Flash Flood Watch 4, NWS Tucson, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
1010 AM MST SAT JUL 27 2013

.SYNOPSIS...A DOWNWARD TREND IN THUNDERSTORM ACTIVITY WILL BEGIN
TODAY AND CONTINUE INTO EARLY NEXT WEEK. THE BULK OF THUNDERSTORMS
WILL BE EAST OF TUCSON WHERE A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS WILL CONTINUE. EXPECT INCREASING THUNDERSTORM COVERAGE
DURING THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...TOWERING CUMULUS DEVELOPING ACROSS SEVERAL MOUNTAIN
RANGES AT THIS TIME. MEANWHILE...CLEAR SKIES WERE NOTED ACROSS WRN
PIMA COUNTY. DEWPOINTS VALID 17Z WERE GENERALLY IN THE 60S F...AND
THESE TEMPS DOWN ABOUT 2-5 DEGS F VERSUS 24 HOURS AGO. SURFACE TEMPS
VALID 17Z WERE ALSO DOWN NEARLY 2-5 DEGS F VERSUS THIS TIME FRI.
27/12Z KTWC SOUNDING DEPICTED SIMILAR MOISTURE/INSTABILITY VALUES
VERSUS 24 HOURS.

TOTAL PRECIP WATER WAS 1.80 INCHES...LIFTED INDEX OF MINUS 7...AND
MODIFIED CAPE AROUND 1500 J/KG. ALTHOUGH THE MID-LEVEL STEERING FLOW
SPEEDS WERE SIMILAR AND THUS VERY LIGHT...THE DIRECTIONAL COMPONENT
WAS MORE WESTERLY VERSUS FRI. 27/12Z UPPER AIR PLOTS INDICATED 594
DM HIGH PRESSURE CENTERED OVER SE AZ WITH 586 DM LOW PRESSURE
CENTERED OFF THE SRN CALIFORNIA COAST VICINITY 34N/126W. VERY LIGHT
GENERALLY WLY/SWLY FLOW PREVAILED OVER SE AZ.

27/12Z UNIV OF AZ WRF-NAM FAVORS THE BEST CHANCE OF SHOWERS/TSTMS
TODAY AND INTO THIS EVENING TO OCCUR ACROSS GREENLEE/GRAHAM/COCHISE
COUNTIES EAST OF TUCSON. THE 27/12Z UNIV OF AZ WRF-GFS WAS SIMILAR
TO THE WRF-NAM...EXCEPT DEVELOPS MORE SHOWERS/TSTMS SW OF TUCSON
VERSUS THE WRF-NAM.

GIVEN THE AFOREMENTIONED DIAGNOSTICS AS WELL AS A MORE WESTERLY
MID-LEVEL STEERING FLOW...APPEARS THAT THE INHERITED OFFICIAL
FORECAST OF CHANCE-CATEGORY POPS EAST/SOUTH OF TUCSON...ISOLATED
SHOWERS/TSTMS TUCSON VICINITY...AND DRY CONDITIONS ACROSS WRN PIMA
COUNTY SHOULD EVENTUALLY BE REALITY THIS AFTERNOON AND THIS EVENING.
THE BULK OF PRECIP SHOULD END BY ABOUT MIDNIGHT. HOWEVER...THERE
WILL BE ENOUGH MOISTURE TO MAINTAIN A SLIGHT CHANCE OF SHOWERS/
TSTMS LATE TONIGHT EAST OF TUCSON WITH CONTINUED DRY CONDITIONS
ACROSS WRN PIMA COUNTY.

HIGH TEMPS THIS AFTERNOON ARE FORECAST TO BE WITHIN A DEGREE-OR-TWO
OF NORMAL. PLEASE REFER TO THE PREVIOUS DISCUSSION SECTION BELOW FOR
ADDITIONAL DETAIL.

&&

.PREV DISCUSSION /300 AM MST SAT JUL 27 2013/...SUNDAY...LESS
THUNDERSTORM COVERAGE AS ATMOSPHERE CONTINUES TO SLOWLY DRY OUT.
BEST CHANCES WILL BE EAST OF TUCSON. HIGHS WILL BE SLIGHTLY WARMER
THAN TODAY.

MONDAY...WITH PRECIPITABLE WATER VALUES PROGGED TO BE LESS THAN ONE
INCH AREAWIDE RESULTING IN AFTERNOON SURFACE DEWPOINTS IN THE UPPER
40S TO LOWER 50S...OUTSIDE OF A FEW MOUNTAIN THUNDERSTORMS NEAR THE
AZ/NM BORDER...LITTLE THUNDERSTORM ACTIVITY IS EXPECTED ACROSS THE
AREA.

TUESDAY...THE CENTER OF THE UPPER HIGHS...WHICH WAS SOUTH OF THE
AREA SINCE FRIDAY...WILL MOVE INTO NEW MEXICO...THUS BRINGING A
SLIGHT INCREASE IN MOISTURE UNDER E-SE FLOW ALOFT. HOWEVER...ONLY
EXPECTING SLIGHT CHANCE OF STORMS OVER THE EASTERN MOUNTAINS.

WEDNESDAY...BASED ON 00Z GFS/ECMWF/CANADIAN 850-700 MB THICKNESS
VALUES...THIS WILL BE THE HOTTEST DAY IN THIS FORECAST CYCLE. HAVE
INCREASED HIGHS A COUPLE OF DEGREES. WITH MOISTURE INCREASING ACROSS
THE AREA UNDER E-SE FLOW ALOFT...WILL SEE AN UPTICK IN AFTERNOON AND
EVENING THUNDERSTORMS...MAINLY FROM TUCSON EAST AND SOUTH.

THURSDAY...LOW GRADE MONSOON FORECAST WITH SLIGHTLY COOLER DAYTIME
HIGHS.

&&

.AVIATION...VALID THRU 28/12Z. FEW-SCT060 SCT-BKN120 SCT-BKN350 WITH
ISOLD-SCTD TSRA BTWN 27/18Z AND 28/05Z.  LCL MVFR CIGS AND VSBYS
WITH HEAVY RAIN AND WIND GUSTS TO 45 KTS NEAR STRONGEST STORMS.
SURFACE WIND VARIABLE AND GENERALLY LESS THAN 10 KTS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A MOIST AIR MASS REMAINS OVER THE AREA TODAY BUT
THERE WILL BE A BIT OF DRYING LATE IN THE DAY.  THE RESULT WILL BE
ANOTHER DAY WITH SCATTERED WET THUNDERSTORMS AROUND THE AREA MAINLY
THE EASTERN TWO THIRDS OF SE AZ.  THE DRYING TREND WILL BECOME MORE
NOTICEABLE SUNDAY ONWARD WITH LOWER DEWPOINTS AND LESS OF A THREAT
OF THUNDERSTORMS SUNDAY...AND EVEN MORE SO MONDAY AND TUESDAY.
MOISTURE WILL BEGIN TO SLOWLY INCREASE AGAIN WEDNESDAY ONWARD.
LIGHT WINDS TODAY WILL GIVE WAY TO NORMAL DIURNAL WINDS MONDAY
ONWARD.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

VISIT US ON FACEBOOK...TWITTER...YOUTUBE...AND AT WEATHER.GOV/TUCSON

DISCUSSION...FRANCIS
PREV DISCUSSION...JG
AVIATION/FIRE WEATHER...CERNIGLIA