Flash Flood Warning 18, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-050545-

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX ARIZONA
225 PM MST THU SEP 4 2003

.SYNOPSIS...
AN INCREASE IN LOW LEVEL MOISTURE FROM THE GULF OF CALIFORNIA WILL
BRING AT LEAST A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS OVER FAR
SOUTHEAST CALIFORNIA...AS WELL AS SOUTHWEST AND SOUTH CENTRAL
ARIZONA...THROUGH FRIDAY EVENING. HIGH PRESSURE ALOFT WILL MOVE FROM
EASTERN ARIZONA TO NEAR SAN DIEGO BY SATURDAY MORNING...WITH SOME
DRYING AND A LITTLE WARMER DAYTIME HIGHS OVER THE WEEKEND. THE
CHANCE FOR STORMS ON SATURDAY WILL EXIST MAINLY OVER THE HIGHER
TERRAIN OF SOUTH CENTRAL ARIZONA. STRONG UPPER LEVEL LOW PRESSURE
WILL MOVE INTO THE PACIFIC NORTHWEST LATE IN THE WEEKEND...PERSIST
THROUGH THE MIDDLE OF NEXT WEEK...AND KEEP HIGH PRESSURE ALOFT TO
OUR SOUTH. THIS WILL RESULT IN DRY WEST TO NORTHWEST FLOW...AND LEAD
TO MOSTLY CLEAR SKIES AND NEAR NORMAL TEMPERATURES NEXT WEEK.

.DISCUSSION...
18Z PHOENIX SOUNDING QUITE UNSTABLE...WITH MLCAPE (SFC-850MB LAYER)
OF 1200 J/KG. NEGATIVE AREA BELOW LFC...SO DECENT OUTFLOW FROM
STORMS OVER HIGHER TERRAIN WILL BE REQUIRED TO RELEASE INSTABILITY
OVER LOWER DESERT. SFC-500 MB WINDS VERY LIGHT...1O KT OR LESS...
GENERALLY FROM THE SOUTHEAST...AND 0-6KM SHEAR NEARLY NON-EXISTENT
...SO EXPECT SHORT LIVED...DISORGANIZED...AND VERY SLOW MOVING
STORMS THIS AFTN AND EVENING. DECENT WEST WIND AT AND ABOVE 350 MB
LVL ...WITH 40 KT OBSERVED NEAR 200 MB...BUT MOST DIFFLUENT FLOW
NOTED MAINLY NORTH OF OUR CWA IN SOUTHEAST CALIFORNIA. SO...WILL
HOLD ONTO SLGT CHC FOR STORMS THIS EVENING OVER MOST OF CWA. GIVEN
OBSERVED THUNDERSTORM DEVELOPMENT OVER YAVAPAI AND NORTHERN GILA
COUNTIES ...AND EXPECTATION OF HALFWAY DECENT OUTFLOW TO MOVE SOUTH
AND WEST TOWARD LOWER DESERT...WOULD EXPECT THE BEST CHANCE FOR
STORMS OVER SOUTH CENTRAL AZ LOWER DESERT THIS EVENING. GIVEN THE
LARGE CAPE ...ANY STORMS THAT DO GET TRIGGERED COULD BE
SEVERE...WITH LOCALLY HEAVY RAIN...HIGH WINDS AND HAIL POSSIBLE.

WILL HOLD ONTO A CHANCE FOR AFTN/EVENING STORMS FRIDAY ALSO...AS
HIGH MOVES TO OUR WEST AND DEEP LAYERED LIGHT NORTH-NORTHWEST FLOW
DEVELOPS. NOT SURE HOW UNSTABLE IT WILL BE FRIDAY AFTN/EVENING...AS
EVOLUTION OF STORMS THIS EVENING IS NOT CLEAR CUT...BUT STILL A LOT
OF CONVECTION TO OUR SOUTH THIS AFTN...SO WOULD NOT BE SURPRISED TO
SEE LOW LEVEL MOISTURE REMAIN PLENTIFUL OVER OUR CWA THRU AT LEAST
FRIDAY EVENING...ALONG WITH AT LEAST LOW-END CAPE.

DRYING STILL EXPECTED TO COMMENCE IN LOW LEVELS BY SATURDAY...FROM
WEST TO EAST ACROSS THE CWA...AND WE WILL HAVE TO WATCH FOR THE
POSSIBILITY OF ISOLATED SEVERE STORMS SAT AFTN/EVENING...ESPECIALLY
OVER THE HIGHER TERRAIN NORTH AND EAST OF PHOENIX. FURTHER DRYING IS
EXPECTED NEXT WEEK AS DEEP WEST TO NORTHWEST FLOW DEVELOPS. UPPER
HIGH PROGGED TO REMAIN FAIRLY STRONG AND BE CENTERED NEAR OR JUST
SOUTH OF YUMA THIS WEEKEND...SO WENT WITH A BIT WARMER DAYTIME HIGHS
COMPARED TO WHAT WILL OCCUR FRIDAY. EXPECT A TREND TOWARD NEAR
NORMAL TEMPS TO BEGIN EARLY NEXT WEEK AS TROUGH DIGS INTO WESTERN
UNITED STATES...WITH 500 MB HEIGHTS LOWERING TO NEAR NORMAL LEVELS
BY TUESDAY.  LATEST GFS INDICATES SOMEWHAT PROGRESSIVE UPPER FLOW
EXPECTED TOWARD THE END OF NEXT WEEK...WITH A CHANCE FOR A BIT OF
WARMING BY THURSDAY AS HEIGHTS/THICKNESSES EDGE UPWARD. DG

.PSR...NONE.

AZZ020>028-CAZ030>033-050100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
100 PM MST THU SEP 4 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHWEST AND
SOUTH-CENTRAL ARIZONA...AND SOUTHEAST CALIFORNIA.

.DAY ONE...TODAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.
HOWEVER...ISOLATED STRONG THUNDERSTORMS ARE EXPECTED TO DEVELOP
MAINLY OVER THE HIGHER TERRAIN THIS AFTERNOON...WITH A FEW STRONG
STORMS POSSIBLE OVER THE LOWER DESERT. STORMS WILL MOVE VERY
SLOWLY...SO LOCALLY HEAVY RAIN WILL BE POSSIBLE. IN
ADDITION...STRONG GUSTY WINDS...HAIL...AND INTENSE CLOUD TO GROUND
LIGHTNING WILL ACCOMPANY THE STRONGEST STORMS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.
HOWEVER...ISOLATED THUNDERSTORMS ARE EXPECTED TO AFFECT MAINLY SOUTH
CENTRAL ARIZONA FRIDAY AFTERNOON AND EVENING...WITH A CHANCE FOR
STORMS MAINLY OVER THE HIGHER TERRAIN OF SOUTH CENTRAL ARIZONA
SATURDAY AFTERNOON AND EVENING.