Flash Flood in Arizona, August 6, 2002

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
215 PM MST TUE AUG 6 2002

.SYNOPSIS...AN UPPER LEVEL DISTURBANCE OVER NEW MEXICO WILL HELP TO
GENERATE SCATTERED SHOWERS AND THUNDERSTORMS THIS EVENING...ALTHOUGH
THE RISK OF STRONGER STORMS WILL REMAIN CONFINED EAST OF TUCSON
WHERE THERE HAS BEEN MORE SUNSHINE TODAY. HIGH PRESSURE CENTERED
OVER THE CENTRAL UNITED STATES WILL SHIFT WEST AND STRENGTHEN OVER
ARIZONA BY FRIDAY. THIS WILL BEGIN A SUSTAINED DRYING TREND WHICH
WILL CONTINUE INTO NEXT WEEK.

.DISCUSSION...WERE SEEING A MUCH LATER AND MORE BENIGN START TODAY
WITH ISOLATED TSTMS OVER THE MOUNTAINS AND SPRINKLES/LIGHT SHOWERS
OVER THE CENTRAL CWA WHERE CLOUDS HAVE HELD SINCE DEVELOPING AROUND
MID MORNING. NOT MUCH CHANGE IN THINKING WITH THE E CWA THE MOST
LIKELY PLACE TO SEE STRONGER TSTMS THIS EVENING, WITH THE SANTA CRUZ
VALLEY THE LEAST. MODELS AND SATELLITE STILL SHOW DECENT DYNAMICS
AND SYNOPTIC-SCALE LIFT ACROSS THE E 2/3 OF THE CWA, SO DESPITE THE
OBVIOUS DOWNTICK IN INTENSITY, WELL CARRY SCATTERED POPS FOR MOST
AREAS TONIGHT, WITH PERHAPS A SHOWER OR TWO LINGERING INTO THE
OVERNIGHT.

THE WELL-ADVERTISED DRYING TREND WILL START TOMORROW AS THE EASTERLY
WAVE OVER NM SHEARS OUT, LEAVING A WEAKENING DEFORMATION AREA ACROSS
THE E CWA. WERE NOT BUYING INTO THE RAPID DRYING OF THE AVN, OR THE
ETA FOR THAT MATTER, SIMPLY BECAUSE MID LEVEL TEMPS REALLY WONT
WARM UP UNTIL THE HIGH ITSELF SHIFTS INTO THE CWA ON FRI AND THE
UPPER LEVEL STRETCHING DEFORMATION SHIFTS OUT OF THE AREA. WITH
WIDESPREAD 1-4 OF RAIN IN THE PAST 5 DAYS (SOME MOUNTAIN LOCATIONS
IN EXCESS OF 8 BASED ON RADAR ESTIMATES), THERE WILL BE A LOT OF
MOISTURE TO RECYCLE, SO WE SHOULD BE FAIRLY UNSTABLE FOR AT LEAST
THE NEXT TWO AFTERNOONS. FLOW IS ALSO EXPECTED TO GO WEAK, SO AGAIN
WE WONT BE ABLE TO SCOUR OUR WHAT WE HAVE VERY EASILY. WELL START
TO TAKE POPS DOWN LITTLE-BY-LITTLE, BUT BY MON, EVEN MOUNTAIN TSTMS
BECOME TOUGH TO GENERATE AS 500MB TEMPS WARM TO -4C TO -5C. THE
ISSUE BY THEN WILL REVOLVE AROUND TEMPS AS THE DAYS GET WARMER, BUT
NIGHTS ACTUALLY COOL OFF DUE TO THE GRADUALLY SINKING DEWPOINTS.
HERE AGAIN, THE DOWNWARD HUMIDITY TREND WILL MOST LIKELY BE SLOWER
THAN MODEL GUIDANCE. THE MEX POPS DONT JIVE AT ALL WITH THE PARENT
MODEL (AVN) MOISTURE FIELD, AND NEITHER DO THE TEMPS, PROBABLY
BECAUSE OF THE MEXS STRONG CLIMO BIAS. HOWEVER, I WONDER IF THE
STATISTICAL PACKAGE IS ALSO ATTEMPTING TO ACCOUNT FOR OUR MOISTURE
RECYCLING. SOMETHING TO PONDER.

EVEN THOUGH WE THINK THE MODELS ARE TOO BULLISH IN DRYING US OUT
(THEY WERE REALLY BAD WITH A DRYING TREND TWO WEEKENDS AGO), THE
SUSTAINED RETROGRESSION AND CONTINUED W FLOW WELL BEYOND DAY 7
INDICATES WE WILL INDEED DRY OUT. IN FACT, IF THE SEPTEMBER-LIKE
AVN/GFS ENDS UP BEING CORRECT, ALL OF NEXT WEEK WILL BE DRY WITH THE
LOWS SINKING WELL BELOW NORMAL AND EVEN THE DESERT HIGHS SINKING IN
THE LOW-MID 90S. IT SEEMS MUCH TOO EARLY FOR THAT TO HAPPEN, AND THE
AVN ENSEMBLES/ECMWF/UKMET ARE MUCH LESS AMPLIFIED. EVEN THOSE
SOLUTIONS, THOUGH, KEEP US MAINLY DRY AFTER DAY 6, ALBEIT QUITE A
BIT WARMER. PYTLAK

.TWC...NONE.