Severe Thunderstorm Warning 90, NWS Flagstaff, AZ

NORTHERN ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
345 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...HIGH PRESSURE CONTINUES TO MOVE TO THE EAST THIS
MORNING ALLOWING A DEEP SOUTHERLY FLOW TO DEVELOP OVER MUCH OF
ARIZONA. A S/W TROUGH IS EXITING THE STATE INTO UTAH THIS MORNING
AND CONVECTION CONTINUES WITH THIS FEATURE. ANOTHER S/W TROUGH
REMAINS TO THE SOUTHWEST OF ARIZONA THIS MORNING. MODELS SHOW
DIFFERENT DETAILS BUT ARE IN AGREEMENT THAT THIS FEATURE WILL MOVE
ACROSS THE STATE TODAY. WITH DEEP MOISTURE IN PLACE AND MODERATE
DYNAMICS WITH THIS S/W TROUGH...EXPECT ANOTHER ROUND OF CONVECTION
TO DEVELOP DURING THE DAY TODAY AND CONTINUE INTO THE NIGHT. HAVE
CHOSEN TO MAINTAIN HIGHER POPS INTO THE NIGHT SINCE IT APPEARS THAT
THE CONVECTION WILL CONTINUE WELL AFTER SUNSET.

ON TUESDAY...A STRONG S/W TROUGH APPROACHES THE AREA FROM THE WEST.
DIVQ FIELDS FROM BOTH AVN AND ETA INDICATE THAT THERE IS A STRONG
FORCING COUPLET ASSOCIATED WITH THIS WAVE. ZERO LINE OF THE COUPLET
MOVES ACROSS ARIZONA LATE IN THE AFTERNOON AND INTO THE EVENING
HOURS. MODELS ATTEMPT TO DRY OUT THE ATMOSPHERE IN ADVANCE OF THIS
SYSTEM BUT BELIEVE THIS IS OVERDONE AND ADEQUATE MOISTURE WILL BE IN
PLACE WHEN THE DYNAMICS ARRIVE. SHEAR PROFILES SHOULD INCREASE
SUBSTANTIALLY WITH THE APPROACH OF THE WAVE AND WILL NEED TO MONITOR
THE SITUATION FOR THE POSSIBILITY OF STRONG TO SEVERE THUNDERSTORMS
DEVELOPING ACROSS THE CWFA.

.EXTENDED...STRONG MID-LATITUDE TROUGH WILL MOVE ACROSS THE REGION
ON WEDNESDAY BRINGING MUCH DRIER CONDITIONS. EXPECT MOSTLY SUNNY
DAYS AND CLEAR NIGHTS THROUGH THE EXTENDED. THE ONLY EXCEPTION WILL
BE THE FAR EASTERN ZONES WHERE PARTLY CLOUDY SKIES AND A CHANCE OF
SHOWERS LINGER THROUGH WEDNESDAY BEFORE CLEARING.  DB

.FGZ...NONE.