Winter 2009-2010 mid-Atlantic snowfall map
Imaging historic D.C., Maryland, and Virginia snow
This is the latest in a series of feature articles revisiting the historic winter of 2009-2010 leading up to Thursday's release of the 2010-2011 winter outlook.
The fascination with winter 2009-2010 has already proven to last much longer than the winter itself. And for the most avid snow lovers, that fascination has only just begun. The numbers are still staggering to think about. 56.1" at National compared to 15.2" average; 77.0" at Baltimore compared to 18.2" average; and 73.2" at Dulles compared to 21.2" average.
While doing research for a forthcoming book, co-authored with Kevin Ambrose, I found it difficult to come across a snowfall map for the entire season. Maps for individual storms are available from the local National Weather Service, and maps of combined snow, like for both February blizzards, are available from the Northeast Regional Climate Center. But the season in total? Such a map may exist, but I couldn't find it. So I created one myself, with the help of a geographic information systems (GIS) analyst.
Keep reading for more on how the map above was made and what went into it.
It started simply enough. Kevin and I were discussing a seasonal range for the region. But we wanted numbers more expansive than just official NWS totals. So, I sent out a query to the weather boards and got numerous answers. More importantly, I found a volunteer to create the map -- Katie Wheatley, a geographic information system (GIS) analyst who also happens to love snow.
I initially gathered the data from weather board users, the NWS and a report issued by The Johns Hopkins University Advanced Physics Laboratory in March, which listed additional seasonal totals. The first dataset included about 60 locations, but it proved to be too small to create an accurate picture.
Fortunately, CoCoRaHS was there to bail us out. Combing through each station, county by county, I was able to find a number of additional seasonal totals and compile a list of locations well into the 100s. Finally, we had enough information to produce a coherent and quite accurate map.
After seeing the product and getting excited about the visual results, I asked Katie about her method, and she responded with the following:
The total snowfall overlay found on the map is the result of the interpolation of several "known" measurements from the 2009-2010 winter season. Using an Inverse Distance Weighted (IDW) interpolation scheme, I was able to produce a seamless estimate of snowfall totals for the mid-Atlantic region. IDW interpolation assumes that known measurements have spatial influence that diminishes with distance.
Once the seamless estimate of snowfall totals was produced, I categorized the values by increments of 15 to show a total snowfall range in inches.
Kevin and I had some concerns with the dataset. As easy as it is to measure snow, many people do it differently. The official method is to measure on a snowboard every 6 hours then clear and repeat. However, some folks measure every hour and others measure when the snow is done. With this in mind, we wanted to hide some of the detail. Katie suggested using a 15 inch increment so the overall pattern of snow could still be shown clearly. We tested at both 10" and 20" as well. 10" may be my ultimate goal, but the data probably isn't good enough to support such resolution.
This is still probably not a complete map. There are still holes and extrapolated data that may be producing inconsistencies. In that light, please feel free to share additional totals in the comments section below, if you kept records. If there are any needed changes to the map, I'll try to note it somewhere and also update this page.
While 2010-2011 is unlikely to produce seasonal snowfall across the region anywhere near the 300% to 450% above normal that we received in 2009-2010, I'm hopeful snow lovers will get the opportunity to pick up new memories after so many were formed last winter. We'll offer our thoughts on the coming season's snow potential tomorrow in the Capital Weather Gang 2010-2011 Winter Outlook!
The snowfall map in this post was created for use in "Snowmageddon: Washington's Record-breaking Winter of 2009-2010," authored by Kevin Ambrose and Ian Livingston, which will be available this month. The book includes numerous photos of the winter, a top-10 D.C. snowstorms comparison, photo comparisons of Snowmageddon to past major snowstorms, as well as in-depth write-ups on the three 2009-2010 blizzards and shorter pieces on other events during the season.
| November 3, 2010; 10:00 AM ET
Categories: Recaps, Snowmageddon, Winter Storms
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