Warning in Effect Now: Affected Areas and Timeframe
An Extreme Heat Warning is currently in effect across a large portion of Arizona, issued beginning July 23, 2026 at 12:13 PM MST and running through July 24, 2026 at 5:00 AM MST. The warning covers a broad and geographically varied set of communities and regions, including the Upper Santa Cruz River and Altar Valleys including Nogales, Western Pima County including Ajo and Organ Pipe Cactus National Monument, Lake Havasu and Fort Mohave, Grand Canyon Country, Marble and Glen Canyons, the Aguila Valley, Kofa, the Parker Valley, the Northwest Valley, and the Tonto Basin.
The warning has been issued jointly by four National Weather Service offices: NWS Tucson AZ, NWS Las Vegas NV, NWS Flagstaff AZ, and NWS Phoenix AZ, a coordinated response that reflects how extensively this heat event spans the state. Residents and visitors anywhere within these named zones should treat this warning as active and take protective action immediately.
What NWS Is Telling You to Do Right Now
The National Weather Service is issuing direct, specific guidance that applies for the full duration of this warning. First and most urgently: do not leave young children or pets in unattended vehicles. According to the NWS, car interiors can reach lethal temperatures within a matter of minutes, not hours. This applies even during brief stops.
For anyone who works or spends time outdoors, the NWS guidance draws on recommendations from the Occupational Safety and Health Administration (OSHA): schedule frequent rest breaks in shaded or air-conditioned environments throughout your workday or outdoor activity. If at all possible, reschedule strenuous physical tasks to early morning or evening hours when temperatures are lower.
The NWS also emphasizes clothing and hydration: wear lightweight, loose-fitting clothing when possible, and drink plenty of water. Knowing the signs of heat exhaustion and heat stroke is equally important during a warning of this level. If someone is overcome by heat, move them immediately to a cool, shaded location. Heat stroke is a medical emergency, call 9-1-1. Do not wait to see if symptoms improve on their own.
These instructions are not general summertime reminders. They are the active, official guidance tied to this specific warning and these specific conditions across Arizona right now.
Connecting This Warning to Broader Preparedness
Extreme Heat Warnings at this scale, spanning desert communities near the U.S.-Mexico border, remote national monument areas, river valleys, and canyon country simultaneously, are a reminder that heat preparedness is not a single-day task. At USRiskRadar, we track these events because the gap between awareness and action is where preventable harm occurs. If you live in or are traveling through any of the named zones before July 24 at 5:00 AM MST, review your household’s heat plan now: confirm you have access to cooling, check on neighbors or family members who may be elderly or isolated, and do not underestimate how quickly extreme heat escalates into a life-threatening situation. For the most current updates and any extensions to this warning, monitor the National Weather Service directly at weather.gov.
For the fundamentals that apply beyond this specific alert, see our Power Outage Preparedness guide.
Source: National Weather Service (NWS Tucson AZ, NWS Las Vegas NV, NWS Flagstaff AZ, NWS Phoenix AZ), active alert data retrieved 2026-07-23 22:00 UTC via api.weather.gov.
