NEW YORK (MainStreet) – The Northeast blizzard directly following Christmas cost retailers approximately $1 billion in post-holiday sales, according to the latest estimates from ShopperTrak.

The retail data analysis company, which pairs data aggregated from more than 70,000 malls and shopping facilities with data from the Commerce Department, found that the total U.S. foot traffic on Dec. 26 was 11.2% below what would have been expected without the blizzard. Total foot traffic on Dec. 27 was also 13.9% below expectations.

Preliminary sales estimates from the Commerce Department for Dec. 26 and Dec. 27 combined were roughly $10 billion. ShopperTrak assumed the blizzard had a 10% impact on sales nationally over the two days, which accounts for the estimated $1 billion loss.

“The 2010 blizzard throughout the Northeast halted nearly all retail visits and spending during a period that is fairly crucial for retailers,” Bill Martin, founder of ShopperTrak, said in a press release.

The research company is also reporting that total sales for the week of Christmas, which ended Dec. 25, fell 4.1% compared to last year. The decrease is due to the fact that the day after Christmas (and the major sales numbers that happen that day) were included in last year’s numbers, but not this year’s data since Christmas fell on different days of the week.

Additionally, “in some locations retailers didn’t have the ability to extend store hours on a Sunday due to various regulations, so there was a shorter window to move merchandise that day,” Martin said.

Despite the dip, ShopperTrak didn’t adjust its earlier estimates, which forecasted a 4% sales rise during this holiday shopping season. The optimism is bolstered by retailers’ strong Black Friday, Cyber Monday and Super Saturday sales. 

Additionally, the company found Christmas Eve sales increased to $7.86 billion from $7.58 billion in 2009.

“While we do think there will be some retail strength later this week and into the weekend as folks begin to dig out, it will be interesting to see if levels recover in time to boost December sales and the overall holiday shopping season,” Martin said.

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