Severe Thunderstorm Warning 79, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
200 PM MST FRI AUG 22 1997

HIGH PRESSURE IN THE MID- TO UPPER-LEVELS CONTINUES TO BE LOCATED
OVER THE CENTRAL BORDER AREA OF ARIZONA AND NEW MEXICO.

THE 1200 UTC ETA AND NGM MODELS RUNS SHOW ONLY SUBTLE CHANGES TO
THIS PATTERN OVER THE NEXT 24- TO 48-HOUR PERIOD. THE STRONGEST
WIND BELOW 100 MB AT 1200 UTC WAS 10 KNOTS AND THE ESTIMATED CAPE
FOR THE LATE AFTERNOON AND EVENING IS ABOUT 200 J/KG WHICH WILL
ALLOW A FEW STORMS TO MOVE INTO THE VALLEYS THIS EVENING.

FOR THE WEEKEND...WITH THE RIDGE VIRTUALLY OVERHEAD...THE
VERTICAL SHEAR WILL REMAIN WEAK AND DISORGANIZED. A GRADUAL
DRYING TREND IS ALSO LIKELY WITH THE RIDGE OVERHEAD. CANT SEE A
GULF OF CALIFORNIA MOISTURE SURGE OCCURING UNTIL SUNDAY AT THE
EARLIEST. THE 1200 UTC SOUNDING AT GUAYMAS IS ON THE DRY SIDE AND
A RIDGE AXIS EXTENDS SOUTHWARD ALONG THE NORTHWEST MEXICO COAST.
IT ISNT UNTIL LATE SATURDAY...AS THE RIDGE AXIS SHIFTS AWAY FROM
NORTHWEST MEXICO...THAT THE PATTERN OVER MEXICO BECOMES MORE
FAVORABLE FOR MCS DEVELOPMENT. ANOTHER FACTOR IS THAT THE SURFACE
PRESSURE DIFFERENCE BETWEEN GUAYMAS AND YUMA IS ONLY ABOUT 3 MB.
LIKE TO SEE A 6 TO 8 MB DIFFERENCE BEFORE I GET TOO EXCITED ABOUT
MOISTURE FROM THE SOUTH. THIS MEANS THE NEXT CHANCE FOR A
MOISTURE SURGE WILL BE SUNDAY INTO MONDAY.

IN OTHER WORDS A MEDIUM GRADE MONSOON FOR THIS EVENING THEN LOW
GRADE FOR SATURDAY AND SUNDAY ACROSS SOUTHEAST ARIZONA.
TEMPERATURES WILL REMAIN WELL ABOVE NORMAL WITH RIDGE OVERHEAD.
TUS 3222. MCCOLLUM

TUS...NONE.

AZZ019-026>030-222300-
SPECIAL WEATHER STATEMENT...SOUTHEAST ARIZONA CONVECTIVE OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1145 AM MST THU AUG 21 1997...THIS PRODUCT IS NOT UPDATED

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

COCHISE          30          60          80          0     NW  5
GRAHAM           20          30          20          0     NW  5
GREENLEE         40           0          20          0     SW  5
TUCSON/ERN PIMA  30          60          50          0     NW  5
TOHONO OODHAM   20          60          50          0     NW  5
WESTERN PIMA     10          60          20          0     NW  5
SOUTHEAST PINAL  20          60          20          0     NW  5
SANTA CRUZ       40          60          80          0     NW  5

SYNOPSIS...THE AIR MASS ACROSS SOUTHEAST ARIZONA REMAINS MOIST
AND UNSTABLE WITH MOUNTAIN AND VALLEY THUNDERSTORMS TODAY.
MOISTURE VALUES ARE HIGH ENOUGH TO SUPPORT LOCALIZED HEAVY
RAINFALL AND WITH HIGHER TEMPERATURES AN ISOLATED SEVERE STORM
WILL BE POSSIBLE. WIDESPREAD HEAVY RAIN AND SEVERE WEATHER IS NOT
ANITCIPATED.
*****************************************************************
KEY...
AREAL COVERAGE - PERCENT OF COUNTY OR AREA THAT WILL EXPERIENCE
                  THUNDERSTORMS
PROB OF SEVERE - THE PROBABILITY THAT ANY ONE OF THE STORMS WILL
                  REACH SEVERE LEVELS (DAMAGING WIND AND/OR
                  LARGE HAIL)
RAIN GRTR THAN - THE PROBABILITY THAT ANY ONE OF THE STORMS 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 NOON 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.

END/MCCOLLUM