Severe Thunderstorm Warning 53, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
137 PM MST TUE JUL 29 2003

.SYNOPSIS...ARIZONA IS CURRENTLY BETWEEN AN AREA OF HIGH PRESSURE
CENTERED OVER NEVADA AND A LOW PRESSURE SYSTEM OVER BAJA. THE BAJA
LOW WILL MOVE WESTWARD A BIT TONIGHT AND WEDNESDAY...ALLOWING THE
STEERING FLOW TO BECOME MORE SOUTHERLY. THIS MORE SOUTHERLY FLOW
WILL KEEP THE AIRMASS VERY MOIST OVER SOUTHEAST ARIZONA THE NEXT FEW
DAYS. THIS MOISTURE COMBINED WITH DAYTIME HEATING WILL LEAD TO MORE
SCATTERED AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS. HIGH
PRESSURE CENTERED OVER NEVADA WILL EVENTUALLY SHIFT OVER NEW MEXICO
AND SOUTHWEST TEXAS BY THE WEEKEND. THIS MAY LEAD TO A GRADUAL
DECREASE IN AREAL COVERAGE TO THUNDERSTORMS OVER THE WESTERN DESERTS
BY THE END OF THE WEEK AS DRIER AIR TRIES TO FILTER INTO THE REGION
FROM THE WEST...BUT CONFIDENCE IN THIS IS LOW.

.DISCUSSION...WATER VAPOR IMAGERY AND LIGHTNING DATA SHOWS
CONVECTION DEVELOPING IN FAVORED AREAS AS ANTICIPATED...GENERALLY
OVER EXTREME SOUTHEAST ARIZONA BUT ALSO EXTENDING SOUTHEAST INTO
SONORA AND CHIHUAHUA. RADARS DETECTING SCATTERED TO NUMEROUS SHOWERS
AND THUNDERSTORMS IN THIS AREA AND WILL CONTINUE TO DEVELOP AND/OR
MOVE INTO THE REGION. AS SUSPECTED THE 12Z TUCSON SOUNDING WAS NOT
REPRESENTATIVE AND 18Z SOUNDING REVEALED A SIGNIFICANTLY WARMER
AIRMASS ABOVE 500MB. ABOVE THE VALLEY BOUNDARY LAYER...750MB OR
SO...FLOW IS NEARLY UNIDIRECTIONAL WITH NOT MUCH SPEED SHEAR.

IN THE 300-500MB LAYER MODELS ARE PROGGING THE LOW OVER THE BAJA
PENINSULA TO MOVE WEST THROUGH WEDNESDAY AS THE HIGH SHIFTS POSITION
FROM NORTHERN CALIFORNIA AND NEVADA INTO UTAH/NRN ARIZONA WITH THE
RIDGE NOSING INTO NEW MEXICO AND WEST TEXAS BY THURSDAY. MODELS PROG
THE DEFORMATION ZONE OVER TEXAS TO DRIFT WEST THROUGH WEDNESDAY BUT
AS THE RIDGE BUILDS SOUTH THIS FEATURE ALSO GETS PUSHED MUCH FARTHER
SOUTH. AT 300MB...AVN IS ADVERTISING SOME DECENT OMEGA AND
DIVERGENCE FIELDS MOVING INTO ARIZONA BEGINNING WEDNESDAY NIGHT AND
CONTINUING THROUGH FRIDAY...BUT ESPECIALLY ON FRIDAY NEAR THE GULF
OF CALIFORNIA.

AIRMASS WILL REMAIN RATHER JUICY THROUGH THE END OF THE WEEK...BUT
THE GFS IS HINTING AT SOME DRYING FROM THE WEST DURING THE WEEKEND
AS A TROUGH DEVELOPS ALONG THE WEST COAST...BUT I AM NOT CONFIDENT
IN THIS OCCURRING...SO UNTIL I SEE SOME CONSISTENCY BETWEEN MODEL
RUNS...WILL KEEP A STANDARD MONSOON FORECAST OF SCATTERED AFTERNOON
AND EVENING THUNDERSTORMS GOING THROUGH EARLY NEXT WEEK.

AVN MOS TEMP GUIDANCE SEEMS TO COOL...SO USED A BLEND OF PREVIOUS
FORECAST NUMBERS AND ETA/NGM. FOR THE EXTENDED PERIOD WENT SLIGHTLY
ABOVE MRF MOS.

MOLLERE

.TWC...FLOOD WARNING FOR CENTRAL PIMA COUNTY/ZONE 32 UNTIL 5 PM MST.

AZZ019-029>035-301400-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1220 PM MST TUE JUL 29 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST ARIZONA

.DAY ONE...TODAY

SYNOPSIS...A COOL START TO THE DAY WILL BE OVERCOME THIS AFTERNOON
AS TEMPERATURES CLIMB INTO THE NINETIES OVER THE VALLEYS. SOUTHERN
COCHISE COUNTY AND AREAS SOUTH AND WEST OF TUCSON SEEM THE LIKELY
AREA FOR THE STRONGEST STORMS TODAY.

DISCUSSION...

CONVECTION HAS ALREADY BEGUN THIS AFTERNOON AS MOISTURE CONTINUES TO
BE ADVECTED INTO THE AREA FROM THE SOUTHEAST. UPPER LEVEL HIGH
PRESSURE TO THE NORTHWEST WILL SLOWLY EXPAND TO THE EAST ALLOWING
ADDITIONAL MOISTURE TO BE PULLED INTO THE REGION. ALSO...SOME
COOLING HAS TAKEN PLACE AT THE UPPER LEVELS RESULTING IN ADDITIONAL
CAPE. HOWEVER...AN ELEVATED INVERSION IN THE MID LEVELS WILL NEED TO
BE OVERCOME...WHICH SHOULD NOT BE A PROBLEM DUE TO THE CONVECTIVE
TEMPERATURE BEING 92. ONLY A DELAY TO THE CONVECTION COMPARED TO
YESTERDAY IS EXPECTED. THEREFORE...WITH THE MOISTURE REMAINING OVER
SOUTHERN ARIZONA THE BEST CHANCE OF HEAVY RAIN AND STRONG WINDS WILL
BE WITHIN THE SOUTHERN PORTION OF THE COUNTY WARNING AREA. THIS
WOULD INCLUDE SANTA CRUZ...SOUTHERN COCHISE AND SOUTHERN PIMA
COUNTIES. THE STORMS ARE EXPECTED TO MOVE GENERALLY TOWARD THE WEST
OR NORTHWEST.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

SEASONAL SCATTERED THUNDERSTORMS WITH THE NORMAL IMPLIED THREAT OF
HEAVY RAIN AND STRONG WINDS WILL CONTINUE THROUGH THE WEEK.

.SPOTTER INFORMATION STATEMENT...

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

EVANS