A severe thunderstorm warning was issued by the National Weather Service in Flagstaff at 1:15 p.m. on Thursday, July 23, following a flash flood warning at 12:52 p.m. Both warnings applied to Coconino.
Meteorologists warn of winds as strong as Up to 50 mph.
Use caution: Officials warn of hail as large as 1 inch.
The National Weather Service warns: "Seek shelter inside a well-built structure and stay away from windows. This storm is capable of producing large hail."
The National Weather Service also warned: "Flash flooding is occurring or imminent downstream of the Dragon Bravo Fire scar. Severe debris flow are expected downstream of the North Rim into Bright Angel Creek and Crystal Creek. Campers and hikers should get away from creeks and move to higher ground immediately! Stay away or be swept away!"
See weather radar for northern Arizona
What are weather service meteorologists saying?
At 1:15 p.m., the weather service issued a statement:
"The National Weather Service in Flagstaff has issued a Severe Thunderstorm Warning for: Coconino County in north central Arizona north of Munds Park, Until 1:45 p.m. MST. At 1:15 p.m. MST, a severe thunderstorm was located near Munds Park, or 15 miles south of Flagstaff, moving northwest at 15 mph.
HAZARD: Quarter size hail.
SOURCE: Radar indicated.
IMPACT: Damage to vehicles is possible. Locations impacted include: Munds Park and Mountainaire. This includes Interstate 17 between mile markers 326 and 331."
At 12:52 p.m., the National Weather Service issued a statement:
"The National Weather Service in Flagstaff has issued a Flash Flood Warning for: The Bright Angel Creek Basin below the Dragon Bravo Fire scar in, Coconino County in north central Arizona, Until 3:45 p.m. MST. At 12:52 p.m. MST, Doppler radar indicated thunderstorms producing heavy rain over the Bright Angel Creek Basin below the Dragon Bravo Fire scar. Between 0.5 and 1 inch of rain has fallen. The expected rainfall rate is 0.75 to 1.5 inches in 1 hour. Flash flooding is ongoing or expected to begin shortly.
HAZARD: Life threatening flash flooding. Thunderstorms producing flash flooding in and around the Bright Angel Creek Basin below the Dragon Bravo Fire scar.
SOURCE: Radar indicated.
IMPACT: Life threatening flash flooding of areas in and around the Bright Angel Creek Basin below the Dragon Bravo Fire scar. Some locations that will experience flash flooding include: Phantom Ranch, North Rim Visitor Center, Point Imperial Picnic Area, Saddle Mountain Overlook, Cape Royal Point, Bright Angel Point and Vista Encantada. This includes the Colorado River between river miles 87 and 89, and between river miles 99 and 100. This includes the following recreation areas and campgrounds, Ribbon Falls, Bright Angel Campground, North Rim Campground, Cottonwood Campground, Clear Creek Camp Site, Upper Cremation Camp Site, Lower Cremation Camp Site, Roy's Beach Camp Site, Boat Beach Camp Site, Crystal Camp Site, Ego Beach Camp Site, Above Tuna Creek Camp Site, Above Tuna Rapids Camp Site, Manzanita Rest Area and Roaring Springs. This includes the following creeks, washes and rivers, Zoroaster Canyon, Kwagunt Creek, Slate Creek, South Canyon, Lava Canyon, North Canyon, Tuna Creek, Clear Creek, Nankoweap Canyon, Shinumo Creek, Saddle Canyon, Colorado River, Unkar Creek, Bright Angel Creek, Crystal Creek and Buck Farm Canyon."
What is a flash flood?
Arizona's desert landscape is highly prone to flash flooding. A flash flood is a flood caused by heavy or excessive rainfall in a short period of time, generally less than six hours, according to the weather service.
A flash flood can be sudden and violent and take just minutes to develop. Even if skies are clear overhead, rainfall upstream can funnel into dry riverbeds and create dangerous flows miles away.
How much water is needed to cause a flash flood?
It doesn't take much water to trigger a flooding event in the desert: An inch of rain or less in an hour is often enough to cause a flood. How quickly and where rain falls determines flooding more than rain totals.
Desert soils struggle to absorb water, especially after extended dry spells. The surface can become almost waterproof, causing runoff.
Topography also plays a role, as steep canyons, mountains and dry washes are susceptible to floods. Areas impacted by wildfires are more at risk, as the flames can burn the top layer of the soil, preventing absorption and increasing runoff.
What's the difference between a flash flood watch and a flash flood warning?
A flash flood watch means conditions are favorable for flash flooding to develop, but it isn't happening yet. In Arizona, this often happens when monsoon storms or heavy upstream rainfall could send sudden surges of water through washes, canyons or urban areas.
During a flood watch, it's important to monitor local forecasts and alerts, plan evacuation routes in case flooding begins, move vehicles out of low-lying areas and avoid recreation in areas that could fill with water quickly.
A flash flood warning is more urgent, meaning flooding is impending or already occurring. Warnings are typically issued when rainfall is recorded at levels that can suddenly overwhelm desert drainage or when flooding has already been observed.
What is a severe thunderstorm warning?
Thunderstorms are a staple in Arizona, especially during the state's monsoon season, which runs from June 15 to Sept. 30. The monsoon is characterized by intense heat, surges of moisture and atmospheric instability, creating clouds and storm chances in the afternoon.
While storms in Arizona are most frequent during the monsoon, they can happen year-round. Storms can be spotty and short-lived, while others can unleash strong winds, flashes of lightning and torrential downpours.
A severe thunderstorm warning means the area is experiencing or is about to experience a storm with winds of 58 mph or higher and/or hail an inch in diameter or larger.
Tips for staying safe during thunderstorms in Arizona
- Go indoors at the first sound of thunder. Lightning strikes can occur miles away from the parent storm.
- Resume outdoor activities 30 minutes after the storm passes.
- Avoid electronics, plumbing and windows.
- Remember to bring pets inside.
- If there is time, secure loose objects outside as these objects often become dangerous flying debris in high winds.
Warnings are typically issued when rainfall is recorded at levels that can suddenly overwhelm desert drainage or when flooding has already been observed.
This weather report was generated automatically using information from the National Weather Service and a story written and reviewed by an editor.
See the latest weather alerts and forecasts here.
This article originally appeared on Arizona Republic: Severe thunderstorm, hail, flash flood warnings for northern Arizona
