Strong thunderstorms across south-central Arizona produced damaging winds, hail and extremely heavy rainfall. Heavy rain with near zero visibility led to a massive traffic pileup in downtown Phoenix.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS PSR wrote it up.
Strong thunderstorms across south-central Arizona produced damaging winds, hail and extremely heavy rainfall. Heavy rain with near zero visibility led to a massive traffic pileup in downtown Phoenix.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Phoenix, AZ wrote its last area forecast discussion before the first event at Aug 28, 3:11 PM MST, 19 minutes earlier.
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
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1017 AM MST SAT AUG 28 2010
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0530 AM TSTM WND GST 10 WNW TYSON 32.86N 114.03W
08/27/2010 M63 MPH YUMA AZ OTHER FEDERAL
SEVERAL POWER POLES KNOCKED DOWN. 0.70 INCHES OF RAIN
MEASURED.
&&
LEINSPRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE PHOENIX AZ
1018 AM MST SAT AUG 28 2010
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0530 PM TSTM WND GST 10 WNW TYSON 32.86N 114.03W
08/27/2010 M63.00 MPH YUMA AZ OTHER FEDERAL
SEVERAL POWER POLES KNOCKED DOWN. 0.70 INCHES OF RAIN
MEASURED.
&&
LEINSSPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE PHOENIX AZ 309 PM MST SAT AUG 28 2010 AZZ028-282300- PINAL AZ- 309 PM MST SAT AUG 28 2010 THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A SIGNIFICANT WEATHER ADVISORY FOR... WEST CENTRAL PINAL COUNTY IN SOUTH CENTRAL ARIZONA UNTIL 400 PM MST AT 304 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A STRONG THUNDERSTORM 9 MILES SOUTH OF MARICOPA...MOVING NORTHEAST AT 20 MPH. HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN. LOCATIONS IMPACTED INCLUDE... MARICOPA... OLBERG AND BAPCHULE... IF THIS STORM INTENSIFIES...A WARNING MAY BE NEEDED. STAY TUNED TO NOAA WEATHER RADIO...LOCAL RADIO OR TV FOR THE LATEST UPDATES. LOCALLY DENSE BLOWING DUST IS POSSIBLE. IF YOU ENCOUNTER BLOWING DUST WHILE DRIVING...PULL OVER AS FAR OFF THE ROADWAY AS POSSIBLE AND PARK. TURN OFF YOUR HEADLIGHTS AND KEEP YOUR FOOT OFF THE BRAKE. LAT...LON 3320 11191 3297 11173 3282 11207 3298 11219 TIME...MOT...LOC 2209Z 236DEG 17KT 3295 11203 MP
The Phoenix radar (KIWA), 42 km away, was scanning. The volume nearest the first event began at 22:32 UTC.
7 thunderstorm wind, 3 heavy rain. Local standard time, as filed.
A trained spotter reported that power poles were blown down at the junction of the Casa Grande Highway, and north White and Parker Road. Winds were estimated to be in excess of 50 kt.
A trained spotter near South Mountain Park reported that multiple large tree limbs, at least 7 inches in diameter, were blown down by strong thunderstorm winds estimated to be in excess of 50 kt.
A trained spotter reported that power poles were blown down at 19th Avenue and Dunlap. The poles were downed by thunderstorm microburst winds estimated to be in excess of 50 kt.
Power poles were blown down at 19th Ave and Dunlap.
A trained spotter in Phoenix measured 1.24 inches of rainfall between 1800MST and 1845MST. The rain fell in the area near 16th Street and Northern.
Strong thunderstorms with extremely heavy rain led to mutiple collisions on Interstate 10 in downtown Phoenix during the afternoon hours on August 28. A total of 69 vehicles were involved in a series of crashes; one collision alone involved 35 vehicles and spanned over 2 miles from 16th street to 7th street. Trained spotters reported visibilities below one quarter mile in heavy rain in downtown Phoenix, and it was low visibility in heavy rain that led to the collisions. Seven people were taken to area hospitals and two were in serious condition. Fire officials medically evaluated at least 40 people.
A trained spotter reported numerous large tree branches down on Shea Boulevard, partially blocking traffic. The trees limbs were downed by strong thunderstorm winds estimated to be in excess of 50 kt. In addition, there was minor flooding along Shea between 120th and 136th street. In Fountain Hills very strong winds blew trees down and blew tiles off roofs, according to the Fountain Hills Times. Nearly every major street in Fountain Hills had tree limbs down, according to Ken Kurth.
An amateur radio operator reported six inch diameter trees blown down in south central Maricopa. A trained spotter also reported a couple tree limbs blown down near the town of Maricopa. Winds were estimated in excess of 50 kt.
Trained spotters reported that throughout Maricopa, over 13 power poles were blown down by thunderstorm microburst wind estimated to be in excess of 60 kt. In addition, numerous buildings sustained roof damage and trees up to 10 inches in diameter were blown over.
Strong thunderstorms produced locally heavy rainfall across portions of west central Pinal county, including the town of Maricopa and the Ak-Chin Village. Radar and trained spotters indicated up to 3 inches of rain fell along the Santa Rosa and Green washes, and several reports of curb-to-curb street flooding in Maricopa were received.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2010Every state in 2010This day in weather historyWarnings in Arizona, August 2010
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 254543, 254566, 254565, 255698, 254570, 254625, 254567, 254557, 254562, 254572.