Flash Flood Warning 30, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
230 PM MST TUE JUL 27 1999

SYNOPSIS...ANOTHER SUBTROPICAL WEATHER DISTURBANCE IS EXPECTED TO
MOVE INTO SOUTHEAST ARIZONA TODAY...RESULTING IN NUMEROUS
THUNDERSTORMS...SOME WITH LOCALLY HEAVY RAIN. THUNDERSTORM ACTIVITY
WILL DECREASE SOMEWHAT BY WEDNESDAY. HIGH PRESSURE WILL REMAIN OVER
THE EASTERN GREAT BASIN THROUGH THE END OF THE WEEK...FOR THE
CONTINUED THREAT OF MAINLY AFTERNOON AND EVENING THUNDERSTORMS.

DISCUSSION...CAP/INVERSION NEAR 700 MB HAS PRODUCED A SLOW START TO
THUNDERSTORM ACTIVITY THIS AFTERNOON. BUT SUNNY SKIES AND AFTERNOON
HEATING WILL BREAK THE INVERSION. SPC HAS AREA UNDER A SLIGHT CHANCE
OF SEVERE WEATHER THIS AFTERNOON. SO MAY HAVE TO DEAL WITH ISOLATED
DAMAGING WINDS IN ADDITION TO FLASH FLOODING. WATER VAPOR SHOWS LOTS
OF CONVECTIVE ACTIVITY NEAR THE CENTER OF THE TROUGH AND NORTHWARD
TO NEAR EL PASO. BOTH ETA/NGM MOVE THE WAVE INTO CENTRAL
ARIZONA...AND MOVEMENT OF THIS SYSTEM SEEN ON THE WATER VAPOR
IMAGERY SEEMS TO CONFIRM THIS.  SOUTHEAST ARIZONA WILL BE ON THE
BACKSIDE OF THE TROUGH WEDNESDAY. WITH NO DYNAMICS TO WORK WITH
STORMS WILL HAVE TO TRIGGER ON AFTERNOON HEATING...THUS WEDNESDAY
MAY BE A LOW GRADE MONSOON DAY. THURSDAY THROUGH THE EXTENDED PERIOD
MODELS MAINTAIN EASTERLY OR NORTHEASTERLY FLOW WITH THE HIGH CENTER
NORTH OF TUCSON. ANOTHER EASTERLY WAVE COULD PUSH THROUGH AT ANY
TIME. WITHOUT ANY CONFIDENCE ON TIMING OF FEATURES...WILL KEEP A
STANDARD MONSOON FORECAST GOING.

.TWC...FLASH FLOOD WATCH UNTIL 03Z ZONES 29,30,32,33,34,AND 35.

AZZ019-029>035-280500-
SPECIAL WEATHER STATEMENT...SOUTHEAST ARIZONA CONVECTIVE OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1230 PM MST TUE JUL 27 1999...THIS PRODUCT IS NOT UPDATED

                          *CONDITIONAL*   *CONDITIONAL*
COUNTY            AREAL    PROBABILITY  RAIN GREATER THAN   STORM
                 COVERAGE   OF SEVERE     1.00      2.00    MOTION

COCHISE             70          35         50        30     WNW15
GRAHAM              50          30         45        25     WNW12
GREENLEE            50          20         40        25     W12
TUCSON/ERN PIMA     55          35         45        25     WNW12
TOHONO O'ODHAM      45          40         45        25     WNW12
SOUTHEAST PINAL     45          35         40        25     WNW12
WESTERN PIMA        40          40         40        20     WNW12
SANTA CRUZ          70          30         55        35     WNW15

SYNOPSIS...A FLASH FLOOD WATCH IS IN EFFECT FOR MOST OF SOUTHEAST
ARIZONA UNTIL 800 PM. A DISTURBANCE IN NORTHEAST SONORA PROVINCE
WILL PASS ALONG THE ARIZONA-MEXICAN BORDER THROUGH THIS EVENING.
THUNDERSTORMS HAVE INITIALLY HAD A HARD TIME DEVELOPING DUE TO A
POCKET OF WARM AIR AT ABOUT 15000 FEET IN THE ATMOSPHERE. AS THE
AFTERNOON WEARS ON...THE HEATING IN LOWER LEVELS OF THE
ATMOSPHERE SHOULD BREAK THIS CAP AND RESULT IN RAPID DEVELOPMENT.
THE STORMS WILL TEND TO MOVE AT 10-15 MPH BUT MAY ALSO SHOW A
TENDENCY TO BUILD BACKWARD TOWARD THE EAST. SUCH A SITUATION
OCCURRED IN A FEW SPOTS YESTERDAY AND RESULTED IN 2 INCHES OF
RAIN IN AN HOUR OR LESS. BECAUSE THE ATMOSPHERE WILL BE ABLE TO
HEAT UP CONSIDERABLY BEFORE THE STORMS DEVELOP...THERE IS A
BETTER CHANCE THAT THEY WILL PRODUCE DAMAGING MICROBURST WINDS.
THIS WILL BE ESPECIALLY TRUE IN THE DESERTS FROM TUCSON WEST.

*****************************************************************
KEY...
AREAL COVERAGE - PERCENT OF COUNTY OR AREA THAT WILL EXPERIENCE
                 THUNDERSTORMS
PROB OF SEVERE - THE PROBABILITY THAT AN INDIVIDUAL STORM WILL
                 REACH SEVERE LEVELS (DAMAGING WIND AND/OR
                 LARGE HAIL)
RAIN GRTR THAN - THE PROBABILITY THAT AN INDIVIDUAL STORM WILL
                 PRODUCE RAIN EXCEEDING 1 INCH OR 2 INCHES IN
                 ANY LOCATION
STORM MOTION   - GENERAL DIRECTION TO WHICH THE STORMS WILL
                 LIKELY MOVE AND SPEED IN MPH

NOTE...
VALID TIME IS FROM 12:45 PM TO 12 MIDNIGHT OF THE DAY OF ISSUANCE.
THIS PRODUCT IS NOT TO BE USED IN PLACE OF SEVERE THUNDERSTORM OR
FLASH FLOOD WARNINGS OR WATCHES. THIS PRODUCT IS ONLY USED FOR
OUTLOOK PURPOSES. CORRESPONDING GRAPHICSx MAY BE FOUND ON THE NWS
TUCSON INTERNET PAGE AT
HTTP://NIMBO.WRH.NOAA.GOV/TUCSON/SWO/SWO.SHTML

END/PYTLAK