXIS LIFTING
NORTH/NORTHWEST ACROSS SOUTHEAST ARIZONA. THIS OUTFLOW BOUNDARY
PUSHED NORTH FROM AN MCS WHICH DEVELOPED OVER NORTHERN SONORA LAST
NIGHT. IN ADDITION...A MOISTURE INCREASE FROM THE GULF OF CALIFORNIA
IS ALSO UNDERWAY AS REMNANTS OF ERIKA PUSH ACROSS THE MOUTH OF THE
GULF AND LARGE PRESSURE DIFFERENTIAL CAUSES MOISTURE TO SURGE
NORTHWARD. FURTHERMORE...SATELLITE IMAGERY INDICATES A WEAKNESS IN
THE FLOW OVER SOUTHERN ARIZONA...WITH AN IMPULSE LIFTING NORTHWARD
FROM NORTHERN MEXICO. ALL OF THIS IS ACTING IN CONJUNCTION TO
ENHANCE CURRENT ACTIVITY ACROSS THE REGION. THE 12Z KTUS SOUNDING
SHOWS THAT THE MAIN CONCERN TODAY WILL BE HEAVY RAIN WITH PW VALUES
AROUND 1.30 INCHES...ALTHOUGH ISOLATED SEVERE WIND GUSTS ARE NOT OUT
OF THE QUESTION THIS EVENING.

THE MODELS ARE IN GENERAL AGREEMENT OVER THE NEXT 48 HOURS...AND
INDICATE THAT THE CURRENT ACTIVITY COULD STRETCH INTO THE OVERNIGHT
HOURS TONIGHT. THEREFORE...HAVE GONE WITH SCATTERED POPS TONIGHT FOR
MUCH OF THE CWA. OTHERWISE...LOW LEVEL FLOW PATTERN ACROSS SOUTHERN
ARIZONA NOT EXPECTED TO CHANGE MUCH IN THE SHORT-TERM...ALTHOUGH AS
THE HIGH SHIFTS EAST INTO THE FOUR CORNERS REGION EXPECT THE MID AND
UPPER LEVEL FLOW TO SWITCH AROUND TO THE SOUTHEAST. OVERALL...THIS
IS A FAVORABLE FLOW PATTERN FOR THE CHANCE OF AFTERNOON AND EVENING
SHOWERS AND THUNDERSTORMS ACROSS SOUTHEAST ARIZONA INTO THE UPCOMING
WEEKEND. IN ADDITION...THE MODELS INDICATE THAT A COUPLE OF WEAK
DISTURBANCES ARE EXPECTED TO PUSH INTO THE REGION LATER THIS WEEK
WHICH COULD ENHANCE ACTIVITY. HOWEVER...WILL HAVE TO DEAL WITH THESE
FEATURES ON A DAILY BASIS TO DETERMINE ACTUAL IMPACT AS THEY MOVE
INTO THE REGION.  ZELL

.TWC...NONE.

AZZ019-029>035-191400-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1158 AM MST MON AUG 18 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST ARIZONA

.DAY ONE...TODAY

SYNOPSIS...THUNDERSTORMS ARE FORECAST TO DEVELOP THIS AFTERNOON AND
INTO EARLY EVENING. HOWEVER...THE AREAL EXTENT WILL BE LIMITED AS A
WEAKNESS ALOFT WILL RESULT IN A VERY WEAK STORM MOTION. THEREFORE...
THE PROBABILITY FOR PRECIPITATION IN EXCESS OF ONE INCH WILL BE NEAR
CLIMATOLOGY IN THE MOUNTAINS...WITH BELOW CLIMATOLOGICAL CHANCES IN
THE VALLEYS. THE THREAT OF DAMAGING THUNDERSTORM DOWNBURST WINDS
WILL REMAIN LOW. A DISTURBANCE MOVING INTO SOUTHERN ARIZONA LATE
THIS EVENING WILL BRING ALLOW SCATTERED SHOWERS AND THUNDERSTORMS TO
PERSIST OVERNIGHT.

DISCUSSION....THE MORNING UPPER AIR BALLOON SOUNDING FROM TUCSON
INDICATED THAT ATMOSPHERE HAS BECOME SLIGHTLY MORE UNSTABLE ALOFT
WITH A COUPLE OF DEGREES OF COOLING ABOVE 600 MB. IN ADDITION...THE
STEERING FLOW ALOFT REMAINS QUITE WEAK...WHICH WILL HINDER THE
CHANCES FOR STORMS THAT DO DEVELOP THIS AFTERNOON OVER THE HIGHER
TERRAIN FROM MOVING ACROSS VALLEY LOCATIONS...THUS REDUCING THE
OVERALL AREAL COVERAGE. ALTHOUGH THIS WILL REDUCE THE CHANCES FOR
HEAVY PRECIPITATION IN THE VALLEYS...IT WILL INCREASE THE
PROBABILITY FOR MOUNTAIN LOCATIONS TO RECEIVE PRECIPITATION IN
EXCESS OF ONE INCH.

LATER THIS EVENING...A MID LEVEL DISTURBANCE NEAR GUYMAS WILL PUSH
NORTHWARD INTO SOUTHERN ARIZONA. THIS DISTURBANCE...AIDED BY AN AREA
OF UPPER LEVEL DIFFLUENCE...WILL REGENERATE SCATTERED SHOWERS AND
THUNDERSTORMS BEGINNING LATE THIS EVENING AND PERSISTING OVERNIGHT.
ALTHOUGH THESE STORMS WILL NOT BE STRONG SINCE THEY ARE OUT OF PHASE
WITH THE MAXIMUM DIURNAL HEATING...THE POSSIBILITY FOR LOCALLY HEAVY
PRECIPITATION WILL EXIST AS SOUTHERN ARIZONA WILL ALSO BE
EXPERIENCING AN INCREASE IN LOW LEVEL MOISTURE FROM THE SOUTH.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

THUNDERSTORM ACTIVITY WILL BE INCREASING IN AREAL COVERAGE AROUND
MID WEEK AS HIGH PRESSURE BUILDS BACK OVER THE REGION AND BECOMES
CENTERED NEAR THE FOUR CORNERS.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.