The "Total SWE Monday" Habit . . . Please give it a try!

The National Operational Hydrologic Remote Sensing Center utilizes CoCoRaHS reports of precipitation, snowfall, snow depth and the water equivalent of the snow on the ground every day. CoCoRaHS data provide critical "Ground Truth" information that can improve the skill of their products and models. This will improve the accuracy of flood forecasts in the weeks and months ahead. Click here to see how your CoCoRaHS SWE Reports are used by NOHRSC

Their guidance to us has been that if you can only report one day a week it’s best to all report on the same day. Monday was chosen:

"The analysts at NOHRSC prefer a Total Snow Water Equivalent (SWE) observation taken once a week on Monday. The simple reason is that digging cores every day ruins your sample snowfield area (unless you have a big yard or open fields nearby).

A flood of Monday morning SWE reports gives us a better picture of the overall snowpack instead of a few scattered results trickling in throughout the week. Daily total SWE would be great, but let's make "Total SWE Monday" a habit.

(Note: If you have the room, more frequent observations are appreciated, especially when conditions are changing. For areas that only infrequently get snow, there is no need to wait for Monday -- report SWE whenever you have the chance). For instructions on how to take core samples and report the snowpack SWE, please view our on-line training materials on snow: Training Slide Shows or watch the YouTube short animation on: SWE.

Hilberg's Tips -- The Difference between the Rain Gauge Amount and Snow Water Equivalent (SWE)

If you measure snow, there are five (yes, five) potential separate measurements you can make:

• 1) The melted precipitation in your rain gauge (daily precipitation).
• 2) The depth of the new snow that has accumulated in the past 24 hours (since your last daily observation) to the nearest tenth of an inch.
• 3) The liquid water equivalent of the new snow, obtained from taking a snow core then melting and measuring the water. THIS IS NOT THE AMOUNT FROM YOUR RAIN GAUGE!
• 4) The total depth of snow and ice on the ground, old and new, reported to the nearest half inch.
• 5) The liquid water equivalent of the total snow on the ground, obtained from taking a snow core then melting and measuring the water. In the instance where new snow is the only snow on the ground, then 2 and 4, and 3 and 5 could be the same.

We see too many observers copying their precipitation amount into the new SWE field. SWE is a separate measurement! If there has been rain followed by snow, or snow changing to rain, the amount in your rain gauge does not represent the liquid water equivalent of the snow. In windy situations where gauge catch may be poor, SWE from a snow core will likely be a more accurate measurement of the precipitation. In such a case, you can enter the SWE as your precipitation with a note in the comments about the situation and what was in your rain gauge. Here is a recent example. I had an inquiry from an observer who found her liquid precipitation in the gauge was 1.03" and that from a snow core from her from her snow board was 1.16". It was windy during the storm and she wondered if perhaps the wind had prevented all of the snow from making it into her gauge. Yes! The 4-inch gauge is not a great collector of snow in windy situations, so a correctly done snow core is more accurate. In this case, she should enter her SWE as the daily precipitation amount and indicate, in the comments, her gauge amount and that it was likely affected by the winds.

MAIN POINT: If you don't take a snow core and melt and measure the water, then leave "Melted value from the core to the nearest hundredth" as NA.

You can view a short video on how measure SWE on YouTube