Severe Thunderstorm Warning 47, NWS Tucson, AZ

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.

AZZ019-029>035-100700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
1110 AM MST FRI AUG 9 2002

.SYNOPSIS...HIGH PRESSURE HAS DEVELOPED NEAR THE WHITE MOUNTAINS AND
HAS STOPPED THE DRIER AIR OVER THE WESTERN DESERTS FROM SPREADING
EAST. WITH THE HIGH SO CLOSE TO THE REGION...STEERING FLOW WILL
REMAIN WEAK AND MID LEVEL TEMPERATURES WILL REMAIN ON THE WARM SIDE.
THUS...WHILE MOUNTAIN THUNDERSTORMS WILL BE MORE NUMEROUS TODAY...
ONLY A FEW OF THEM WILL MAKE IT INTO THE VALLEYS BEFORE DISSIPATING
EARLY THIS EVENING.

.DISCUSSION...AS WAS SEEN YESTERDAY IN COMPUTER RANGE FORECAST
MODELS...THE ANTICIPATED DRYING TREND HAS BEEN STOPPED. HIGH
PRESSURE WHICH WAS EXPECTED EARLIER IN THE WEEK TO DEVELOP ACROSS
SOUTHERN ARIZONA HAS INSTEAD FORMED JUST TO OUR NORTH. THIS HAS
RESUMED WEAK EAST FLOW OVER THE REGION AND HAS PUSHED PRECIPITABLE
WATERS BACK TO AROUND 1.4 INCHES...MAINLY SOUTHEAST OF A LINE FROM
SAN CARLOS TO SELLS. THE CAPPING INVERSION WHICH KEEP VALLEY
THUNDERSTORMS LIMITED YESTERDAY HAS WEAKENED BUT WAS STILL PRESENT
THIS MORNING. THE LOWER LEVELS OF THE ATMOSPHERE WERE JUST A BIT
DRIER COMPARED TO YESTERDAY BUT ALSO SEVERAL DEGREES WARMER. THIS
WILL RESULT IN A MORE UNSTABLE ATMOSPHERE FOR THIS AFTERNOON AND
EVENING...ESPECIALLY OVER SANTA CRUZ AND COCHISE COUNTIES WHERE THE
CAP APPEARS TO BE SLIGHTLY WEAKER.

THE MAIN LIMITING FACTORS TODAY ARE ONCE AGAIN WEAK STEERING FLOW...
A CAPPING INVERSION AROUND 25000 FEET...AND NO TRIGGERING MECHANISM.
THIS WILL TEND TO KEEP MOST THUNDERSTORMS NEAR THE MOUNTAINS.
HOWEVER...DUE TO THE GREATER INSTABILITY TODAY...THEY WIL TEND TO BE
STRONGER...PRODUCE MORE RAIN...AND COULD SURVIVE A WHILE LONGER AS
THEY TRY TO MOVE INTO THE VALLEYS LATE THIS AFTERNOON. ANY STORMS
THAT DO SURVIVE IN THE VALLEYS WILL BE CAPABLE OF PRODUCING ISOLATED
DOWNBURST WINDS NEAR SEVERE LEVELS SINCE SURFACE DEWPOINTS ARE ON
THE LOW SIDE. BECAUSE OF THE LACK OF A TRIGGER...THUNDERSTORMS WILL
QUICKLY FADE AFTER SUNSET AND WILL REMAIN DISORGANIZED.

THE RISK OF SEVERE THUNDERSTORMS IS A BIT BELOW CLIMATOLOGY FROM THE
SANTA CRUZ VALLEY EAST...ONLY BECAUSE THUNDERSTORM COVERAGE WILL BE
LIMITED. THE RISK OF ONE INCH OF RAIN OR GREATER IS NEAR CLIMATOLOGY
EAST OF THE SANTA CRUZ VALLEY...AND WELL ABOVE CLIMATOLOGY OVER THE
EASTERN MOUNTAINS. IN THE WESTERN DESERTS WHERE THE ATMOSPHERE IS
STRONGLY CAPPED AND MUCH DRIER...NO THUNDERSTORMS ARE EXPECTED AT
ALL. STORM MOTION WILL BE GENERALLY NORTHEAST OR EAST AT 5 MPH.

PYTLAK