A thunderstorm over the Prescott area produced flash flooding in Granite Creek.
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The episode as NWS FGZ wrote it up.
A thunderstorm over the Prescott area produced flash flooding in Granite 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 23, 9:07 AM MST, 4 hours 36 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 907 AM MST Sun Aug 23 2020 .SYNOPSIS...Isolated showers this morning will give way to scattered afternoon and evening thunderstorms later today. A more typical monsoon pattern remains on track to occur this week with daily thunderstorm chances. && .UPDATE...Slight adjustments were made to precipitation chances to this afternoon and evening to match hi-res trends this morning. Morning satellite shows continuing cloud cover over much of Coconino County. It is possible that for portions of northern Coconino County daytime heating may be limited from yesterday as morning shower activity continues along with less sun peaking through the low to mid level cloud deck. This could result in less instability from yesterday for thunderstorm development. Showers and thunderstorms are still expected with rich precipitable water values, however these may not be as strong as what we say yesterday. Further south, sunshine is out this morning across much of the southern and eastern portions of the area. These areas will have ample time to become unstable before thunderstorm development. Similar to yesterday, expect to see storms form along the high terrain first before slowly moving into the lower terrain areas by the late afternoon/evening. Hi-res models do indicate an early start to some scattered convection over the Bradshaws near Prescott. So, we could see an earlier start to thunderstorms in Yavapai County than the last few days. Threats remain largely the same today. Expect developing thunderstorms to have gusty winds, hail, frequent lightning, and heavy rainfall. && .PREV DISCUSSION /334 AM MST/...Showers and isolated thunderstorms have continued overnight and into the early morning hours today. Look for expanding coverage of thunderstorms early this afternoon and early evening. Continued monsoon activity will last through much of this week. This morning....GOES-17 infrared satellite imagery is highlighting some low and mid-level cloud cover across much of northern Arizona. Surface observations are show a few areas with cloud bases down to around 5,000 feet above ground level along the Mogollon Rim. Embedded within this sky cover are isolated showers and thunderstorms that have persisted through the overnight hours. Slight chances of precipitation for early this morning remain limited to mainly Coconino, Yavapai and northern Gila counties. Sky cover will slowly decrease through this morning. Today....Model forecast soundings show a similar setup today as we experienced on Saturday. Daytime heating will occur throughout the morning with maximum temperatures likely being observed shortly before afternoon cloud cover spreads across the region. Maximum temperatures are expected to be around five to ten degrees above normal today. Thunderstorms will begin to initiate around the noon hour today. These first thunderstorms will form over the higher terrain features of the Chuska Mountains, Black Mesa, Kaibab Plateau, along the Mogollon Rim and over the White Mountains. Weak steering flow today will produce very slow move to nearly- stationary thunderstorms which will drift in a general westerly to southwesterly direction by mid-afternoon. High resolution guidance then progs continued lower terrain thunderstorm activity through early this evening. The primary hazards today will be small hail, localized heavy rainfall, lightning and strong outflow winds. While many thunderstorms will remain below severe criteria, there is a chance again today for some severe thunderstorms with larger hail and very strong winds. Slightly higher precipitable water values today could also produce more localized heavy rainfall today compared to Saturday. Always be aware of the possibility for ponding on roadways and slick driving conditions during the monsoon season. Late This Evening....Thunderstorm coverage is expected to decrease tonight as cloud cover, remnant cold pools and decreased daytime heating sets up a more stable boundary layer. Slight chances for showers do persist though into early Monday morning. Rest of the Week....The Four Corners high pressure will remain in place through much of this week. The result will be a more typical monsoonal pattern than what much of northern Arizona has experienced this summer. Look for afternoon and early evening chances of thunderstorms, highest over the higher terrain, each day through the work week. Operational deterministic guidance does show a shift and degradation of the high pressure by later Friday. The result would be an affect on precipitation chances by next weekend. Stay tuned. && .AVIATION...For the 18Z package...VFR conditions and generally light wind expected outside of convective activity over the next 24 hours. Scattered showers and thunderstorms will develop again after 18Z Sunday over the high country, shifting toward the lower terrain to the southwest through the evening, with only isolated showers possible after 04Z. TAF discussion not updated for amendments. && .FIRE WEATHER...Look for scattered afternoon and evening thunderstorms through Monday, with the most widespread activity extending from the Coconino plateau along the Mogollon Rim to the White Mountains. High temperatures are will be 5-10 degrees above normal. Tuesday through Thursday...Daily chances for showers and thunderstorms will persist. Daytime temperatures will be slightly above normal. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...ET AVIATION...DL FIRE WEATHER...JJ For Northern Arizona weather information visit weather.gov/flagstaff
The Flagstaff radar (KFSX), 116 km away, was scanning. The volume nearest the first event began at 20:43 UTC.
1 flash flood. Local standard time, as filed.
Heavy rain from a thunderstorm caused Granite Creek to rise 2.9 feet in an hour at the Granite Creek Gauge (GCRA3).
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, August 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: 918471.