Deep monsoon moisture over Arizona allowed strong thunderstorms to for over and north of Payson. The heavy rain caused flash flooding in town.
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The episode as NWS FGZ wrote it up.
Deep monsoon moisture over Arizona allowed strong thunderstorms to for over and north of Payson. The heavy rain caused flash flooding in town.
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 11, 2:16 PM MST, 59 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 216 PM MST Wed Jul 11 2018 .SYNOPSIS...The monsoon weather pattern will persist over Arizona through the coming weekend, with daily rounds of showers and thunderstorms. && .DISCUSSION... A very moist monsoonal surge continues to move into the area today. Precipitable water amounts from this mornings upper air soundings show nearly an inch of precipitable water in Flagstaff with amounts approaching 2 inches down in the Phoenix area. Additional moisture is forecast to move into the area creating even more efficient heavy rain producing storms this afternoon and evening. An interesting wrinkle in today's forecast is the development and movement of a mesoscale convective vortex associated with an overnight mesoscale convective complex in Sonora, Mexico. This additional source of vorticity aloft could help promote storm growth later today as it moves through the lower elevation deserts to the south. Because of the aforementioned potential, a flash flood watch is in effect through late this evening for Yavapai County and Northern Gila county because of the enhanced threat of flash flooding. Areas of particular concern include water recreation areas across Yavapai and Gila counties, along with low water crossings and fire scars in the watch area. Further north along the rim widespread convection is already ongoing with slow moving storms producing significant amounts of rain. Thankfully these storms remain relatively small, pulse storms. This type of storm formation is helping mitigate flash flood potential due to the small area of impact and short lived nature of these storms currently forming on the high country. Generally speaking storm motion will continue to be light and to the northwest, with a more northerly push expected as the evening goes on. Continuing Thursday through early next week...Monsoon moisture will remain across Arizona with medium to high grade monsoon activity will continue each day. && .AVIATION...For the 18Z package...Quickly decaying higher level cloud shield will allow for Thunderstorm development after 18z and continuing across Northern Arizona through the afternoon and evening. Most of the storm activity is expected to decrease by 03z. The stronger storms will be capable of producing MVFR, hail, heavy rain and wind gusts to 40kts. Storm motion generally to the west and northwest. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Scattered to numerous afternoon and evening showers and thunderstorms will continue through the forecast period. Daytime relative humidity values ranging from 25 to 45 percent, with good overnight recovery from 80 to 100 percent. Expect generally light winds, except near storms or associated with outflows. && .FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch through late tonight FOR AZZ008-018-037. && PUBLIC...Suk AVIATION...Suk FIRE WEATHER...Suk For Northern Arizona weather information visit weather.gov/flagstaff
The Flagstaff radar (KFSX), 37 km away, was scanning. The volume nearest the first event began at 22:14 UTC.
1 flash flood. Local standard time, as filed.
Forest Drive in Payson was closed with barricades because swiftly running water covered the road. A nearby rain gauge reported 1.82 inches of rain between 2:06 and 3:37 PM.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2018Every state in 2018This day in weather historyWarnings in Arizona, July 2018
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: 774929.