Severe Thunderstorm Warning 3, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-231045-

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
915 PM MST FRI JUN 22 2001

.SYNOPSIS...
SOUTHEAST FLOW ALOFT AROUND AN UPPER LEVEL HIGH PRESSURE SYSTEM WILL
CONTINUE ACROSS MUCH OF ARIZONA THROUGH THE WEEKEND. THIS FLOW WILL
MAINTAIN THE CURRENT LEVELS OF MOISTURE OVER SOUTH-CENTRAL AND
SOUTHWEST ARIZONA...WITH A DRIER SOUTHWEST FLOW EXPECTED OVER
SOUTHEAST CALIFORNIA DURING THIS TIME. THEREFORE...A CONTINUED
THREAT OF AFTERNOON AND EVENING THUNDERSTORMS WILL EXIST OVER SOUTH-
CENTRAL ARIZONA THROUGH SUNDAY. LATER ON NEXT WEEK...LOW PRESSURE
ALOFT SITUATED TO OUR NORTHWEST WILL ALLOW FOR A STRONGER AND DRIER
SOUTHWEST FLOW TO PUSH FURTHER INTO SOUTH-CENTRAL ARIZONA.

.DISCUSSION...
ANOTHER ROUND OF AFTERNOON AND EVENING MOUNTAIN CONVECTION DEVELOPED
NORTH...EAST...AND SOUTHEAST OF THE GREATER PHOENIX AREA. THE
WESTERN PART OF THE CWA...I.E SOUTHEAST CA AND SOUTHWEST AZ WAS
MOSTLY CLEAR. AS PER USUAL (THE LAST 3 EVENINGS)..SEVERAL CONVECTIVE
OUTFLOW BOUNDARIES WERE MOVING THROUGH...OR APPROACHING THE GREATER
PHOENIX AREA AT 0345Z.  THE NORTHWESTWARD MOVING BOUNDARY (GENERATED
FROM SEVERE CONVECTION NEAR TUCSON) HAD THE STRONGEST WINDS OF 20 TO
30 KTS...WITH AN E.T.A OF 0430Z AT THE RADAR SITE NEAR
WILLIAMS-GATEWAY (IWA).   THIS BOUNDARY SHOULD COLLIDE AT THAT TIME
WITH A SOUTHWARD MOVING BOUNDARY OF 20 KTS.  AN EARLIER PHOENIX
SOUNDING AT 18Z...(NO 00Z SOUNDING WAS TAKEN) STILL SUGGESTS NO
THREAT FOR CONVECTIVE REDEVELOPMENT IN PHOENIX FROM OUTFLOWS OR
THEIR COLLISIONS.

OTHERWISE... OH BROTHER...HOW THE UPPER LEVEL FLOW PATTERN IS
STARTING TO CHANGE...WITH EACH MODEL FORECASTING SOMETHING
DIFFERENT.  LET US EXPLAIN.  FOR THE PAST TWO DAYS THE 300/250 MB
HIGH CENTERS HAD BEEN CO-LOCATED (STACKED) OVER CENTRAL AZ (A
FAVORABLE POSITION FOR LARGE MOUNTAIN CONVECTION). THE MODELS ARE
NOW FORECASTING THESE HIGH CENTERS TO DRIFT TO NEAR EL PASO BY 12Z
SAT. AS A RESULT...THE 300/250 MB FLOWS ARE BECOMING SOUTHWESTERLY
WITH TIME... BUT WITH DIFFERENT MODEL SCENARIOS. FOR EXAMPLE...THE
NEW ETA FORECASTS A VERY MINOR UPPER LEVEL DISTURBANCE TO DRIFT
ACROSS SOUTH CENTRAL AND SOUTHEAST AZ BY 00Z SUN. THIS PIECE OF
ENERGY COMES OUT OF THE MASSIVE INVERTED TROF SEEN IN WATER VAPOR
IMAGERY JUST WEST OF THE BAJA PENNISULA.  IN CONTRAST... THE NEW AVN
FORECASTS A STRONGER SHORTWAVE TO MOVE NORTH INTO CENTRAL ARIZONA...
BUT LATER...OR BY 12Z SUN.

PLOT DATA AND PRECIPITABLE WATER SATELLITE IMAGERY STILL SHOW THE
850 AND 700 MB MOISTURE PLUMES LOCATED OVER SOUTHWEST AND SOUTH
CENTRAL AZ. THIS BOUNDARY LAYER MOISTURE HAS MIGRATED EAST A LITTLE
EACH DAY...AND SHOULD ADD SOME ADDITIONAL CONVECTIVE AVAILABLE
POTENTIAL ENERGY SHOULD ANY OF THESE WEAK DISTURBANCES FROM MEXICO
BECOME A PLAYER.  CURRENT FORECASTS FOR CONVECTIVE THREATS FOR SOUTH
CENTRAL AZ OVER THE WEEKEND STILL LOOK OK.  NO UPDATES PLANNED.
VASQUEZ