Dust Storm Warning 20, NWS Phoenix, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
350 PM MST SUN SEP 11 2011

.SYNOPSIS...
A LOW PRESSURE SYSTEM IS EXPECTED TO REMAIN CENTERED NEAR THE
SOUTHERN CALIFORNIA COAST THROUGH MONDAY NIGHT THEN MOVE ONLY SLOWLY
EAST THE FIRST HALF OF THE WEEK. THIS MEANS A CONTINUED  CHANCE OF
MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS ACROSS MOST
OF THE AREA THROUGH EARLY THIS WEEK. SHOWERS AND THUNDERSTORMS ARE
LIKELY IN SOUTH-CENTRAL ARIZONA INCLUDING THE GREATER PHOENIX AREA
THROUGH THIS EVENING. STRONG GUSTY DAMAGING WINDS...HAIL...AND HEAVY
RAIN ARE PROBABLE WITH SOME STORMS ALONG WITH BLOWING DUST AHEAD OF
THE STORMS. DRIER AIR IS EXPECTED TO BRING A DECREASE IN THE CHANCE
OF STORMS WEDNESDAY WITH DRY AND GRADUALLY WARMER WEATHER THE LATTER
PART OF THE WEEK.

&&

.DISCUSSION...
PARTLY TO MOSTLY CLOUDY SKIES COVERED SOUTHWEST AND ESPECIALLY
SOUTH-CENTRAL ARIZONA INCLUDING THE GREATER PHOENIX AREA AND IT WAS
MOSTLY SUNNY ACROSS SOUTHEAST CALIFORNIA AT MID AFTERNOON TODAY.
SIGNIFICANT SHOWERS AND THUNDERSTORMS WERE DEVELOPING SOUTH THROUGH
WEST OF PHOENIX AND MOVING TOWARD PHOENIX. THERE WERE ISOLATED
SHOWERS AND THUNDERSTORMS IN YUMA COUNTY AND LA PAZ COUNTY.
TEMPERATURES WERE GENERALLY 2 TO 5 DEGREES LOWER IN SOUTH-CENTRAL
ARIZONA INCLUDING THE GREATER PHOENIX AREA...AND CLOSE TO THE SAME
OR A DEGREE OR SO LOWER IN FAR SOUTHWEST ARIZONA AND SOUTHEAST
CALIFORNIA INCLUDING YUMA AND THE EL CENTRO-IMPERIAL AREA. WIND WAS
GENERALLY FROM THE SOUTHEAST AND SOUTH 5 TO 15 MPH WITH SOME HIGHER
GUSTS...EXCEPT STRONG...GUSTY AND VARIABLE NEAR THUNDERSTORMS.
ALSO...WINDS WERE LIGHTER AND VARIABLE IN SOUTHEAST CALIFORNIA WEST
OF THE LOWER COLORADO RIVER VALLEY.

THE LOW PRESSURE SYSTEM THAT HAS BEEN CENTERED NEAR THE SOUTHERN
CALIFORNIA COAST THE PAST COUPLE OF DAYS IS EXPECTED TO CONTINUE
THERE THROUGH MONDAY NIGHT. MOISTURE FROM WESTERN MEXICO IS EXPECTED
TO CONTINUE OVER SOUTH-CENTRAL ARIZONA AND HAS EXPANDED SOMEWHAT
FARTHER WEST. THIS MEANS SOME CHANCE OF MAINLY AFTERNOON AND EVENING
SHOWERS AND THUNDERSTORMS AS FAR WEST AS THE LOWER COLORADO RIVER
VALLEY THROUGH TUESDAY. IN ADDITION...A PLUME OF TROPICAL MOISTURE
FROM OFF THE COAST OF BAJA CALIFORNIA IS EXPECTED TO MOVE FROM THE
SOUTHWEST OVER SOUTHWEST AND SOUTH-CENTRAL ARIZONA TONIGHT.

THIS MOISTURE IN COMBINATION WITH JET STREAM DYNAMICS ASSOCIATED
WITH THE LOW PRESSURE SYSTEM IS EXPECTED TO RESULT IN A SIGNIFICANT
INCREASE IN THE LIKELIHOOD OF SHOWERS AND THUNDERSTORMS IN
SOUTH-CENTRAL ARIZONA SPREADING FROM SOUTH AND WEST OF PHOENIX
ACROSS MUCH OF SOUTH-CENTRAL ARIZONA INCLUDING THE GREATER PHOENIX
AREA THROUGH THIS EVENING.

SOME SEVERE THUNDERSTORMS ARE PROBABLE IN SOUTH-CENTRAL ARIZONA
INCLUDING THE GREATER PHOENIX AREA BY THIS EVENING. THESE STORMS ARE
EXPECTED TO PRODUCE STRONG GUSTY DAMAGING WINDS...HAIL...AND HEAVY
RAIN. BLOWING DUST WITH REDUCED VISIBILITY IS ALSO POSSIBLE AHEAD OF
THE STORMS.

