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000
FXUS65 KTWC 311110
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
410 AM MST THU JUL 31 2014

.SYNOPSIS...EXPECT SCATTERED SHOWERS AND THUNDERSTORMS THROUGH
TONIGHT FOLLOWED BY A GOOD CHANCE OF SHOWERS AND THUNDERSTORMS INTO
THIS WEEKEND. GUSTY OUTFLOWS WILL PRODUCE AREAS OF BLOWING DUST...
ESPECIALLY FRIDAY AFTERNOON. PERIODS OF HEAVY RAINFALL MAY THEN
OCCUR THIS WEEKEND. A COOLING TREND WILL PREVAIL INTO THE WEEKEND
FOLLOWED BY DRIER CONDITIONS AND WARMER TEMPERATURES BY THE MIDDLE
OF NEXT WEEK.

&&

.DISCUSSION...CLOUDINESS ALONG WITH SCATTERED SHOWERS PRODUCING
LIGHT RAIN HAS INCREASED DURING THE PAST 2-3 HOURS IN RESPONSE TO A
DECAYING MCS OVER SONORA MEXICO. A FEW LIGHTNING STRIKES HAVE BEEN
DETECTED NEAR SELLS AND GREEN VALLEY. OTHERWISE...LIGHTNING STRIKES
HAVE BEEN LIMITED TO NERN SONORA AND ACROSS SWRN NEW MEXICO. 31/08Z
RUC HRRR DEPICTS FAIRLY EXTENSIVE COVERAGE OF SHOWERS PRODUCING
MOSTLY LIGHT RAINFALL THRU ABOUT MID-MORNING. RAINFALL COVERAGE IS
THEN PROGGED TO DECREASE LATE THIS MORNING INTO EARLY THIS
AFTERNOON.

A POTENTIAL SCENARIO FOR TODAY INTO THIS EVENING IS THAT CONVECTIVE
DEBRIS CLOUDS THIS MORNING WILL INHIBIT MORE WIDESPREAD COVERAGE OF
SHOWERS/TSTMS THIS AFTERNOON/EVENING. HOWEVER...HAVE OPTED FOR THE
SCENARIO CONSISTING OF MORE SUBSTANTIAL SHOWER/TSTM ACTIVITY TO
OCCUR THIS AFTERNOON AND THIS EVENING. THUS...THE OFFICIAL FORECAST
DEPICTS ISOLATED SHOWERS/TSTMS AREA-WIDE THIS MORNING...THEN
SCATTERED SHOWERS/TSTMS THIS AFTERNOON/EVENING. GUSTY OUTFLOWS MAY
PRODUCE LOCALIZED BLOWING DUST SIMILAR TO WED. HOWEVER...WIDESPREAD
BLOWING DUST IS NOT EXPECTED TO OCCUR AT THIS TIME. LOCALLY HEAVY
RAINFALL MAY OCCUR WITH THE STRONGER SHOWERS/TSTMS. HAVE MAINTAINED
ISOLATED SHOWERS/TSTMS FOR MUCH OF THE AREA LATE TONIGHT.

FRI...
A GREATER COVERAGE OF SHOWERS/TSTMS WILL OCCUR FRI DUE TO THE
PROGGED MOISTURE INCREASE AND A MORE FAVORABLE SELY MID-LEVEL FLOW.
GUSTY OUTFLOWS PRODUCING MORE WIDESPREAD AREAS OF BLOWING DUST IS A
MORE DISTINCT POSSIBILITY FRI AFTERNOON INTO FRI EVENING...
ESPECIALLY NW OF TUCSON. THUS...HAVE OPTED FOR AREAS OF BLOWING DUST
ACROSS SOUTH CENTRAL PINAL COUNTY FRI AFTERNOON/EVENING. ISOLATED TO
SCATTERED SHOWERS/TSTMS SHOULD CONTINUE LATE FRI NIGHT.

SAT-SUN...
31/00Z GFS/ECMWF MOISTURE FIELDS WERE SUFFICIENT TO JUSTIFY
INCREASED POPS VERSUS THE INHERITED FORECAST. GFS/ECWMF ALSO
CONTINUED TO DEPICT A WEAK AREA OF LOW PRESSURE ALOFT TO BE OVER SE
AZ...BETWEEN HIGH PRESSURE CENTERED OVER NRN AZ AS WELL AS OVER SRN
CHIHUAHUA. SLIGHTLY DRIER CONDITIONS MAY ENCROACH UPON WRN SECTIONS
SUN AS THE WEAK UPPER LOW DRIFTS INTO NRN AZ.

AT ANY RATE...THE COMBINATION OF AMPLE MOISTURE ALONG WITH THE WEAK
AREA OF LOW PRESSURE ALOFT SHOULD PROVIDE SCATTERED TO NUMEROUS
SHOWERS/TSTMS. AM CONCERNED THAT THE POTENTIAL FOR HEAVY RAINFALL
AND FLASH FLOODING WILL BE ENHANCED...ESPECIALLY SAT...AS WEAK
MID-LEVEL STEERING FLOW TRANSLATES INTO SLOW STORM MOTIONS.

MON-WED...
GFS/ECMWF WERE SIMILAR WITH DEPICTING DRIER AIR TO ADVECT INTO SE AZ
MON AS HIGH PRESSURE ALOFT WILL BE CENTERED OVER CHIHUAHUA...AND A
TROUGH OF LOW PRESSURE EXISTS OVER THE GREAT BASIN. A GRADUAL DRYING
TREND SHOULD CONTINUE TUE-WED UNDER WLY/NWLY FLOW ALOFT.
THUS...EXPECT ISOLATED TO SCATTERED SHOWERS/TSTMS MON AFTERNOON/
EVENING...THEN ISOLATED SHOWERS/TSTMS ARE FORECAST TO BE CONFINED TO
MAINLY NEAR THE NEW MEXICO BORDER NEXT WED.

A COOLING TREND WILL OCCUR THRU SAT FOLLOWED BY WARMER DAYTIME
TEMPERATURES EARLY NEXT WEEK.

&&

.AVIATION...VALID THRU 01/12Z.
SCATTERED TSRA/SHRA WILL OCCUR INTO EARLY FRIDAY MORNING AS MOISTURE
INCREASES ACROSS THE AREA. EXPECT MVFR VISIBILITIES WITH +TSRA AS
WELL AS WIND GUSTS TO AROUND 40-45 KTS. THE BEST OCCURRENCE FOR THE
STRONGEST GUSTS WILL BE THIS AFTERNOON AND EARLY THIS EVENING.
OTHERWISE...CLOUD DECKS WILL GENERALLY BE AT 8-15K FT AGL INTO EARLY
FRIDAY MORNING. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...SCATTERED SHOWERS AND THUNDERSTORMS WILL OCCUR
THROUGH TONIGHT FOLLOWED BY A GOOD CHANCE OF SHOWERS AND
THUNDERSTORMS INTO THIS WEEKEND. EXPECT STRONG...GUSTY AND ERRATIC
WINDS WITH THE STRONGER THUNDERSTORMS. INCREASING MOISTURE WILL ALSO
TRANSLATE INTO PERIODS OF HEAVY RAINFALL AND COOLER TEMPERATURES
THIS WEEKEND...PARTICULARLY SATURDAY. THEREAFTER...A DRYING TREND
WITH WARMER TEMPERATURES WILL PREVAIL BY THE MIDDLE OF NEXT WEEK.

&&

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

&&

$$

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