Severe Thunderstorm Warning 118, NWS Tucson, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
155 PM MST FRI AUG 29 2008

.SYNOPSIS...AN ACTIVE MONSOON PATTERN WILL OCCUR THIS WEEKEND. LOW
PRESSURE ALOFT OVER SONORA IN COMBINATION WITH A DEEP TROUGH OVER
THE GREAT BASIN WILL BRING SCATTERED TO NUMEROUS THUNDERSTORMS
TONIGHT INTO SUNDAY. DRIER AIR WILL MOVE IN FROM THE NORTHWEST BY
THE MIDDLE OF NEXT WEEK...AND PUSH MOST OF THE MONSOON MOISTURE WELL
SOUTH AND EAST OF THE AREA.

&&

.DISCUSSION...KEMX WSR-88D DETECTED ISOLATED 30-50 DBZ ECHOES MOVING
WWD ACROSS NRN GRAHAM/GREENLEE/COCHISE/SANTA CRUZ COUNTIES AT 2050Z.
PIMA AND SE PINAL COUNTIES WERE VOID OF PRECIP ECHOES. SPECIAL
29/18Z KTWC SOUNDING DEPICTED A SLIGHTLY DRIER AND MORE-STABLE
PROFILE VERSUS THE 29/12Z KTWC SOUNDING. SURFACE-300MB ELY FLOW OF
5-40 KTS ALSO OBSERVED...AND THIS FLOW MAY BE CONTRIBUTING TO THE
DRIER AND MORE-STABLE REGIME. HOWEVER...CURRENT THINKING IS THAT THE
SLIGHTLY DRIER AND MORE-STABLE ENVIRONMENT WILL BE VERY SHORT-LIVED
AS MOISTURE INCREASES FROM THE SOUTHEAST DURING THE NEXT FEW HOURS.

PER COORD WITH WFO PSR/FGZ AS WELL AS SATELLITE/RADAR TRENDS AND
VARIOUS 29/12Z GUIDANCE...WILL OPT FOR SCATTERED SHOWERS AND
THUNDERSTORMS AREAWIDE THIS EVENING...PARTICULARLY EMPHASIZING THE
TUCSON METRO AREA WWD WITH HIGHER POPS. WILL REFLECT SCATTERED
SHOWERS/TSTMS AFTER MIDNIGHT ACROSS SE PINAL AND FAR WRN/CENTRAL
PIMA COUNTIES WITH LOWER-GRADE POPS TUCSON METRO AREA EWD.

CONVECTIVELY-ACTIVE PERIOD ON TAP SATURDAY INTO EARLY MONDAY AS GULF
OF CALIFORNIA LOW PRESSURE SYSTEM IS DRAWN NWD WHILE TROUGH DEEPENS
OVER THE WRN CONUS. BELIEVE SAT MORNING WILL BE FAIRLY INACTIVE
CONVECTIVELY. WILL THEN REFLECT AT LEAST SCATTERED SHOWERS AND
THUNDERSTORMS AREAWIDE SAT AFTERNOON AND SAT EVENING. MAY BE TOO
CONSERVATIVE WITH POPS LATE SAT NIGHT INTO SUN MORNING BUT WILL
DEFER TO SUBSEQUENT SHIFTS FOR FURTHER REFINEMENT. WILL AGAIN OPT
FOR AT LEAST SCATTERED SHOWERS AND THUNDERSTORMS SUNDAY AFTERNOON/
EVENING WITH DECREASED COVERAGE BY LATE SUN NIGHT INTO LABOR DAY
MORNING.

THEREAFTER...INCREASINGLY WLY FLOW IS EXPECTED ACROSS THIS FORECAST
AREA STARTING LABOR DAY IN RESPONSE TO DEEPENING UPPER LOW OVER THE
GREAT BASIN. DEEP MOISTURE IS FORECAST TO BE SHUNTED SWD AND EWD
ESPECIALLY BY THE MIDDLE OF NEXT WEEK AS WLY FLOW CONTINUES. WILL
REFLECT PRECIP-FREE CONDITIONS TUCSON METRO AREA WWD WED-FRI WITH
LOW-GRADE POPS EAST. BELOW NORMAL DAYTIME HIGH TEMPS THROUGH THE
LABOR DAY WEEKEND THEN TEMPS TRENDING CLOSER TO NORMAL VALUES DURING
THE WED-FRI PERIOD.

&&

.AVIATION...EXPECT SCATTERED TSRA/SHRA ACROSS SE AZ THIS EVENING...
THEN MAINLY ISOLATED TSRA/SHRA AFTER 10Z AND CONTINUING INTO
SATURDAY MORNING. CLOUD DECKS GENERALLY 6-9K FT AGL...THOUGH
CEILINGS AROUND 3-5K FT AGL AND VISIBILITIES AS LOW AS 1-3SM
VICINITY STRONGEST TSRA. SURFACE WINDS ELY/SELY 5-15 KTS
TONIGHT...THEN ELY/SELY 10-20 KTS AND GUSTY SATURDAY. SCATTERED TO
NUMEROUS TSRA/SHRA SATURDAY AFTERNOON AND EVENING. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

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

BF

WEATHER.GOV/TUCSON

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
947 AM MST FRI AUG 29 2008

AZZ019-029>035-300800-
NORTHERN GREENLEE COUNTY-SOUTHEAST PINAL COUNTY-
UPPER GILA RIVER VALLEY-WESTERN PIMA COUNTY-TOHONO OODHAM NATION-
TUCSON METRO/MARANA/GREEN VALLEY-SANTA CRUZ COUNTY-COCHISE COUNTY-
947 AM MST FRI AUG 29 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL
ARIZONA AND SOUTHEAST ARIZONA.

.DAY ONE...TODAY AND TONIGHT

EXPECT SCATTERED SHOWERS AND THUNDERSTORMS ACROSS SOUTHEAST
ARIZONA AGAIN THIS AFTERNOON INTO TONIGHT. AS WAS THE CASE LATE
THURSDAY AFTERNOON AND EVENING...SOME THUNDERSTORMS LATER THIS
AFTERNOON AND EVENING WILL BE CAPABLE OF PRODUCING SEVERE
DAMAGING WIND GUSTS. ALSO...LOCALLY HEAVY RAINFALL OF 1 TO 2
INCHES MAY OCCUR FROM THE STRONGEST STORMS. THE POTENTIAL FOR ANY
SEVERE THUNDERSTORMS WILL DECREASE MARKEDLY BY MIDNIGHT.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

A TROUGH OF LOW PRESSURE ALONG THE WEST COAST WILL COMBINE WITH A
LOW PRESSURE SYSTEM JUST SOUTH OF THE AREA TO MAINTAIN A DEEP
EASTERLY FLOW OVER SOUTHEAST ARIZONA THIS WEEKEND. THUS...ANY
THUNDERSTORMS THAT OCCUR PARTICULARLY LATE SATURDAY INTO SUNDAY
MAY BE STRONG AND PRODUCE HEAVY RAINFALL. THOSE WITH OUTDOOR PLANS
THIS HOLIDAY WEEKEND SHOULD MONITOR FORECASTS CLOSELY. DRIER
CONDITIONS ARE EXPECTED ACROSS SOUTHEAST ARIZONA STARTING TUESDAY
AND CONTINUE DURING THE LATTER PART OF NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

WEATHER.GOV/TUCSON