I finally got the call I was expecting from my dad this weekend. After all, the S&P 500 index has risen nearly 7.2% over the past month, and I hadn't called to signal a thumbs-up to increase his equity positions.

But it wasn't that I had forgotten to call, or didn't find the time. As I explained to him, despite the positive momentum the market is experiencing right now, the fundamentals just aren't there to back up this energy.

But the market's going up ... and I'm missing out on gains
My dad uttered these exact words to me, and I'm sure many of you have similar thoughts. It's a typical situation: The market starts recovering and embarks on an upswing. Everyone thinks it's time to get in. Sure, sometimes this is true -- but investors need to be wary at a time like this.

Of course, when all the pieces are moving in the right direction -- GDP is robust, the dollar is strengthening, cash is pouring into major companies, and earnings are coming in better than expected -- the market has reason to rise in value. But not all of those economic factors favor the market right now. Ultimately, supply and demand for a company's stock determine where its price will end up.

If enormous demand gushes into the market, driving prices up without any data to support those appreciating prices, investors' returns won't be permanent. I believe that's exactly the force behind the extraordinary gains we've experienced over the last 30 days -- which is why October could be a scary month for investors.

Numbers don't lie
You don't have to look far for data to back up my argument. As the retail and consumer-goods editor here at the Fool, I see all of the numbers coming in day after day, suggesting that companies most likely won't perform well in the near term. The "softness" in the economy has been an excuse across the board for lower sales and earnings guidance. We are long-term investors, so I'm not advising you to time the market and sell. I'm merely offering a warning that it's certainly not the time to be buying.

Just look at Target (NYSE:TGT). It recently reduced its earnings guidance from 4% to 6% to its current range of 1.5% to 2.5%. Correct me if I'm wrong, but did that news really warrant a jump of more than 10% in its stock price since the beginning of August? And congrats to Wal-Mart (NYSE:WMT) investors, who have profited 7% over the past month, despite the company's reduction of its yearly earnings guidance not too long ago.

Sure, there are companies still growing out there, posting respectable sales and profit growth, but I find it hard to justify McDonald's (NYSE:MCD) 14% return and Chipotle Mexican Grill's (NYSE:CMG) 21.5% return in September, no matter how many Big Macs or burritos they've sold. Even the companies that remain solid investments have become too expensive.

Consumer spending makes up 70% of GDP, and at the end of September, consumer confidence was at its lowest level in two years. Shoppers are pressured by rising gas and food prices, $50 billion worth of ARMs will be adjusting this month alone, and credit is a bit harder to come by these days. During September, I read headlines stating the upcoming holiday season could be the worst we've seen in five years. Yet during that same time, Mattel (NYSE:MAT) shot up by more than 9% -- even after numerous toy recalls concerning tainted goods from China.

Talk about artificial
Speaking of unjustifiable returns, D.R. Horton (NYSE:DHI) and Toll Brothers (NYSE:TOL) are up 14% and 11%, respectively, over the past week. Residential sales in August were down more than 21% from last year. And The Wall Street Journal recently reported that D.R. Horton was auctioning off homes in San Diego at a 50% discount. Unless I missed a major recovery story on either of these companies -- and the entire housing industry -- it's hard to believe these homebuilders will retain this latest surge in price, since the outlook on the industry remains very hazy.

Wait for the sale
The moral of this story: The growth priced into the market right now isn't realistic. In many cases, current economic conditions don't support the values the market's putting on company stocks. As the market continues its temporary climb, investors will succumb to greed and try to get in on the gains. Yet sooner or later, something will throw this upswing into reverse. While I can't tell you which economic indicator will wake the bears from hibernation, I can warn you that now's the wrong time to buy.

It's hard to resist missing out on the returns you think you could be earning. But keep in mind that the 7.2% S&P return was only lucrative if you bought and sold in that 30-day time frame last month. If you're patient, these stocks will go on sale -- and over time, your long-term gains will be enhanced by buying your stocks at a low, more reasonable price.

Investors will eventually get past their initial jubilance from the lower Fed rate cuts. They'll realize that inflation is a problem, the housing market is miles away from being solved, and consumer confidence is dropping. There are still some great value stocks out there, but for the most part, I think the recent gains we've seen won't last. My dad has decided to sit this bull run out. If you're in this game for the long haul, you will, too.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.