Monsoon moisture brought thunderstorms with heavy rain and hail to northern Arizona.
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 brought thunderstorms with heavy rain and hail to northern Arizona.
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 2, 9:37 AM MST, 2 hours 8 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 937 AM MST Thu Aug 2 2018 .SYNOPSIS...Expect afternoon and evening chances for showers and thunderstorms through Friday. For the weekend, chances decrease as a passing disturbance brings drier air across our area. Moisture returns early next week with storm chances increasing across the northland. && .DISCUSSION...For today, convection is expected to favor areas along and southwest of the Mogollon Rim. This morning's surface analysis reveals the highest dew points are in this area, and model forecasts indicate the highest instability will develop in this area as well. In addition, streamlines and vorticity show a low level trough stretching from northern Baja to southern California. This feature will slowly move toward the northeast today, helping initiate convection along and southwest of the Mogollon Rim. Convective initiation will be delayed somewhat by residual cloud cover evident on this mornings satellite imagery. However, clearing can be seen across Yavapai County, so we may see storms form there first. Storm motion will be slow today, generally moving from the west to east (southwest to northeast in Yavapai County). Deep layer bulk shear is low. Given the slow storm motion, flash flooding will be the primary hazard today, especially for urban areas in Yavapai County. The risk of large hail is low, expect where strong, converging outflows supplement the modest instability and weak shear. Made a few minor increases to the chances for showers and thunderstorms in Yavapai County this afternoon. Otherwise, no updates were made to the forecast. && .PREV DISCUSSION /343 AM MST/...An outflow boundary moved in from the south overnight producing light showers over central Yavapai County overnight. These showers have now ended along with the remaining few showers over portions of Coconino and northern Gila County. In terms of what to expect for Thursday, hi-res models continue to indicate another active day across northern Arizona with widespread shower and thunderstorm coverage by the afternoon. Being that many areas received moderate amounts of rainfall today with convection ongoing into the late evening, there is some doubt to how well models are handling any remnant stable air left over in areas that were well overturned yesterday. It does appear there will be a sunny start to the day again with only minimal cloud cover left over from earlier convection as of this morning. The question will be how well and quickly things destabilize in the morning. For now, have made minimal changes to precipitation chances that are in line with the current model trends of widespread shower and thunderstorm coverage. Will continue to monitor environmental changes through the morning and make adjustments as needed. Beyond Thursday, models continue to indicate a drying trend into the weekend with only isolated to scattered chances for showers and storms by Saturday and Sunday. This is due to a disturbance moving across the Pacific Northwest that will weaken the high pressure ridge and providing a more dry westerly zonal flow and slightly cooler temperatures across the area. By the beginning of next week, the ridge will build back in with the center of high pressure over New Mexico and the return of moist southerly flow across Northern Arizona with afternoon thunderstorm chances increasing through Wednesday. Toward the end of next week, models continue to struggle to handle a developing Pacific trough and the movement of the ridge. Long range models tend to agree the ridge will build into the Great Basin region through the end of the week but differ on where to take the Pacific trough and the overall strength of the ridge. This will likely continue to evolve and change so will wait for better agreement in the coming days. && .AVIATION...For the 18Z package...Expect scattered thunderstorms to develop this afternoon, particularly from KFLG to KSOW southward. Local IFR in +RA, erratic wind gusts, and hail will be possible from stronger storm cells. VFR conditions expected outside of any storms. Storm activity should begin to diminish after 02Z Fri. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Areas from the Coconino Plateau and Mogollon Rim southward will continue to remain favored for daily thunderstorms through Friday. Erratic outflow winds should be expected near any thunderstorm activity. In addition, heavy rain and hail will also be possible. Temperatures will remain above average. Saturday through Monday...A downward trend in thunderstorm coverage is expected over the weekend. An increase in monsoonal activity is possible on Monday as some deeper moisture could return to the region. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...RR/ET AVIATION...SUK FIRE WEATHER...MCT For Northern Arizona weather information visit weather.gov/flagstaff
Special Weather Statement National Weather Service Flagstaff AZ 1140 AM MST THU AUG 2 2018 AZZ008-037-021930- Yavapai County Valleys and Basins-Yavapai County Mountains- 1140 AM MST THU AUG 2 2018 ...SIGNIFICANT WEATHER ADVISORY FOR YAVAPAI COUNTY UNTIL 1230 PM MST... At 1139 AM MST, Doppler radar was tracking a strong thunderstorm over Yavapai Campground, or near Prescott Valley, moving east at 5 mph. Half inch hail and winds in excess of 40 mph will be possible with this storm. Locations impacted include... Prescott Valley, Prescott, Yavapai Campground, Downtown Prescott, Prescott Airport, Indian Hill West Prescott and Prescott Gateway Mall. PRECAUTIONARY/PREPAREDNESS ACTIONS... Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. && LAT...LON 3453 11250 3464 11258 3474 11247 3454 11234 TIME...MOT...LOC 1839Z 249DEG 8KT 3461 11249 RR
The Flagstaff radar (KFSX), 119 km away, was scanning. The volume nearest the first event began at 18:45 UTC.
1 hail, 1 heavy rain, 1 flash flood. Local standard time, as filed.
Quarter-sized (1 inch in diameter) hail was reported in the Prescott area.
Heavy rain caused flowing water on Highway 69 at Lee Boulevard.
The gauge on Havasu Creek rose from 7.46 to 11.24 feet in 15 minutes (500 to 515 PM MST). The peak flow was 1157 CFS (base flow is less than 90 CFS).
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, 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: 781592, 781593, 781594.