Severe Thunderstorm Warning 83, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-080545-

SOUTHWEST ARIZONA/SOUTHEAST CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX ARIZONA
315 PM MST SUN SEP 7 2003

.SYNOPSIS...
A VERY MOIST MONSOON AIRMASS WILL REMAIN OVER SOUTHWEST AND SOUTH
CENTRAL ARIZONA THROUGH AT LEAST WEDNESDAY. A RATHER STRONG PACIFIC
LOW PRESSURE SYSTEM IS FORECAST TO MOVE INTO THE WESTERN STATES
...INCLUDING NORTHERN AND CENTRAL ARIZONA...EARLY THIS WEEK... WHICH
WILL RESULT IN A GOOD CHANCE FOR SHOWERS AND THUNDERSTORMS MAINLY
OVER SOUTH-CENTRAL ARIZONA MONDAY NIGHT THROUGH EARLY WEDNESDAY.
ARIZONA WILL BE BETWEEN WEATHER SYSTEMS THURSDAY...BUT A NORTHWARD
MOVING LOW PRESSURE SYSTEM FROM BAJA CALIFORNIA WILL BRING A SLIGHT
CHANCE FOR MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS
OVER SOUTHWEST AND SOUTH-CENTRAL ARIZONA NEXT WEEKEND.

.DISCUSSION...
EXPECTED A MUCH QUIETER AFTERNOON TODAY THAN WHAT OCCURRED SATURDAY
...AND THAT HAS BEEN THE CASE SO FAR. EARLIER THIS AFTERNOON
...THUNDERSTORMS OVER SOUTHERN GILA COUNTY PRODUCED LOCALLY HEAVY
RAINFALL...ESPECIALLY NEAR THE TOWN OF MIAMI...AND SATELLITE AND
RADAR INDICATE SOUTHERN GILA COUNTY IS STILL UNDER THE GUN FOR
ISOLATED STRONG STORMS THRU THIS EVENING. OTHERWISE...DO NOT EXPECT
MORE THAN AN ISOLATED SHOWER OR STORM OVER AZ PTN OF CWA AS MID
-TROPOSPHERIC RIDGE APPROACHES WHILE UPPER JET DEPARTS AREA...AND
HAVE DROPPED POP TO 5% OR SO OVER LOWER DESERT FOR TONIGHT.  HOWEVER
...AIRMASS IS STILL QUITE MOIST...ESPECIALLY IN LOWER LEVELS...AND I
DONT SEE THE LOW LEVEL MOISTURE GETTING SCOURED OUT BY THE
APPROACHING SHORT WAVE RIDGE.  EVEN IF WE DO DRY OUT A LITTLE BIT
TONIGHT INTO EARLY MONDAY...THERES PLENTY OF MOISTURE RESIDING JUST
SOUTH AND WEST OF OUR CWA.

AS MENTIONED THIS MORNING...LOOKS LIKE THE WEATHER WILL BECOME VERY
ACTIVE OVER AT LEAST THE EASTERN TWO THIRDS OF OUR CWA MONDAY
EVENING THROUGH WEDNESDAY AS A VIGOROUS SHORT WAVE TROUGH MOVES INTO
THE WESTERN UNITED STATES. IN ADVANCE OF THIS TROUGH...LOWER AND MID
LEVEL WINDS WILL STRENGTHEN AND BACK...WHICH SHOULD INCREASE
MOISTURE OVER OUR FORECAST AREA. SOME OF THE MOST SEVERE
THUNDERSTORMS WE EXPERIENCE OCCUR DURING THE TRANSITION FROM THE
SUMMER MONSOONAL FLOW TO WESTERLY FLOW (IN THESE SITUATIONS...
INCREASING WINDS ALOFT AND INCREASING VERTICAL WIND SHEAR COMBINE
WITH AN UNSTABLE AIRMASS...WITH ABUNDANT MOISTURE IN THE LOWER THIRD
OF THE TROPOSPHERE). MORNING GFS GENERATES IMPRESSIVE UPWARD
VERTICAL MOTION MAINLY OVER SOUTH CENTRAL AZ MONDAY NIGHT THRU
TUESDAY NIGHT...WITH PEAK VERTICAL MOTION TUESDAY AFTN/EVENING. IN
ADDITION TO THE POTENTIAL FOR SEVERE STORMS...TRAINING OF ECHOES
COULD RESULT IN LOCALLY HEAVY RAIN...ESPECIALLY TUESDAY AFTN/EVENING.
WILL HANG ONTO LOW POPS WEDNESDAY OVER AZ PTN OF CWA AS LOW LEVELS
REMAIN VERY MOIST...BUT THEN SHOW A BREAK ON THURSDAY AS GFS
FORECASTS DRIER LOW LEVEL CONDITIONS. CONFIDENCE IN FORECAST BEYOND
THURSDAY NOT VERY HIGH AS MEDIUM RANGE MODELS DISAGREE ON KEY UPPER
LEVEL FEATURES. HOWEVER...WITH ABUNDANT MOISTURE FORECAST TO REMAIN
CLOSE TO THE FORECAST AREA...AND WITH GFS FORECASTING UPPER LOW TO
BE POSITIONED JUST SOUTHWEST OF US...A SLIGHT CHANCE FOR AFTERNOON
AND EVENING SHOWERS/STORMS LOOKS GOOD. DG

.PSR...NONE.

AZZ020>028-CAZ030>033-080100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
600 AM MST SUN SEP 7 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.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.