Flash Flood Warning 14, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-292245-

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
945 AM MST TUE AUG 29 2000

.SYNOPSIS...
A COUPLE OF UPPER LEVEL IMPULSES WILL MOVE UP INTO SOUTHWEST ARIZONA
AND SOUTHEAST CALIFORNIA AND ACT UPON OUR VERY MOIST AIRMASS TO
PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS INTO WEDNESDAY. THE MAIN
THREAT FROM THESE THUNDERSTORMS WILL BE HEAVY RAINFALL. MEANWHILE...
A STRONG PACIFIC LOW PRESSURE AREA WILL BE DEVELOPING THE NEXT COUPLE
OF DAYS OFF THE CALIFORNIA COAST. AS IT APPROACHES...IT WILL HELP TO
INCREASE THE SOUTHWEST FLOW ALOFT WHICH WILL IMPORT MUCH DRIER AIR
INTO THE REGION AFTER MIDWEEK.

.DISCUSSION...
AIRMASS REMAINS VERY MOIST AS MORNING PHX RAOB JUST ABOUT SATURATED
FROM SURFACE THROUGH 300 MB. NEW ETA/NGM INITIALIZED FAIRLY WELL AND
TRENDS SIMILIAR BUT HAVE SLIGHT DIFFERENCES ON PATH OF VORTMAX.
DYNAMICS FROM FIRST VORTMAX OVER NORTHWEST MEXICO HAS CAUSED SHOWERS
OVER MUCH OF CWA THIS MORNING. BOTH MODELS MOVE THIS VORTMAX MOVING
NORTH AND SORT OF MERGING IT WITH VORTLOBE OVER NORTHERN ARIZONA
TODAY. AS IT MOVES NORTH AND MERGES...200 MB DIVERENGE OVER CWA MOVES
NORTH AND A MININUM IS FORECASTED BY BOTH MODELS TONIGHT OVER SOUTH
CENTRAL AZ. THIS SEEMS REASONABLE AS SOME NVA MAY OCCUR IN WAKE OF
SYSTEM. SATELLITE PHOTOS SHOW SOME CLEARING OVER SE AZ THIS MORNING
AND THIS SHOULD PROGRESS NORTHWESTWARD. HOWEVER...WITH THE VERY MOIST
AIRMASS...AFTERNOON HEATING SHOULD DEVELOP SOME AFTERNOON/EVENING
THUNDERSTORMS...THEN EXPECT SOME DECREASE LATER THIS EVENING. NEXT
VORTMAX NOW NEAR CENTRAL BAJA IS BROUGHT NORTH INTO THE NOGALES AREA
BY WEDNESDAY MORNING BUT THEN ETA TAKES IT NORTHWEST WHEREAS NGM
MOVES IT NORTH TO NORTHEAST...BUT TRENDS BASICALLY THE SAME. THIS
WILL PROVIDE MORE DYAMICS ON WEDNESDAY. PLUS 200 MB DIVERVERGENCE IS
ALSO MOVED OVER ESPECIALLY SOUTH CENTRAL AZ WEDNESDAY AND IS
ESPECIALLY NOTED ON NGM. BY TONIGHT AND INTO WEDNESDAY BOTH MODELS
BRING SOME 500 MB DRYING KEEPING LOWER LAYERS VERY MOIST. THUS CHANCE
OF THUNDERSTORMS OVER CWA WEDNESDAY BUT MORE FAVORABLE OVER SW AND
SOUTH CENTRAL AZ WITH SOME POSSIBLE SEVERE, ISOLATED THUNDERSTORMS
WEDENSDAY OVER SE CA AS MOST DYNAMICS WILL BE EAST OF THAT AREA. NO
UPDATES.   DKS

AZZ020>028-CAZ030>033-300050-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
1147 AM MST (1147 AM PDT) TUE AUG 29 2000

...SLIGHT RISK OF HAZARDOUS WEATHER OVER SOUTH CENTRAL AND SOUTHWEST
ARIZONA...AND SOUTHEAST CALIFORNIA THIS AFTERNOON AND THIS EVENING...

COUNTIES IN THE RISK AREA INCLUDE:
     IN ARIZONA...MARICOPA...SOUTHERN GILA...NORTHWEST PINAL...
     LA PAZ...AND YUMA.
     IN CALIFORNIA...IMPERIAL AND EASTERN RIVERSIDE.

THE PRIMARY HAZARDOUS WEATHER RISKS INCLUDE:
     HEAVY RAIN THAT COULD CAUSE FLOODING OF STREETS...
     UNDERPASSES...AND NORMALLY DRY CREEKS AND WASHES.

ADDITIONAL THREATS INCLUDE:
     SEVERE THUNDERSTORMS PRODUCING WIND GUSTS IN EXCESS OF 60
     MPH.
     BLOWING DUST WHICH COULD REDUCE VISIBILITY TO LESS THAN
     ONE QUARTER MILE.

STORM SPOTTER ACTIVATION MAY BE NECESSARY LATER TODAY.

MB