Severe Thunderstorm Warning 20, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
149 PM MST SUN JUL 20 2003

.SYNOPSIS...A FEW WEAK IMPULSES ARE FORECAST TO BRING AN INCREASE IN
SHOWERS AND THUNDERSTORMS TONIGHT INTO TUESDAY. OTHERWISE...THE
LARGE SCALE WEATHER PATTERN WILL REMAIN FAVORABLE THROUGH THE REST
OF THE WEEK FOR A TYPICAL SUMMERTIME FORECAST OF SCATTERED AFTERNOON
AND EVENING THUNDERSTORMS. DAYTIME TEMPERATURES WILL FLUCTUATE A BIT
WITH THE VARIABILITY IN THUNDERSTORM ACTIVITY EACH DAY...BUT OVERALL
WILL REMAIN SLIGHTLY ABOVE NORMAL THIS WEEK.

.DISCUSSION...CLOUD BUILD-UPS WERE A LITTLE DELAYED THIS AFTERNOON
COMPARED TO THE PAST COUPLE OF DAYS DUE TO THE DRIER AIRMASS IN
PLACE AND THE ADDITIONAL SURFACE HEATING NEEDED. HOWEVER...STORMS
HAVE HAD NO TROUBLE DEVELOPING ALONG THE RIM COUNTRY INTO PARTS OF
THE WHITE MOUNTAINS TODAY. ADDITIONAL SHOWERS AND ISOLATED
THUNDERSTORMS WERE TRYING TO ORGANIZE IN COCHISE AND SANTA CRUZ
COUNTIES SOUTH INTO NORTHERN SONORA MEXICO. HAVE NOT NOTED MUCH OF A
WESTWARD PUSH TO ANY OF THESE SHWRS/TSTMS YET...BUT THE UPSLOPE
VALLEY-MOUNTAIN FLOW WAS MUCH STRONGER TODAY THAN WHAT WE HAVE SEEN
THE PAST SEVERAL DAYS. THIS MODERATE AFTERNOON UPSLOPE FLOW SHOULD
HELP TRIGGER NEW CELLS AS THE MOUNTAIN OUTFLOWS DROP DOWN THE
WESTERN SLOPES LATER THIS AFTERNOON. WILL NOT MAKE ANY MAJOR
ADJUSTMENTS TO THE TONIGHT FORECAST PERIOD AS SCATTERED LEVEL POPS
STILL LOOK ON TRACK. ONE CONCERN FOR THIS EVENING WILL BE THE
POTENTIAL FOR STRONG DOWNBURST AND OUTFLOW WINDS FROM SOME OF THE
STRONGER STORMS. DO NOT THINK HEAVY RAINFALL WILL BE A FLOODING
CONCERN BASED ON THE RATHER DRY SUB-CLOUD LAYER AND STORM MOTION.
BEYOND TONIGHT...MODELS WERE STILL INDICATING OTHER SHORTWAVE
TROUGHS DROPPING SOUTH THROUGH NEW MEXICO AGAIN MONDAY AND TUESDAY.
A FEW OF THESE FEATURES MIGHT BE SHOWING UP A LITTLE STRONGER IN THE
MODELS DUE TO SOME CONVECTIVE FEEDBACK IN THEIR SOLUTIONS. AT ANY
RATE...THE FLOW PATTERN LOOKS FAVORABLE THROUGH THE WEEK FOR A
TYPICAL SUMMERTIME FORECAST OF ISOLATED TO SCATTERED AFTN/EVEN
TSTMS. TEMPERATURES WILL BE A BIT TRICKY BASED OF THE DAY-TO-DAY
VARIABILITY IN PRECIP AND CLOUD COVER...BUT WILL JUST KEEP HIGHS
RUNNING A FEW DEGREES ABOVE NORMAL.

.TWC...NONE.

AZZ019-029>035-211400-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1130 AM MST SUN JUL 20 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST ARIZONA

.DAY ONE...TODAY

SYNOPSIS...A FEW WEAK IMPULSES ARE FORECAST TO BRING AN INCREASE IN
SHOWERS AND THUNDERSTORMS LATE TODAY AND MONDAY. OTHERWISE...THE
LARGE SCALE WEATHER PATTERN WILL REMAIN FAVORABLE THROUGH THE WEEK
FOR A TYPICAL SUMMERTIME FORECAST OF SCATTERED AFTERNOON AND EVENING
THUNDERSTORMS. DAYTIME TEMPERATURES WILL FLUCTUATE A BIT WITH THE
VARIABILITY IN THUNDERSTORM ACTIVITY EACH DAY...BUT OVERALL WILL
REMAIN SLIGHTLY ABOVE NORMAL THIS WEEK.

