Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 300952
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
250 AM MST WED JUL 30 2014

.SYNOPSIS...THUNDERSTORMS WILL BE CONFINED MOSTLY SOUTH TO SOUTHEAST
OF TUCSON THIS AFTERNOON AND EVENING. INCREASING CHANCES OF
THUNDERSTORMS WILL START ON THURSDAY FOLLOWED BY SCATTERED MAINLY
AFTERNOON AND EVENING THUNDERSTORMS FRIDAY THROUGH SUNDAY. EXPECT
HOTTER DAYTIME TEMPERATURES TODAY...THEN A MODERATION IN HIGH
TEMPERATURES WILL PREVAIL THIS WEEKEND.

&&

.DISCUSSION...BROAD UPPER RIDGE PREVAILED ACROSS THE WRN CONUS EARLY
THIS MORNING WITH 595 DM HIGH PRESSURE CENTERED NEAR THE FAR SE AZ/
FAR SW NEW MEXICO BORDER. A DRYING TREND CONTINUED ACROSS SE AZ
UNDER A LIGHT GENERALLY WLY FLOW ALOFT REGIME. DEWPOINTS AT LOWER
ELEVATIONS VALID 30/09Z RANGED FROM THE 50S-MID 60S F...AND THESE
TEMPS WERE NEARLY 5-15 DEGS F LOWER VERSUS 24 HOURS AGO. BLENDED
TOTAL PRECIP WATER VALUES VALID 0756Z RANGED FROM ONE INCH ACROSS
THE WHITE MOUNTAINS TO 1.30 INCHES ACROSS WRN PIMA COUNTY. THESE
VALUES WERE NEARLY ONE QUARTER OF AN INCH LOWER VERSUS 24 HOURS AGO.

VARIOUS NWP MESOSCALE MODELS JUSTIFY ISOLATED TO SCATTERED SHOWERS/
TSTMS TO OCCUR MAINLY SOUTH-TO-SOUTHEAST OF TUCSON THIS AFTERNOON/
EVENING. THE OTHER FAVORED AREA FOR ISOLATED SHOWERS/TSTMS IS ACROSS
THE WHITE MOUNTAINS. PRECIP-FREE CONDITIONS WILL OCCUR AREA-WIDE
LATE TONIGHT. MOISTURE WILL THEN INCREASE ESPECIALLY EAST-TO-SOUTH
OF TUCSON THURSDAY FOLLOWED BY A MORE PRONOUNCED INCREASE OF
MOISTURE AREA-WIDE FRI AND INTO THIS WEEKEND.

THUR-FRI...
EXPECT SCATTERED SHOWERS/TSTMS THUR AFTERNOON/EVENING EAST AND SOUTH
OF TUCSON WITH ISOLATED SHOWERS/TSTMS FROM TUCSON WWD/NWWD INTO WRN
PIMA/SOUTH CENTRAL PINAL COUNTIES. GREATER COVERAGE OF SHOWERS/TSTMS
WILL OCCUR FRI DUE TO THE PROGGED MOISTURE INCREASE AND A MORE
FAVORABLE SELY MID-LEVEL FLOW. A SCENARIO CONSISTING OF GUSTY
OUTFLOWS PRODUCING AREAS OF DENSE BLOWING DUST IS A POSSIBILITY FRI
AFTERNOON INTO EARLY FRI EVENING...PARTICULARLY NW OF TUCSON.
HOWEVER...WILL DEFER DEPICTING AREAS OF BLOWING DUST IN THE GRIDDED
DATA WEATHER FIELD UNTIL FORECAST CONFIDENCE INCREASES.

SAT-SUN...
SCATTERED TO NUMEROUS MAINLY AFTERNOON/EVENING SHOWERS/TSTMS WILL
PREVAIL AS HIGH PRESSURE ALOFT BECOMES CENTERED NEAR THE FOUR
CORNERS REGION. 30/00Z GFS/ECMWF WERE FAIRLY SIMILAR WITH DEPICTING
AN INVERTED TROUGH/WEAK UPPER LOW TO BE OVER THE AREA. THIS SYSTEM
WILL ENHANCE THE POTENTIAL FOR LOCALLY HEAVY RAINFALL AND PERHAPS
FLASH FLOODING.

MON-TUE...
GFS/ECMWF WERE SIMILAR WITH DEPICTING DRIER AIR TO ADVECT INTO SE AZ
FROM THE SOUTHWEST MON AS HIGH PRESSURE ALOFT BECOMES CENTERED SE OF
THE AREA. GFS/ECMWF CONTINUED TO BE SIMILAR WITH ESTABLISHING AN
UPPER HIGH OVER THE NRN GULF OF CALIFORNIA TUE. THIS SCENARIO WOULD
YIELD ANOTHER DRYING TREND EARLY NEXT WEEK. THUS...HAVE OPTED FOR A
GRADUAL DECREASE IN SHOWER/TSTM COVERAGE...WITH CHANCE-CATEGORY POPS
BY TUE ACROSS ERN SECTIONS AND DRY CONDITIONS ACROSS WRN PIMA COUNTY.

HIGH TEMPS THIS AFTERNOON WILL GENERALLY BE ABOUT 2-5 DEGS F WARMER
VERSUS TEMPS ACHIEVED TUE...AND WILL AVERAGE NEARLY 3-7 DEGS F ABOVE
NORMAL. A GRADUAL COOLING TREND WILL THEN OCCUR THUR-SUN...WITH
FORECAST HIGH TEMPS SUN TO BE A FEW DEGS BELOW NORMAL. A WARMING
TREND IS ON TAP MON-TUE DUE TO THE EXPECTED DRIER REGIME.

&&

.AVIATION...VALID THRU 31/12Z.
ISOLATED -TSRA/-SHRA WILL BE LIMITED TO MAINLY NEAR THE MOUNTAINS
AND NEAR THE INTERNATIONAL BORDER SOUTH-TO-SOUTHEAST OF KTUS THIS
AFTERNOON/EVENING. OTHERWISE...MOSTLY CLEAR SKIES WILL PREVAIL WEST
OF KTUS THRU EARLY THURSDAY MORNING. FROM KTUS VICINITY EASTWARD
EXPECT A FEW TO BROKEN CUMULOFORM CLOUDS AT 8-12K FT AGL THIS
AFTERNOON AND THIS EVENING...AND CLOUD BASES MAINLY ABOVE 15K FT AGL
AT OTHER TIMES. SURFACE WIND WILL BE MOSTLY LESS THAN 10 KTS INTO
EARLY THURSDAY MORNING. AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.

&&

.FIRE WEATHER...EXPECT THUNDERSTORMS TO BE LIMITED MOSTLY TO LOCALES
SOUTH-TO-SOUTHEAST OF TUCSON THIS AFTERNOON AND THIS EVENING.
THEREAFTER...SCATTERED MOSTLY AFTERNOON AND EVENING THUNDERSTORMS
WILL RETURN STARTING THURSDAY AND CONTINUE INTO THIS WEEKEND AS
DEEPER MOISTURE MOVES INTO THE AREA. OTHERWISE...NORMAL DIURNAL WIND
TRENDS WILL OCCUR WITH OCCASIONAL GUSTS DURING THE AFTERNOON HOURS
DUE TO DAYTIME HEATING.

&&

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

&&

$$

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

FRANCIS




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