Winter Criteria

Precipitation by Type

Precipitation by Type – image in public domain

Winter Precipitation Types

  • Rain – moisture condenses into drops and then falls.
  • Freezing Rain – rain that freezes when it lands on surfaces below freezing.
  • Sleet – frozen precipitation melts and refreezes into ice pellets.
  • Snow – water crystalizes and falls to the ground without any melting.
  • Radar can make a “best guess” at the precipitation type, but it could still change before it hits the ground underneath the radar beam.
  • Snow to sleet, sleet to rain, rain to freezing rain, etc. but wait till the change has “taken hold.”
  • Thunder during a snow event.

Ice accretion

Ice Accretion on Tree Branch

Ice Accretion on Tree Branch – image in public domain

  • Measured radially from the twig, grass blade, fence, etc.
  • Report accretion starting at ¼″
  • Can cause a lot of damage to trees and power lines due to the added weight of the ice
  • If the ice is uneven, measure both sides and take the average.
  • Report rain when temperatures are below 30°F.
  • Structural damage
  • Coastal flooding

Measuring Snow Fall

  • First 2″ of snow
  • Every additional 2″-3″ of snow
  • 1”/hr or greater snow
  • If total snowfall is less than 2″ just report final depth.
  • Always report final total, don’t leave NWS hanging!

    Measuring Snow Depth, Graham Horn, licensed for reuse

    Measuring Snow Depth – image by Graham Horn

Proper methods to measuring snow depth:

  • Measure in several places that are not affected by trees, buildings, or other local obstructions.
  • Areas that are clear, flat and open. Avoid drifts and bare areas.
  • Average your numbers together and report to the nearest 0.1″. For example 3.25″ becomes 3.3″.

Should you clear your spot?

  • Not necessary.
  • If you do decide to clear, wait 6 hours between clearings.
  • Useful during larger storms as snow compaction can lessen total snowfall amounts.
© 2013- Clay Center for Science and Techology