An ice storm warning is a hazardous weather statement issued by the Weather Forecast Offices of the National Weather Service in the United States which indicates that freezing rain produces a significant and possibly damaging accumulation of ice on surfaces. The criteria for this warning vary from state to state, but typically an ice storm warning will be issued any time more than 1⁄4 inch (6.4 mm) of ice at peak is expected to accumulate in an area, else a freezing rain or drizzle advisory is issued; in some areas, the criterion is 1⁄2 inch (13 mm) instead.
Prior to October 2017, a freezing rain advisory or freezing drizzle advisory was issued when a small amount of icing was possible.
In Canada, a freezing rain warning has the same meaning.
Example of an ice storm warning
632 WWUS44 KLZK 200235 WSWLZK URGENT - WINTER WEATHER MESSAGE National Weather Service Little Rock AR 835 PM CST Tue Feb 19 2019 ARZ003-012-013-200600- /O.UPG.KLZK.WW.Y.0004.000000T0000Z-190220T0600Z/ /O.NEW.KLZK.IS.W.0001.190220T0235Z-190220T0600Z/ Boone-Newton-Searcy- Including the cities of Harrison, Omaha, Lead Hill, Jasper, Western Grove, Deer, Marshall, Leslie, and Gilbert 835 PM CST Tue Feb 19 2019 ...ICE STORM WARNING IN EFFECT UNTIL MIDNIGHT CST TONIGHT... * WHAT: Significant icing. Storm total ice accumulations of around two to three tenths of an inch are expected...mainly on trees and power lines. * WHERE: Boone, Newton and Searcy Counties. * WHEN: Until midnight CST tonight. * ADDITIONAL DETAILS: The ice will result in tree limbs breaking and potential for power outages. There may also be some slick spots on bridges and overpasses. PRECAUTIONARY/PREPAREDNESS ACTIONS... An Ice Storm Warning means significant amounts of ice accumulation are expected and may result in snapped power lines and falling tree branches. Be sure to check road conditions before traveling in these areas. Visit the Arkansas Department of Transportation's website Idrivearkansas.com for the latest road and traffic conditions. && $$