Heavy Rain and Thunderstorms in the Plains; Snow in the Northern Rockies

A storm system moving eastward will bring widespread showers and thunderstorms over parts of the Northern Plains to the Southern Plains and Upper Great Lakes through Friday. Heavy snow will continue over parts of the Northern Rockies. Read More >

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Summary

The October 2010 tornado outbreak was the largest in Arizona history and was also notable for producing the highest count of tornadoes ever in a single event that took place west of the Continental Divide. At least eleven tornadoes were recorded during the morning hours of October 6, 2010. The most active time was from 4:00 AM - Noon MST. The National Weather Service office in Flagstaff issued 28 Tornado Warnings, 25 Severe Thunderstorm Warnings, and 1 Flash Flood Warning during this event. Multiple tornadic storms repeatedly developed over the same locations in north-central Arizona, keeping the small area under a constant tornado threat for several hours. Large hail (up to baseball-sized) was reported. The duration, intensity, and number of tornadoes distinguished this event apart from any other event in history west of the Continental Divide and in Arizona.

Map Overview and Event Meteorology

This was an unusual event meteorologically for northern Arizona. All parameters that are required to generate severe thunderstorms and tornadoes were in place at once. A cold low pressure system off the California coast and strong southwesterly winds allowed enough moisture, instability, and atmospheric rotation to produce the observed tornadoes.