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Winter & Cold Weather Criteria

Dense Fog

  • Advisory: A dense fog advisory is issued when widespread fog is expected to reduce visibilities to 1/4 of a mile or less over a large area for an extended period of time (2 hours or more).
  • Watch: N/A
  • Warning: N/A

Freezing Rain

  • Advisory: A freezing rain advisory is issued when freezing precipitation is expects, however ice accumulations are anticipated to be less than 1/4 inch.
  • Watch: N/A
  • Warning: N/A

Ice Storm

  • Advisory: N/A
  • Watch: N/A
  • Warning: An ice storm warning is issued when freezing precipitation is expected with 1/4 inch or more of ice accumulation. These are generally issued twelve (12) to twenty-four (24) hours prior to the expected start of the event.

Winter Weather

  • Advisory: Hazardous winter weather conditions are occurring, imminent or likely. Conditions will cause a significant inconvenience and if caution is not exercised, will result in a potential threat to life and/or property. The generic term, winter weather advisory, is used for a combination of two (2) or more of the following events – snow, freezing rain or drizzle, sleet and blowing snow.
  • Watch: N/A
  • Warning: N/A

Winter Storm

  • Advisory: N/A
  • Watch: Conditions are favorable for hazardous winter weather conditions including heavy snow, blizzard conditions, or significant accumulations of freezing rain or sleet. These watches are usually issued twelve (12) to thirty-six (36) hours in advance of the event. Specific criteria are subjective based on region, however generally speaking significant and hazardous winter weather is defined as a combination of – four (4) inches or more of snow/sleet within a twelve (12) hour period or seven (7) inches or more of snow within a twenty-four (24) hour period AND/OR enough ice accumulation to cause damage to trees and power lines AND/OR a life threatening or damaging combination of snow and/or ice accumulation with wind.
  • Warning: Significant combination of hazardous winter weather is occurring or imminent. Specific criteria are subjective based on region. The criteria listed are consistent with the St. Louis, MO National Weather Service Office – heavy snow of six (6) inches or greater AND/OR heavy sleet of half-inch or more AND/OR conditions meet the criteria of two (2) or more separate warnings; for example if you have Heavy Snow Warning conditions along with Wind Chill Warning conditions.

Blizzard

  • Advisory: N/A
  • Watch: N/A
  • Warning: A blizzard warning means that the following conditions are occurring or expected for three (3) hours or longer within the next twelve (12) to eighteen (18) hours – snow and/or blowing snow reducing visibility to 1/4 mile or less AND sustained winds of 35MPH or greater or frequent gusts to 35MPH or greater; there is not temperature requirement.

Snow Advisory

  • Advisory: A snow advisory will be issued when three (3) to five (5) inches is expected to fall
  • Watch: N/A
  • Warning: N/A

Lake Effect

  • Advisory: N/A
  • Watch: N/A
  • Warning: Lake effect snowfall of six (6) inches or more in twelve (12) hours or less, or eight (8) inches or more in twenty-four (24) hours or less.

Heavy Snowfall

  • Advisory: N/A
  • Watch: N/A
  • Warning: A heavy snow fall warning will be issued if six (6) or more inches of snow is expected in a twelve (12) hour period.

Blowing Snow

  • Advisory: A blowing snow advisory will be posted for events in which visibility is intermittently 1/4 mile or less.
  • Watch: N/A
  • Warning: N/A

Frost Advisory

  • Advisory: A frost advisory is issued when the minimum temperature is forecast to be 33-36 degrees on clear calm nights or generally when frost is expected to occur during the growing season. The growing season in the U.S. is generally defined as the period of time between the last occurrence of a frost or freeze in the Spring and the first occurrence of a frost or freeze in the Autumn.
  • Watch: N/A
  • Warning: N/A

Freeze

  • Advisory: N/A
  • Watch: A freeze watch is issued during the growing season when there is a potential for significant, widespread freezing temperatures within the next twenty-four (24) to thirty-six (36) hours. The growing season in the U.S. is generally defined as the period of time between the last occurrence of a frost or freeze in the Spring and the first occurrence of a frost or freeze in the Autumn.
  • Warning: A freeze warning is issued when significant, widespread freezing temperatures are occurring during the growing season. The growing season in the U.S. is generally defined as the period of time between the last occurrence of a frost or freeze in the Spring and the first occurrence of a frost or freeze in the Autumn.

Wind Chill

  • Advisory: A wind chill advisory will be issued when the wind chill is less than or equal to -20°F AND the winds are greater than or equal to 10MPH.
  • Watch: N/A
  • Warning: A wind chill warning is issued when the wind chill will be less than or equal to -30°F AND the winds are greater than or equal to 10MPH.