Flash Flood in Arizona, August 13, 2001

NORTHERN ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
955 AM MST MON AUG 13 2001

.SYNOPSIS...A MOIST AND UNSTABLE AIR MASS WILL REMAIN OVER NORTHERN
ARIZONA TODAY WITH WIDESPREAD SHOWER AND THUNDERSTORM DEVELOPMENT.
SOME THUNDERSTORMS MAY PRODUCE LOCALLY HEAVY RAIN...WITH RAINFALL
AMOUNTS BETWEEN 2 TO 4 INCHES. MOST OF THE SOIL CONDITIONS IN
NORTHERN ARIZONA ARE MOIST...SO THAT HEAVY RAIN COULD PRODUCE RAPID
RUNOFF AND FLASH FLOODING IN NORMALLY DRY WASHES AND CREEK BEDS. DRIER
AIR WILL MOVE ACROSS NORTHERN ARIZONA STARING LATER TONIGHT AND
TUESDAY. THIS DRIER AIR WILL REDUCE THE THREAT OF HEAVY RAIN...BUT
THE CHANCE FOR SHOWERS AND THUNDERSTORMS WILL STILL PERSIST ALL WEEK.

.DISCUSSION...A VERY MOIST AIR MASS IS IN PLACE ACROSS NORTHERN
ARIZONA. KGCN HAD 2.69 IN OF +RA OVERNIGHT IN 2 TO 3 HOURS PERIOD
WITH FAIRLY WARM TOPS AND REFLECTIVITY BETWEEN 40 TO 50 DBZ. FGZ
SOUNDING SHOWING A 1.10 IN PRECIP H2O. ANY THUNDERSTORMS WILL
PRODUCE HEAVY RAIN AS PRECIPITABLE WATER VALUES REMAIN HIGH (1.0 TO
1.75 INCHES ACROSS THE COUNTY WARNING AREA). DIVERGENCE OVER THE
AREA THRU THE DAY AHEAD OF WEST COAST TROUGH. PSR SOUNDING SHOWING
DESCENT IN STABILITY WHICH WILL AFFECT EASTERN PARTS OF ARE ZONES TO
HELP SUPPORT DEEP CONVECTION IN THAT AREA LATER THIS AFTERNOON.
CLEARING IN SOME OF OUR EASTERN ZONES WILL HELP INCREASE INSTABILITY
AS WELL. WEAK INERTIAL INSTABILITY MAY AID MORE CONVECTION ACROSS
COCONINO PLATEAU AND UP INTO THE PAGE AREA. AS THE UPPER LEVEL
DIVERGENCE TRANSITIONS TO THE EAST LATER THIS AFTERNOON AND
EVENING...THEN EASTERN ZONES WILL HAVE A THREAT OF FLOODING.

DRIER AIR BEGINS TO WORK INTO WESTERN PARTS OF YAVAPAI COUNTY AND
THE WESTERN PART OF THE COCONINO AND KAIBAB PLATEAUS BY EARLY EVENING. THE
DRIER AIR IS MOVING EAST AT AROUND 10 MPH AND WILL MOVE INTO THE
EASTERN ZONES BY TUESDAY MORNING...SO THE HEAVY RAIN THREAT WILL BE
ENDING OVERNIGHT.

CLEMMONS
.FGZ...FLASH FLOOD WATCH UNTIL 1200 AM MST TUESDAY MORNING
       FOR THE ENTIRE FORECAST AREA.

AZZ004>018-037>040-131930-
HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
1015 AM MST MON AUG 13 2001

...FLASH FLOOD WATCH UNTIL 1200 AM MST TONIGHT FOR PORTIONS OF
NORTHERN ARIZONA...

...THUNDERSTORMS TODAY AND TONIGHT ACROSS NORTHERN ARIZONA WITH THE
POTENTIAL FOR HEAVY RAINFALL...

A MOIST AND UNSTABLE AIR MASS WILL REMAIN OVER NORTHERN ARIZONA TODAY
WITH WIDESPREAD SHOWER AND THUNDERSTORM DEVELOPMENT. SOME
THUNDERSTORMS MAY PRODUCE LOCALLY HEAVY RAIN...WITH RAINFALL AMOUNTS
BETWEEN 2 TO 4 INCHES. MOST AREAS HAVE MOIST SOIL CONDITIONS IN
NORTHERN ARIZONA...SO THAT HEAVY RAIN COULD PRODUCE RAPID
RUNOFF CREATING FLASH FLOODING IN NORMALLY DRY WASHES AND CREEK
BEDS...AS WELL AS MUD AND ROCK SLIDES IN AREAS OF STEEP TERRAIN.
THERE WILL ALSO BE A LOW THREAT THAT A FEW THUNDERSTORMS EAST
OF THE FLAGSTAFF AREA COULD PRODUCE LARGE HAIL.

DRIER AIR WILL MOVE ACROSS NORTHERN ARIZONA STARING LATER TONIGHT AND
TUESDAY...THUS REDUCING THE FLOOD POTENTIAL.

SPOTTER ACTIVATION IS REQUESTED FOR LOCALLY SEVERE WEATHER AND HEAVY RAIN
FALL TODAY. PEOPLE IN THE WATCH AREA ARE ADVISED TO CHECK
PREPAREDNESS REQUIREMENTS...KEEP INFORMED BY LISTENING TO NOAA
WEATHER RADIO OR YOUR FAVORITE MEDIA SOURCE...AND BE READY FOR QUICK
ACTION IF FLASH FLOODING IS OBSERVED OR A WARNING IS ISSUED BY THE
NATIONAL WEATHER SERVICE.