As of Friday, the S&P 500 was within 1% of its upper Bollinger band at virtually every horizon, including daily, weekly and monthly bands. The last time the S&P 500 reached a similar extreme was Friday April 29, 2011, when I titled the following Monday's comment Extreme Conditions and Typical Outcomes . I observed when the market has previously been overbought to this extent, coupled with more general features of an "overvalued, overbought, overbullish, rising yields syndrome", the average outcome has been particularly hostile:
"Examining this set of instances, it's clear that overvalued, overbought, overbullish, rising-yields syndromes as extreme as we observe today are even more important for their extended implications than they are for market prospects over say, 3-6 months. Though there is a tendency toward abrupt market plunges, the initial market losses in 1972 and 2007 were recovered over a period of several months before second signal emerged, followed by a major market decline. Despite the variability in short-term outcomes, and even the tendency for the market to advance by several percent after the syndrome emerges, the overall implications are clearly negative on the basis of average return/risk outcomes."
As it happened, April 29, 2011 turned out to mark the exact high of the S&P 500 for the year, and was followed by a steep intermediate market plunge. My impression is that despite the recent run of speculation the market has enjoyed - largely reflecting a reprieve in European debt concerns and what appears to be a drawing-forward of jobs into the first quarter due to unseasonably favorable weather - the extended implications of present market conditions remain decidedly negative.
If you examine the components of the S&P 500 individually, you'll quickly find that the majority of those stocks are also at or through their own upper Bollinger bands. In overvalued, overbought, overbullish, rising-yield conditions, those extensions are often resolved in unison, which is what produces the characteristic "air pocket" where the index can give up weeks or sometimes months of upside progress in a handful of sessions (though we often see a knee-jerk reaction to buy that initial dip before more serious follow-through occurs).