.DISCUSSION...THE MORNING UPPER-AIR SOUNDINGS ACROSS THE REGION
INDICATED A MUCH DRIER AIRMASS IN PLACE TODAY COMPARED TO THE PAST 2
DAYS. THIS DRIER AIR SPREAD INTO THE AREA YESTERDAY FROM THE EAST
AND HELPED LIMIT THE THUNDERSTORM ACTIVITY LAST EVENING. THE MOST
SIGNIFICANT CHANGE WAS IN THE TEMPERATURES ABOVE 20KFT WHERE THEY
HAD UNDERGONE SOME COOLING DURING THE PAST 24 HOURS. THESE SLIGHTLY
COOLER TEMPERATURES ALOFT SHOULD NOT BE AN INHABITING FACTOR IN
THUNDERSTORM FORMATION LATER THIS AFTERNOON AND EVENING LIKE THEY
WERE YESTERDAY. AS FAR AS THE FLOW PATTERN GOES...TODAY IS REFERRED
TO A TRANSITION DAY. THE MID LEVEL HIGH PRESSURE CELL IS FORECAST TO
MIGRATE NORTHWEST AND CONSOLIDATE WITH ANOTHER HIGH CIRCULATION
CENTERED OVER NORTHERN NEVADA. THIS WILL RESULT IN A SHIFT IN THE
STEERING FLOW FROM SOUTHEAST TO NORTHEAST BY EARLY MONDAY. CURRENT
THINKING IS THAT LATER THIS AFTERNOON AND EVENING WILL STILL BE MORE
ACTIVE THUNDERSTORM WISE THAN YESTERDAY EVEN THOUGH THIS AIRMASS HAD
DRIED OUT. THIS THINKING IS MAINLY BASED ON THE CONSIDERATION OF TWO
LARGER SCALE FEATURES THAT MAY HELP ORGANIZE STORMS TODAY AND
TONIGHT. THE FIRST ONE WAS AN INVERTED SHORTWAVE TROUGH EXTENDING
NORTHWARD FROM SOUTHERN SONORA TO NEAR THE INTERNATIONAL BORDER.
THIS FEATURE SHOULD HELP FOCUS STORMS ACROSS SANTA CRUZ AND
SOUTH-CENTRAL PIMA COUNTIES SOUTH INTO NORTHERN SONORA BY THIS
EVENING. ANOTHER PIECE OF SHORTWAVE ENERGY IS FORECAST TO DROP SOUTH
THROUGH NEW MEXICO BY TONIGHT WHICH SHOULD AID IN SUSTAINING MOIST
CONVECTION ALONG THE EASTERN RIM AND WHITE MOUNTAINS INTO THE
MOUNTAINS OF GRAHAM COUNTY. THE STORMS THAT DEVELOP IN THE HIGHER
TERRAIN WILL HAVE A GOOD CHANCE OF PROPAGATING INTO THE LOWER
CENTRAL DESERTS AROUND TUCSON AND SELLS LATER THIS EVENING. THE
POTENTIAL FOR STRONG THUNDERSTORM OUTFLOWS IS GREATER TODAY DUE TO
THE DRIER AIRMASS AND WARMER SURFACE TEMPERATURES. THE RISK OF HEAVY
RAINFALL IN EXCESS OF ONE INCH WILL BE LOW.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SUNDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

ON MONDAY A WEAK IMPULSE DROPPING SOUTH THROUGH NEW MEXICO WILL CLIP
SOUTHEAST ARIZONA. THIS FEATURE SHOULD AID IN THE DEVELOPMENT OF
AFTERNOON AND EVENING THUNDERSTORMS. AS HIGH PRESSURE ALOFT SETTLES
NORTHWEST OF ARIZONA OVER NORTHERN NEVADA...THE STEERING FLOW WILL
BECOME MORE FAVORABLE FOR STORMS OVER THE EASTERN RIM AND WHITE
MOUNTAINS TO PROPAGATE SOUTHWEST INTO THE LOWER CENTRAL AND WESTERN
DESERTS MONDAY EVENING. OTHERWISE...ENOUGH MOISTURE WILL BE IN PLACE
FOR A STANDARD SUMMERTIME THUNDERSTORM SEASON FORECAST. EXPECT
SCATTERED MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS.

.SPOTTER INFORMATION STATEMENT...

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