High pressure aloft shifted to western Arizona on July 20th, creating northwest flow aloft over southeast Arizona. Scattered afternoon thunderstorms developed over the region.
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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 TWC wrote it up.
High pressure aloft shifted to western Arizona on July 20th, creating northwest flow aloft over southeast Arizona. Scattered afternoon thunderstorms developed over the region. A relatively dry boundary layer encouraged the production of strong thunderstorm downburst winds.
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 Tucson, AZ wrote its last area forecast discussion before the first event at Jul 20, 1:06 PM MST, 1 hour 41 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TUCSON AZ 110 PM MST MON JULY 20 2009 .SYNOPSIS...STRONG HIGH PRESSURE ALOFT WILL BRING HOT CONDITIONS TO SOUTHEAST ARIZONA THROUGH AT LEAST THE MIDDLE OF THE WEEK. MOISTURE WILL ALSO BE SUFFICIENT FOR THE DAILY CYCLE OF SCATTERED MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS. && .DISCUSSION...SOME CLOUDS ARE BEGINNING TO FORM OVER THE MOUNTAIN TOPS AND HIGHER ELEVATIONS OF SOUTHEAST ARIZONA...THOUGH SCATTERED SHOWER AND THUNDERSTORM ACTIVITY STILL LOOKING TO HOLD OFF. LOOKING OUTSIDE THE CWA...ACTIVITY HAS STARTED IN EARNEST ALONG THE RIM. GIVEN WEAK FLOW SEEN IN THE 12Z SOUNDING...NOT CONFIDENT THAT MUCH OF THAT WILL MAKE ITS WAY DOWN HERE. WILL LIKELY NEED TO WAIT FOR HOMEGROWN STORMS. STARTING TO SEE JUST A SMALL HANDFUL OF THOSE AT THE TIME OF THIS WRITING...MAINLY ALONG THE INTERNATIONAL BORDER AND ONE ISOLATED CELL OVER CENTRAL PIMA COUNTY. DEWPOINTS HAVE FALLEN TO THE UPPER 40S AND THAT DRYING WILL HELP IN THE FORMATION OF GUSTY WINDS/DOWNBURSTS FROM ANY STORMS THAT MAY DEVELOP TODAY. NOT MUCH CHANGE IN THINKING WITH REGARDS TO FORECAST...SO FOR DETAILS...PLEASE SEE PREV DISCUSSION SECTION BELOW. && .AVIATION...EXPECT ISOLATED TO SCATTERED TSRA/SHRA THE REST OF THIS AFTERNOON AND EVENING. THE STRONGEST TSRA WILL BE ACCOMPANIED WITH WIND GUSTS OF 40-45 KTS. OTHERWISE...SCATTERED TO OCCASIONALLY BROKEN CUMULOFORM CLOUDS WITH BASES 11-13K FT AGL INTO THIS EVENING. TSRA/ SHRA TO DECREASE IN COVERAGE AFTER 04Z AND ANY CONVECTIVE CLOUD DEBRIS TO DISSIPATE DURING THE NIGHT. SURFACE WINDS WLY/NWLY 5-15 KTS THRU 06Z THEN SLY/SELY 5-15 KTS LATE TONIGHT AND INTO TUESDAY MORNING. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS. && .FIRE WEATHER...ISOLATED TO SCATTERED THUNDERSTORMS WILL OCCUR THIS WEEK...WITH THE BULK OF ACTIVITY DURING THE AFTERNOON AND EARLY NIGHTTIME HOURS. GENERALLY LIGHT DIURNALLY DRIVEN SURFACE WINDS EXCEPT STRONG AND ERRATIC WINDS NEAR THE STRONGEST THUNDERSTORMS. ABOVE NORMAL DAYTIME TEMPERATURES TO OCCUR THIS WEEK. && .PREV DISCUSSION...SOME DEBRIS CLOUDINESS TO START THE MORNING...WHICH LOOKS MORE IMPRESSIVE ON SATELLITE THAN IT DOES OUT THE WINDOW. TRENDS HAVE IT THINNING...SO THAT IS NOT EXPECTED TO INTERFERE WITH DEVELOPMENT TODAY. MORE ON THAT LATER. DEWPOINTS AT AREA ASOS STATIONS WERE MOSTLY IN THE MID 50S...WITH THE EXCEPTION OF KDUG JUST SHY OF 50. TAKING A LOOK AT THE 12Z SOUNDING...A LITTLE MORE WET BUT SLIGHTLY MORE STABLE THAN 24 HOURS AGO WITH BETTER DIRECTIONAL SHEER...THOUGH STILL FAIRLY WEAK FLOW. ALSO OF NOTE ON THE SATELLITE...ALREADY GETTING SOME ACTIVITY SOUTH OF THE BORDER...WAY SOUTH...AS WELL AS SOME LINGERING ACTIVITY SOUTHEAST OF PRESCOTT. TAKING WHAT IS ALREADY HAPPENING INTO ACCOUNT...12Z NAM SHOWS A COUPLE OF DISTURBANCES THAT WILL IMPACT SE AZ TODAY...ONE OVER SOUTHERN NV AT THIS TIME MOVING INTO NORTHERN AZ...THE OTHER PUSHING INTO SE AZ FROM THE SOUTH. SHOULD THIS HOLD...AND THE AFOREMENTIONED ACTIVITY HINTS STRONGLY IN FAVOR OF THIS...SHOULD SEE A SIMILAR DAY TODAY AS WHAT WAS SEEN YESTERDAY...WITH ACTIVITY FLARING UP BOTH ON THE RIM AND ALONG THE INTERNATIONAL BORDER...EACH SPREADING