HAVE KEPT THE ADJUSTED FORECAST THROUGH THIS EVENING THAT WAS ISSUED
THIS MORNING. AND...A SPECIAL WEATHER STATEMENT WAS ALSO ISSUED THIS
MORNING ALONG WITH AN UPDATED HAZARDOUS WEATHER OUTLOOK ISSUED EARLY
THIS AFTERNOON. THE NET CONTROLLER WAS ALERTED THAT SPOTTER
ACTIVATION MAY BE NEEDED BY THIS EVENING.

IT LOOKS AS IF ONLY ENOUGH MOISTURE WILL MAKE IT TO SOUTHEAST
CALIFORNIA WEST OF THE LOWER COLORADO RIVER VALLEY FOR A SLIGHT
CHANCE OF SHOWERS AND THUNDERSTORMS THERE TUESDAY AFTERNOON.
HOWEVER...WITH THE LOW PRESSURE SYSTEM MOVING VERY LITTLE THROUGH
MONDAY NIGHT AND ONLY MOVING SLOWLY EAST TUESDAY...HAVE KEPT A
CHANCE OF MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS IN
SOUTH-CENTRAL ARIZONA INCLUDING THE GREATER PHOENIX AREA THROUGH
TUESDAY.

THE LOW PRESSURE SYSTEM IS EXPECTED TO MOVE EAST TO SOUTHERN UTAH
WEDNESDAY. DRIER AIR FROM THE SOUTHWEST IS EXPECTED TO COVER
SOUTHEAST CALIFORNIA AND FILTER INTO THE REST OF THE AREA FROM THE
SOUTHWEST. THIS MEANS LESS OF A CHANCE...BUT STILL SOME CHANCE OF
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS OVER SOUTH-CENTRAL
ARIZONA MAINLY OVER THE HIGHER TERRAIN WEDNESDAY.

THE LOW PRESSURE SYSTEM IS EXPECTED TO CONTINUE WEAKENING WITH DRIER
SPREADING OVER MOST OF THE AREA. THE DRY AIR IS EXPECTED TO CONFINE
A SLIGHT CHANCE OF AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS
TO THE HIGHER TERRAIN EAST OF THE GREATER PHOENIX AREA THURSDAY.
THEN DRY AND SLIGHTLY WARMER IS EXPECTED ACROSS THE ENTIRE AREA
FRIDAY AND NEXT WEEKEND.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX AND KIWA...
UPPER LEVEL LOW REMAINS NEARLY STATIONARY OVER SOUTHERN CALIFORNIA
PROVIDING SOUTHWEST UPPER FLOW ACROSS ARIZONA. MODEST INSTABILITY IN
COMBINATION WITH UPPER LEVEL JET ENERGY ACROSS SOUTHERN ARIZONA IS
EXPECTED TO LEAD TO THUNDERSTORM DEVELOPMENT THIS AFTERNOON AND
EVENING. THE MAIN FOCUS AREA SHOULD BE ACROSS SOUTH-CENTRAL ARIZONA
WHERE THE GREATEST INSTABILITY AND UPPER LEVEL SUPPORT IS SHOWN.
ISOLATED TO SCATTERED THUNDERSTORMS WITH GUSTY WINDS AND POSSIBLY
BLOWING DUST WILL LIKELY AFFECT PORTIONS OF THE PHOENIX METRO AREA
EARLY THIS EVENING. STORM MOVEMENT WILL GENERALLY BE TO THE NORTH
NORTHEAST LIKELY RESULTING A SOUTHWESTERLY OUTFLOW WIND DIRECTION. A
BRIEF PERIOD OF RESTRICTED VISIBILITIES MAY OCCUR DUE TO BLOWING
DUST...BUT NOT CONFIDENT ENOUGH TO ADD TO TAFS AT THIS TIME.

SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH....
UPPER LEVEL LOW OVER SOUTHERN CALIFORNIA WILL BRING GENERALLY DRY
CONDITIONS ACROSS SOUTHEAST CALIFORNIA AS MID LEVEL SOUTHWESTERLY
FLOW CONTINUES TO BRING IN DRY AIR. A FEW THUNDERSTORMS ACROSS
SOUTHWEST ARIZONA MAY BRUSH CLOSE TO KBLH...BUT EXPECTING STORMS TO
STAY TO THE EAST.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
THE THUNDERSTORM CHANCE WILL DECREASE WEDNESDAY...ALTHOUGH SCATTERED
SHOWERS AND STORMS REMAIN POSSIBLE MAINLY EAST OF PHOENIX WEDNESDAY
AND EAST OF THE GREATER PHOENIX AREA THURSDAY. DRY WEATHER IS
EXPECTED OVER THE ENTIRE AREA FRIDAY AND NEXT WEEKEND. DRIER AIR
WILL MOVE IN FROM THE WEST THIS WEEK BUT AFTERNOON HUMIDITIES WILL
ONLY DROP TO AROUND 20 PERCENT WITH GOOD OVERNIGHT RECOVERY. NO
SIGNIFICANT DRYING TRENDS AND WIND EVENTS EXPECTED THROUGH THE
UPCOMING WEEK.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...ELLIS
PREVIOUS DISCUSSION...AJ
AVIATION...KUHLMAN
FIRE WEATHER...ELLIS/LEINS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
1230 PM MST SUN SEP 11 2011

