Portfolio managers returning from their summer holidays have apparently liked what they’ve heard from the central banks. Although total volume remains modest, U.S. stock indexes have hit new highs. The S&P 500 finally busted out of its 3-month-long bullish rising channel.

Despite last Friday’s disappointing jobs report, stocks are staying strong. The S&P 500 hit yet another new high on Wednesday—its highest level since January 2008, while the Nasdaq is at a level not seen since toppling from its “irrational exuberance” days of late-2000 as the Internet bubble was bursting. The ECB seems to be getting a workable plan together to support the eurozone banking system and sovereign debt.

Volume remains low as the bulls continue to await Wall Street’s return from late summer vacations...and a firm plan from the central banks. (I think many portfolio managers must be spending their days in the stands at the U.S. Open tennis tournament.) The S&P 500 closed out August with a third straight monthly gain.

As we head into the homestretch of summer and the Labor Day holiday weekend, investors are anxious to see if next week brings elevated volume and the reinforcements to help the bulls break out. However, there’s no doubt that the bears are lurking in the wings to drive stocks down hard, given the right scenario.

Volume has elevated somewhat this week, as Wednesday saw more trading volume than we have seen since the beginning of the month—likely due to the release of the FOMC minutes (both in anticipation and aftermath). In any case, equity holders have been loath to sell. Mild intraday weakness continues to be met with buying.

We’re coming down to the final sleepy weeks of a relatively uneventful summer in the equity markets. Volume is quite low, as is expected this time of year with investment managers in vacation mode. Nevertheless, the S&P 500 has now recovered all of its losses since the “Sell-in-May” crowd hit the market hard, sending the S&P 500 falling 9% from a close of 1406 on May 1 to 1278 on June 1.

U.S. equities continue to shrug off worrisome global economics and the doomsday prognostications. The Dow, S&P 500, and Nasdaq are now all above psychological resistance levels of 13,000, 1400, and 3,000, respectively. Even Europe and China have seen a sustained bounce in equities. But everyone is wondering, how long can this continue given the dicey global economic situation?

Bulls have refused to let the market break down. Last week, the ECB’s Mario Draghi came to the rescue by pledging to do “whatever it takes” to support the euro, which launched a big rally to close the week. Still, investors have been eagerly anticipating an announcement of something more concrete, like some bold new action from the central banks, i.e., more global liquidity.

Markets attempted to rebound on Wednesday after two days of fear and loathing, but extreme weakness in Apple (AAPL) held back the Nasdaq and S&P 500 while the Dow was able to finish positive. Whether this is just a dead cat bounce remains to be seen. Without a doubt, this week has changed the technical picture from bullish to iffy.

Markets have been signaling a willingness to look past the deluge of troubling news and move higher. This is bullish behavior. On Tuesday, market psychology displayed its positivity as initial weakness on bad news was quickly reversed. Rather than demanding that the Fed initiate a QE3, investors seem to be happier with indications from the Fed that the economy might be able to muddle along without it.