After opening the day at about the same level as Friday's close, the three major U.S. stock indices fell by over 2 percent Monday (DJIA, -2.08%; S&P 500, -2.28%; NASDAQ, -2.61%).

About half of the rout took place in the first 30 minutes after the 10:00 a.m. release of two reports, one on manufacturing activity and the other on construction spending. The former, from the Institute for Supply Management, showed that its January Manufacturing Index came in at a mildly expansive 51.3% (any reading over 50% indicates expansion), down by over 5 percentage points from December and missing expectations by 4.7 points. The latter, from the Census Bureau, showed that seasonally adjusted construction activity barely budged in December. The market's decline continued throughout the rest of the day as disappointing news on January car sales rolled in. As will be seen after the jump, inclement January weather got a disproportionate share of the blame in the business press for these really weak results — an explanation which clearly didn't impress the markets.