Severe Thunderstorm Warning 59, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
215 PM MST WED AUG 29 2001

.SYNOPSIS...A TROUGH OF LOW PRESSURE EXTENDING FROM NEVADA INTO
WESTERN ARIZONA WILL ENHANCE THUNDERSTORMS THIS EVENING...ESPECIALLY
FROM TUCSON EAST. IN THE WAKE OF THIS DISTURBANCE...THUNDERSTORMS
ARE EXPECTED TO BE MORE ISOLATED AND CONCENTRATED NEAR THE MOUNTAINS
FOR THURSDAY AND FRIDAY. OVER THE HOLIDAY WEEKEND...A MOIST
SOUTHERLY FLOW SHOULD DEVELOP AS HIGH PRESSURE FORMS TO THE EAST OF
ARIZONA. THIS WILL KEEP THE RISK OF THUNDERSTORMS IN THE PICTURE
THROUGH EARLY NEXT WEEK.

.DISCUSSION...STORMS ARE FIRING NICELY ON THE RIM AND MOUNTAINS SE
OF KTUS, BUT THE 18Z KTUS SOUNDING SHOWED EXTREMELY WEAK FLOW -- SO
WEAK THAT ONLY OUTFLOWS WILL BE ABLE TO FOCUS VALLEY DEVELOPMENT
THIS EVENING. ANVILS ARE STARTING TO SHOW THE INCREASE IN DIFFLUENCE
ALOFT AS WE GET INTO THE LEFT-FRONT QUAD OF THE 60KT UPPER JET. THE
JET IS AT THE BASE OF A LARGER SCALE CIRCULATION CENTER OVER N NV,
WITH 18Z MODELS CONTINUING TO MAXIMIZE UPPER DIVERGENCE IN THE E 1/2
OF THE CWA TONIGHT. THAT WILL FURTHER SUPPORT A SHARP WESTERN EDGE
TO THE STORMS THIS EVENING. WE UPDATED AROUND 1230 PM TO ADD
HEIGHTENED WORDING TO THE ZONES E OF THE SANTA CRUZ RIVER, WHICH
WELL LET RIDE BASED ON CURRENT RADAR TRENDS. WE MAY STILL ISSUE A
FLASH FLOOD WATCH E OF KTUS IF THE STORMS GET MORE ORGANIZED, BUT
BASED ON THE LIMITED COVERAGE SO FAR, HEIGHTENED WORDING WILL
SUFFICE. W DESERTS SHOULD STAY QUIET WHERE MID LEVEL TEMPS ARE
WARMER AND FORCING IS LACKING.

THU/FRI SHOULD BE A BIT QUIETER AS WE GET INTO THE WAKE OF THE UPPER
TROUGH. MODELS HAVE BEEN DEAD WRONG FOR 3 DAYS NOW ABOUT DRYING US
OUT, AND WITH AN 8-10MB PRESSURE DIFFERENTIAL BETWEEN GUYMAS AND
YUMA, THE SURGE WILL CONTINUE. AN MCS DRIFTING INTO SONORA TONIGHT
WOULD ONLY INCREASE THE STRENGTH OF THE SURGE. THUS, WELL KEEP POPS
LOW-MID GRADE THROUGH FRI, ESPECIALLY WITH 500MB TEMPS REMAINING IN
THE -8C TO -10C RANGE.

