Flash Flooding and Damaging Wind in Arizona, July 31, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
135 PM MST TUE JUL 31 2007

.SYNOPSIS...COPIOUS MOISTURE AND WEAK DISTURBANCES ALOFT WILL KEEP
THE REGION IN AN ACTIVE MONSOON PATTERN THROUGH THE WEEK. EARLY NEXT
WEEK THE MEDIUM RANGE FORECAST MODELS INDICATE A DRYING TREND
RESULTING IN A LOWER CHANCE FOR THUNDERSTORMS.

&&

.DISCUSSION...THUNDERSTORM DEVELOPMENT HAS BEGUN TODAY SPARKED BY
COPIOUS MOISTURE AND WEAK DISTURBANCES WHICH HAVE PROVIDED THE
DYNAMICS NEEDED FOR THE EARLY START. HEAVY RAIN IS THE MAIN THREAT
LEADING TO SMALL STREAM AND FLASH FLOODING...ALTHOUGH THERE IS AN
OFF CHANCE OF A WET MICROBURST. SO FAR RAINFALL RATES ON THE
MOUNTAINS HAVE BEEN UP TO 2 INCHES PER HOUR AND UP TO 1 INCH PER
HOUR IN THE VALLEYS. THIS IS RIGHT IN LINE WITH HPC/S QPFERD.

THE TWO WEAK CIRCULATIONS...ONE LOCATED SOUTH OF DOUGLAS MOVING
NORTH AND THE OTHER JUST EAST OF HANNAGAN MEADOW WILL CONTINUE TO
PROVIDE DIFFLUENCE ALOFT FOR GREATER UPWARD MOTION. THE DRY PUNCH
ALOFT SOUTH OF DOUGLAS HAS BEGUN TO INITIATE CONVECTION AS IT MOVES
INTO THE DIFFLUENCE ZONE. ON WATER VAPOR IMAGERY ONE CAN SEE THE
LINE OF CONVECTION ALONG THIS ZONE. AS THESE FEATURES MOVE OVER
SOUTHERN ARIZONA TONIGHT THEY SHOULD PROVIDE ENOUGH DYNAMICS FOR
NOCTURNAL CONVECTION ALLOWING THUNDERSTORM DEVELOPMENT TO CONTINUE
THROUGH THE NIGHT.

FOR THE REMAINDER OF THE WEEK...MOISTURE REMAINS IN PLACE THROUGH
THE WEEKEND AS SOUTHEAST FLOW ALOFT CONTINUES OVER ARIZONA. THE HIGH
PRESSURE CENTER WILL BEGIN A JOURNEY EASTWARD ON SUNDAY AS A LOW
PRESSURE SYSTEM ENTERS THE PACIFIC NORTHWEST. THE MEDIUM RANGE
MODELS FORECAST THIS LOW TO BRING A DRIER SOUTHWEST FLOW TO ARIZONA
LATE ON MONDAY REDUCING THE AVAILABLE MOISTURE FOR THUNDERSTORM
DEVELOPMENT. ALTHOUGH THE STRENGTH OF THIS SYSTEM VARIES WITH THE
MODELS THEY ALL AGREE THAT A TROUGH WILL MOVE INTO THE WESTERN U.S.

&&

.AVIATION...ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL
CONTINUE THIS AFTERNOON AND EVENING. THERE WILL BE A SLIGHT CHANCE
FOR THUNDERSTORMS OVERNIGHT AS WELL. CEILINGS OF BKN050-070CB AGL
ARE EXPECTED. OTHERWISE...EXPECT SKIES MAINLY SCT-BKN120 BKN-OVC250.
HEAVY DOWNPOURS MAY AFFECT TAF SITES. AVIATION DISCUSSION NOT
UPDATED FOR TAF AND TWEB AMENDMENTS.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

EVANS
WEATHER.GOV/TUCSON

HAZARDOUS WEATHER OUTLOOK...CORRECTION
NATIONAL WEATHER SERVICE TUCSON AZ
925 AM MST TUE JUL 31 2007

AZZ019-029>035-010700-
NORTHERN GREENLEE COUNTY-SOUTHEAST PINAL COUNTY-
UPPER GILA RIVER VALLEY-WESTERN PIMA COUNTY-TOHONO OODHAM NATION-
TUCSON METRO/MARANA/GREEN VALLEY-SANTA CRUZ COUNTY-COCHISE COUNTY-
925 AM MST TUE JUL 31 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL
ARIZONA AND SOUTHEAST ARIZONA.

.DAY ONE...TODAY AND TONIGHT

SOUTHEAST ARIZONA IS EXPECTED TO REMAIN IN A RATHER ACTIVE MONSOON
PATTERN TODAY AND TONIGHT WITH SCATTERED THUNDERSTORMS THIS
AFTERNOON AND EVENING. GIVEN THE EXCESSIVE RAINFALL ACROSS MUCH OF
THE AREA THE PAST SEVERAL DAYS IT WILL NOT TAKE MUCH ADDITIONAL
RAINFALL TO CAUSE MORE FLASH FLOODING AND SMALL STREAM FLOODING. IN
ADDITION TO POSSIBLE FLOODING...SOME OF THE STRONGER THUNDERSTORMS
WILL PRODUCE GUSTY WINDS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

A CONTINUATION OF THE FAVORABLE MONSOON PATTERN IS EXPECTED INTO
THIS WEEKEND AS EASTERLY FLOW AROUND THE UPPER LEVEL HIGH TO OUR
NORTH CONTINUES. AS A RESULT...THE RISK FOR STRONG THUNDERSTORMS
WITH HEAVY RAIN AND FLASH FLOODING WILL CONTINUE.

.SPOTTER INFORMATION STATEMENT...

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