Dust Storm and Heavy Rain in Arizona, July 28, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
515 PM MST WED JUL 28 2010

.UPDATED...UPDATED AVIATION DISCUSSION.

&&

.SYNOPSIS...
SEVERAL LOW PRESSURE SYSTEMS WILL MOVE TOWARD ARIZONA THE NEXT FEW
DAYS...LEADING TO AN INCREASE IN RAIN CHANCES MOST AREAS.
THUNDERSTORM ACTIVITY WILL PEAK THURSDAY ACROSS ARIZONA AS ONE LOW
MOVES IN FROM THE EAST...WITH ANOTHER UP TICK SATURDAY FOR ARIZONA
AND SOUTHEAST CALIFORNIA AS ANOTHER LOW ARRIVES FROM THE SOUTH.
TEMPERATURES WILL TREND DOWN HEADING INTO THE WEEKEND DUE TO
INCREASED CLOUD COVER AND SHOWER AND THUNDERSTORM ACTIVITY. DRIER
AIR WILL FILTER IN EARLY NEXT WEEK CAUSING RAIN CHANCES TO DROP AND
TEMPERATURES TO RISE.

&&

.DISCUSSION...
SAT AND RADAR TRENDS ARE SHOWING ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS OVER SOUTH-CENTRAL ARIZONA EASTWARD. STORM MOVEMENT
APPEARS RELATIVELY SLOW...OUT OF THE EAST AT 10KT OR SO...WITH THE
BIGGEST THREAT THIS AFTERNOON AND EARLY EVENING BEING MODERATE TO
HEAVY RAINFALL. PWATER OVER THE CENTRAL DESERTS IS AROUND 2.25
INCHES...AT LEAST THREE STANDARD DEVIATIONS ABOVE NORMAL FOR THIS
TIME OF YEAR. MODIFIED 12Z PSR SOUNDING...USING A MEAN LAYER MIXING
RATIO OF 14 G/KG AND AFTERNOON SFC TEMPS AROUND 100...YIELD SEVERAL
HUNDRED J/KG OF CAPE WITH MINIMAL CIN. WE STARTED OFF WITH LESS
CLOUD COVER OVER THE CENTRAL DESERTS THAN WE HAVE THE PAST FEW
MORNINGS...AND GIVEN THE UNUSUALLY HIGH AMOUNTS OF MOISTURE AND
INCREASING INSTABILITY WITH WARMING TEMPS...IT SHOULD NOT TAKE MUCH
TO GET TALL STORMS GOING THIS AFTERNOON/EVENING WITH SIGNIFICANT
RAINFALL AMOUNTS ON THE ORDER OF ONE INCH PER HOUR OR MORE. THE
GREATEST RAINFALL THREAT REMAINS OVER THE HIGHER TERRAIN OF SOUTHERN
GILA COUNTY AND NORTHWESTERN PINAL COUNTY. THE CHANCE FOR SEVERE
/60MPH OR GREATER/ WINDS IS NOT GENERALLY A THREAT TODAY...BUT
CANNOT RULE OUT A MET MICROBURST. WENT WITH COVERAGE WORDING IN THE
ZONES...SCATTERED SHOWERS/THUNDERSTORMS WITH A 40% CHANCE OF
MEASURABLE RAIN ACROSS THE PHOENIX METRO AREA. THE THREAT DECREASES
/SOMEWHAT/ INTO THE EVENING AND OVERNIGHT HOURS...BUT WILL HANG ONTO
SLIGHT CHANCE THROUGH EARLY MORNING HOURS.

A VERY MOIST FLOW WILL CONTINUE INTO THE WEEKEND...WITH A GENERAL
INCREASE IN THE THREAT OF SHOWERS/THUNDERSTORMS. BEYOND TODAY...
FORECAST FOCUSES ON THE NEXT WAVE /INVERTED TROUGH/ CURRENTLY
SPINNING OVER NORTHERN TEXAS AND EXPECTED TO MOVE THROUGH NEW MEXICO
AND INTO ARIZONA THURSDAY/FRIDAY. HAVE INCREASED THE POPS FOR THIS
TIME PERIOD...WITH THE GREATEST THREAT ONCE AGAIN HEAVY RAINFALL AND
POSSIBLE FLOODING. MEANWHILE...TEMPS WILL REMAIN BELOW NORMAL FOR
THIS TIME OF YEAR.

