SAN FRANCISCO -- In this era where a stock like Citigroup (C) is swapped among traders with the same forethought given to any random Bulletin Board issue, momentum can be a strange thing.

Stocks, those of the nonfinancial variety, took quite a ride on Monday, ending a four-day rally that, with each successive close higher, had given hope to the notion that market lows touched on March 6 would stand throughout 2009.

As investors have died by the financial-stock sword, so too have they been living by it, before Monday: The Financial Select Sector SPDR ( XLF) exchange-traded fund, which you may remember from its drop of about 70% from last September to just more than a week ago, closed 16 cents lower to close at $8.03.

Individual financial stocks were similarly volatile: Citigroup was up 26% to $2.24, JPMorgan Chase ( JPM) fell 3.2% to $22.98 and Bank of America ( BAC) was up 5.4% to $6.07.

Monday's tumult comes after a week that saw the XLF run up nearly one-third, combining with regional-bank and homebuilder-stock ETFs as the only sectors that outperformed the iShares Russell 2000 ( IWM) ETF last week.

Several factors have contributed to bucking up financials, and with them, the overall market, not the least of which is was an extremely oversold condition. It has been widely accepted for a week or two that a bounceback rally was coming, whether your version was a "dead cat bounce" to set up another move down or something of the more sustained variety.

But one must also bow to the lift in sentiment, if not fundamental change, provided from last week's comments by the major banks related to the cryptic "profit from operations" for January and February, as well as the possible revisiting of mark-to-market accounting and the uptick rule -- all of which led to the perception that a bottom in financial stocks could be at hand.

This has done nothing to help investors on the short side of financials, who have been in the unfamiliar position of considering whether to close out positions.

At this point, however, it seems that financial stocks were moving higher for most of Monday because they moved higher on Friday, and the day before, and the day before.

With the S&P 500 Index now about 13% above its intraday low on March 6, the question for investors is how much faith they should put in the upside continuing.

For some investors, that's an easy choice. Atlantic Advisors ' Bennett Sedaca announced on Friday that his firm was taking profits after last week's jump. "The macro-economic view is just too negative for me," he said. "It never, ever hurts to take a profit. We are back to 0% equities."

Sedaca, however, is on the bearish extreme of market-watchers, expecting an eventual low of 350-400 on the S&P 500, which he expects as late as October 2010.

For others who lean toward Federal Reserve Chairman Ben Bernanke's take of a recovery in 2010, it's harder to walk away from the market's current momentum windfall.

Despite Monday's slightly down day, the short-term bias for stocks is higher. And as the news flow begins to subside -- 98% of the S&P 500 has reported earnings -- there seems to be little on the horizon to significantly jar a continued near-term climb, save for the March jobs report April 3.

As with the snowball effect on the way down, a similar effect could be seen over the next several weeks. As beaten-down stocks begin to approach and pass technical indicators like 50-day moving averages, calls for a near-term S&P 500 high of 900 could seem increasingly reachable.

On the other hand, Monday's momentum suggested signs of weakening. Overall trading volume was down, and recent evidence of improving breadth in the market was not present. Down volume was 6-to-1 on the New York Stock Exchange, while new lows out-recorded by 9-to-1. In addition, the market's late-day fade doesn't bode well for continued strength at Tuesday's opening bell.

Eventually, the fundamental economic argument about when a recovery happens -- and how strong it might be -- comes back into play, and this is where pundits who expect we have not yet seen 2009 lows are placing their bets.

But on a day when Citigroup trades more than 1.4 billion shares, fundamentals are for another time.

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