U.S. sales receipts fell sharply in the week ending Friday as a trade group said low volumes of sales can produce more volatile swings than high volumes. Sales for the week ending Saturday \"tumbled by 2 percent,\" the International Council of Shopping Centers said in their weekly sales tracking report. \"The current low-volume period can be more volatile than otherwise,\" the report said. From the same week a year earlier, sales were up 2.8 percent. For the second consecutive week, national average temperatures were well above the long-term historical averages. However, the week concluded with a \"deep freeze (that) ... erased memories of mild weather early in the week, as shoppers hit the stores, snapping up any remaining winter-clearance items.\" The weather has a strong correlation to the sales volume on any given week. Stormy weather, even rainy weather, can keep shoppers from venturing out, while unseasonable temperatures can undermine seasonal sales promotions.