Severe Thunderstorm Warning 97, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
225 PM MST MON SEP 8 2003

.SYNOPSIS...A TROUGH MOVING THROUGH THE WESTERN U.S. TUESDAY AND
EARLY WEDNESDAY WILL BRING AN ABUNDANCE OF MOISTURE OVER ARIZONA.
THIS TROUGH COMBINED WITH THE MOISTURE HAS THE POTENTIAL FOR
PRODUCING LOCALLY HEAVY RAIN ON TUESDAY.  DRYING AND CLEARER SKIES
WILL BEGIN WEDNESDAY NIGHT THROUGH THE WEEKEND. TEMPERATURES WILL
DROP BELOW SEASONAL NORMS ON TUESDAY WITH A SLOW WARMING TREND
THROUGH SATURDAY.

.DISCUSSION...MOISTURE AND DYNAMICS WILL COMBINE ON TUESDAY FOR
SHOWERS STATEWIDE. THIS SCENARIO IS NOT A BIG CHANGE FROM PREVIOUS
MODEL RUNS.  THE DURATION OF THIS EVENT HAS SOME VARIABILITY IN THE
MODELS.  THE 12Z GFS BEGINS DRYING OUT THE STATE ON WEDNESDAY
MORNING...WHERE AS THE ETA IS NOT QUITE AS RESPONSIVE.  GIVEN THESE
VARIATIONS...SCATTERED SHOWERS WILL BE IN THE FORECAST FOR TUESDAY
WITH ISOLATED SHOWERS TAPERING ON WEDNESDAY. DEPENDING ON THE
STABILITY OF THE ATMOSPHERE...A FLASH FLOOD WATCH MAY BE NEEDED FOR
TOMORROW.  WILL NOT ISSUE AT THIS TIME...ALTHOUGH THE POTENTIAL FOR
HEAVY RAIN IS PRESENT.

AS THE TROUGH SETTLES IN OVER THE WEST...HEIGHTS WILL DROP OVER US
AND LIKEWISE TEMPERATURES WILL DECREASE.  WITH THE DRIER AIR ON
THURSDAY AND FRIDAY...MORNING LOWS WILL FINALLY GET CLOSER TO
NORMAL.  MODEL VARIABILITY ON THE WEEKEND IS STILL HIGH.  HOWEVER
ALL MODELS TEND TO FAVOR A WESTERLY COMPONENT TO THE FLOW.  THIS
CHANGE IN THE PATTERN IMPLIES THE SUMMERTIME MONSOON CIRCULATION IS
LEAVING.  SOUTHERN ARIZONA MAY STILL HAVE DAYS WITH CONVECTION IN
SEPTEMBER ALTHOUGH WE ARE DEFINITELY SWITCHING TO A FALL PATTERN
WITH A DRIER WESTERLY OR SOUTHWESTERLY FLOW.

GWS

.TWC...NONE.

AZZ019-029>035-091400-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1130 AM MST MON SEP 8 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST ARIZONA

.DAY ONE...TODAY

SYNOPSIS...THUNDERSTORMS WILL CONTINUE TO DEVELOP ACROSS THE AREA
TODAY AS A TROUGH APPROACHES FROM THE NORTHWEST ADVECTING MOISTURE
INTO SOUTHERN ARIZONA. THE MAIN THREAT FROM THESE THUNDERSTORMS WILL
BE FOR MODERATE RAIN CAUSING LOCAL NUISANCE FLOODING. THERE IS THE
POTENTIAL...ALTHOUGH SLIGHT...FOR AN ISOLATED THUNDERSTORM TO CREATE
FLASH FLOODING.

DISCUSSION...THUNDERSTORMS HAVE ALREADY DEVELOPED THIS MORNING JUST
AS THEY DID YESTERDAY. BUT...A FEW THINGS HAVE CHANGED IN THE LAST
24 HOURS. SOME WARMING AND DRYING HAS TAKEN PLACE IN THE MID
LEVELS...THE CAP HAS LOWERED TO AROUND 650 MB AND A TROUGH IS
APPROACHING FROM THE NORTHWEST. THE TROUGH WILL HELP TO PULL SOME
ADDITIONAL MOISTURE INTO SOUTHERN ARIZONA FROM THE SOUTH.
ACTUALLY...MOISTURE HAS ALREADY BEGUN TO INCREASE AT THE LOW AND MID
LEVELS AS SEEN ON THE GOES TOTAL PRECIPITABLE WATER IMAGERY. THIS
ADVECTION OF MOISTURE WILL HELP TO PRODUCE SOME MODERATE RAIN
SHOWERS IF THUNDERSTORMS ARE ABLE TO BREAK THROUGH THE CAP. THE MID
AND UPPER LEVEL FLOW PATTERN IS SUCH THAT MOST MOVEMENT OF THE
STORMS WILL BE TO THE EAST AT ABOUT 10 MPH. THEREFORE...THE MAIN
THREAT FROM THESE STORMS IS FLASH FLOODING...HOWEVER THE THREAT WILL
BE LOW COMPARED TO CLIMATOLOGY.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH MONDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

EVANS