THEN COMES THE WEEKEND. FOR THE PAST COUPLE OF DAYS, IT APPEARED
THAT HURRICANE FLOSSIE WOULD BE TOO FAR S AND W OF US BY NOW TO BE A
THREAT. HOWEVER, SHES BEEN MOVING NNW FOR MUCH OF THE DAY AND THE
NEW AVN IS TRYING TO PEEL MID/UPPER LEVEL MOISTURE OFF OF HER INTO
AZ THIS WEEKEND. NHC TRACK TAKES FLOSSIE BACK TO THE WNW AND
EVENTUALLY THE W, BUT IF SHE DOESNT MAKE THAT TURN, THE AVN IDEA
BECOMES MUCH MORE LIKELY. THE PROBLEM WITH TROPICAL REMNANTS, IS
THAT THE HIGH LEVEL MOISTURE CAN EITHER ENHANCE STORMS, OR CAN CLOUD
US OVER AND KEEP THEM ISOLATED. THE OTHER PROBLEM IS THAT THE
MOISTURE WE HAVE NOW IS SOLELY THE PRODUCT OF 3 DAYS OF GULF OF CA
INFLOW. IF THE THERMAL LOW WEAKENS ALONG THE CO RIVER, THE SURGE
WOULD SHUT DOWN AND ALLOW DRYING TO TAKE PLACE FROM THE W. WERE
CARRYING UNCERTAINTY WORDING THROUGH DAY 7, AND THAT SEEMS TO BE THE
BEST COURSE OF ACTION FOR NOW. PYTLAK

.TWC...NONE.

AZZ019-029>035-300700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1230 PM MST WED AUG 29 2001

.SYNOPSIS...FOR THE THIRD DAY IN A ROW...CONSIDERABLE MOISTURE HAS
SURGED OUT OF THE GULF OF CALIFORNIA. SOUTH WINDS GUSTED UP TO 45
MPH OVER SOUTHWEST ARIZONA EARLIER THIS MORNING. IN ADDITION...AN
UPPER LEVEL DISTURBANCE OVER SOUTHERN CALIFORNIA IS EXPECTED TO PASS
ACROSS ARIZONA THIS EVENING. THE COMBINATION OF THE TWO IS EXPECTED
TO PRODUCE SCATTERED STRONG THUNDERSTORMS ACROSS THE REGION THIS
AFTERNOON AND EVENING.

.DISCUSSION...SOUTH WINDS UP TO 45 MPH POURED MOISTURE OFF THE GULF
OF CALIFORNIA LAST NIGHT. DEWPOINTS HAVE RISEN TO NEAR 60...WITH
PRECIPITABLE WATERS UP NEAR 1.4 INCHES ACCORDING TO A SPECIAL
WEATHER BALLOON SENT UP BEFORE 1100 AM. AN UPPER LEVEL JET STREAK IS
MOVING INTO SOUTHERN CALIFORNIA AND IS ALREADY STARTING TO INDUCE
DIVERGENCE ALOFT. TEMPERATURES IN THE MID AND UPPER LEVELS OF THE
ATMOSPHERE HAVE COOLED CONSIDERABLY SINCE MONDAY WITH LITTLE IF ANY
CAPPING INVERSION TO IMPEDE THUNDERSTORM DEVELOPMENT. THE ONLY THING
WHICH MAY PREVENT AN OUTBREAK OF SEVERE THUNDERSTORMS AND FLASH
FLOODING IS THE FACT THAT STEERING WINDS ARE VERY WEAK THIS
AFTERNOON. THESE WEAK WINDS WILL MAKE IT DIFFICULT FOR THUNDERSTORMS
OR ORGANIZED OUTFLOWS TO MOVE OFF THE MOUNTAINS. THOSE SAME WEAK
WINDS...HOWEVER...INCREASE THE THREAT OF FLASH FLOODING IN THE
MOUNTAINS. IF THE STORMS GROW LARGER AND BECOME MORE NUMEROUS
THROUGH MID AFTERNOON...A FLASH FLOOD WATCH MAY BECOME NECESSARY FOR
PARTS OF SOUTHEAST ARIZONA.

THERE WILL BE A SHARP WESTERN EDGE TO THUNDERSTORM DEVELOPMENT AND
STRENGTH THIS AFTERNOON AND EVENING. UPPER LEVEL TEMPERATURES ARE
SEVERAL DEGREES WARMER OVER THE WESTERN DESERTS. THAT SHOULD BE
ENOUGH TO CAP DEVELOPMENT WEST OF SELLS. THE RISK OF SEVERE
THUNDERSTORMS AND FLASH FLOODING INCREASES AS ONE LOOKS FURTHER
EAST...ESPECIALLY EAST AND SOUTH OF TUCSON.

STORM MOTION WILL BE TO THE SOUTH AT 5 TO 10 MPH.

PYTLAK