Snowfall Measurement Guide

I. Problems & Challenges In Measuring Snow

II. Basic Snowfall Measurements

III. Snowfall Measurement Equipment

A. The Snow-Board

B. The Snow-Post

IV. Snowfall Measurement Procedures

A. New Snowfall

B. Snow Depth

V. Reporting Your Measurements

Problems & Challenges In Measuring Snow

To the uninitiated, measuring snow seems simple. All you need to do is push a measuring stick into the snow, then read the number on the stick and write it down, right? Unfortunately, it's not that easy.

Three properties of snow are responsible for most of the difficulties in making accurate and consistent measurements:

  1. Snow often melts as it lands or as it lies on the ground, both from warm soil below or from warm air, wind, or sunshine above. As a result, the observer may be in a dilemma. The observer may wonder, "It snowed for three hours, but there is nothing on the ground. Do I report zero or a trace, or do I make something up?"
  2. Snow settles as it lies on the ground. Depending on the initial density of fresh snowfall and on other coincident weather conditions, the snow may settle rapidly or very gradually. This can have profound effects on observations. Observers who measure more often than once a day may report much more snowfall than a once-daily observer.
  3. Snow is easily blown and redistributed. It tends not land or lie uniformly on the ground, but instead forms deep drifts in some areas while exposed areas may be blown completely clear. A related problem is precipitation gauge "catch." Even at relatively low wind speeds, snow is easily deflected around the top of precipitation gauges. Most winter precipitation measurements using standard precipitation gauges underestimate the precipitation that actually fell, sometimes by large amounts.

Consistent and comparable snow data is only possible if standard procedures are established and followed. The use of snow-boards and snow-posts, for example, is an important first step towards standardizing snowfall measurements.

Two crucial issues in measuring snowfall accurately are:

  1. Determining a representative location for measuring snow.
  2. Establishing a consistent time interval between measurements of the depth of freshly fallen snow.

Unless observing locations and the interval between measurements are standardized, snowfall data will be erratic and inconsistent, and not comparable from one site to another.

For example, an observer who measures new snow accumulation very frequently, and each time clears the snowboard to begin a new accumulation, will report snowfall totals that exceed what has actually accumulated on the ground. Frequent observations (hourly or every few hours) may be very useful for evaluating the intensity of snowfall, but these incremental measurements cannot be added together to give a meaningful snowfall accumulation.

Basic Snowfall Measurements

There are two basic measurements that we will use here in Lake County to evaluate snowfall:

  1. New Snowfall - The amount of snow that has accumulated since the last measurement was taken.
  2. Snow Depth - The total amount of snow that has accumulated on the ground.

Both of these measurements will be reported as tenths of inches (i.e. 1.3").

Snowfall Measurement Equipment

A. The Snow-Board

A snow-board is a flat board that can be used to collect new snowfall. A snow-board should be placed horizontally in a location that will be most representative of the average snowfall - not under trees, obstructions, or on the north side of structures in the shadows. For example, a good placement would be near the middle of your lawn away from any nearby trees. A good general size for a snow-board is 24" x 16", and any type of wood should work fine. A few coats of latex paint or perhaps deck sealant would be a good idea, to seal out the moisture and prevent the board from warping. Be sure to mark the location of the board with a flag or other marker, so that you can find the board after a new snowfall.

B. The Snow-Post

A snow-post is a vertical post with height markings used to measure the total depth of snow that has accumulated on the ground. For our purposes the markings may be as rough as halves of inches or as fine as tenths of inches. A guide on building a basic snow-post from the University of Minnesota can be found here.

Snowfall Measurement Procedures

A. New Snowfall

  1. After a new snowfall, take a ruler out to your snow-board.
  2. Holding the ruler vertically, sink your ruler down through the accumulated snow until the end hits the snow-board.
  3. Record the level that the snow reaches on the ruler, accurate to the tenth of an inch if possible.
  4. Remove your ruler from the snow.
  5. Remove your snow-board from underneath the accumulated snow.
  6. Place the snow-board onto the top of the snow adjacent to it's previous location.
  7. Press the snow-board down until the top surface of the snow-board is even with the level of the snow.
  8. Mark the new position with a flag or other marker.
  9. Report this measurement to Lake County SKYWARN.
  10. Upon the next snowfall, repeat this procedure.

B. Snow Depth

  1. After a new snowfall, approach your snow-post.
  2. Observe the level that the snow reaches on the snow-post, and record this level accurate to the half-inch if possible.
  3. Report this measurement to Lake County SKYWARN.
  4. Upon the next snowfall, repeat this procedure.

Reporting Your Measurements

To report your snowfall measurements, we would like you to take the measurements once every 24 hours. Please pick a time during the day when you will record the snowfall measurements and then forward them to Lake County SKYWARN (i.e. 6:00 PM every day). If no snow has fallen that day, do not take the trouble to send in a report. During an emergent situation, you may be requested to take more frequent measurements in order to determine the intensity of the snowfall and not just the accumulation. All reports will be compiled and recorded, and all significant reports will be forwarded to the National Weather Service. There are three options available to submit your snowfall reports:

  1. Use the Weather Observation Report form on the Lake County RACES website: http://www.races.org/wxreport.htm.
  2. Email your observations to snowfall@lakecountyskywarn.org.
  3. Send your observations via packet in a private message to KC9GHZ on the KC9GAX bulletin board system.

© 2006 Lake County SKYWARN

Webmaster - Greg Perkins