563
FXUS65 KTWC 060444
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
945 PM MST SAT JUL 5 2008
SYNOPSIS
HIGH PRESSURE ALOFT WILL REMAIN CENTERED TO THE NORTH
AND EAST OF ARIZONA INTO NEXT WEEK. THE FLOW AROUND THIS SYSTEM
ALONG WITH AVAILABLE MOISTURE WILL GENERATE THE DAILY CYCLE OF
ISOLATED TO SCATTERED AFTERNOON AND EVENING THUNDERSTORMS.
DISCUSSION
SHOWERS AND THUNDERSTORMS CONTINUE TO WEAKEN LATE THIS
EVENING ACROSS THE MAJORITY OF SOUTHEAST ARIZONA...WITH THE
EXCEPTION OF A STRONG THUNDERSTORM PRODUCING FLASH FLOODING OVER THE
W AND NW PORTIONS OF THE TUCSON METRO AREA. AN AUTOMATED RAIN GAGE
AT THE CDO WASH NEAR INA ROAD REPORTED 1.54 INCHES OF RAIN HAD
FALLEN ROAD IN APPROXIMATELY 45 MINUTES. THIS STORM THE PRODUCT OF
AN OUTFLOW MOVING SOUTHWEST OFF THE RIM AND INTERSECTION WITH A
MID-LEVEL BOUNDAY ASSISTED BY THE EDGE OF THE CI SHIELD THAT
EXTENDED WEST TO EAST FROM STRONG THUNDERSTORMS OVER THE TOHONO
OODHAM NATION EARLIER THIS EVENING. IN ANY EVENT...WITH THE
EXCEPTION OF LIGHT TO MODERATE RAIN SHOWERS THAT WILL PERSIST ACROSS
SOUTH CENTRAL ARIZONA OVER THE NEXT HOUR OR TWO...THINGS CONTINUE TO
WIND DOWN FOR THE EVENING. THIS TREND IS WELL HANDLED IN THE DIGITAL
GRIDS...AND NO UPDATES WILL BE NECESSARY.
PREV DISCUSSION
WATER VAPOR IMAGERY SHOWS WEAK HIGH PRESSURE IN
THE MID LEVELS GENERALLY OVER NORTHERN NEW MEXICO WITH AN
APPROACHING WEAK TROUGH MAKING ITS WAY TOWARD NORTHWEST ARIZONA.
VISIBLE SATELLITE IMAGERY AND RADAR MOSAIC SHOWS LINGERING DEBRIS
CLOUDINESS FROM LAST EVENING/OVERNIGHT CONVECTION OVER THE NORTHERN
PART OF THE STATE...BUT ALSO OVER SONORA MEXICO AND SOUTHWESTERN
ARIZONA. MEANWHILE...A PRETTY GOOD CUMULUS FIELD IS DEVELOPING OVER
MUCH OF SOUTHWESTERN NEW MEXICO...NORTHEASTERN SONORA AND ALL OF
CHIHUAHUA MEXICO AND INTO EXTREME SOUTHEAST ARIZONA. RADAR IS
DETECTING ISOLATED SHOWERS AND THUNDERSTORMS DEVELOPING ALONG THE
RIM AND ALSO THE MOUNTAINS OF GRAHAM...COCHISE AND SANTA CRUZ
COUNTIES.
THIS MORNINGS KTWC SOUNDING UNMODIFIED SHOWED SLIGHT WARMING ABOVE
AROUND 550MB AND SLIGHT COOLING BELOW THAT LEVEL. THE SOUNDING
EXHIBITED A PWAT OF 1.49 INCHES WITH A LIFTED INDEX OF MINUS 5 AND A
CAPE OF AROUND 2700 J/KG. HOWEVER...MODIFYING THE SOUNDING USING
T=100;TD=60 YIELDED A CAPE OF AROUND 2400 J/KG IF USING THE SURFACE
PARCEL LIFTING METHOD...BUT AROUND 1800 J/KG IF USING THE MEAN TEMP
LIFTING METHOD. SO...THE BOTTOM LINE IS STILL A FAIRLY ACTIVE DAY ON
TAP. BASED ON THE SOUNDING AND MODEL FORECAST SOUNDINGS THE STORMS
SHOULD MOVE WEST OR SLIGHTLY NORTH OF WEST TODAY. POP FORECAST OF
CHANCE CATEGORY FOR MOST PLACES LOOKS GOOD FOR THIS AFTERNOON AND
INTO THE EVENING.