INTO SE AZ. WITH THE WEAK FLOW...NOT EXPECTING ANY STORMS THAT DEVELOP TO MOVE ALL THAT FAST. MORE MOISTURE AT THE SURFACE...SHOULD IT HOLD...MAY HELP MITIGATE A WIND THREAT FROM STORMS THAT DEVELOP...BUT GIVEN THAT THERE IS NOT MUCH DIFFERENCE IN CONDITIONS VERSUS 24 HOURS AGO...DO NOT FEEL COMFORTABLE RULING THAT OUT AT THIS TIME. MOVING OUT OF THE VERY SHORT TERM...THE HIGH WOBBLES WESTWARD AND THIS WOBBLING WILL MAKE TUES AND WEDS LOOK SIMILAR TO TODAY ACCORDING TO THE MODELS. MOVING BEYOND MID WEEK...MID TO LONG RANGE MODELS SHOW THE RIDGE INTENSIFYING WITH THE HIGH CENTER NORTH OF THE FOUR CORNERS. THIS WOULD TAKE IT OUT OF THE PRIME REAL ESTATE FOR BRINGING MOISTURE INTO SE AZ WHICH WOULD VALIDATE THE INHERITED LOW RANGE MONSOON POPS. WILL WAIT AND SEE WHAT THE 12Z RUN OFFERS...BUT CAN SEE NO REASON TO ARGUE. ONE LAST THING TO MENTION...WITH THE RIDGE REMAINING IN PLACE...AND EVEN INTENSIFYING...AFTERNOON HIGH TEMPERATURES ARE EXPECTED TO REMAIN ABOVE CLIMATOLOGICAL NORMALS AND SHOW LITTLE VARIANCE FROM DAY TO DAY. THIS WOULD KEEP THE TUCSON METRO OVER THE CENTURY MARK FOR THE ENTIRE FORECAST PERIOD...PUSHING THE WESTERN DESERTS TO CLOSER TO 110 AND EASTERN VALLEYS TO THE UPPER 90S. INHERITED FORECAST APPEARS TO BE ON TRACK. EXPECT TO MAKE SOME SLIGHT TWEAKS TO TAKE INTO ACCOUNT CURRENT OBS AND NEWEST MODEL DATA...BUT OTHERWISE NO SIGNIFICANT CHANGES EXPECTED. && .TWC WATCHES/WARNINGS/ADVISORIES...NONE. WEATHER.GOV/TUCSON
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE TUCSON AZ 857 AM MST MON JUL 20 2009 AZZ019-030-034-035-211200- NORTHERN GREENLEE COUNTY-UPPER GILA RIVER VALLEY- SANTA CRUZ COUNTY-COCHISE COUNTY- 857 AM MST MON JUL 20 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST ARIZONA. .DAY ONE...TODAY AND TONIGHT ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON AND CONTINUE INTO THIS EVENING. THE STRONGEST STORMS MAY PRODUCE BRIEF HEAVY RAIN AND WIND GUSTS UP TO 45 MPH. THE BULK OF THE ACTIVITY IS FORECAST TO END BY AROUND MIDNIGHT TONIGHT. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY THE DAILY CYCLE OF ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS IS EXPECTED TO CONTINUE THROUGH SUNDAY...WITH ACTIVITY EXPECTED TO DEVELOP DURING THE AFTERNOON AND CONTINUE INTO THE EVENING HOURS. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES. AZZ029-031>033-211200- SOUTHEAST PINAL COUNTY-WESTERN PIMA COUNTY-TOHONO OODHAM NATION- TUCSON METRO/MARANA/GREEN VALLEY- 857 AM MST MON JUL 20 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL ARIZONA AND SOUTHEAST ARIZONA. .DAY ONE...TODAY AND TONIGHT ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS THE AREA THIS AFTERNOON INTO THIS EVENING. THE STRONGEST STORMS MAY PRODUCE BRIEF PERIODS OF HEAVY RAIN...WIND GUSTS UP TO 45 MPH AND REDUCED VISIBILITIES DUE TO BLOWING DUST. THE MAJORITY OF ACTIVITY IS EXPECTED TO END BY MIDNIGHT TONIGHT. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY THE DAILY CYCLE OF ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS IS EXPECTED TO CONTINUE THROUGH WEDNESDAY BEFORE BECOMING MORE ISOLATED FOR THE REMAINDER OF THE WEEK. ACTIVITY IS EXPECTED TO DEVELOP DURING THE AFTERNOON AND CONTINUE INTO THE EVENING HOURS. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES. WEATHER.GOV/TUCSON
The Tucson radar (KEMX), 57 km away, was scanning. The volume nearest the first event began at 21:45 UTC.
2 thunderstorm wind. Local standard time, as filed.
Severe thunderstorm winds downed 20 power poles near the intersection of Valencia Road and Ajo Way.
Strong thunderstorm downburst winds downed 4 small trees. Minor roofing damage was reported with missing roof tiles, and one street sign was blown down.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2009Every state in 2009This day in weather historyWarnings in Arizona, July 2009
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: 173108, 173548.