Severe Thunderstorm Warning 84, NWS Flagstaff, AZ

NORTHERN ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
930 PM MST MON AUG 20 2001

.SYNOPSIS...AN AREA OF HIGH PRESSURE OVER THE SOUTHWEST WILL
CONTINUE TO MOVE EASTWARD TODAY. AS A RESULT...SOUTHERLY FLOW ALOFT
WILL DEVELOP AND BRING AN INCREASE IN MONSOONAL MOISTURE TO MUCH OF
THE STATE. A SERIES OF UPPER LEVEL DISTURBANCES EMBEDDED IN THE FLOW
WILL KEEP THE ATMOSPHERE UNSTABLE. LOOK FOR THUNDERSTORMS TO DEVELOP
ONCE AGAIN TODAY AND TO CONTINUE INTO TONIGHT. BY WEDNESDAY...A
WESTERLY FLOW ALOFT WILL BRING DRIER AND WARMER WEATHER TO THE STATE
AND WILL CONTINUE INTO THE WEEKEND.

.DISCUSSION...S/WV OVER NORTHWEST ARIZONA THIS MORNING WILL MOVE
EAST THROUGHOUT THE DAY. ALREADY A WELL DEFINED AREA OF CONVECTION
ASSOCIATED WITH THIS WAVE...AND THIS FEATURE WILL TRACK EASTWARD
WITH TIME AS WELL. DYNAMICS AND INCREASED SHEAR WITH THE WAVE WILL
LEAD TO WIDESPREAD DEVELOPMENT TODAY AS FAIRLY DEEP MOISTURE EXISTS
ACROSS THE REGION. WOULD NOT BE SURPRISED TO SEE A FEW SEVERE CELLS.
ANOTHER AREA FOR FOCUSED CONVECTION WILL BE OVER YAVAPAI COUNTY AS
THE OUTFLOW FROM LAST NIGHTS SYSTEM REMAINS STALLED ACROSS THE
SOUTHERN SECTIONS OF THE COUNTY. FINALLY...YET ANOTHER S/WV WILL
MOVE UP LATER IN THE DAY FROM THE NORTHERN GULF OF CALIFORNIA. THIS
WAVE MAY LEAD TO NOCTURNAL ACTIVITY...ESPECIALLY FROM FLAGSTAFF
EASTWARD. ALL THIS POINTS TO LOTS OF RAIN...AND A FLASH FLOOD WATCH
HAS ALREADY BEEN ISSUED.

A DEEPER AND LONGER-WAVE TROUGH TO AFFECT THE STATE ON TUESDAY.
WHILE THIS WILL LIKELY LEAD TO ANOTHER ROUND OF ORGANIZED
CONVECTION...THE DRYING BEHIND IT WILL BE PRONOUNCED. COULD BE
THE END OF MONSOONAL ACTIVITY FOR SEVERAL DAYS...STAY TUNED. FOR
NOW...THE ZONES HAVE ALL BEEN UPDATED FOR THE FLASH FLOOD WATCH
EARLIER THIS MORNING. ALL OTHER TRENDS LOOK GOOD...NO FURTHER
UPDATES NEEDED. PETERSON.

.FGZ...NONE.

AZZ004>018-037>040-201930-
HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
845 AM MST MON AUG 20 2001

...FLASH FLOOD WATCH FOR ALL OF NORTHERN ARIZONA UNTIL 1000 PM
MST TONIGHT...

...STRONG STORMS AND HEAVY RAINFALL EXPECTED OVER NORTHERN ARIZONA
TODAY...

HIGH PRESSURE MOVED TO THE EAST OF ARIZONA OVERNIGHT AND HAS ALLOWED
A VERY MOIST AND UNSTABLE SOUTHWESTERLY FLOW TO DEVELOP OVER
ARIZONA. IN ADDITION...A WEAK LOW PRESSURE DISTURBANCE WAS LOCATED
OVER EXTREME NORTHWESTERN ARIZONA THIS MORNING. THIS DISTURBANCE IS
EXPECTED TO MOVE TO THE EAST DURING THE DAY TODAY. THE COMBINATION
OF THE MOIST UNSTABLE FLOW AND THE INFLUENCE OF THE LOW PRESSURE
SYSTEM WILL RESULT IN NUMEROUS SHOWERS AND THUNDERSTORMS DEVELOPING
OVER NORTHERN ARIZONA BY MID-MORNING...AND CONTINUING INTO THE
EVENING HOURS.

THIS LOW HAS ALSO GENERATED A STRONG OUTFLOW BOUNDARY THAT MOVED
SOUTH OF THE MOGOLLON RIM DURING THE NIGHT. THIS BOUNDARY WILL ACT
AS A FOCUS FOR THE INITIATION OF THUNDERSTORMS OVER THE LOWER
TERRAIN OF YAVAPAI COUNTY THIS AFTERNOON.

WINDS ALOFT HAVE INCREASED SOME OVERNIGHT SO THAT THUNDERSTORMS THAT
DEVELOP HAVE A GREATER CHANCE OF ORGANIZING INTO LARGER CLUSTERS.
THESE STORMS WILL BE CAPABLE OF PRODUCING HEAVY RAINFALL OF UP TO 2
INCHES PER HOUR..AS WELL AS LARGE HAIL AND STRONG WINDS OF UP TO 50
MPH.