AccuWeather’s Local StormMax for rainfall from Wednesday through Thursday, Oct. 21 and 22, is 6 inches in a part of the Southwest that covers Phoenix, Flagstaff and Tucson. The forecast pairs it with an 80 mph StormMax for wind gusts in severe thunderstorms, and both figures are worst-case local values rather than statewide expectations.
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Because the label covers a single worst-hit location inside a broad area, many neighborhoods between Flagstaff and Tucson would be expected to see less, while a few washes and slopes could take the brunt of repeated downpours.
AccuWeather’s Local StormMax for Phoenix, Flagstaff and Tucson
The forecast, written by AccuWeather’s Brandon Buckingham and published on Oct. 18 and updated on Oct. 20, describes a non-tropical storm approaching the West Coast with tropical moisture from the eastern Pacific. It reaches California between Tuesday and Wednesday, moves inland midweek, and brings its heaviest rain and flash flood risk to the Southwest on Wednesday and Thursday, in Arizona, Utah, western Colorado and New Mexico. AccuWeather meteorologist Kai Kerkow said the storm “will pull moisture from the tropics into the Southwest.”
The same article notes that several storms this fall have brought flash flooding to the Southwest while also easing drought conditions. That mix of benefit and hazard is typical of desert rainfall: the water is welcome in a dry basin, but a single heavy burst falling on hard, dry ground runs off quickly instead of soaking in.
Severe Storm Timing: Wednesday Evening, Then Eastern Nevada
AccuWeather says some thunderstorms could turn severe, with damaging wind gusts and hail, and puts the greatest severe risk on Wednesday evening across much of Arizona. On Thursday the severe threat expands from eastern Nevada into parts of New Mexico, with localized damaging gusts and hail possible. The 80 mph StormMax gust is the top end of that wind forecast and, like the rain figure, is a worst-case local value.
The Weather Channel’s own forecast, updated for Oct. 22, reported that Flagstaff had already recorded hail about 1.75 inches in diameter and a 72 mph gust at Flagstaff Airport, and that northern Arizona had its first tornado watch in more than 16 years. Those observations show that the upper end of the severe forecast is plausible in northern Arizona, even though any single storm is hard to place in advance.
The same Weather Channel forecast says Wednesday carried an enhanced severe weather risk for Arizona, southern Utah, western New Mexico and coastal Southern California, with large hail, strong gusts and a couple of tornadoes possible along the Mogollon Rim. It also cites the Weather Prediction Center for rainfall rates as high as 2 inches per hour, with storms training over the same areas, which is the mechanism that can stack a few hours of heavy rain into the kind of total AccuWeather’s StormMax describes. For Thursday, the outlet again put Arizona at the greatest risk of strong winds, hail and an isolated tornado.
How 6 Inches Compares With Arizona Rainfall Records
Six inches would be a very large amount for a desert state, and the regional record shows how little it takes to cause trouble. National Weather Service Phoenix documented what a much smaller burst can do: on Sept. 16, 2 to 4 inches fell in two to three hours across northern Pinal and northern Maricopa counties, with rates of 1 to 2 inches per hour, flooded streets and washes, impassable low-water crossings and multiple swift water rescues. The Weather Prediction Center raised its outlook that day to a Moderate Risk, the first for the Phoenix area since 2023.
The Weather Channel, in a separate forecast, expects up to 3 inches across parts of the Desert Southwest and isolated spots possibly reaching 5 inches, with some models showing near-record October moisture. That is a different outlook from AccuWeather’s 6-inch ceiling, and the gap between 5 and 6 inches shows how forecasters differ on the extreme tail while agreeing on the broad picture.
Burn Scars, Slot Canyons and Where Water Collects
The danger is not evenly spread. An earlier Weather Channel outlook warned of debris flows and mudslides over recent burn scars and of flash flooding in slot canyons and arroyos, with tropical moisture feeding a multiday flood risk across seven states from California to Colorado. In Arizona that means narrow washes that can fill within minutes, roads that dip through dry channels, and slopes stripped of vegetation by fire.
For live conditions, the Weather Prediction Center posts its Excessive Rainfall Forecasts, and local National Weather Service offices in Phoenix, Flagstaff and Tucson issue the flood watches and warnings. Forecast totals are estimates that can shift as the storm moves, and a StormMax figure describes a possibility, not a promise. Anyone traveling through Arizona on Oct. 22 should expect conditions to differ sharply from one drainage to the next, because thunderstorm rain falls in narrow, fast-moving cells rather than evenly across a region.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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