Flash Flood Warning 48, NWS Tucson, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
1015 AM MST MON SEP 21 2015

.SYNOPSIS...EXPECT PERIODS OF SHOWERS WITH ONE OR TWO THUNDERSTORMS
POSSIBLE THROUGH TONIGHT AS THE WEAKENED REMAINS OF A TROPICAL
SYSTEM MOVES THROUGH THE AREA FROM THE SOUTH. AREAS OF HEAVY RAIN
ARE EXPECTED. SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL
OCCUR TUESDAY AS A WEAKENING UPPER LOW PRESSURE SYSTEM MOVES ACROSS
THE AREA. A FLASH FLOOD WATCH IS IN EFFECT THROUGH TUESDAY AFTERNOON
WITH HEAVY RAINFALL LIKELY. A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS CONTINUES WEDNESDAY FOLLOWED BY DRY CONDITIONS
THURSDAY INTO SATURDAY.

&&

.DISCUSSION...TROPICAL DEPRESSION 16-E MADE LANDFALL EARLIER THIS
MORNING IN NORTHWEST MEXICO JUST SOUTH OF OUR AREA. THE LOWER AND
MID LEVEL REMNANT CIRCULATIONS WILL NOW QUICKLY SHEAR AND SCATTER
INTO SOUTHERN ARIZONA IN OUR GENERAL DIRECTION. WE'VE ALREADY SEEN
RAINFALL AMOUNTS OF .75 TO 1.5 INCHES NEAR THE INTERNATIONAL BORDER
WITH VALLEY LOCATIONS FURTHER NORTH...INCLUDING THE TUCSON
AREA...BETWEEN 1/3 TO 1/2 INCH. MOUNTAIN LOCATIONS DOING BETTER WITH
THE HUACHUCAS SOUTH OF SIERRA VISTA BETWEEN 1 AND 1.75 INCHES.
OVERALL STILL ON TRACK FOR 1 TO 2 INCHES IN TUCSON AND OVER 3 INCHES
IN THE MOUNTAINS...HEAVIER AMOUNTS FURTHER SOUTH IN SANTA CRUZ AND
SOUTHERN COCHISE COUNTY. IF YOU LOOK AT THE IR SATELLITE IMAGE YOU
SEE WARMING CLOUD TOPS AND MIGHT THINK THINGS ARE TAPERING OFF. THE
VISIBLE SATELLITE IMAGERY TELLS THE REAL STORY AS OTHER PROCESSES
ARE KICKING IN TO ENHANCE THE CHANCE OF HEAVY RAINFALL THROUGH THE
REST OF TODAY AND INTO THIS EVENING. THE ELONGATED SHEARING AXIS ON
THE NORTHEAST SIDE OF THE REMAINING SURFACE CIRCULATION IS PUSHING
ENHANCED SOUTHERLY LOW LEVEL WINDS INTO SANTA CRUZ AND SOUTHWEST
COCHISE COUNTY WITH A STRONG LOW LEVEL MOISTURE CONVERGENCE FIELD
PUSHING FROM THAT AREA INTO EASTERN PIMA COUNTY THIS AFTERNOON.

SO MORE TO COME TODAY AND THIS EVENING WITH DECENT CONVECTIVE
POTENTIAL TOMORROW BEHIND THE SYSTEM AS A LOW APPROACHES FROM THE
WEST COAST...ESPECIALLY FROM TUCSON WESTWARD AND NORTHWESTWARD.

&&

.AVIATION...VALID THRU 22/18Z.
WIDESPREAD -SHRA AND SCATTERED -TSRA WILL OCCUR INTO TUESDAY
MORNING. EXPECT MVFR CONDITIONS AND OCCASIONAL IFR CONDITIONS DUE TO
THIS PRECIPITATION. OTHERWISE...CLOUD DECKS AROUND 10K FT AGL THIS
MORNING WILL LOWER TO AROUND 4-7K FT AGL THIS AFTERNOON AND CONTINUE
INTO TUESDAY MORNING. SURFACE WIND WILL GENERALLY BE SELY AT 5-15
KTS. SURFACE WIND GUSTS OF 15-25 KTS MAY ALSO OCCUR...ESPECIALLY
THIS AFTERNOON AND EVENING. AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.

&&

.FIRE WEATHER...EXPECT WIDESPREAD SHOWERS WITH EMBEDDED
THUNDERSTORMS THROUGH TONIGHT. SCATTERED TO NUMEROUS SHOWERS AND
THUNDERSTORMS WILL OCCUR TUESDAY FOLLOWED BY A SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS WEDNESDAY. DRY CONDITIONS WILL THEN
PREVAIL THURSDAY INTO SATURDAY FOLLOWED BY A SLIGHT CHANCE OF
THUNDERSTORMS EAST AND SOUTH OF TUCSON SUNDAY.

&&

.PREV DISCUSSION...THE FOCUS OF ATTENTION ON TUESDAY WILL THEN TURN
TOWARD THE WEAK UPPER LOW THAT SHOULD BE NEAR THE NRN BAJA
CALIFORNIA COAST EARLY TUE MORNING. THIS SYSTEM IS PROGGED TO EJECT
EWD ACROSS THE AREA BY MIDDAY WED. AMPLE REMNANT MOISTURE IN
COMBINATION WITH A PROGGED MODERATELY UNSTABLE ENVIRONMENT AND
FAVORABLE WIND PROFILES IMPLIES THAT GREATER COVERAGE OF
THUNDERSTORMS MAY OCCUR TUE VERSUS TODAY. THUS...HAVE OPTED FOR
SCATTERED TO NUMEROUS SHOWERS/TSTMS TUE. THE BULK OF ANY HEAVY
RAINFALL SHOULD THEN DIMINISH RAPIDLY TUE EVENING AND LATE TUE NIGHT
AS THE MID-LEVEL TROUGH AXIS MOVES EWD ACROSS THE AREA.

RAIN CHANCES WILL CONTINUE TO DECREASE WED AS INCREASINGLY WLY FLOW
ALOFT SHUNTS DEEPER MOISTURE EWD INTO THE SRN ROCKIES. HOWEVER...
PROGGED MOISTURE APPEARS TO REMAIN SUFFICIENT TO JUSTIFY A SLIGHT
CHANCE OF SHOWERS/TSTMS MAINLY FROM TUCSON EWD TO THE NEW MEXICO
BORDER. DRY CONDITIONS WILL THEN OCCUR AREA-WIDE LATE WED NIGHT THRU
FRI NIGHT IN RESPONSE TO AN EXPANSIVE AREA OF HIGH PRESSURE ALOFT
OVER THE SWRN CONUS. THEREAFTER...HAVE CONTINUED WITH A SLIGHT
CHANCE OF SHOWERS/TSTMS MAINLY NEAR THE MOUNTAINS EAST-TO-SOUTH OF
TUCSON SUN.

HIGH TEMPS TODAY AND TUE ARE THEN FORECAST TO AVERAGE ABOUT 5-15
DEGS F BELOW NORMAL DEPENDING UPON LOCATION. A WARMING TREND WILL
THEN OCCUR WED-THUR FOLLOWED BY DAYTIME TEMPS TO AVERAGE A FEW DEGS
ABOVE NORMAL FRI-SUN.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    FLASH FLOOD WATCH THROUGH TUESDAY AFTERNOON FOR AZZ501>515.

&&

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MEYER/RASMUSSEN/FRANCIS