The Tomorrow.io REST Weather API winter insight category will trigger for any of the events below.
Winter Storm (Watch/Warning)
Issued when conditions are favorable for a winter storm event (such as heavy sleet, heavy snow, ice storm, heavy snow and blowing snow or any combination), in cases where the following criteria are met:
(1) snow is 6 inches within 8 hours, 8 inches or more in 12 hours or more covering at least 50 percent of the zone or encompassing most of the population
(2) ice is 1/4 inch or more over at least 50 percent of the zone or encompassing most of the population, enough to cause damage to trees or powerlines
(3) sleet is 1/2 inch or more, enough to cause damage to trees or powerlines, or over 3 inches in 12 hours or less
(4) sustained winds or frequent gusts of 35 mph or greater with visibility frequently at or below 1/4 mile in snow or blowing snow for 3 or more hours
(5) wind Chill forecast or observed at or below -20°F with a wind of 10 mph or greater, in all valley and plateau locations with population centers
Wind Chill (Watch/Warning/Advisory)
Issued when conditions are favorable for wind chill temperatures to meet or exceed local wind chill, temperatures may reach or exceed -10°F with a wind of 10 mph or greater.
Blizzard (Warning)
Issued when conditions are favorable for a blizzard, in cases where the following criteria are met:
(1) sustained wind or frequent gusts greater than or equal to 35 mph will accompany falling and/or blowing snow to frequently reduce visibility to less than 1/4 mile for three or more hours
(2) snow and/or blowing snow reducing visibility to 1/4 mile or less for 3 hours or longer
Note that there is no temperature requirement that must be met to achieve blizzard conditions.
Ice Storm (Warning)
Issued when conditions are favorable for a blizzard, where ice is 1/2 inch or more over at least 50 percent of the zone or encompassing most of the population.
Lake Effect Snow (Warning)
Issued when widespread or localized lake induced snow squalls or heavy snow showers which produce snowfall accumulation to 7 or more inches in 12 hours or less.
Note that lake effect snow usually develops in narrow bands and impacts a limited area within a county or forecast zone.
Winter Weather (Advisory)
Issued when conditions are favorable for a winter weather event (such as heavy sleet, heavy snow, ice storm, heavy snow and blowing snow or any combination), in cases where the following criteria are met:
(1) snow is 4 inches or more in 12 hours or less covering at least 50 percent of the zone or encompassing most of the population, enough to cause a significant inconvenience
(2) ice is any ice accumulation less than 1/2 inch over at least 50 percent of the zone or encompassing most of the population
(3) blowing Snow reducing visibilities to 1/4 mile or less with winds less than 35 mph
(4) freezing rain accumulation less than 1/4"
(5) sleet accumulation less than 1/2"
(6) sustained wind or frequent guest of 25 to 34 mph accompanied by falling and blowing snow, occasionally reducing visibilities to 1/4 mile or less, for 3 hours or more
Note that "Winter Weather" can also be issued for black ice. This is optional.
Snow Squall (Warning)
Issued when there is an expectation of an intense snow shower, which could produce a brief period of heavy snow, gusty winds, near-zero visibility (reduced to 1/4 mile or less, for 15 minutes or more), and potential flash freeze conditions.
Heavy Snow (Warning)
Issued when snow is expected to accumulate 4 inches or more in 12 hours, or 6 inches or more.
Heavy Sleet (Warning)
Issued when a period of sleet is expected to produce ice accumulations of 1" or greater, or cause significant disruptions to travel or utilities.
Sleet (Advisory)
Issued for accumulating sleet of 1/4" to 1". Because sleet usually occurs with other precipitation types, a Winter Weather Advisory will almost always be used in such cases.
Freezing Rain (Advisory)
Issued for freezing rain when ice accumulations are expected to cause travel problems, but not exceed 1/4".
Freezing Drizzle (Advisory)
Issued for freezing rain when ice accumulations are expected to cause travel problems, but not exceed 1/4".
Snow (Advisory)
Issued when accumulating snow of 2 to 4 inches is expected. An advisory may still be warranted if lesser accumulations will produce travel difficulties, especially early in the winter season.
Blowing Snow (Advisory)
Issued when blowing snow is expected to occasionally reduce visibilities to 1/4 mile or less with winds generally 25 to 34 mph. The event should last at least 3 hours.