Severe Thunderstorm Warning 30, NWS Tucson, AZ

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
208 PM MST SUN AUG 5 2001

.SYNOPSIS...ALTHOUGH THUNDERSTORM ACTIVITY WILL BE SOMEWHAT LIMITED
THROUGH MONDAY NIGHT...HIGH PRESSURE ALOFT WILL REMAIN OVER THE
GREAT BASIN THIS WEEK. THIS WILL BRING AN UPPER LEVEL DISTURBANCE
WEST FROM THE MISSISSIPPI VALLEY INTO ARIZONA BY TUESDAY NIGHT. THIS
DISTURBANCE WILL LIKELY CAUSE AN INCREASE IN RAINFALL BY MIDWEEK.

.DISCUSSION...WE'RE DEFINITELY FEELING THE EFFECTS OF YESTERDAY'S
BIG CONVECTION IN SE AZ. TEMPS ARE RUNNING 3 TO 7 DEGREES BELOW
YESTERDAY, WITH TSTMS JUST GETTING STARTED OVER THE MOUNTAINS. WE DO
HAVE A CU FIELD OVER W PIMA COUNTY ON THE N EDGE OF THE MESOSCALE
VORTEX CENTER HEADING WNW TOWARD THE NORTHERN GULF OF CA. OTHER
STORMS ON THE RIM ARE TRYING TO THROW A SMALL OUTFLOW BOUNDARY OUT
TOWARD N GRAHAM COUNTY. THOUGHTS FROM THIS MORNING ARE PRETTY MUCH
UNCHANGED: WE WILL SEE A FEW STORMS THIS EVENING, WITH PERHAPS
SLIGHTLY BETTER COVERAGE NEAR THE RIM AND W PIMA COUNTY, BUT WE'RE
GOING TO BE DOWN OVERALL. I MAY TWEAK A POP HERE AND THERE BASED ON
RADAR TRENDS, BUT CURRENT FORECAST WORDING LOOKS GOOD. MON/MON NIGHT
WILL BE WARMER, BUT SO WILL OUR 400-300MB TEMPS DUE TO SHORT WAVE
RIDGING. E FLOW WILL TRY TO FEED DRIER AIR IN FROM NM WHICH COULD
CONCEIVABLY SET UP SOME KIND OF MOISTURE BOUNDARY AND PUSH A STORM
OR TWO INTO THE VALLEYS. WE COULD EVEN END UP WITH A MICROBURST OR
TWO IF THE 700-500 MB LAYER DRIES OUT AS MUCH AS THE AVN SUGGESTS.
HOWEVER, WITHOUT A CONCRETE TRIGGER AND WITH WEAK CONVERGENT FLOW
ALOFT, COVERAGE WILL REMAIN RATHER ISOLATED.

OUR NEXT INTERESTING FEATURE ARRIVES LATE TUE. EASTERLY WAVE WHICH
HAS HAD QUITE A HISTORY (FLASH FLOODS IN KY/TN, CURRENTLY YANKING
T.S. BARRY TOWARD THE FL COAST) IS PROGGED BY ALL MODELS TO MOVE W
UNDER THE RIDGE FROM MS/AL, PICK UP AN OTHER EASTERLY WAVE OVER THE
W GULF OF MEXICO, AND THEN MOVE INTO THE NEIGHBORHOOD LATE TUE. EVEN
THOUGH THE ETA/NGM/AVN ARE A LITTLE DIFFERENT WITH THE DETAILS, THEY
ALL FIRE TSTMS OVER THE RIM TUE AFTERNOON AND THEN DROP THEM SW. RIM
SHOTS HAVE BEEN AS MYTHICAL AROUND HERE AS PIXIES AND THE TOOTH
FAIRY SINCE 1998, BUT IT'S HARD TO GO AGAINST SUCH A SCENARIO AFTER
2 DAYS OF STRONG HEATING, NE FLOW OF 20KTS BY 00Z WED, AND 2-3C OF
COOLING IN THE 400-300MB LAYER JUST AHEAD OF THE WAVE(S). WE'LL
START TO RAMP POPS UP ON TUE TO SHOW THE TREND, ALTHOUGH IF WE DO
INDEED GET A RIM SHOT, CLIMATOLOGY WOULD FAVOR TUE EVENING JUST
AFTER 00Z. OBVIOUS CAUTION IS ALSO REQUIRED IN TERMS OF TIMING SINCE
ALL 3 MODELS WERE TOO SLOW WITH THE WAVE WHICH DUMPED ON US
YESTERDAY.

AVN/MRF ARE IN MUCH BETTER AGREEMENT WITH UKMET/ECMWF IN FAVORING A
DEEPER LOW OVER THE CANADIAN MARITIMES AND A CLOSED HIGH TO OUR N.
WITH BARRY GETTING OUT OF THE WAY, THE EASTERLY WAVE(S) MOVING INTO
US LATE TUE MAY BE THE FIRST OF SEVERAL. STANDARD MID/HIGH GRADE
FORECAST STILL LOOKS GOOD, ALTHOUGH I'M SURE WE'RE GOING TO HAVE A
DOWN DAY SOMEWHERE IN THERE, MUCH LIKE WE'RE EXPERIENCING TODAY.
PYTLAK

.TWC...NONE.