Severe Thunderstorm Warning 86, NWS Flagstaff, AZ

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

.SYNOPSIS...SCATTERED EVENING SHOWERS AND THUNDERSTORMS WILL
DECREASE BY MIDNIGHT AS DRIER AIR MOVES INTO THE STATE. EXPECT
SCATTERED SHOWERS AND THUNDERSTORMS TO AGAIN DEVELOP BY TUESDAY
AFTERNOON...ALTHOUGH ACTIVITY WILL NOT BE AS WIDESPREAD AS TODAY.
DRIER AIR WILL CONTINUE TO MOVE INTO THE STATE THROUGH THE WEEK.
MOSTLY SUNNY SKIES AND WARMER TEMPERATURES ARE EXPECTED BY
WEDNESDAY...LASTING INTO THE COMING WEEKEND.

.DISCUSSION...NO REAL CHANGES FROM THE MORNING THINKING. WEAKENING
S/WV STILL MOVING EAST THROUGH NORTH-CENTRAL ARIZONA THIS AFTERNOON.
DECENT CONVECTION HAS BEEN BLOOMING ALL DAY AHEAD OF THIS WAVE IN
THE DEEPER MOISTURE AND DYNAMICS. SOME SUBSIDENCE AND COOLER
BOUNDARY LAYER AIR BEHIND THIS WAVE CAUSED CONVECTION TO DIE OFF
FROM FLG WESTWARD. HOWEVER...ENOUGH INSOLATION AND REMAINING
MOISTURE HAS CAUSED CONVECTION TO FINALLY BEGIN DEVELOPING OFF
TERRAIN IN THE WESTERN ZONES. THINK CONVECTION WILL LAST INTO THE
EVENING TO THE EAST...DYING OFF BY MIDNIGHT. CONVECTION TO THE WEST
WILL BE QUITE DIURNAL...LIKELY NOT MAKING IT MUCH PAST SUNSET. MOST
OF THE STORMS ARE MOVING RAPIDLY AND ARE NOT PUTTING DOWN TREMENDOUS
AMOUNTS OF RAIN...THE FFA FOR THE REGION WILL BE CANCELED WITH THE
AFTERNOON PACKAGE BARRING ANY MAJOR CHANGES. DRIER WESTERLY FLOW
WILL BEGIN TO WORK IN BEHIND THIS WAVE INTO TUESDAY. A LONGER-WAVE
TROUGH WILL MOVE THROUGH THE SAGGING WESTERLIES LATE IN THE
DAY...WITH ANOTHER ROUND OF DYNAMICS DUE OVER NORTHERN ARIZONA.
ENOUGH MOISTURE WILL REMAIN FOR SCATTERED AFTERNOON AND EARLY
EVENING ACTIVITY...ESPECIALLY OVER THE MOISTER EASTERN ZONES. THE
DRYING BEHIND THIS LAST WAVE ON TUESDAY WILL BE SIGNIFICANT...AND
ASIDE FROM ISOLATED POPS WEDNESDAY OVER THE HIGHER TERRAIN...EXPECT
NO ACTIVITY INTO THE EXTENDED. WITH LESS CLOUD COVER AND DRIER
AIR...ALSO EXPECT A WARMING TREND IN THE EXTENDED...DESPITE THE
LOWER HGHTS. 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.