Monsoon moisture returning to northern Arizona caused thunderstorms to develop over the Prescott area. A storm dropped enough rain to cause a flash flood on Lynx Creek.
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The episode as NWS FGZ wrote it up.
Monsoon moisture returning to northern Arizona caused thunderstorms to develop over the Prescott area. A storm dropped enough rain to cause a flash flood on Lynx Creek.
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 9, 3:02 PM MST, 1 hour 3 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 302 PM MST Mon Aug 9 2021 .SYNOPSIS...Moisture will begin to increase today leading to higher chances for thunderstorms through the week. There will be a threat of localized flash flooding with the stronger storms. Temperatures will decrease to near normal. && .DISCUSSION...A couple of isolated storms have developed early this afternoon across central Arizona. The rest of the state has been capped so far due to morning cloud cover from the remnants of an MCS in southern Arizona. Daytime heating and moisture being pushed northward from that MCS will help to increase convective activity later this afternoon into the evening hours. A boundary of 500 J/Kg of ML CAPE extends along the Mogollon Rim so most convection that occurs today will be along and south of the Rim. The storms that have formed so far have been nearly stationary, but weak steering flow will likely slowly move these storms to the west this afternoon. Due to the slow storm motion, there is a risk of flash flooding near stalled storms with heavy rain rates of 0.5"-1" per hour. Storms in central Arizona may organize this evening and form into a cluster that moves to the northwest late tonight into the early morning hours. Storms on Tuesday will extend north to the AZ/UT border as moisture surges northward from southern Arizona. Increased cloud cover and moisture in the region will bring temperatures down about 5 degrees from today before increasing back to near average on Wednesday. A weak ridge will remain in place across the region through at least the middle of the week. A southerly low-level flow will continue to bring moisture up from the Gulf of California into northern Arizona. Isolated to scattered showers and storms will be likely each day, with the greatest chance of storms south of I-40 where PW content will be greater. By late week, an inverted trough may set-up to our east, increasing moisture flow and bringing more favorable dynamics into the region. This would increase precipitation coverage and the risk of flash flooding as well. && .AVIATION...For the 0Z package...Mostly VFR conditions will exist for the next 24 hours. MVFR conditions are possible through 0Z tomorrow due to scattered showers and storms tonight through tomorrow afternoon. The best likelihood for MVFR conditions through 6Z tonight will be south of KFLG. On Tuesday, storms will be more widespread so MVFR conditions are possible across northern Arizona through evening. Through 0Z tomorrow, winds will be out of the southwest at 5-10 knots with gusts of 15 knots Tuesday afternoon. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Scattered storms will develop Tuesday and Wednesday along and south of the Mogollon Rim with isolated storms north of the Rim. Temperatures will decrease about 5 degrees on Tuesday before increasing again on Wednesday. Thursday through Saturday...Moisture will remain in place across the region through at least Saturday. Scattered afternoon thunderstorms are likely each day with the best chances for precipitation south of I-40. Frequent lightning and isolated flash flooding are expected with stronger storms that do form. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...DeMaria/Humphreys AVIATION...DeMaria/Humphreys FIRE WEATHER...DeMaria/Humphreys For Northern Arizona weather information visit weather.gov/flagstaff
Special Weather Statement
National Weather Service Flagstaff AZ
1230 PM MST Mon Aug 9 2021
AZZ008-037-092000-
Yavapai County Valleys and Basins-Yavapai County Mountains-
1230 PM MST Mon Aug 9 2021
...A strong thunderstorm is currently over the Prescott Airport
through 100 PM MST...
At 1229 PM MST, Doppler radar was tracking a strong thunderstorm over
Prescott Airport, or near Prescott Valley, moving north at 5 mph.
HAZARD...Winds in excess of 40 mph and half inch hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
Locations impacted include...
Chino Valley, Prescott Airport and Williamson Valley.
This includes the following highways...
State Route 89 between mile markers 318 and 326.
State Route 89A between mile markers 318 and 321.
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 3461 11237 3460 11245 3473 11255 3475 11232
TIME...MOT...LOC 1929Z 178DEG 6KT 3466 11242
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH
TPSThe Flagstaff radar (KFSX), 107 km away, was scanning. The volume nearest the first event began at 23:06 UTC.
1 flash flood. Local standard time, as filed.
A trained spotter reported that Lynx Creek in Walker was running four to five feet deep in spots.
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: 982032.