Flash Flood in Arizona, September 8, 2002

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
210 PM MST SUN SEP 8 2002

.SYNOPSIS...THE FLOW BETWEEN A LOW PRESSURE SYSTEM ALONG THE WEST
COAST AND HIGH PRESSURE OVER TEXAS WILL KEEP A STEADY STREAM OF DEEP
MOISTURE THROUGH THE AREA INTO THE EARLY THIS WEEK. THIS WILL LEAD
TO MORE SHOWER AND THUNDERSTORM ACTIVITY WITH THE THREAT OF LOCALLY
HEAVY RAINFALL. THE LOW PRESSURE SYSTEM ALONG THE WEST COAST WILL
WEAKEN BY LATE THIS WEEK AS A RIDGE OF HIGH PRESSURE BUILDS INTO THE
REGION. AS A RESULT...EXPECT LESS THUNDERSTORM ACTIVITY IN ADDITION
TO WARMER DAYTIME TEMPERATURES BY THURSDAY OR FRIDAY.

.DISCUSSION...A LARGE AREA OF LIGHT TO MODERATE RAIN COVERED MUCH OF
CENTRAL AND WESTERN PORTIONS OF OUR CWA THIS AFTERNOON. IT LOOKS
LIKE THIS WILL CONTINUE TO BE THE CASE THIS EVENING AND
OVERNIGHT...WITH THE THREAT OF STRONG THUNDERSTORMS SHIFTING TO OUR
EASTERN ZONES. EXPECT STRATIFORM TYPE RAINFALL WITH EMBEDDED
THUNDERSTORMS ACROSS MOST THE AREA TONIGHT. MAIN THREAT WILL BE SOME
POSSIBLE FLOODING PROBLEMS...ESPECIALLY BY TOMORROW AFTERNOON IF
INDEED THE REMNANTS OF TROPICAL DEPRESSION ELEVEN-E MAKE IT UP INTO
THE REGION. OTHERWISE...THE WEATHER PATTERN IS NOT FORECAST TO
CHANGE MUCH THE NEXT TWO OR THREE DAYS AS AN UPPER LOW REMAINS
NEARLY STATIONARY OVER SOUTH TEXAS AND SOME SORT OF LOW PRESSURE
TROUGHINESS STAYS ALONG THE WEST COAST. THIS FLOW PATTERN WILL
PROVIDE A STEADY STREAM OF MOISTURE INTO THE STATE THROUGH EARLY
THIS WEEK MAKING THINGS INTERESTING T-STORM WISE. TO ENHANCE OUR
CHANCES OF RAINFALL AND INCREASE THE THREAT OF FLASH FLOODING...
REMNANTS OF TROPICAL DEPRESSION ELEVEN-E JUST WEST OF THE TIP OF
BAJA IS FORECAST TO TRACK NORTHWARD AND INTO THE REGION LATE TONIGHT
AND MONDAY. EVENTUALLY...HIGH PRESSURE IS PROGGED TO BUILD BACK INTO
THE REGION LEADING TO A GRADUAL DECREASE IN T-STORM ACTIVITY AND
WARMER DAYTIME HIGHS. LATEST MEDIUM RANGE MODELS...HOWEVER...HAVE
BACKED OFF ON BUILDING A SIGNIFICANT RIDGE OVER THE AREA.
THUS...WILL BACK OFF A BIT ON THE DRYING TREND IN THE EXTENDED
PERIOD BASED ON THIS.

.TWC...NONE.

