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Summary

Thunderstorms built over the greater Flagstaff area on Tuesday, July 13, 2021 and produced heavy rainfall over the Museum Fire scar by mid-afternoon. Runoff and debris from the scar travelled downstream and resulted in flash flooding in much of northeastern Flagstaff late that afternoon. Roads were closed, homes were inundated and hazardous travel conditions were observed. Another active day setup on Wednesday, July 14 as anomalously high rain rates were again observed in the Upper and Lower Greenlaw neighborhoods in northeastern Flagstaff. Considerable flash flooding was captured on video with many inches of water clogging roads and inundating even more homes in local communities. Moderate rainfall was also observed on the 14th over the Museum Fire scar area, but most runoff came from the urban Flagstaff area that day.

 

Timeline and Impacts

 

Flooding due to heavy rainfall over the Museum Fire scar - Radar loop from 11 AM - 5 PM July 13, 2021 showing very strong thunderstorms directly over the Museum Fire scar area immediately north of the city.

Flooding mainly due to heavy rainfall in northeast Flagstaff - Radar loop from 11 AM - 5 PM July 14, 2021 showing a second day in a row of very strong thunderstorms directly over Flagstaff, AZ and the Museum Fire scar area immediately north of the city.

Flooding due to heavy rainfall over the Museum Fire scar - High rain rates were observed on the Museum Fire scar around 2 PM MST on July 13, 2021. Between 1-2" of rain was estimated by radar from 2-3 PM MST. Shown are 1-hourly precipitation estimates from the KFSX WSR-88D radar from that day.

 

Flooding mainly due to heavy rainfall in northeast Flagstaff - Another day of heavy rainfall were observed in northeastern Flagstaff around 2-3 PM MST on July 14, 2021.Shown are 1-hourly precipitation estimates from the KFSX WSR-88D radar from that day.

 

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• July 13, 2021 - Flooding due to heavy rainfall directly on the Museum Fire scar
  • Around Noon - First thunderstorm formed over the San Francisco Peaks region
  • 2:15 - 3:15 PM MST - Heaviest rain fell over the fire scar
  • Mid-afternoon - First reports of flooding
  • Mid to late afternoon - Flash flooding ongoing in the Mount Elden Estates, Grand View and Sunnyside neighborhoods
  • Late afternoon - Last rain fell over the scar with flooding decreasing in coverage through the evening
  • Impacts from this day
    • Multiple roads were closed as water flowed out of washes
    • Twelve homes or garages were inundated with flood waters
    • Mud, sticks and other debris clogged some storm-water waterways
• July 14, 2021 - Nearly all flooding due to heavy rainfall in northeastern Flagstaff
  • Late morning - Thunderstorms began to form in the greater Flagstaff area
  • 2:00 - 3:00 PM MST - Heaviest rain fell over northeastern Flagstaff
  • Mid to late afternoon - Flash flooding ongoing in the Upper and Lower Greenlaw and Sunnyside neighborhoods
  • Early evening - Light rain continued, but coverage and intensity of flooding quickly decreased
  • Impacts from this day
    • Five roads were closed: Linda Vista Drive at Paradise channel, Cedar Ave at West St to 4th St, Fallen Pine Trail, 2500 block of E Linda Vista Dr, 6th Ave between 4th St and West St
    • Fifteen homes were inundated with flood waters
    • Vehicles were swept away in flood waters in the Greenlaw neighborhood (not due to Museum Fire scar flooding)
• Coconino County and the City of Flagstaff each declared State of Emergencies from these two high impact days of flooding

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Deep monsoonal moisture was entrenched over north-central Arizona by mid-July 2021. Diurnally-driven thunderstorms formed over the San Francisco Peaks area by late morning to Noon on July 13 and 14, 2021. The Museum Fire scar (formed in July 2019 after the fire was extinguished) had not yet had a moderate to high intensity rainfall over it, therefore July 13, 2021 was a "first flush" of debris from the scar. Nearly-stationary thunderstorms produced an estimated 1 - 2" of rainfall in 30 to 45 minutes across much of the scar. Flood waters flowed downstream within the Spruce Creek watershed and created flash flooding that was two to four feet deep. Debris was also carried downstream and embedded within the flood waters. Another active day occurred on July 14, 2021 as a continued moist atmosphere allowed for very high rainfall rates in area thunderstorms. Peak radar estimated rainfall rates were 4-8" per hour over the urban northeastern Flagstaff area by mid-afternoon. That extremely heavy rainfall over a short-period caused considerable sheet flooding on area roads and resulting damage. Observed rainfall totals on July 14 were 2.5 - 3.5".

Flooding due to heavy rainfall over the Museum Fire scar - High rain rates were observed on the Museum Fire scar on July 13, 2021. Shown is the storm total estimated rainfall from around 5:40 AM to 6 PM MST from the KFSX WSR-88D radar.

 

Flooding mainly due to heavy rainfall in northeast Flagstaff - Another day of heavy rainfall were observed in northeastern Flagstaff on July 14, 2021. Shown is the storm total estimated rainfall from around 8:30 AM to 9 PM MST from the KFSX WSR-88D radar.

 

For more information on impacts and general inquiries about this event, please reference the contacts below:

• National Weather Service:
  • Brian Klimowski, Meteorologist-in-Charge at brian.klimowski@noaa.gov
  • Tony Merriman, Warning Coordination Meteorologist at tony.merriman@noaa.gov
• Coconino County Public Works: at 928-679-8300