Isolated thunderstorms developed over southeast Arizona during the afternoon. One cluster of storms tracked north across western Pima County and downed power poles in Ajo.
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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.
Isolated thunderstorms developed over southeast Arizona during the afternoon. One cluster of storms tracked north across western Pima County and downed power poles in Ajo.
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 Aug 13, 1:05 PM MST, 2 hours 3 minutes earlier.
Area Forecast Discussion National Weather Service Tucson AZ 105 PM MST Thu Aug 13 2020 .SYNOPSIS...An extended period of excessive heat can be anticipated today into next week as high pressure aloft strengthens over the region. There might be a break in the heat from time-to-time as a chance of showers and thunderstorms remain in the forecast. The weather pattern will become favorable next week for a daily dose of thunderstorms more typical of the monsoon season. && .DISCUSSION...High pressure aloft will continue to strengthen overhead as it starts to build northward today through the weekend. Eventually, the upper high will become centered over the Great Basin region north of the area by Monday. Latest models showed this upper high remaining centered north of the area, mainly over the Great Basin region, through most of next week. Although the position and strengthen of the upper high will bring an extended period of excessive heat to the Desert Southwest, an increase in deeper moisture might spare southeast Arizona a bit after the weekend. That said, will keep the Excessive Heat Warning going through Monday for now. Thereafter, the larger scale weather pattern will resemble one more typical of the monsoon season. Thus, will transition the message from the heatwave to increasing thunderstorm chances next week. Hopefully, the potential for wetting rains will keep the hotter temperatures in check next week. && .AVIATION...Valid through 15/00Z. FEW-BKN clouds 10-15k ft MSL this afternoon, with scattered TSRA/SHRA favoring areas south and east of KTUS. Precipitation dissipates this evening, returning tomorrow afternoon in a similar area as today. SFC wind generally less than 12 kts through the forecast period, with WLY/NWLY winds in the afternoon and early evening, becoming variable in direction at other times. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Isolated to scattered afternoon and evening showers and thunderstorms are forecast the next 7 days, primarily south and east of Tucson. There's a chance that the weather pattern becomes more favorable for thunderstorm development toward early next week. Temperatures will remain hot and moisture generally drier compared to average. 20-foot winds will follow typical diurnal patterns at less than 15 mph outside of any thunderstorm wind gusts. Daytime humidity will generally be in the 15 to 25 percent range in the valleys and 20 to 30 percent in the mountains with moderate to good overnight recoveries. && .TWC WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 8 PM MST Sunday for AZZ503-509. Excessive Heat Warning until 8 PM MST Monday for AZZ501-502- 504>506. && Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
Special Weather Statement
National Weather Service Tucson AZ
255 PM MST Thu Aug 13 2020
AZZ501-502-132230-
Western Pima County Including Ajo/Organ Pipe Cactus National
Monument-Tohono O'odham Nation including Sells-
255 PM MST Thu Aug 13 2020
...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN PIMA COUNTY UNTIL
330 PM MST...
At 254 PM MST, Doppler radar was tracking a strong thunderstorm 8
miles south of Ajo, moving north at 10 mph.
Winds in excess of 40 mph will be possible with this storm.
Locations impacted include...
Ajo, Organ Pipe Cactus National Monument and Why.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Heavy rainfall is also occurring with this storm, and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3251 11308 3251 11302 3250 11302 3251 11270
3217 11270 3217 11300
TIME...MOT...LOC 2154Z 178DEG 10KT 3225 11290
RHThe Phoenix radar (KIWA), 151 km away, was scanning. The volume nearest the first event began at 22:10 UTC.
1 thunderstorm wind. Local standard time, as filed.
Thunderstorm winds downed several power poles in Ajo, causing a power outage for about 100 customers for 2 to 3 hours.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2020Every state in 2020This day in weather historyWarnings in Arizona, August 2020
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: 919501.