Friday, July 25, 2014
Inquirer Daily News

Snow: A measure of doubt

Measuring snow can be trickier than predicting it.

Snow: A measure of doubt

The government recently freshened its snow-measuring guidelines with the aim of imposing some uniformity in the methods used by its network of cooperative observers.

The update, the first in about 15 years, was roughly two years in the making, according to guideline- committee member Dave Robinson, the Rutgers University professor who is the New Jersey state climatologist and a national expert on snowfall.

One might reasonably ask, how many experts does it take to figure out how to stick a ruler into a pile of snow and jotting down the inch count? Turns out this process if far-more complicated than it looks.

And judging from some of the disparate totals we have seen consistently after snowfalls, we have to wonder how often poetry undercuts the science.

Ray Martin, a National Weather Service meteorologist, took the trouble to examine the reports of coop observers and calculated all the 2012-13 seasonal totals. On this link, scroll down about a quarter of the way to find the list and the map.

 (A footnote: Martin works in Nevada but has local roots and remains a go-to meteorologist on local climate and weather issues.)

What you’ll see are some head-scratching differences, particularly in Chester County. The disparities might have something to do with the overall quality and quantity of observer reports.

But we could cite any number of individual events where totals were substantially different in the space of a few miles. See, for example, this summary of the Feb. 5-6, 2010, totals.

The new guidelines for the most part repeats old guidance: Use a snowboard, measure away from roofs and trees, take multiple readings and average the totals when it’s windy, etc.

One big difference, however, is that a coop observer is to report only the highest total within a 24-hour period – as opposed to clearing off a snowboard every six hours, and adding new measurements to a running total.

The six-hour measurements tended to bump up the totals, said Robinson, although the first-order stations, such as the one at National Park, N.J., still we be reporting every six hours.

The guidelines to allow for some “educated judgment,” Robinson said, given that many volunteer coop observers actually have to make a living and might even miss a flake or two.

As to when the new system will be put to the test, computer models continue to show that at least some small accumulation of snow is possible Sunday before a changeover to rain.

Tony Wood Inquirer Weather Columnist
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Tony Wood Inquirer Weather Columnist
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