Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Bon-Ton Stores (NASDAQ:BONT) were fraying at the seams today, falling as low as 18% and finishing down 13% after lowering its guidance for the year.

So what: The department-store chain said that its December same-store sales were significantly affected by severe weather in several of its markets, and revised its full-year same-store sales forecast downward to 3.5% and earnings per share down to a range of a $0.30 loss to a $0.15 gain. CEO Brendan Hoffman commented, "We are disappointed with the deceleration in sales during December, particularly given the strong start to the holiday season beginning with Black Friday and extending through the early part of the month." He added that poor weather caused a sharp reduction in traffic on key weekend and pre-Christmas selling dates.

Now what: Bon-Ton's downward guidance echoes myriad other retailers who have reported disappointing holiday seasons this year. The excuses vary, including poor weather, a shortened selling season, and a heavy promotional environment, but the results are almost all the same -- drastically lower sales than the businesses had hoped for. Analysts had been expecting a per-share profit of $0.78 for the year, as the fourth quarter is a key one, so this miss is big. The bigger question for Bon-Ton shareholders may be: Why be invested in a company that seems to plan on losing money three out of four quarters of the year only to make it all back during the holidays? A same-store sales decline of 3.5% is yet another red flag.