An extreme cold warning is a weather warning issued by Environment and Climate Change Canada (ECCC) and by the United States' National Weather Service (NWS) to inform the public about active or imminent severe cold temperatures in their local region.
Under the new system the extreme cold warning is issued based on either the temperature or the wind chill being a certain value for at least two hours.
In October 2024, the NWS officially implemented these changes to its wind chill and hard freeze warnings, watches, and advisories (WWAs) as part of its "Hazard Simplification initiative."
The goal of these WWA name changes, per the NWS, is "simplifying a suite of cold weather forecast products to improve messaging of winter hazards and provide better decision support."
Local NWS offices will still determine the standards governing the issuance of such WWAs.