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: Westport Innovations (NASDAQ:WPRT) stock shot up almost 13% today, more than making up for yesterday's 9% drop. However, the stock is still way, way down for the year:

WPRT Chart

WPRT data by YCharts

So what: As we discussed in yesterday's note, Westport has really struggled to establish its business -- selling injection technology for natural gas engines -- with a lot of weakness in its primary markets of Europe, Russia, and China. Furthermore, falling oil prices have reduced the cost benefit of natural gas versus gasoline or diesel, which has driven fears that this will further hurt the company's efforts to establish a strong business in the U.S. heavy-duty trucking segment. 

Today's rebound looks like nothing more than a short-term reaction to the substantial sell-off the stock has gone under in the past few months. It could drop again tomorrow, or go higher. At this point, it's just a lot of speculation, and that's likely to remain the case until Westport next reports earnings in 2015. 

Now what: There's nothing really material to report. With it being the end of the year, there could still be some selling for tax purposes, as well as some buyers looking to pick shares up on the cheap. Either way, we don't really know anything new about the company, or its prospects. 

Whatever you decide to do with Westport's stock, remember that the business faces some pretty serious challenges going forward, and probably isn't a good "go big" investment right now. There's potential, but the business faces a lot of serious risks.