Severe Thunderstorm Warning 63, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-020545-

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
305 PM MST MON SEP 1 2003

.SYNOPSIS...
SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA WILL BE UNDER A LARGE
HIGH PRESSURE AREA ALOFT THE NEXT FEW DAYS...WITH THE CENTER NEAR
THE ARIZONA UTAH BORDER. THIS POSITION WILL BE FAVORABLE FOR STORMS
TO MOVE OFF THE MOUNTAINS AND DOWN ONTO THE ADJACENT DESERTS. IN
ADDITION...AN UPPER LOW OVER CENTRAL BAJA WILL MOVE TOWARDS THE
DESERT SOUTHWEST TONIGHT AND TUESDAY...WHICH COULD HELP TO TRIGGER
THUNDERSTORMS. AFTER MIDWEEK...THE UPPER HIGH WILL BEGIN TO SHIFT
BACK TO THE SOUTH...WITH A SOMEWHAT DRIER WESTERLY FLOW EXPECTED TO
TAKE OVER...RESULTING IN LESS THUNDERSTORMS. TEMPERATURES WILL START
OUT WARM THROUGH WEDNESDAY...BUT WILL GRADUALLY LOWER A FEW DEGREES
THE LATTER HALF OF THE WEEK.

.DISCUSSION...
UPPER LOW OVER CENTRAL BAJA CONTINUES SHIFTING NORTH...WITH THE
DEFORMATION ZONE/DIFLUENT AREA ALOFT AHEAD OF IT FOCUSED MAINLY OVER
CENTRAL AZ AT 230 PM. BAND OF THUNDERSTORMS HAVE FORMED FROM JOSHUA
TREE NP EAST/NE THRU LA PAZ COUNTY RUNNING UP INTO CENTRAL AZ NORTH
OF ZONE 24...WITH PARTLY CLOUDY SKIES SEEN ACROSS THE REST OF THE
CWA. TEMPS AGAIN WARMING NICELY WITH PHX LIKELY TO REACH AROUND 107
TODAY...AND SURFACE DEWPOINTS ARE UP IN THE 60S TO LOW 70S. THUS
INSTABILITY IS THERE...CAPE IS RATHER HIGH...AND THERE ARE SOME
DYNAMICS TO WORK WITH. STEERING FLOW IS SLY TO SELY TONIGHT...AND
THERE WILL BE ABOUT A 20 PERCENT CHANCE FOR STORMS OVER THE WHOLE
CWA THRU MIDNIGHT. PROGS AGREE THE UPPER LOW WILL EVENTUALLY TURN TO
THE NE AND MOVE OUT OF OUR CWA LATER TUESDAY...LEAVING A RATHER
NONDESCRIPT ELY STEERING FLOW BEHIND OVER THE AREA...WITH THE UPPER
HIGH CENTERED TO OUR NORTH. NO BIG FORCING FEATURES SEEN FOR
TOMORROW BUT MOISTURE REMAINS HIGH...PWAT OVER 1.5 INCHES MOST
PLACES AND 850MB DEWPOINTS WELL ABOVE 8C...SO WILL CONTINUE A SLIGHT
CHANCE FOR STORMS EVERYWHERE TUE AFTERNOON AND NIGHT...WITH ABOUT 30
PERCENT CHANCE A GOOD BET FOR ZONE 24. LITTLE CHANGE ON TAP FOR
WED...THEN THURSDAY THE FLOW STARTS BECOMING MORE WEST TO NW ACROSS
THE CWA AS THE UPPER HIGH IS SHUNTED SOUTH. THIS OCCURS AS THE
WESTERLIES START TO APPROACH AND PUSH DOWN ALONG THE PAC NW COAST.
FROM FRIDAY THRU THE WEEKEND MED RANGE PROGS AND MRF FORECAST THE
WESTERLIES TO STRENGTHEN AND THE FLOW TO BECOME MORE
WESTERLY...GRADUALLY DRYING THE CWA FROM WEST TO EAST. THUS
FORECASTS SHOW A DECREASING THREAT FOR AFTERNOON AND EVENING STORMS
FRI THRU THE WEEKEND. BY SUNDAY THERE WILL ONLY BE A SLIGHT CHANCE
FOR STORMS OVER ZONE 24...WITH MOSTLY CLEAR TO PARTLY CLOUDY SKIES
ELSEWHERE. STRONG TROF MOVING IN OVER THE PAC NW WILL SCOUR THE
REMAINING MOISTURE OUT BY MONDAY...THUS WILL REMOVE SLIGHT CHANCE
FOR ZONE 24 ON THAT DAY WITH LOTS OF SUNSHINE TO BE SEEN OVER THE
CWA. AS FOR TEMPERATURES...OVER THE NEXT FEW DAYS THEY WILL REMAIN
WELL ABOVE NORMAL AS HEIGHTS REMAIN HIGH...AND DECENT SUNSHINE WILL
BE HAD EACH AFTERNOON. THEN THERE WILL BE A GRADUAL FALLOFF IN DAILY
HIGHS AS THE HEIGHTS SLOWLY LOWER AHEAD OF THE ENCROACHING
WESTERLIES.  11

.PSR...NONE.

AZZ020>028-CAZ030>033-020100-

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
652 AM MST MON SEP 1 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...AN APPROACHING UPPER LOW PRESSURE SYSTEM FROM THE SOUTH
WILL LIKELY GIVE RISE TO AFTERNOON AND EVENING THUNDERSTORMS ACROSS
MUCH OF SOUTH-CENTRAL AND SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA
THIS AFTERNOON AND EVENING. SOME OF THE THUNDERSTORMS COULD PRODUCE
GUSTY WINDS...BLOWING DUST IN THE DESERTS AND BRIEF HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.