FEW CHANGES MADE BEYOND THE FRIDAY PERIOD...AND THE PREVIOUS
DISCUSSION/FORECAST REMAIN ON TRACK...

PREVIOUS DISCUSSION...
THINKING NOW IS THAT THURSDAY WILL SEE MUCH MORE ACTIVITY ACROSS OUR
EASTERN CWA AS THE EFFECTS OF THE LOW OVER TEXAS ARE BETTER FELT AS
IT MOVES INTO NEW MEXICO. INSTABILITY SHOULD BE A BIT HIGHER...SREF
PROBABILITIES OF MLCAPE HIGHER THAN 1000 J/KG PERK-UP THURSDAY...AND
AN AREA OF Q-VECTOR CONVERGENCE WILL BE MOVING INTO THE EASTERN HALF
OF ARIZONA BY THE EVENING. STORM MOTION WILL STILL BE OUT OF THE
EAST AT 10-15 KT HELPING TO PUSH STORMS INTO THE PHOENIX AREA.

CURRENT PRECIPITABLE WATER VALUES ARE APPROACHING RECORD HIGH VALUES
THUS HEAVY RAIN WORDING WAS ADDED TO THE GRIDS FOR TODAY AND
THURSDAY. HEAVY RAIN/FLASH FLOODING THREAT WILL ALSO BE PLAYED-UP IN
THE HAZARDOUS WEATHER OUTLOOK ISSUED LATER THIS MORNING. DON/T
EXPECT ACTIVITY TO BE WIDESPREAD ENOUGH TO WARRANT A FLASH FLOOD
WATCH.

POPS AND TEMPERATURES COME DOWN A BIT FRIDAY AFTER AN EXPECTED
ACTIVE THURSDAY. ANOTHER UPPER LEVEL LOW...CURRENTLY WEST OF THE
YUCATAN PENINSULA...WILL ROUND THE SOUTHWEST PERIPHERY OF THE H5
ANTI-CYCLONE SATURDAY AND SUNDAY WHICH WILL KEEP TEMPERATURES
COOLER...PLENTY OF CLOUDS AROUND...AND MAY ENHANCE CONVECTION A BIT.

BOUNDARY LAYER FINALLY STARTS TO DRY OUT MONDAY INTO THE MIDDLE OF
NEXT WEEK AS WEST COAST TROUGHING EDGES EASTWARD. DROPPED POPS DOWN
TO CLIMATOLOGY LEVELS FOR NEXT WEEK. TEMPERATURES WILL WARM
AGAIN...APPROACHING OR SLIGHTLY EXCEEDING NORMAL LEVELS.

&&

.AVIATION...
SOUTH-CENTRAL AZ...INCLUDING KPHX...KIWA AND SURROUNDING AIRFIELDS...
TO 07Z THU...SCT SHWRS AND TSTMS TOPS TO 45 THSD WITH VARIABLE WIND
GUSTS TO 40 KNOTS. SCT CLDS NEAR 45 HUNDRED WITH BKN-OVC CLDS BASED
NEAR 6 THSD MSL. BETWEEN 07Z THU AND 11Z THU...BKN CLDS BASED NEAR 6
THSD AGL WITH ISOLATED SHOWERS. FROM 11Z THU TO 18Z THU...SCT CLDS
NEAR 6 THSD WITH BASES NEAR 10 THSD.