MODELS INDICATE THE AFOREMENTIONED WEAK TROUGH WILL MAKE ITS WAY
EAST ACROSS NORTHERN ARIZONA AND INTO COLORADO THROUGH SUNDAY. AS
THIS OCCURS THE HIGH GETS PUSHED EAST AND ANOTHER TROUGH IS BACK TO
THE NW OVER CALIFORNIA...AND THIS ONE MOVES GENERALLY ACROSS THE
FOUR CORNERS REGION THROUGH MONDAY. BY TUESDAY AND WEDNESDAY HIGH
PRESSURE BECOMES ESTABLISHED OVER THE GREAT BASIN WITH A COL
GENERALLY OVER NEW MEXICO. BY LATE IN THE WEEK THE GFS AND ECMWF
SHOW A SERIES OF DISTURBANCES MOVING UP FROM MEXICO INTO THE DESERT
SOUTHWEST WHICH WILL LIKELY ENHANCE THUNDERSTORM DEVELOPMENT FOR
LATE IN THE WEEK AND INTO THE WEEKEND. NAM HAS BEEN DOING A FAIRLY
GOOD JOB AT DEPICTING THE DAY TO DAY ACTIVITY FOR THE MOST PART...SO
MY FORECAST FOR THE NEXT 2 TO 3 DAYS GENERALLY FOLLOWS THE NAM...BUT
WITH ADJUSTMENTS TO BLEND WITH THE SURROUNDING OFFICES. WITH THAT
SAID...I INCREASED THE RAIN CHANCES FOR SUNDAY AND MONDAY...BUT NOT
DRAMATICALLY. BASICALLY INCREASED POPS BY A CATEGORY OR SO. SHOULD
THEN SEE A SLIGHT DECREASE IN ACTIVITY TUESDAY AND WEDNESDAY...BUT
THEN BOTH THE GFS AND ECMWF SHOW A POTENTIALLY WET PERIOD FOR LATE
IN THE WEEK AND INTO THE WEEKEND...SO I INCREASED POPS FOR THAT TIME
PERIOD. THE PHOENIX OFFICE SAID THEY WOULD DO LIKEWISE.
HIGH TEMPS GENERALLY NEAR NORMAL THROUGH THE FORECAST PERIOD...WITH
LOWS TEMPS SLIGHTLY ABOVE NORMAL.
FIRE WEATHER
HIGH PRESSURE ALOFT CENTERED OVER NORTHERN NEW
MEXICO WITH A WEAK TROUGH PUSHING EAST ACROSS NORTHERN ARIZONA AND
INTO COLORADO THROUGH SUNDAY. FLOW AROUND THE HIGH WILL RESULT IN A
DAILY CYCLE OF AFTERNOON AND EVENING THUNDERSTORMS... ALONG WITH
SEASONABLY HOT DAYTIME TEMPERATURES. EXPECT A SLIGHT DECREASE IN
THUNDERSTORM COVERAGE TUESDAY AND WEDNESDAY...BUT A WET PERIOD COULD
BE STORE FOR LATE IN THE WEEK AND EARLY NEXT WEEKEND. ANY
THUNDERSTORMS THAT DO DEVELOP WILL HAVE THE POTENTIAL TO PRODUCE
STRONG... ERRATIC...AND GUSTY WINDS.
AVIATION
ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED THIS
EVENING...WITH A SLIGHT CHANCE OF SHOWERS PERSISTING AFTER MIDNIGHT.
WINDS WILL GENERALLY BE LIGHT AND DIURNALLY DRIVEN EXCEPT NEAR
THUNDERSTORMS THROUGH 06Z...WHERE WINDS WILL BE VARIABLE AND
GUSTY AT TIMES. OUTFLOW WINDS WITH STORMS COULD HAVE GUSTS TO NEAR
35 KTS. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
TWC WATCHES/WARNINGS/ADVISORIES
NONE.
WEATHER.GOV/TUCSON
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