Thunderstorms across northern Arizona produced strong winds and hail as monsoon moisture remained over the area.
Every event with a place to put it. Tap one for its entry below.
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.
Thunderstorms across northern Arizona produced strong winds and hail as monsoon moisture remained over the area.
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 Aug 15, 9:55 AM MST, 4 hours 30 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 955 AM MST Sun Aug 15 2021 .SYNOPSIS...Scattered thunderstorms will continue each day through Monday, with the best coverage along and south of the Mogollon Rim where a few strong storms are possible. Expect more widespread showers and storms and cooler temperatures by mid next week. && .DISCUSSION...Observations across northern Arizona show dewpoints at or above 50F at most areas, with values in the 60s and 70s south of the Mogollon Rim. This morning's upper-air sounding from near Flagstaff shows less precipitable water than yesterday morning, with PW dropping from 0.87 to 0.61. In addition, 500 mb temperatures have warmed since yesterday morning, which may explain the lack of storm activity observed in the Flagstaff area yesterday afternoon. Despite the decrease in PW and warmer mid-level temperatures, model guidance generally agrees that there will be sufficient instability for thunderstorms today. HREF model output suggests between 1000-2000 J/kg of CAPE south of a line from the Grand Canyon to Flagstaff to Show Low. North of that line, less instability is forecast, but some HiRes model guidance predicts a few storms forming near the Black Mesa area in far northeast Arizona. 0-6 km Bulk Shear is highest across Yavapai County this afternoon, with values ranging from 25-35 kts there. So, the best combination of instability and shear will once again be across Yavapai County this afternoon. We did see a couple of rotating storms yesterday, and it looks like we may see a few more again today. Storms will be moving to the southwest between 10-15 mph today, while the storm anvil clouds will be moving to the southeast. This may aid in keeping convection more vigorous by preventing shading ahead of the moving storms. So, considering everything, the main concern for severe weather today will be from organized storms propagating southwestward off the Mogollon Rim into Yavapai County this afternoon. The threat of large hail and damaging winds is increased today, while Flash Flooding is less of a concern - except over burn scars. && .PREV DISCUSSION /208 AM MST/...Expect another round of isolated storms this afternoon, moving to the west-southwest. A disturbance could enhance storm activity over the eastern part of the state this evening. Monday, conditions look to remain the same except storms look to move north to south. Tuesday and Wednesday still look to be our big weather event days for the week, with low level moisture increasing up into northern Arizona. Anticipate more widespread coverage of storms with hazards being flash flooding and the potential for an increased chance of severe storms. Thursday onward a downturn in storm activity looks to be possible with dry air taking over the region. Expect isolated shower activity primarily over higher elevations if this plays out. && .AVIATION...For the 18Z package...Look for mainly VFR conditions over the next 24 hours. Another round of isolated to scattered showers and thunderstorms will develop this afternoon, first over high terrain then moving southwestward. Storms will gradually diminish after 03Z-05Z. Locally heavy rain and wind gusts to 40 kts possible near any storms. Otherwise, generally light winds. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Scattered afternoon showers and thunderstorms are expected through Monday. The greatest coverage will be along and south of the Mogollon Rim. Localized flash flooding and gusty outflow winds are the main hazards. Warmer temperatures along with light winds are otherwise expected. Tuesday through Thursday...Chances for showers and thunderstorms increase next week with the highest coverage on Tuesday and Wednesday. Temperatures are expected to be slightly below normal. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...RR/Kobold AVIATION...JJ FIRE WEATHER...MCT For Northern Arizona weather information visit weather.gov/flagstaff
Special Weather Statement
National Weather Service Flagstaff AZ
1237 PM MST Sun Aug 15 2021
AZZ015-038-152000-
Western Mogollon Rim-Oak Creek and Sycamore Canyons-
1237 PM MST Sun Aug 15 2021
...A strong thunderstorm will impact portions of Coconino County
through 100 PM MST...
At 1235 PM MST, Doppler radar was tracking a strong thunderstorm 8
miles south of Parks, or 19 miles west of Flagstaff, moving southwest
at 20 mph.
HAZARD...Winds in excess of 30 mph and pea size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible. Minor flooding and peasized hail is possible
over portions of Interstate 17 near Williams.
Locations impacted include...
Raymond Boy Scout Camp.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3521 11193 3516 11187 3505 11194 3518 11207
TIME...MOT...LOC 1935Z 048DEG 19KT 3514 11196
MAX HAIL SIZE...0.25 IN
MAX WIND GUST...30 MPH
RRThe Flagstaff radar (KFSX), 127 km away, was scanning. The volume nearest the first event began at 21:22 UTC.
3 hail, 1 thunderstorm wind. Local standard time, as filed.
A trained spotter reported hail the size of a quarter (1 inch diameter) 7 miles north-northwest of Williams. Other people reported golf ball sized hail (1 3/4 inch diameter) around the Williams area.
Hail the size of a quarter (1 inch in diameter) was reported in the community of White Cone.
Quarter sized hail (1 inch diameter) was reported by three different sources around Chino Valley.
A weather station north-northeast of Iron Springs recorded a peak wind gust of 58 MPH at 11:29 PM MST from a thunderstorm. Wind gusts to 56 MPH continued for another 10 minutes.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2021Every state in 2021This day in weather historyWarnings in Arizona, August 2021
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: 983207, 983208, 983224, 983220.