SOUTHEASTERN CA...INCLUDING KIPL...KBLH AND SURROUNDING AIRFIELDS...
EXPECT SOUTHERLY WINDS 5 TO 15 KTS WITH SCT-BKN CLOUDS AOA 12K FT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
PRECIP CHANCES WILL LINGER THROUGH FRIDAY WITH DRIER WEATHER
EXPECTED SATURDAY THROUGH EARLY NEXT WEEK. HUMIDITIES WILL DROP ON
SUNDAY AS DRIER AIR IS ADVECTED INTO THE REGION. NO SIGNIFICANT
SYNOPTIC SCALE WINDS EXPECTED AT ANY TIME DURING THE FORECAST
PERIOD.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FLOOD WATCH UNTIL 9 PM MST THIS EVENING AZZ024-028.

CA...NONE.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...WANEK/INIGUEZ
AVIATION...PVASQUEZ
FIRE WEATHER...LEINS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PHOENIX AZ
509 AM MST WED JUL 28 2010

AZZ021>024-026>028-291215-
WEST CENTRAL DESERTS-NORTHWEST MARICOPA COUNTY-GREATER PHOENIX AREA-
SOUTHERN GILA COUNTY/TONTO NATIONAL FOREST FOOTHILLS-
SOUTHWEST DESERTS-SOUTHWEST MARICOPA COUNTY-
NORTHWEST AND NORTH CENTRAL PINAL COUNTY-
509 AM MST WED JUL 28 2010

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

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS WILL DEVELOP LATE THIS AFTERNOON OVER THE MOUNTAINS OF
EASTERN AND SOUTHERN ARIZONA...INCLUDING THE GLOBE-MIAMI AREA...THEN
MIGRATE INTO THE CENTRAL ARIZONA DESERTS...INCLUDING THE PHOENIX
AREA...THIS EVENING. WITH THE ATMOSPHERE CURRENTLY VERY MOIST HIGH
RAINFALL RATES WILL BE POSSIBLE WITH ANY THUNDERSTORM THAT DEVELOPS.
STORMS WILL GENERALLY BE SLOW MOVING RAISING THE THREAT OF LOCALIZED
FLASH FLOODING. GUSTY WINDS AND FREQUENT LIGHTNING WILL ALSO BE
POSSIBLE.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

GREATER THUNDERSTORM COVERAGE IS EXPECTED THURSDAY AFTERNOON AND
EVENING. HEAVY RAINFALL WITH LOCALIZED FLASH FLOODING WILL REMAIN
POSSIBLE AS WELL AS GUSTY WINDS AND FREQUENT LIGHTNING.

LESS THUNDERSTORM ACTIVITY IS EXPECTED FRIDAY FOLLOWED BY ANOTHER
INCREASE SATURDAY. THE AIRMASS WILL STILL BE VERY MOIST THROUGH
SATURDAY MEANING LOCALIZED FLASH FLOODING WILL REMAIN POSSIBLE.

THUNDERSTORM ACTIVITY WILL BEGIN TO DECREASE IN COVERAGE SUNDAY THEN
BE CONFINED TO THE EASTERN ARIZONA MOUNTAINS MONDAY THROUGH
WEDNESDAY. MOISTURE LEVELS WILL LOWER ALLOWING THE FLASH FLOOD THREAT
TO DECREASE.

.SPOTTER INFORMATION STATEMENT...

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

SPOTTER ACTIVATION WILL NOT BE NEEDED.

AZZ020-025-CAZ030>033-291215-
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-
509 AM MST WED JUL 28 2010 /509 AM PDT WED JUL 28 2010/

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

.DAY ONE...TODAY AND TONIGHT

NO WEATHER HAZARDS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THUNDERSTORMS WILL BE POSSIBLE SUNDAY AS A LOW PRESSURE SYSTEM MOVES
NORTH OUT OF SONORA INTO THE SOUTHWEST U.S. LOCALIZED FLASH FLOODING
WILL BE POSSIBLE AS THE ATMOSPHERE WILL BE VERY MOIST. GUSTY WINDS IN
EXCESS OF 45 MPH AND FREQUENT LIGHTNING WILL ALSO BE POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

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

SPOTTER ACTIVATION WILL NOT BE NEEDED.

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

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