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Posted at 10:00 AM ET, 11/ 3/2010

Winter 2009-2010 mid-Atlantic snowfall map

By Ian Livingston

Imaging historic D.C., Maryland, and Virginia snow

* Rainy Thurs. morning commute? Full Forecast thru weekend *
* Why was it so snowy? El Nino and the North Atlantic Oscillation *
* Tomorrow: Capital Weather Gang's 2010-2011 winter outlook *

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.

Full-season snowfall map for the D.C. area and broader mid-Atlantic. Shaded contours are at a 15" increment. Map created by Katie Wheatley. See larger version.

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.

Map of the mid-Atlantic showing many of the data points entered to create the contour map above. Created by Katie Wheatley. See a full list of gathered data points (PDF).

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.

See a full list of gathered data points (PDF).

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.

By Ian Livingston  | November 3, 2010; 10:00 AM ET
Categories:  Recaps, Snowmageddon, Winter Storms  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Forecast: Thursday rain threat as cold remains
Next: The winter of 2009-2010: Could it have been colder?


Nicely done! Can't wait for the book.

Posted by: Brian-CapitalWeatherGang | November 3, 2010 10:45 AM | Report abuse

This area of snowfall mapping is a bit of a pet peeve of mine. Have you seen the snowfall maps produced by Barbara Watson from the early 2000's? I have a printed copy on my wall, but will try to dig up an electronic version. They look better and seem to be more accurate (a better match to the topography and storm tracks). Using more modern tools has actually produced a less accurate result, I believe the main problem is lack of topographic data.

Posted by: eric654 | November 3, 2010 11:02 AM | Report abuse

Ian, thanks so much for taking the time to prepare the data for this map, for the great job Katie Wheatley did in preparing it and, finally, for posting it. We had c.a. 70" where I live in Glover Park last winter, and the map reflects this, so great job!

I'm eager to learn more about the reasons for 76"-90" snow "fist" ("claw"?) that extended southward from PA and why its punch/grasp stopped just north and west of D.C.

I kvetched last week about The Post's weather page being one cooling degree day out of synch with NWS data, and some readers are too quick to holler "epic fail", even when a forecast is slightly off. But like so many of your other readers, I'm very grateful for the time you and your CWG colleagues spend to ensure data and reporting accuracy.

Posted by: JerryFloyd1 | November 3, 2010 11:07 AM | Report abuse

P.S. When will be book be available for pre-ordering on Amazon? Just checked, not listed yet.

And will there be a book signing, with the authors clad in snazzy "I survived the Snowmageddon Shirts"?

Posted by: JerryFloyd1 | November 3, 2010 11:14 AM | Report abuse

Actually, there may be one blip on the map. I think Richmond officially had about 28" of snow.

Posted by: JerryFloyd1 | November 3, 2010 11:54 AM | Report abuse

Spot on for me...I was at 85 inches and POSITIVE that I'd hit 100 by the end of the season, but after Snoverkill all I had was some flurries and dusting or two. Not sure why IAD came in a bit under that 75 inch #. Being about 8 miles SW of the measuring station at IAD I was at the 32 inch mark right with them (and thinking I was screwing the measurment up...couldnt be THAT much, could it?) with Snowmageddon. I must have had some enhancements throughout being just East of the Bull Run Mountains...

Posted by: DullesARC | November 3, 2010 12:22 PM | Report abuse

eric654: While I have not seen the maps you note, I'm not sure topo data hurts much in this view. We cut out WV and far western MD because there were clearly some issues out there. We do still have some chunks of land with no data which is probably a bigger issue in my opinion. Perhaps N MD suffers some topo issues, I wouldnt be surprised if there were some more areas of 91"+ up there, but I think it's somewhat isolated as the map shows. As noted though, we will probably still make some slight corrections if we can get more info.

Posted by: Ian-CapitalWeatherGang | November 3, 2010 12:34 PM | Report abuse

Yikes! When I first saw the map, I thought it was a projection for the coming winter! What a relief that it wasn't. But speaking of this winter, have you done a seasonal forecast yet? Are there others available from NWS or others? Thanks.

Posted by: lhaller | November 3, 2010 12:35 PM | Report abuse

JerryFloyd1, if you look at individual storm maps from LWX etc (or radar loops) you see a similar pattern to many of the storms. I guess it's kind of typical anyway for the heaviest snow to end up north and west of the cities. Regarding the book: we will share info on how to purchase it in the next week or two. I will also look into the RIC note, thanks.

Posted by: Ian-CapitalWeatherGang | November 3, 2010 12:37 PM | Report abuse

The RIC snow issue has been beaten to death but it is obvious that the reports from the RIC observers were seriously flawed. The head of the local AMS chapter in central VA proved beyond all doubt that the snow measurements from the dec 18 and Jan 30 snwofalls were well... crap. When NWSFO akq visted the RIC location where the FAA folks were taking snow obs they found it was under or close to a large tree.

This issue has beena problem for over a decade at richmond but since there had not been a snowy winter for over 10 years at RIC this was never an issue until last winter

Posted by: wxrisk | November 3, 2010 1:08 PM | Report abuse

Thanks for the note, wxrisk.. good to see you stop by! I checked with Katie and she reminded me we smoothed out the RIC hole in an earlier version. We did this in several spots... though as you can see above, we left a few like the one over IAD. Perhaps that should go as well. We have a few additional numbers in sparse regions just since publishing this as well, so there should be an update of some sort. It is still interesting to me how hard it seems to be to measure snow correctly!

Posted by: Ian-CapitalWeatherGang | November 3, 2010 1:16 PM | Report abuse

wow...really fun looking at those maps and remembering last winter... ...ah..sigh...

anyway, one comment on those maps is that i suppose the resolution is not fine enough or something, but it doesn't show the "bubble" right over my house... seems like it snows more across the street than at my house... irritates the heck out of me...

we're only a month away from the quasi-annual dec 5th-ish storm!

Posted by: walter-in-fallschurch | November 3, 2010 1:24 PM | Report abuse

Ian, thanks for responding. I recall the radar images, but it's odd that there is areas in the Ridge and Valley area of Washington and Allegheny Counties, MD and adjacent parts of VA WA that were outside the southward-extending snow "fist". I guess the Arctic Oscillation was situated just so.

I hope you turn your book launch into a media event of sorts, given how freely and quickly Snowmaggedon, etc. entered into the lingua franca, from the President to many others.

The RIC info/dispute was quite interesting to learn about.

Tom Kieran made a general upcoming winter snowfall prediction during his 11 a.m. forecast but since your prediction is due out tomorrow, let's see what CWG has to say.

Posted by: JerryFloyd1 | November 3, 2010 2:08 PM | Report abuse

If given the chance, I would relive that winter a thousand times over. Sigh...At least we have a better a chance of seeing ice storms this year! : )

Posted by: Yellowboy | November 3, 2010 2:51 PM | Report abuse


Note the notes at the top of the post, and in the last paragraph -- our winter outlook comes out tomorrow.

Posted by: Dan-CapitalWeatherGang | November 3, 2010 3:27 PM | Report abuse

Yes, I love snow.

Posted by: FIREDRAGON47 | November 3, 2010 6:06 PM | Report abuse

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