Even on the market's worst days, buyout news and other short-term forces can send individual stocks up by 10%, 25%, even 50%.

For example, shares of Downey Financial rose 33% last Friday as investors anticipated more moves to better capitalize the savings and loan company -- only to see shares retreat back to earlier levels when details were announced after the market close.

But beyond less-predictable events like that one are stocks with fundamentally compelling reasons for recent momentum. The trick is to find those stocks. That's where Motley Fool CAPS comes in.

The story behind the story
CAPS is no crowd of lemmings. Its best-performing members' opinions do more to shape each company's rating than the picks of their poorer-performing peers. Let's use the collective wisdom of more than 115,000 CAPS members to filter out the noise and find companies offering strong momentum.

We'll use CAPS' handy stock screening tool to quickly zero in on companies with a stock price increase of at least 30% in the past four weeks, a market cap of greater than $100 million, and a beta of less than 3.

Here's a sample of stocks our CAPS screen returned:

Company

CAPS Rating
(out of 5)

4-Week
Price Change

Rubicon Minerals (AMEX:RBY)

*****

44.1%

Icad

*****

38.1%

Alon USA Energy (NYSE:ALJ)

*****

55%

Terra Nitrogen (NYSE:TNH)

****

36.9%

Source: Motley Fool CAPS. Price return from Aug. 8 through Sept. 5.

With our list of screened stocks pulled up in CAPS, it then only takes a single click on individual companies to get some context behind the recent momentum.

The mother lode
Shares of Rubicon have been on the rise since it recently announced it had struck bonanza-grade gold from its Phoenix Gold Project in Red Lake, Ontario, a region that yielded 700,000 ounces of gold for Goldcorp (NYSE:GG) in 2007. Rubicon’s Phoenix resource is still being defined, but a couple of early drills have turned up outstanding results. These results show gold densities far above those from premier mines from other major plays, such as Barrick Gold's Goldstrike Mine in Nevada and Newmont Mining (NYSE:NEM) and Buenaventura's expected yield from their joint-venture mine in Peru.

Rubicon is the second-largest landowner in the Red Lake area, which U.S. Gold's CEO Rob McEwen calls the “world’s richest gold district.” Goldcorp’s recent $1.5 billion takeover bid for Rubicon peer Gold Eagle Mines has also highlighted the area’s potential, and has increased investors’ enthusiasm for Rubicon's takeover potential. Giving investors one more reason to love Canadian stocks, the rich find has nearly 99% of the 361 CAPS members rating Rubicon expecting the company to outperform the market.

Sowing seeds of strength
Once a sleepy fertilizer-products maker that few investors knew about, Terra Nitrogen is quickly becoming a household name as growing alternative-fuel demand and soaring commodities prices have brought more attention to the company. And with Terra’s shares returning 5,400% in the last five years, some investors wonder if it can go any higher.

Terra Nitrogen has come down from recent highs over the past few months (along with many other fertilizer companies, like Potash (NYSE:POT) and Mosaic (NYSE:MOS)). Still, the stock has soared higher in the past month, with factors like wealth in emerging markets and raw-materials shortages keeping prices for fertilizer and key components strong. Higher selling prices for nitrogen and increased ammonia sales volumes pushed Terra’s net income for the second quarter to $130.2 million, more than double the $57.1 million reported a year ago.

With zero long-term debt and shares currently yielding around 11%, many investors have latched on to Terra to keep their portfolios afloat in rough market waters. The prospect of continued demand for raw-fertilizer materials has more than 95% of the 1,023 CAPS members rating Terra Nitrogen expecting the company to outperform the market.

And you?
What's your story? Whether you buy the tale of a stock that's soaring or souring, your own research is more important than collective opinions. But these collective opinions can make your due diligence a whole lot easier.

Add your take on these, or any of the 5,500 stocks that our 115,000-plus members have covered, in Motley Fool CAPS. It's totally free to be a part of the community, and the payback is more than worth it.

The Motley Fool Hidden Gems service looks for little-known small caps poised to be tomorrow's great companies. Check out what other gems lead analysts Tom Gardner and Bill Mann are recommending today with a free 30-day trial of the service.

Fool contributor Dave Mock has his own story, but there's no "happily ever after" at the end of it. He owns no shares of companies mentioned here and is the author of The Qualcomm Equation. The Fool's disclosure policy has the momentum of a freight train, but can stop on a dime.