Severe Thunderstorm Warning 36, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
210 PM MST SAT AUG 11 2001

.SYNOPSIS...A LOW PRESSURE AREA OVER WESTERN SONORA WILL PASS JUST
SOUTH OF THE MEXICAN BORDER TONIGHT. ANOTHER DISTURBANCE SOUTH OF
THE TEXAS BIG BEND WILL ALSO MOVE NORTHWEST TOWARD ARIZONA ON
SUNDAY. BOTH OF THESE SYSTEMS ARE BEING STEERED BY HIGH PRESSURE
WHICH IS CENTERING ITSELF OVER THE FOUR CORNERS REGION. THIS HIGH
WILL STALL OUT FOR THE REST OF THE UPCOMING WEEK...AND WILL KEEP AN
AMPLE SUPPLY OF MOISTURE AIMED AT THE REGION.

.DISCUSSION...LOTS OF MODERATE CU IN THE VALLEYS AS OF 20Z, AND A
FEW MOUNTAIN STORMS HAVE BEEN PRETTY HEALTY SO FAR WITH SOME 2
RAINS/HR. HOWEVER, DEVELOPMENT HAS SO FAR BEEN VERY ISOLATED,
PULSEY, AND RESTRICTED TO THE MOUNTAINS. SURFACE FLOW IS TRYING TO
TURN UP THE TUCSON VALLEY, WHICH IF IT CAN HOLD, WILL INDUCE A NICE
LOW LEVEL CONVERGENCE AREA AS THE INVERTED TROUGH CONTINUES TO MARCH
W ALONG THE AZ/SONORA BORDER THIS EVENING. THE EASTERN RIM IS ALSO
QUITE ACTIVE, AND COULD EASILY THROW AND OUTFLOW BOUNDARY INTO
GRAHAM AND PINAL COUNTIES WITHIN THE NEXT COUPLE OF HOURS. AS
MENTIONED EARLIER, PLENTY OF SUN IS THEORETICALLY GIVING US PLENTY
OF VALLEY CAPE. ON THE FLIP SIDE, THE SUBSIDENCE FIELD WHICH MOVED
INTO COCHISE COUNTY IS STILL CAPPING DEVELOPMENT. THE NEXT HOUR OR
TWO WILL BE CRITICAL. IF I DONT SEE SOME INDICATION OF VALLEY
DEVELOPMENT, ILL MOST LIKELY CARBON-COPY YESTERDAY EVENINGS
FORECAST WITH FAIRLY LOW CLIMO POPS BUT WITH HEAVY RAIN WORDING. IF
WE DO START TO POP THE CAP, THEN WELL CONSIDER A FLASH FLOOD WATCH
FOR THE EVENING AND RAISE THE POPS. IN OTHER WORDS, ITS A VERY
CONDITIONAL 1ST PERIOD FORECAST.

THE NEXT EASTERLY WAVE UP THE PIKE IS MAKING GOOD PROGRESS NW AND IS
ALREADY APPROACHING THE BIG BEND.  MODELS INITIALIZED THIS FEATURE
BADLY, SO IM PRETTY MUCH IGNORNING THEM AFTER THIS EVENING.
EXTRAPOLATION WOULD BRING IT INTO SE AZ SUN AFTERNOON. STORM
COVERAGE AND STRENGTH BOTH SUN AND MON ARE GOING TO DEPEND A LOT ON
WHAT HAPPENS TONIGHT. THE FLOW IS TOO WEAK OUT OF THE E TO RELOAD
THE ATMOSPHERE QUICKLY. AS THE HIGH ANCHORS OVER THE 4 CORNERS AND
BECOMES MORE VERICALLY STACKED, WE COULD RUN INTO THE SAME PROBLEM
WEVE HAD ALL SUMMER WITH EITHER TOO MUCH LIFT CLOUDING US OVER, OR
ANVILS CLOUDING US OVER. EITHER WAY, IT COULD MEAN LIMITED RAIN
DESPITE TROPICAL PRECIP WATERS. FOR THIS REASON, EVEN THOUGH WERE
IN A NEARLY CLASSIC HIGH-GRADE PATTERN, I WILL ONLY GO FOR SLIGHTLY
ABOVE CLIMO POPS FOR THE DURATION (RIGHT ON THROUGH DAY 7), WHILE
KEEPING TEMPS BELOW FWC GUIDANCE. ITS SIMPLY TOO DIFFICULT TO
PINPOINT UP VERSUS DOWN DAYS WHILE THE PATTERN IS IN TRANSITION LIKE
TODAY. PYTLAK

