Severe Thunderstorm Warning 53, NWS Phoenix, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
311 PM MST SAT AUG 28 2010

.SYNOPSIS...
AN APPROACHING TROUGH OF LOW PRESSURE WILL HELP TO TRIGGER SOME
SHOWERS AND THUNDERSTORMS THIS EVENING. THESE WILL DEVELOP PRIMARILY
OVER THE HIGHER TERRAIN NORTH AND EAST OF THE PHOENIX METROPOLITAN
AREA. DRY AIR USHERED IN BY THE TROUGH WILL KEEP THE STORM THREAT
LIMITED PRIMARILY TO THE HIGHER TERRAIN OF SOUTH-CENTRAL ARIZONA
NEXT WEEK. TEMPERATURES WILL CONTINUE TO BE BELOW NORMAL INTO MONDAY
BEFORE A WARMING TREND BEGINS TUESDAY.

&&

.DISCUSSION...
AT 2 PM THIS AFTERNOON VISIBLE SATELLITE IMAGERY SHOWED A CUMULUS
FIELD BEGINNING TO DEVELOP ACROSS THE EASTERN HALF OF THE FORECAST
AREA. CONVECTION HOWEVER IS STRUGGLING TO GET GOING OVER EAST
CENTRAL ARIZONA. FURTHER TO THE SOUTHEAST OVER SRN PINAL AND PIMA
COUNTY A FEW THUNDERSTORMS HAVE MANAGED TO GET INITIATED. THIS
APPEARS TO BE IN AN AREA OF DEEPER MOISTURE. GPS IPW DATA INDICATES
HIGHER PWAT IN THE SOUTHEAST PORTION OF THE STATE. GFS AND ECMWF
BOTH INDICATE SUFFICIENT INSTABILITY FOR SHOWER AND STORM
DEVELOPMENT THIS AFTERNOON...WITH LI/S AROUND -4 AND SB CAPE IN
EXCESS OF 1000 J/KG. APPEARS RIGHT NOW THAT INHIBITOR IS THE LACK OF
SUFFICIENT FORCING TO GET STORMS DEVELOPING. MODEL SOUNDINGS SHOW
FAIRLY STRONG SOUTHWEST TO WEST FLOW ABOVE 85H. THIS IS CONSISTENT
WITH VAD WIND PROFILE DATA FROM KIWA. SHEAR MAY BE TWO STRONG FOR
UPDRAFT DEVELOPMENT. MODELS SHOW INCREASED UPPER LEVEL DEFORMATION
MOVING ACROSS FORECAST AREA AFTER 00Z...AS TROUGH TO OUR WEST BEGINS
MOVING FURTHER INLAND FROM THE COAST. WATER VAPOR IMAGERY THOUGH
SHOWS VERY DRY AIR THOUGH IN ADVANCE OF THE TROUGH AND THE LACK OF
DEEP MOISTURE MAY ALSO BE A NEGATIVE FACTOR FOR ANY WIDESPREAD
DEVELOPMENT. ALL BEING SAID...IT LOOKS LIKE BIGGEST THREAT TODAY
WILL BE OVER THE HIGHER TERRAIN WHERE MOISTURE IS DEEPER AND
OROGRAPHIC FORCING IS THE PRIMARY TRIGGER. WILL STILL KEEP CHANCE
POPS OVER MARICOPA...PINAL...AND GILA COUNTY THROUGH EARLY
EVENING...THEN CHANCE POPS OVER GILA COUNTY OVERNIGHT.

MODELS ARE IN AGREEMENT IN BRINGING COOLER AND DRIER AIR INTO THE
REGION...AS THE TROUGH DEEPENS....DROPS SOUTHEAST...AND SWINGS
ACROSS THE STATE SUNDAY AND MONDAY. AFTERNOON AND EARLY EVENING
SHOWERS WILL REMAIN IN THE FORECAST FOR BOTH DAYS...BUT WILL BE
CONFINED PRIMARILY TO THE HIGHER TERRAIN NORTH AND EAST OF THE
PHOENIX METROPOLITAN AREA. AFTERNOON HIGH TEMPERATURES FOR SUNDAY
AND MONDAY SHOULD BE SEVERAL DEGREES BELOW NORMAL. IS THIS THE END
OF THE 2010 MONSOON? PROBABLY TOO EARLY TO SAY ONE WAY OR THE OTHER
RIGHT NOW. BOTH THE ECMWF AND THE GFS HOWEVER STRUGGLE TO FIND MUCH
MOISTURE THROUGH NEXT WEEK...ADVERTISING A DRY WEATHER PATTERN FOR
THE FORECAST AREA. HIGH TEMPERATURES FOR THE WEEK WILL START OUT A
FEW DEGREES BELOW NORMAL...BUT SHOULD WARM BACK UP TO NEAR NORMAL
VALUES BY THURSDAY.

