Flash Flood in Arizona, August 9, 2002

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
200 PM MST FRI AUG 9 2002

.SYNOPSIS...THUNDERSTORMS WILL MAINLY BE LIMITED TO THE MOUNTAINS
THROUGH SATURDAY...ALTHOUGH A FEW STRONGER ONES WILL TRY TO DRIFT
INTO THE VALLEYS DURING THE EARLY EVENING HOURS. THERE WILL BE A
BETTER CHANCE OF THUNDERSTORMS SUNDAY AFTERNOON AND EVENING AS A
WEAKENING COLD FRONT MOVES WEST FROM THE SOUTHERN PLAINS AND THE
REMNANTS OF TROPICAL DEPRESSION BERTHA MOVE INTO SONORA. HIGH
PRESSURE EXTENDING FROM WESTERN ARIZONA INTO THE EASTERN PACIFIC
WILL THEN TRY TO DRY US OUT BEFORE IT WEAKENS LATE NEXT WEEK AND A
NEW RIDGE FORMS OVER THE SOUTHERN PLAINS.

.DISCUSSION...SITUATION HAS DEFINITELY BECOME MORE COMPLICATED OVER
THE NEXT WEEK COMPARED TO WHAT IT LOOKED LIKE A COUPLE OF DAYS AGO.
AS EXPECTED, OUR CROP OF TSTMS TODAY IS SHOWING MORE STRENGTH BUT
LITTLE TENDENCY TO PUSH INTO THE VALLEYS, AT LEAST SO FAR. WITHIN
THE PAST COUPLE OF HOURS, OUR VAD WIND PROFILER HAS SHOWN A SLIGHT
INCREASE IN NE STEERING FLOW. ITS NOT MUCH (10KTS), BUT IT COULD BE
ENOUGH TO PUSH A COUPLE OF STRONGER CELLS INTO THE VALLEYS FROM KTUS
EAST, ESPECIALLY IF THE MID LEVELS HAVE NOT WARMED UP OVER OUR 12Z
SOUNDING. THE WHITES AND GILAS HAVE ALSO LIT UP THIS AFTERNOON WITH
AN OUTFLOW TRYING TO ORGANIZE. PER OUR LATE MORNING HWO, ANY STORMS
MOVING INTO THE VALLEYS WILL HAVE TO BE WATCHED FOR DOWNBURST WIND
POTENTIAL ALTHOUGH COVERAGE SHOULD BE RATHER ISOLATED. W CWA WILL
REMAIN SHUT DOWN WITH SATELLITE SHOWING CU BEING SQUASHED BY THE CAP.

NOT MUCH CHANGE FOR SAT WITH THE UPPER RIDGE JUST TO OUR N, 500MB
TEMPS REMAINING NEAR -6C, PRECIP WATERS HOLDING NEAR 1.4 OVER SE
2/3 OF THE CWA, AND VERY WEAK E-NE STEERING FLOW. ALL THIS ADDS UP
TO A SIMILAR DAY COMPARED TO TODAY. WE THEN TURN TO SUN AFTERNOON
AND EVENING AS THE COLD FRONT DROPPING INTO KS BACKS INTO NM AND THE
UPPER LEVEL REMAINS OF T.D. BERTHA PASS INTO THE NORTHERN SIERRA
MADRES. MODELS STILL SHOW NE FLOW INCREASING TO 20-25KTS WITH THE
RIM AND GILAS LIGHTING UP. HOWEVER, THEY HAVE BACKED OFF ON THE
UPPER DIVERGENCE INCREASE SINCE BY THEN THE HIGH SHOULD BE OVER W AZ
AND NOT DUE N. IF WE HAD A FOUR CORNER HIGH, THIS WOULD SPELL A VERY
ACTIVE AFTERNOON/EVENING, BUT THE UNFAVORABLE UPPER HIGH POSITION
MAKES US RELUCTANT TO RAISE POPS OVER THE MID SHIFTS UPWARD
ADJUSTMENT. IF ANYTHING, WELL SHIFT THE HIGHER VALLEY POPS INTO SUN
EVENING SINCE WELL NEED EVERY BIT OF DAYTIME HEATING TO FIRE ON THE
OUTFLOWS. ONCE THE REMNANT EASTERLY WAVE CUTS ACROSS THE GULF OF CA
ON MON, THE STAGE WILL BE SET FOR SOME KIND OF SURGE SINCE THE
DESERTS WILL BE OVER 110F FOR THE NEXT 3 DAYS AND THE S GULF WILL BE
QUITE BIT COOLER. THINKING IS THAT IT WILL MOST LIKELY BE SHALLOW,
BUT WITH THE DEEPER MOISTURE AND MUCH WEAKER UPPER FLOW OVER US, AND
LOW LEVEL MOISTURE TRANSPORT WONT BE ABLE TO ENTRAIN OUT AS EASILY.
LIKE THE IDEA OF KEEPING AT LEAST A CHANCE IN FOR THE E CWA,
PRIMARILY OVER THE MOUNTAINS, UNTIL WE SEE HOW DEVELOPMENTS WILL
SHAKE OUT. THU/FRI NEXT WEEK MAY BE THE NEXT CHANCE FOR SOMETHING TO
FIND ITS WAY INTO THE W DESERTS AS AN EXTENSION OF THE BERMUDA HIGH
TRIES TO BUILD INTO THE S PLAINS. CONFIDENCE THERE, THOUGH, IS ALSO
LOW. PYTLAK

.TWC...NONE.