The stock market indices started lower this morning, rallied from late morning to late afternoon and reached new rally highs. But in the last hour they rolled over very hard, completely reversing today’s gains, and ending up at the lows for the day with substantial losses and a rough start to the week.

Is today a reversal day? We’ll see if there is downside follow-through tomorrow, but the areas to be keeping close tabs on are 2000 on the Nasdaq 100 and around the 1138-40 zone on the S&P 500.

Net of the day, the Dow was down 48.22 at 10,812.04, after being at 10,873 earlier. The S&P 500 dropped back from nearly 1150 to 1142.16, down 6.51. The Nasdaq 100 lost 16 points off its high, closing down 12.85 at 2010.99.

Advance-declines were 3 to 2 negative on the New York Stock Exchange, and 3 to 2 negative on Nasdaq. Up/down volume was 5 to 3 negative on New York on total volume of just over 900 million. Nasdaq had about a 5 to 4 negative plurality, and traded a total of 1.845 billion shares traded today.

TheTechTrader.com board was mixed, with quite a few point-plus gainers today. They included Seattle Genetics Inc. (SGEN) up 2.14 to 14.30, Transocean Ltd. (RIG) up 2.30 to 62.36, LogMeIn Inc. (LOGM) 1.15 to 37.37, Green Mountain Coffee Roasters Inc. (GMCR) 1.33 to 37.55, and Acme Packet, Inc. (APKT) 1.05 to 39.39, an all-time new high.

On the downside, Isilon Systems, Inc. (ISLN) dropped back 2.36 to 22.10. Radware Ltd. (RDWR) fell 1.20 to 33.50, Goldman Sachs (GS)1.28 to 146.00, Amazon.com Inc. (AMZN) 1.36 to 159.37, and Apple Inc. (AAPL) 1.16 to 291.16.

So, market leaders reversed early gains in a negative reversal day today, closing to the downside. Perhaps an ominous sign for the indices, but we’ll see how it goes.

Stepping back and reviewing the hourly chart patterns, the indices had a 3-wave move lower today that slightly took out support. They rallied back in what looked like bear flags, but when they failed to move to the downside and broke out to the upside, short covering fueled an advance that tagged new highs at 2026.42 on the NDX and 1149.92 on the S&P 500. But that was short-lived as the last half hour resulted in a sharp setback that closed near the session lows.

Harry Boxer is a technical consultant to many Wall Street hedge funds and large institutional traders, and author of TheTechTrader.com.