&&

.AVIATION...
SOUTH CENTRAL AZ...INCLUDING KIWA AND KPHX...
MOSTLY CLEAR SKIES AT THE MOMENT SHOULD GIVE WAY TO SCATTERED TSRA
THIS AFTERNOON AND EVENING. I WILL CONTINUE WITH A MENTION OF TSRA
IN THE TAFS AROUND 00-04Z AT BOTH SITES ALTHOUGH COVERAGE MAY BE
SPOTTY AT TIMES. STRONG WINDS POSSIBLE WITH ANY STORMS THAT
DEVELOP...WILL MENTION GUSTS TO 30KTS. CONDITIONS SHOULD IMPROVE
LATE TONIGHT.  WINDS WILL TAKE ON THEIR TYPICAL WESTERLY COMPONENT
THIS AFTERNOON BEFORE BACKING TO NORTHEASTERLY LATE TONIGHT.

SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH...
CLEAR SKIES SHOULD PREVAIL AT BOTH SITES THROUGH THE PERIOD. DRY AIR
FINALLY MAKING ITS WAY THROUGH SOUTHEAST CALIFORNIA WITH DEWPOINTS
DROPPING INTO THE MID 60S AT NJK AS OF 16Z. SHOULD SEE DRY AIR AT
IPL/BLH BEFORE 20Z WITH ALL CONVECTION REMAINING EAST OF THE RIVER
TONIGHT. WITH THE ARRIVAL OF THE DRY AIR WILL COME GUSTY WEST WINDS
TO 25-30KTS. WINDS SHOULD DIMINISH AFTER SUNSET...AROUND 03Z. NO
SIGNIFICANT AVIATION CONCERNS TODAY OR TONIGHT.

DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH SATURDAY...
A GENERAL DRYING TREND IS FORECAST THIS WEEK AS MOISTURE ASSOCIATED
WITH HURRICANE FRANKS REMNANTS SHOULD ADVECT WELL EAST OF THE
FORECAST AREA. NO SIGNIFICANT TROUGHS FORESEEN IN THE LATEST 12Z
GUIDANCE...OVERALL A FAIRLY QUIET WEATHER WEEK UNDER A BROAD
SOUTHWESTERLY FLOW ALOFT. AFTERNOON BREEZES AND HUMIDITIES SHOULD
NOT REACH CRITICAL THRESHOLDS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...MCLANE
AVIATION...LEINS
FIRE WEATHER...LEINS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
550 AM MST SAT AUG 28 2010

AZZ022-023-027-028-291300-
NORTHWEST MARICOPA COUNTY-GREATER PHOENIX AREA-
SOUTHWEST MARICOPA COUNTY-NORTHWEST AND NORTH CENTRAL PINAL COUNTY-
550 AM MST SAT AUG 28 2010

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

.DAY ONE...TODAY AND TONIGHT
THERE IS A GOOD CHANCE OF THUNDERSTORMS TODAY AND THIS EVENING.
STORMS TODAY WILL HAVE POTENTIAL TO PRODUCE A WIDE ARRAY OF HAZARDS
INCLUDING DAMAGING WINDS...HAIL...AND LOCALLY HEAVY RAIN...IN
ADDITION TO THE INHERENT DANGER OF LIGHTNING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY
NO WEATHER HAZARDS EXPECTED.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION MAY BECOME NECESSARY LATER TODAY. WEATHER
SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS
ACCORDING TO STANDARD OPERATING PROCEDURES.

AZZ024-291300-
SOUTHERN GILA COUNTY/TONTO NATIONAL FOREST FOOTHILLS-
550 AM MST SAT AUG 28 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST-CENTRAL
ARIZONA.

.DAY ONE...TODAY AND TONIGHT
THUNDERSTORMS ARE LIKELY TODAY AND TONIGHT. THE STORMS WILL HAVE
POTENTIAL TO PRODUCE A WIDE ARRAY OF HAZARDS INCLUDING DAMAGING
WINDS...HAIL...AND LOCALLY HEAVY RAIN...IN ADDITION TO THE INHERENT
DANGER OF LIGHTNING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY
LINGERING MOISTURE WILL MAINTAIN AT LEAST A SLIGHT CHANCE OF
THUNDERSTORMS THROUGH NEXT WEEK. IF ANY STORMS FORM...THE MOST LIKELY
HAZARD WILL BE VERY STRONG WINDS...IN ADDITION TO THE INHERENT DANGER
OF LIGHTNING.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION MAY BECOME NECESSARY LATER TODAY. WEATHER
SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS
ACCORDING TO STANDARD OPERATING PROCEDURES.

AZZ021-026-291300-
WEST CENTRAL DESERTS-SOUTHWEST DESERTS-
550 AM MST SAT AUG 28 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST ARIZONA
AND WEST-CENTRAL ARIZONA.

.DAY ONE...TODAY AND TONIGHT
THERE IS A CHANCE OF THUNDERSTORMS TODAY...MAINLY OVER EASTERN
PORTIONS OF LA PAZ AND YUMA COUNTIES. STORMS TODAY WILL HAVE POTENTIAL
TO PRODUCE A WIDE ARRAY OF HAZARDS INCLUDING DAMAGING
WINDS...HAIL...AND LOCALLY HEAVY RAIN...IN ADDITION TO THE INHERENT
DANGER OF LIGHTNING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY
NO WEATHER HAZARDS EXPECTED.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION MAY BECOME NECESSARY LATER TODAY. WEATHER
SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS
ACCORDING TO STANDARD OPERATING PROCEDURES.

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

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