Severe Thunderstorm Warning 95, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
243 PM MST MON SEP 1 2003

.SYNOPSIS...SUFFICIENT MOISTURE AND INSTABILITY WILL REMAIN ACROSS
SOUTHEAST ARIZONA FOR A CHANCE OF MAINLY AFTERNOON AND EVENING
THUNDERSTORMS THIS WEEK. BY LATE THIS WEEKEND AND EARLY NEXT WEEK A
TROUGH WILL APPROACH FROM THE WEST BRINGING IN DRIER AIR AND A
DECREASE IN SHOWER AND THUNDERSTORM ACTIVITY.

.DISCUSSION...LATEST SATELLITE IMAGERY AND RADARS SHOWING MOST OF
THE CONVECTION DEVELOPING ACROSS THE RIM COUNTRY AT THIS TIME.
ISOLATED SHOWERS AND STORMS HAVE POPPED UP ACROSS THE WESTERN
PORTION OF MY FORECAST AREA...BUT CIRRUS SHIELD STREAMING NORTHWARD
FROM SONORA SEEMS TO BE SUPPRESSING ACTIVITY OVER SOUTHEAST ARIZONA
AT THIS TIME. IN ADDITION...SURFACE DEWPOINTS ACROSS THE CENTRAL AND
EXTREME SOUTHEAST PORTION OF MY CWA ARE RUNNING 7 TO 8 DEGREES LOWER
THAN THIS TIME YESTERDAY AND ARE CURRENTLY IN THE LOWER TO MID 50S
OVER MOST OF THE REGION.

IN THE MID TO UPPER LEVELS THE MODELS ARE ALL IN FAIR AGREEMENT WITH
THE PLACEMENT OF THE RIDGE OVER NORTHEAST ARIZONA AND NORTHWEST NEW
MEXICO...JUST SOUTH OF THE FOUR CORNERS. THE RIDGE WILL MAINTAIN
THIS POSITION THROUGH TUESDAY...BUT BECOMING MORE ELONGATED FROM
WEST TO EAST AND RETROGRADING SLIGHTLY AS THE SHORTWAVE OVER THE
GREAT BASIN IS PROGGED TO RIDE OVER THE TOP OF THE RIDGE AND DIVE
DOWN ACROSS UTAH AND INTO COLORADO BY LATE WEDNESDAY. BY THAT TIME
THE RIDGE WILL HAVE SHIFTED TO A MORE NORTH-SOUTH ORIENTATION FROM
THE GREAT BASIN TO THE LOWER COLORADO RIVER VALLEY.

THE MODELS DEPICT THE BULK OF THE MOISTURE OVER THE NEXT FEW DAYS
GENERALLY ALONG THE RIM AND TO THE SOUTH IN SONORA. HOWEVER...FOR
THIS EVENING WITH THE UPPER LOW OVER THE BAJA PENINSULA AND THE HIGH
TO THE NORTH THE MODELS ADVERTISE SOME UPPER LEVEL DIVERGENCE AND
LIFT OVER SONORA AND PERHAPS INTO SE ARIZONA. THEREFORE CANT RULE
OUT AN ACTIVE EVENING EVEN THOUGH RADARS AT THIS TIME SHOW SCANT
COVERAGE. WITH THAT SAID...I HAVE KEPT THE POPS FOR THE NEXT SEVERAL
DAYS IN THE LOW END OF SCATTERED CATEGORY FOR CENTRAL AND EAST...AND
ISOLATED WEST.

BY SUNDAY THINGS BEGIN TO WIND DOWN AS THE GFS SHOWS A TROUGH
APPROACHING THE WEST COAST AND MUCH DRIER AIR BEGINS TO FILTER INTO
SOUTHERN CALIFORNIA AND THE DESERT SOUTHWEST SUNDAY...AND ESPECIALLY
MONDAY. IF THE GFS IS CORRECT MY POP FORECAST FOR SUNDAY AND MONDAY
MAY BE OVERDONE...BUT DUE TO THE UNCERTAINTY HAVE OPTED TO KEEP
ISOLATED POPS GOING FOR CENTRAL AND EAST.

TEMPS WILL REMAIN RATHER WARM...ABOVE CLIMO...FOR THE NEXT SEVERAL
DAYS BEFORE TEMPS WILL SLOWLY FALL INTO THE WEEKEND AND EARLY NEXT
WEEK WITH THE APPROACH OF THE TROUGH AND THE RESULTING HEIGHT FALLS.

MOLLERE

.TWC...NONE.

AZZ019-029>035-021400-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1215 PM MST MON SEP 1 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST ARIZONA

.DAY ONE...TODAY

SYNOPSIS...HIGH PRESSURE ALOFT WILL REMAIN CENTERED ALONG THE
ARIZONA/UTAH BORDER INTO THE LATER PORTION OF THE WEEK. AN UPPER LOW
NEAR THE BAJA SPUR WILL MOVE NORTH/NORTHWEST TODAY AND THEN
NORTHEAST ACROSS ARIZONA TONIGHT AND TUESDAY. THIS SYSTEM IS
EXPECTED TO MOVE AWAY FROM THE REGION ON WEDNESDAY. THE COMBINATION
OF THESE FACTORS...ALONG WITH SUFFICIENT LOW LEVEL MOISTURE AND
INSTABILITY WILL CONTINUE THE CHANCE OF MAINLY AFTERNOON AND EVENING
SHOWERS AND THUNDERSTORMS THROUGH THE WEEK.

