National Weather Service United States Department of Commerce

Winter Guidelines and Criteria

 

Winter Guidelines For Calling WFO Boulder…

  • 12 and/or 24 hour snow depth and new snowfall by 8 AM and 8 PM.

  • Moderate to heavy snowfall. Example: 1/2-1 inch per hour for several hours and visibilities less than 1/2 mile.

  • Strong winds above 50 mph (sustained or gusts).

  • Freezing rain/drizzle (any intensity).

  • Report changeover from rain to snow or fro.m snow to rain. Dense Fog (visibility less than a quarter of a mile).

  • If current conditions do not coincide with the current WFO Boulder Forecast.

  • Adverse road conditions.

  • If any of the below snow criterion is met.

 

**Our criteria for issuing warnings and advisories are listed above.   Please pay close attention to when your snowfall approaches 4 inches and again at 8 inches at the higher elevations (at or above 6500 feet).    3 and 6 inches are the critical numbers for the stations at lower elevations (below 6500 feet).


NWS Winter Storm Weather Criteria…

 

Mountains and Foothills Criteria…

 
  • WINTER STORM WARNING

    • 8 inches or more in a 12 hour period.

    • 12 inches or more in a 24 hour period.

 
  • SNOW ADVISORY

    • 4 to 7 inches in a 12 hour period.

 
  • HIGH WIND CRITERIA

    • Sustained winds of 50 mph or greater or

    • wind gusts to 75 mph or more

 

Urban Corridor and Plains Criteria…

  • WINTER STORM WARNING

    • 6 inches or more in a 12 hour period.

    • 8 inches or more in a 24 hour period.

 
  • SNOW ADVISORY

    • 3 to 5 inches in a 12 hour period.

 
  • HIGH WIND CRITERIA

    • Sustained winds of 40 mph or greater or

    • Wind gusts to 58 mph or more

 
  • Blizzard Criteria

    • Sustained winds of 35 mph or greater (and)

    • Visibilities frequently less than 1/4 mile (and)

    • Considerable snow and/or blowing snow