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