DISCUSSION...THE 12Z KTUS SOUNDING SHOWS THAT A LITTLE DRIER AIR HAS
MOVED INTO THE REGION...WITH A PRECIPITABLE WATER VALUE OF 1.32...
COMPARED TO 1.61 INCHES YESTERDAY MORNING. REGIONAL OBSERVATIONS
SHOW SURFACE DEWPOINTS ARE CURRENTLY IN THE MID 50S TO MID 60S...
WHICH IS 1 TO 4 DEGREES LOWER ACROSS THE CENTRAL AND WESTERN DESERTS
AND NEARLY 4 TO 7 DEGREES LOWER OVER FAR SOUTHEASTERN PORTIONS OF
THE FORECAST AREA. GOES TOTAL PRECIPITABLE WATER IMAGERY INDICATES
VALUES RANGING FROM NEAR 1 INCH ALONG THE NEW MEXICO BORDER (WHERE
EASTERLY FLOW IS ADVECTING DRIER AIR INTO THE REGION FROM NEW MEXICO
AND WEST TEXAS) TO 1.8 INCHES ACROSS FAR WESTERN PORTIONS OF THE
FORECAST AREA. THE 12Z KTUS SOUNDING ALSO SHOWS A DRY SUB CLOUD
LAYER. THIS COMBINED WITH A FAIRLY SUBSTANTIAL CLOUD DECK ACROSS
SOUTHEAST ARIZONA SHOULD DELAY THE ONSET OF MOST OF THE INITIAL
CONVECTION UNTIL THE MID/LATE AFTERNOON HOURS...WITH THE ACTIVITY
EXPECTED TO PERSIST INTO THE EVENING HOURS. THE 12Z KTUS SOUNDING IS
MODERATELY UNSTABLE (MORE SO THAN YESTERDAY) WITH AN UNMODIFIED
LIFTED INDEX 0F MINUS 4.3 AND A POSITIVE ENERGY VALUE OF 2411 J/KG.

MUCH OF SOUTHERN AND CENTRAL ARIZONA IS IN A DIFFLUENT DEFORMATION
ZONE BETWEEN THE UPPER LOW OVER THE BAJA SPUR AND THE HIGH CENTERED
TO OUR NORTH. THESE WEAK DYNAMICS COULD COME INTO PLAY LATER TONIGHT
AS THE UPPER LOW GRADUALLY LIFTS NORTH. THE MODELS INDICATE THE BEST
PLACE FOR ORGANIZED CONVECTION WILL BE ALONG THE INTERNATIONAL
BORDER CENTERED AROUND NOGALES LATE THIS AFTERNOON/EVENING...
POSSIBLY EDGING NORTHWARD INTO SOUTHERN ARIZONA AS THE EVENING WEARS
ON. THUS...THE BEST CHANCE FOR STORMS TODAY WILL BE WEST OF A LINE
FROM SIERRA VISTA...TO TUCSON AND ALSO IN THE WHITE MOUNTAINS. ONLY
ISOLATED STORMS ARE EXPECTED EAST OF THIS LINE. WITH DRIER AIR IN
THE LOWER LAYERS THERE WILL BE A LITTLE BETTER CHANCE OF SEVERE
THUNDERSTORMS...HOWEVER VALUES WILL REMAIN NEAR CLIMATOLOGICAL
NORMS. THE PROBABILITY OF ONE INCH OR GREATER RAINFALL WILL BE BELOW
CLIMATOLOGY IN THE EAST AND NEAR CLIMATOLOGY ACROSS THE WEST. STORM
MOTION WILL BE TO THE WEST/NORTHWEST AT 10 TO 15 MPH.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH MONDAY.

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

THE MODELS CONTINUE TO INDICATE THE UPPER HIGH WILL REMAIN CENTERED
TO OUR NORTH...PROVIDING A FAVORABLE FLOW FOR ISOLATED TO SCATTERED
THUNDERSTORMS ACROSS SOUTHEAST ARIZONA. EXPECT SCATTERED AFTERNOON
AND EVENING THUNDERSTORMS ACROSS EASTERN PORTIONS OF THE FORECAST
AREA...WITH ISOLATED AFTERNOON AND EVENING THUNDERSTORMS OVER
WESTERN PORTIONS OF THE FORECAST AREA. A FEW OF THESE STORMS MAY BE
ACCOMPANIED BY LOCALLY HEAVY RAIN AND/OR STRONG GUSTY WINDS.

.SPOTTER INFORMATION STATEMENT...

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

ZELL