TL;DR

The NOAA Storm Prediction Center (SPC) has issued a Slight Risk for severe thunderstorms across portions of central and eastern Arizona into western New Mexico today. The primary threats are large hail (isolated stones up to 2 inches possible) and damaging winds, mainly across east-central Arizona this afternoon. The severe threat peaks between mid-afternoon and evening, roughly 12pm–7pm Mountain Time, before weakening overnight.

What's driving today's severe weather?

An upper-level trough and low-pressure system currently positioned over California is moving eastward across the Great Basin today. This system is bringing strong southwesterly mid-level winds of 50–70 knots across Arizona, creating the wind shear necessary for organized thunderstorms.

Supercells have already been active across east-central Arizona through the early morning hours, supported by low-level upslope flow along the Mogollon Rim and atmospheric instability values of 500–1500 J/kg of MUCAPE. As the day progresses, additional heating will destabilize the atmosphere further, setting the stage for more intense storms to develop by late morning and early afternoon.

The combination of strong deep-layer shear (40–50+ knots) and long, straight hodographs—a measure of how wind changes with height—will support supercell thunderstorms capable of producing all severe hazards.

Where is the highest risk today?

The Slight Risk area covers portions of central and eastern Arizona and extends into western New Mexico. Within this zone, the greatest severe threat is expected across:

  • East-central Arizona, including the Mogollon Rim region and areas near Show Low and Payson
  • Western New Mexico, where storms will spread eastward through the afternoon and evening
  • The Phoenix metro area, which sits on the southern edge of the Slight Risk

Farther north into the Great Basin, isolated severe hail and wind potential exists across northern Nevada and southern Idaho, though moisture and instability are more limited in these areas.

When will the storms hit?

Thunderstorms are already ongoing across portions of Arizona as of mid-morning. Additional intense storms are forecast to develop by 12pm–3pm Mountain Time across the higher terrain of east-central Arizona.

The severe threat will peak during the mid to late afternoon—roughly 2pm–7pm Mountain Time—when atmospheric instability is strongest. Storms will gradually spread eastward from Arizona into western and central New Mexico through the evening hours before weakening overnight.

What hazards should you expect?

Large hail

Large hail is the primary threat with any sustained supercells today. Isolated hailstones of 2 inches or larger are possible, particularly across east-central Arizona and western New Mexico. Already this morning, multiple reports of hail up to 2 inches in diameter have been received from the Phoenix metro area, with 33 hail reports logged across Arizona in the last 24 hours.

Damaging winds

The risk for severe and damaging winds may increase by mid to late afternoon as convection spreads from eastern Arizona into western New Mexico. There is some potential for storms to cluster, which would enhance the wind threat. Seven wind reports were logged yesterday, including a 72 mph gust at Flagstaff Airport and multiple reports of downed trees across northern Arizona.

Tornadoes

While the tornado threat is not the primary concern today, residents in the Slight Risk area should remain weather-aware and have multiple ways to receive warnings.

Active severe thunderstorm watches

As of this writing, three Severe Thunderstorm Watches are in effect across Arizona:

  • Apache, Coconino, Navajo, and Yavapai counties: valid until 10am Mountain Time
  • Gila, Maricopa, and Pinal counties: valid until 11am Mountain Time
  • Graham and Greenlee counties: valid until 11am Mountain Time

These watches may be extended or reissued as storms continue to develop through the afternoon.

What about tomorrow and the weekend?

SPC has issued a Marginal Risk for portions of New Mexico and the Northern Plains on Friday, October 23. A Marginal Risk also extends into parts of Texas and New Mexico on Saturday, October 24. Neither day is expected to bring high-end severe weather, but isolated strong to severe storms remain possible.

How to stay safe

If you're in the Slight Risk area today, take these steps:

  • Monitor radar and warnings closely this afternoon and evening, especially if you're across east-central Arizona or western New Mexico.
  • Have multiple ways to receive warnings, including a NOAA Weather Radio, a smartphone weather app, and local news. Third-party weather apps are silenced by Do Not Disturb, though Wireless Emergency Alerts for tornado warnings still break through on most phones.
  • If a warning is issued for your location, move to the lowest floor of a sturdy building, away from windows. For tornadoes, an interior room or hallway is safest.
  • Avoid being outdoors or in a vehicle when storms are nearby. Large hail and damaging winds can develop quickly with supercells.

VORTEX is a free web app at vortexintel.app that monitors severe weather nationwide. Pro ($4.99/month) places phone calls to your phone when a tornado or flash flood warning is issued for a location you care about — calls can ring through Do Not Disturb once you enable Emergency Bypass for the number, unlike most third-party app notifications.