AZZ021>023-026>028-121315-
WEST CENTRAL DESERTS-NORTHWEST MARICOPA COUNTY-GREATER PHOENIX AREA-
SOUTHWEST DESERTS-SOUTHWEST MARICOPA COUNTY-
NORTHWEST AND NORTH CENTRAL PINAL COUNTY-
1230 PM MST SUN SEP 11 2011

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

.DAY ONE...TODAY AND TONIGHT.

SHOWERS AND THUNDERSTORMS ARE LIKELY LATE THIS AFTERNOON AND THIS
EVENING. STRONGER STORMS WILL PROBABLY PRODUCE LOCALIZED AREAS OF
DAMAGING WINDS...HAIL...AND HEAVY RAIN ALONG WITH FREQUENT
LIGHTNING. BLOWING DUST WITH REDUCED VISIBILITY IS ALSO POSSIBLE
AHEAD OF THE STORMS.

SEE THE SPECIAL WEATHER STATEMENT ISSUED FOR THIS AFTERNOON AND THIS
EVENING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

THERE IS AT LEAST A SLIGHT CHANCE OF MAINLY AFTERNOON AND EVENING
THUNDERSTORMS THROUGH WEDNESDAY. THE POTENTIAL WILL REMAIN FOR THE
STRONGEST STORMS TO PRODUCE LOCALIZED AREAS OF DAMAGING
WIND...HAIL...HEAVY RAIN...AND FREQUENT LIGHTNING. HOWEVER...THE
PROBABILITY OF SEVERE STORMS WILL DECREASE SIGNIFICANTLY BY
WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED THIS EVENING.

AZZ024-121315-
SOUTHERN GILA COUNTY/TONTO NATIONAL FOREST FOOTHILLS-
1230 PM MST SUN SEP 11 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST-CENTRAL ARIZONA.

.DAY ONE...TODAY AND TONIGHT.

THERE IS A GOOD CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS. THERE
IS A POTENTIAL FOR THE STRONGER STORMS TO PRODUCE LOCALIZED AREAS OF
DAMAGING WINDS...HAIL...AND HEAVY RAIN ALONG WITH FREQUENT LIGHTNING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

THERE IS A CHANCE OF MAINLY AFTERNOON AND EVENING THUNDERSTORMS
THROUGH TUESDAY...DECLINING TO SLIGHT CHANCES WEDNESDAY THROUGH
SATURDAY.  THE POTENTIAL WILL REMAIN FOR THE STRONGEST STORMS TO
PRODUCE LOCALIZED AREAS OF DAMAGING WIND...HAIL...HEAVY RAIN...AND
FREQUENT LIGHTNING. HOWEVER...THE PROBABILITY OF SEVERE STORMS WILL
DECREASE SIGNIFICANTLY WEDNESDAY ONWARD.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TODAY.

AZZ020-025-CAZ030>033-121315-
LOWER COLORADO RIVER VALLEY AZ-YUMA/MARTINEZ LAKE AND VICINITY-
JOSHUA TREE NATIONAL PARK-LOWER COLORADO RIVER VALLEY CA-
RIVERSIDE COUNTY/EASTERN DESERTS-IMPERIAL COUNTY-
1230 PM MST SUN SEP 11 2011 /1230 PM PDT SUN SEP 11 2011/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EXTREME SOUTHWEST
ARIZONA...EXTREME WEST-CENTRAL ARIZONA...EXTREME SOUTHEAST
CALIFORNIA AND SOUTHEAST CALIFORNIA.

.DAY ONE...TODAY AND TONIGHT.

THERE IS A SLIGHT CHANCE OF THUNDERSTORMS...MAINLY NEAR THE LOWER
COLORADO RIVER VALLEY. THERE IS A POTENTIAL FOR THE STRONGER  STORMS
TO PRODUCE LOCALIZED AREAS OF DAMAGING WINDS...HAIL...AND FREQUENT
LIGHTNING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

THERE IS A SLIGHT CHANCE OF MAINLY AFTERNOON AND EVENING
THUNDERSTORMS THROUGH TUESDAY. THERE IS A POTENTIAL FOR THE
STRONGEST STORMS TO PRODUCE LOCALIZED AREAS OF DAMAGING
WIND...HAIL...AND FREQUENT LIGHTNING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TODAY.

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

ELLIS/AJ

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