Monsoon moisture over northern Arizona caused a tornado, high winds, and flash flooding.
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.
Monsoon moisture over northern Arizona caused a tornado, high winds, and flash flooding.
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 18, 9:57 AM MST, 4 hours 25 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 957 AM MST Sat Aug 18 2018 .SYNOPSIS...Expect a drying trend into early next week, with only isolated thunderstorms expected on Sunday and Monday across northern Arizona. Moisture will increase again starting Tuesday as high pressure moves to a favorable position over New Mexico, promising a return to active monsoon conditions. && .UPDATE... No significant changes to the forecast this morning as clear skies are already showing the first signs of cumulus development for the day over the higher terrain. Upper air sounding this morning shows significant drying of the upper half of the atmosphere above a subsidence inversion. This should limit convective growth and impact rainfall efficiencies this afternoon and evening. There will be an outside chance of some localized flash flooding due to weak steering flow, mainly over Yavapai County where moisture is prevalent at the lower elevations. && .PREV DISCUSSION /304 AM MST/...A high pressure system in the mid- levels was centered over central California this morning. Models show the center of the high moving across Arizona and into New Mexico between today and Monday. In response to the current position of the high, a drier northwest flow aloft was in the process of developing and strengthening across northern Arizona. Along with the drier air mass sinking/warming in advance of the high pressure center was taking place aloft, another signal that stabilization is on the way for the area. For today, just enough monsoon moisture will linger from around Flagstaff southeastward across the Mogollon Rim and White Mountains region for a pretty good chance of showers and thunderstorms. Elsewhere, the drier air and warming aloft will produce a distinct downturn in thunderstorms and even cumulus development. For Sunday and Monday - High pressure centered over central California will move across Arizona and into New Mexico. The drying in combination with warmer temperatures aloft (the result of sinking air associated with the high) will result in only the slightest of chances for a shower or thunderstorm. Sunday will be the driest day. Monday will see a slight increase in the chance for showers and storms as the high center moves into New Mexico and the door begins to open to increasing moisture. From Tuesday onward - The center of high pressure in the mid- levels will generally wobble around just to the east of Arizona over new Mexico. Southerly flow around the western edge of the high will transport a moist monsoon air mass across Arizona with active monsoon weather returning to northern Arizona. && .AVIATION...For the 18Z package...Expect mainly VFR conditions across northern Arizona for the next 24 hrs. The exception, ISOLD to SCT SHRA/TSRA will develop mostly along the Mogollon Rim and over the White Mountains today, ending by about 03Z. Afternoon winds will generally be northwesterly at 10-15 kts gusting 20 kts. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...The area begins to dry out today as northwesterly flow develops. Enough moisture will remain to keep a threat of convection over the southeastern portions of the district where dewpoints remain relatively high. Sunday will see a northerly flow bringing dry air into the area and very little convective activity. .Monday through Wednesday...Continued dry conditions are expected Monday with a southwesterly flow. There may be enough moisture for isolated convection over the White Mountains. The high pressure system shifts to our east Tuesday opening up a southerly monsoonal flow and bringing a return of moisture and isolated to scattered showers and thunderstorms to the southern and western portions of the district. Moisture will continue to increase across the district Wednesday with an increase of convective activity. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...Suk AVIATION...MAS FIRE WEATHER...MAS For Northern Arizona weather information visit weather.gov/flagstaff
Special Weather Statement National Weather Service Flagstaff AZ 114 PM MST SAT AUG 18 2018 AZZ012-015-016-182100- Little Colorado River Valley in Coconino County-Western Mogollon Rim-Eastern Mogollon Rim- 114 PM MST SAT AUG 18 2018 ...SIGNIFICANT WEATHER ADVISORY FOR COCONINO COUNTY UNTIL 200 PM MST... At 110 PM MST, Doppler radar was tracking thunderstorms developing over the area between Flagstaff and Clints Well to Payson. These storms are moving southeast at around 20 MPH. Heavy rain and hail up to half are possible with these storms. Locations impacted include... Dairy Springs Campground, Starlight Pines, Mormon Lake, Tremaine Lake, Upper Lake Mary, Rock Crossing Campground, Chevelon Butte, Pinegrove Campground, Lake View Campground, Chavez Mountain, Double Springs Campground, Blue Ridge Campground, Long Lake and Ashurst Lake Campgrounds. PRECAUTIONARY/PREPAREDNESS ACTIONS... Heavy rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. && LAT...LON 3501 11158 3514 11140 3468 11081 3441 11113 TIME...MOT...LOC 2010Z 326DEG 46KT 3469 11119 MAS
The Flagstaff radar (KFSX), 65 km away, was scanning. The volume nearest the first event began at 21:21 UTC.
4 flash flood, 1 tornado, 1 thunderstorm wind. Local standard time, as filed.
Time lapse video shows a narrow tornado at approximately 30 degrees angle to the ground persisting for several minutes.
A picture posted on social media shows that the East Verde River was flooding over Beaver Flat Road.
A trained weather spotter reported an estimated wind gust to 60 MPH.
Gap Creek flooded across Forest Road 574 making it impassable.
A stream gauge on Granite Creek in Granite Creek showed a 4.6 foot rise with a peak flow of 2,500 CFS (normal flow is less than fifty cubic feet a second).
Flash flooding was reported over Road 5 N just east of Reed Road. Road 1/2 N was also closed near Malapai Drive because of the flooding.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2018Every state in 2018This day in weather historyThe tornado archive for Arizona, 2018Warnings in Arizona, August 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: 786325, 786324, 786320, 786321, 786322, 786323.