AZZ019-029>035-090700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1140 AM MST SUN SEP 8 2002

.SYNOPSIS...CLEARING SKIES IN THE EASTERN ZONES WILL HELP IN SURFACE
HEATING...AND ULTIMATELY SEVERE THUNDERSTORM POTENTIAL.  ALSO
SIGNIFICANT MOISTURE BEING PULLED FROM FROM TROPICAL DEPRESSION
ELEVEN WILL INCREASE FLASH FLOODING POTENTIAL ACROSS SOUTHEAST
ARIZONA. THUS HIGHER THAN CLIMATOLOGICAL PROBABILITIES OF SEVERE
THUNDERSTORM EXTENDING FROM CENTRAL PIMA COUNTY EASTWARD THROUGH
MOST OF COCHISE AND GREENLEE COUNTIES. ALSO HIGHER THAN
CLIMATOLOGICAL PROBABILITIES GREATER THAN ONE INCH PRECIPITATION
ACROSS ALL OF SOUTHEAST ARIZONA.

.DISCUSSION...ANOTHER POTENTIAL DAY FOR SEVERE THUNDERSTORMS AND
FLASH FLOODING...AS THE UPPER LEVEL FEATURE REMAINS STALLED OVER
ARIZONA.  THERE HAS BEEN SOME CLEARING THIS MORNING OUT IN EASTERN
PORTIONS OF THE COUNTY WARNING AREA...WHICH WILL ALLOW FOR AMPLE
SURFACE HEATING. HOWEVER A THICK BAND OF CLOUDS SEEN IN IR IMAGERY
IS DRAPED OVER WESTERN PORTIONS OF THE COUNTY WARNING AREA.
ALTHOUGH THE SEVERE THUNDERSTORM ACTIVITY WILL BE LIMITED IN THIS
AREA...THE CLOUD COVER WILL HELP IN SUPPORTING SOME DIFFERENTIAL
HEATING AND INCREASE POTENTIAL FOR SEVERE THUNDERSTORMS FURTHER
EAST.  ALREADY THERE ARE SOME THUNDERSTORMS STARTING TO DEVELOP OVER
SOUTH CENTRAL ARIZONA...FROM CENTRAL PIMA COUNTY UP THROUGH GRAHAM
AND GREENLEE COUNTIES.  HIGHER THAN CLIMATOLOGICAL PROBABILITIES FOR
SEVERE THUNDERSTORM WILL EXTEND FROM CENTRAL PIMA COUNTY AND
NORTHWARD THROUGH PINAL COUNTY...THEN EXTENDING OVER A MAJORITY OF
COCHISE AND GRAHAM COUNTIES.  EXTREME EASTERN PORTIONS OF THESE
COUNTIES MAY NOT HAVE AS GREAT OF A RISK FOR SEVERE WEATHER ONLY DUE
TO THE DRYING IN THESE SECTIONS.  THE THREAT OF HAIL...WIND...AND
BRIEF HEAVY RAIN CAN BE EXPECTED FROM THE SEVERE THUNDERSTORMS.  THE
FLASH FLOODING POTENTIAL EXISTS OVER THE ENTIRE COUNTY WARNING
AREA.  SIGNIFICANT MOISTURE EXISTS ACROSS THE AREA WITH THE 12Z KTUS
SOUNDING INDICATING 1.72 INCHES PRECIPITABLE WATER.  GOES PWAT
IMAGERY ALSO INDICATES THESE HIGHER VALUES...WITH SOME DRYING
TOWARDS THE EASTERN ARIZONA WITH 1.36 INCHES.  WESTERN PORTIONS OF
THE COUNTY WARNING AREA MAY HAVE HIGHER PROBABILITIES...ONLY BECAUSE
IT IS CLOSER TO THE LARGE SCALE LIFT AND POSSIBLE TRAINING AFFECT.
ALSO MOISTURE WILL INCREASE THROUGH TONIGHT AS THE REMNANTS OF
TROPICAL DEPRESSION ELEVEN GETS PULLED NORTHWARD OVER THE AREA. THUS
PROBABILITIES OF PRECIPITATION GREATER THAN ONE INCH WILL BE GREATER
THAN CLIMATOLOGY IN ALL PORTIONS OF THE COUNTY WARNING AREA...WITH
SLIGHT INCREASE HIGHER ON WESTERN PORTIONS.