.TWC...NONE.

AZZ019-029>035-120700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
NOON MST SAT AUG 11 2001

.SYNOPSIS...A WEAK LOW PRESSURE SYSTEM EXTENDING FROM WESTERN SONORA
INTO SOUTHWEST NEW MEXICO WILL MOVE WEST ACROSS THE REGION THIS
AFTERNOON AND EVENING. THIS SYSTEM...IN ADDITION TO CONSIDERABLE
SUNSHINE...COULD LEAD TO ONE OF THE MORE ACTIVE DAYS THIS MONSOON
SEASON.

.DISCUSSION...SEVERAL PARAMETERS ARE POINTING TOWARD AN ACTIVE
AFTERNOON AND EVENING ACROSS SOUTHEAST ARIZONA. THE DISTURBANCE
APPROACHING FROM THE SOUTHEAST IS ORGANIZED AND HAS ALREADY CAUSED A
FEW STRONG STORMS TO DEVELOP OVER THE MOUNTAINS EAST OF TUCSON. A
WEAKENING COLD FRONT DROPPING SOUTH THROUGH NEW MEXICO APPEARS TO BE
FOCUSING DEVELOPMENT ON THE MOGOLLON RIM AND WHITE MOUNTAINS AS
WELL. PRECIPITABLE WATERS ARE JUST AS HIGH AS YESTERDAY...BUT WITH
THE ADDITION OF FULL SUNSHINE TODAY...THE ATMOSPHERE SHOULD BECOME
VERY UNSTABLE BY THIS AFTERNOON.

HOWEVER...THERE ARE TWO ITEMS WHICH WE ARE WATCHING WHICH MAY
SUPPRESS STORM DEVELOPMENT. RECENT SATELLITE PHOTOS SUGGEST THAT
THERE IS SOME WARMING AND DRYING UNDERWAY IN THE UPPER LEVELS OF THE
ATMOSPHERE. THIS COULD INCREASE STORM STRENGTH BECAUSE IT WILL ACT
AS A CAP ON DEVELOPMENT UNTIL LATER THIS AFTERNOON. IF IT IS TOO
STRONG...THE CAPPING WILL TEND TO KEEP ANY VALLEY STORMS ISOLATED.
WE ARE ALSO WATCHING THE LOWER LEVELS OF THE ATMOSPHERE WHERE THE
FLOW REMAINS VERY WEAK. IF THE SURFACE WINDS DO NOT SWITCH TO THE
NORTHWEST THIS AFTERNOON...LOW LEVEL CONVERGENCE WILL BE VERY WEAK
AND THE STORMS WILL TEND TO STAY NEAR THE MOUNTAINS.

BECAUSE OF THE SUNSHINE AND HIGH PRECIPITABLE WATERS...BOTH THE RISK
OF FLASH FLOODING AND SEVERE DOWNBURST WINDS ARE HIGHER THAN
CLIMATOLOGY. PARTS OF GRAHAM...WESTERN COCHISE...SANTA CRUZ...AND
SOUTHWEST PINAL COUNTIES ARE MORE VULNERABLE TO FLASH FLOODING
BECAUSE THESE AREAS HAVE RECEIVED HEAVY RAIN IN THE PAST COUPLE OF
DAYS.

STORM MOVEMENT WILL BE GENERALLY TO THE SOUTHWEST AT 5 TO 10 MPH.

PYTLAK