Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 311632
AFDTWC

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

.SYNOPSIS...SCATTERED SHOWERS AND THUNDERSTORMS THROUGH TONIGHT
FOLLOWED BY A BETTER CHANCE OF SHOWERS AND THUNDERSTORMS INTO THIS
WEEKEND. GUSTY WINDS FROM THUNDERSTORMS COULD 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...SATELLITE AND RADAR IMAGERY WERE DEPICTING
CONSIDERABLE CLOUDINESS WITH LIGHT SHOWERS OVER MOST OF SOUTHEAST
ARIZONA THIS MORNING. THESE SHOWERS HAD DECREASED IN AREAL COVERAGE
SINCE LAST NIGHT...SO JUST LOOKING AT A LULL IN THE ACTIVITY THIS
MORNING. HAVE UPDATED THE FORECAST TO ADJUST HIGH TEMPERATURES FOR
TODAY DOWN A BIT DUE TO THE CLOUD COVER AND MADE SOME TWEAKS TO RAIN
CHANCES FOR THE REST OF THE DAY. THE OVERALL TREND SUGGESTED BY THE
MODELS WILL BE AN INCREASE IN RAIN CHANCES THROUGH THE WEEKEND
COMPARED TO THE PAST SEVERAL DAYS. THE TIME FRAME FOR THE BEST
CHANCE OF RAIN WILL BE FRIDAY INTO SATURDAY NIGHT...WITH VERY HEAVY
RAINFALL POSSIBLE IN SOME LOCATIONS. FOR LATE FRIDAY INTO SATURDAY
NIGHT...THE AREAS OF CONCERN FOR WIDESPREAD HEAVY RAINFALL AND FLASH
FLOODING OR WASH  AND SMALL STREAM FLOODING WERE IN THE WHITE
MOUNTAINS AND NEAR THE INTERNATIONAL BORDER FROM WEST OF NOGALES
EAST TO DOUGLAS. PLEASE REFER TO THE ADDITIONAL SECTIONS FOR MORE
DETAILS.

&&

.AVIATION...VALID THRU 01/18Z.
INCREASING MOISTURE TODAY...FRIDAY...AND INTO SATURDAY WILL LEAD TO
THE POTENTIAL FOR MORE WIDESPREAD THUNDERSTORM ACTIVITY EACH
AFTERNOON THROUGH THE EVENING HOURS. THUNDERSTORMS MAY IMPACT
TERMINALS...ESPECIALLY KOLS AND KDUG. PERIODS OF MVFR IN +TSRA WILL
BE A POSSIBILITY. GUSTY THUNDERSTORM OUTFLOW WINDS WILL LIKELY
DEVELOP...WITH VALUES IN EXCESS OF 40KT POSSIBLE. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...SHOWER AND THUNDERSTORM ACTIVITY WILL BE ON THE
INCREASE THROUGH THE NEXT 48 TO 72 HOURS AS MONSOON MOISTURE SURGES
IN FROM THE SOUTH. 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.

&&

.PREV DISCUSSION...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.

&&

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

&&

$$

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

PREV DISCUSSION...FRANCIS







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