It's not the start to December investors wanted for the Dow Jones Industrial Average (DJINDICES:^DJI). After opening higher, the index dove and has stayed mired in the red ever since. As of 2:20 p.m. EST, the Dow is down 38 points, or 0.3%. About two-thirds of the index's stocks have fallen on an overall gloomy day for the markets and the economy.

Factory data down
The Institute of Supply Management released its monthly purchasing managers index (PMI) today, and the results weren't good. While October's data had shown increasing manufacturing output across the United States, November's PMI sank sharply, down below the 50% breakeven level of expansion and into contraction territory with a reading of 49.5%. With the uncertainty surrounding the looming fiscal cliff -- predicted to hammer businesses with its tax increases and spending cuts -- the poor PMI result showed just how cautious companies are with uncertainty over the future.

Predictably, the result didn't do any good for the Dow's industrial companies. Manufacturing leader Caterpillar (NYSE:CAT) and aerospace manufacturer Boeing (NYSE:BA) have each seen shares fall today, down 0.5% and 0.3%, respectively. Caterpillar in particular hasn't had the best 2012: Its stock has fallen nearly 10% for the year and is far off highs set in February and March. Falling off the fiscal cliff would likely send this stock into a tailspin.

Chemical maker DuPont (NYSE:DD), which won't have an easy time with the fiscal cliff itself, leads all Dow laggards lower, with shares down 1.4% so far. While the stock's 11% dive the last three months poses an inviting opportunity to buy on a dip, the uncertainty ahead could keep this company from realizing any bounce until a clearer picture of the economy's future is established.

Few bright spots today
Energy giants ExxonMobil (NYSE:XOM) and Chevron (NYSE:CVX) are adding to the losing trend today, with shares down 0.6% and 1%, respectively. Crude oil hit a two-week high earlier in the day on a weak dollar, contributing to an overall good day for commodities. Exxon and Chevron don't have it easy, though: Should the fiscal cliff hit, tightening budgets will force consumers and businesses to be more cautious with their energy demands.

There are few risers of note today, with only Cisco (NASDAQ:CSCO) seeing shares rise significantly. The company spent nearly $1.5 billion in acquiring cloud-computing companies last month over three separate acquisitions -- a sign that Cisco understands the needs it'll have to fulfill in the future. The stock is up 0.85% today.

Dan Carroll has no positions in the stocks mentioned above. The Motley Fool owns shares of ExxonMobil. Motley Fool newsletter services recommend Chevron. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.