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Posted 2/25/2013

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By Michael Janiszewski
Water Management

     The Pittsburgh District drainage area covers more than 25,900 square miles beginning in the upper Allegheny and Monongahela Rivers headwaters to our endpoint just below Hannibal Locks and Dam on the Ohio River.  
     What impact to such a large area could a couple inches of wet snow up in the mountains make? Well, providing the right answer to that question happens to fall right in between goals of the National Weather Service and our Pittsburgh Corps Water Management section.
     What do agencies do when they have overlapping mission goals?  They cooperate and work together. Yes, that is possible. In fact, both offices are working together right now planning ahead for the next major snow event like the Snowmageddon snowfall, Feb. 5-6, 2010, or the snow runoff flood in January 1996 that was 10 feet above flood stage at the Point.
     Part of the new plan has been to reinforce and upgrade the snow sampling stations at 15 reservoir projects and three lock and dam river stations. They have been a steady provider of what the NWS categorizes as A-level weather observation sites. A-level is the highest value assigned to observer data and is given because the record at the stations has been collected by established procedures for numerous consecutive years.
     No automated snow sampler has been invented that can replace snow measurements made by trained observers. The observer measures and records snow fall, snow depth, and the snow-water equivalent, a technique that has been handed down from one group of Corps employees to another. This type of long term meteorological record is useful when predicting climate changes.
     To safeguard the benchmark snow data, a half day review and refresher training was setup at four locations across the district. However, before the training, Bob Coblentz from the Pittsburgh forecast office with the National Weather Service and Mike Janiszewski with the Pittsburgh Corps, were sent out to find how and where data was collected by making site visits to the future snow network stations. Of course, the site visits were schedule when the conditions were most challenging.
     Finally the training time had arrived. That was a good thing because our wake up call, Hurricane Sandy, had already been through the area bringing more than 20 inches of snow to parts of West Virginia Oct. 31 and Nov. 1. Werner Loehlein with the district’s Water Management and Bob Coblentz with NWS, headed out to review existing methods and train for the new snow network. Part of the refresher course was the distribution and instructions for use of the new Adirondack snow density gages.
     The snow sampling tubes give the most complete picture of not only how much water is in the snow, but what type of layering is in the snow column.  That is the most complete type of snow measurement and is of high value.   As of now, 15 reservoir projects, plus three river stations have already started putting in their data into the NWS system using their Weather Coder software.
     The NWS also makes snow sensor sampling flights. The snow observations play a part in the work of the snow flights as well. Because of the wide difference in elevations at our snow sites, from 768 feet at Pike Island to 1513 feet at Youghiogheny Reservoir, plus the geographic distribution of the projects, the snow measurements are used to calibrate the data collected from the airplane sampling runs.
      The various data are all quality checked then finally entered for use. The national snow water equivalent map ends up looking as shown at this link: http://www.nohrsc.noaa.gov/interactive/html/map.html.
      When the Pittsburgh river forecast is made, having a map like this is essential to tell us exactly what difference a couple inches of wet snow up in the mountains can make. It often turns out to be a big difference.

Corps Water Management national snow water maps National Weather Service NWS snow melt snow sampling tubes