Deep monsoon moisture and unstable air moved over northern Arizona. This triggered thunderstorms with heavy rain.
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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 FGZ wrote it up.
Deep monsoon moisture and unstable air moved over northern Arizona. This triggered thunderstorms with heavy rain.
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 Flagstaff, AZ wrote its last area forecast discussion before the first event at Jul 27, 2:09 PM MST, 1 hour 48 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 209 PM MST Mon Jul 27 2020 .SYNOPSIS...Scattered thunderstorms will continue to develop this afternoon, and will develop again Tuesday afternoon, with the best chances east of I-17 and Highway 89. High pressure will then build over the desert southwest by Wednesday and will bring much warmer temperatures and a downturn in monsoon activity through the end of the week. && .DISCUSSION...Scattered thunderstorms are currently developing along the higher terrain of northern Arizona as of this writing. The strongest storms are currently over the Kaibab Plateau and near Navajo Mountain, where the deepest shear is located. Thunderstorm activity should begin to wane later this afternoon and evening with the loss of daytime heating. By Tuesday, lingering moisture and instability should allow for low-end thunderstorm chances during the afternoon hours across the eastern Mogollon Rim into the White Mountains. Slight chances for afternoon thunderstorms will also exist across the Black Mesa and Chuska Mountains, with dry conditions expected elsewhere. Wednesday through Saturday, expect mainly dry and warming conditions through the period as high pressure builds over Arizona. Record heat will be possible Friday. The current excessive heat watch looks good, so will keep it going for now. Sunday and Monday, medium range models begin to break down the ridge a little bit allowing for some moisture and instability to re-enter the region. This will allow for at least low-end chance precipitation chances along the Mogollon Rim Sunday and Monday. && .AVIATION...For the 00Z package... A drier air mass will move across Arizona overnight and on Tuesday. Shower and thunderstorm activity will come to an end overnight with development on Tuesday mainly along and east of a Payson to Four Corners line. Light winds, except gusty near any stronger storms. Aviation discussion not updated for amendments. && .FIRE WEATHER...A warming and drying trend will deliver a significant decrease in shower and thunderstorm activity on Tuesday and Wednesday. Storm activity Tuesday will be mainly limited to the area east of a Payson to Four Corners line with even lower chances on Wednesday. Expect light winds and increasing Haines Indices. Thursday through Saturday...Expect abnormally hot and dry conditions. Shower and thunderstorm activity is unlikely through Friday with only a slight increase in the threat on Saturday. && .FGZ WATCHES/WARNINGS/ADVISORIES...Excessive Heat Watch from Thursday morning through Saturday evening FOR AZZ006-037-038. && PUBLIC...TM AVIATION...McCollum FIRE WEATHER...McCollum For Northern Arizona weather information visit weather.gov/flagstaff
Special Weather Statement National Weather Service Flagstaff AZ 343 PM MDT Mon Jul 27 2020 AZZ005-009-272215- Marble and Glen Canyons-Northeast Plateaus and Mesas Hwy 264 Northward- 343 PM MDT Mon Jul 27 2020 ...SIGNIFICANT WEATHER ADVISORY FOR COCONINO COUNTY NEAR PAGE AND SOUTH END OF LAKE POWELL UNTIL 415 PM MDT/315 PM MST/... At 341 PM MDT/241 PM MST/, Doppler radar was tracking a strong thunderstorm near Antelope Canyon on State Route 98, or 7 miles northeast of Page, moving north at 35 mph. Winds in excess of 40 mph will be possible with this storm. Locations impacted include... Page, Big Five, Wahweap, Antelope Canyon, Antelope Creek Basin and Lake Powell. PRECAUTIONARY/PREPAREDNESS ACTIONS... If on or near Lake Powell, get out of the water and move indoors or inside a vehicle. Remember, lightning can strike out to 10 miles from the parent thunderstorm. If you can hear thunder, you are close enough to be struck by lightning. Move to safe shelter now! Do not be caught on the water in a thunderstorm. && LAT...LON 3685 11119 3687 11152 3700 11150 3700 11116 TIME...MOT...LOC 2141Z 188DEG 28KT 3695 11134 JJ
The Flagstaff radar (KFSX), 109 km away, was scanning. The volume nearest the first event began at 22:55 UTC.
2 flash flood. Local standard time, as filed.
A stream gauge on Carrizo Creek reported a 2.4 foot rise in water.
Flooding was reported along Indian Route 15 between Sunrise Springs and Burnside. Water and mud covered the road between 5 and 10 inches deep. Time and location are best estimates.
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, July 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: 899698, 899696.