The S&P 500 just sent a warning signal to investors

Markets are facing an early summer swoon, and it's not even the July 4 weekend.

The insight: Amid a week of heightened volatility, especially for tech stocks, the S&P 500 (^GSPC) closed below its 50-day moving average for the first time in more than two months on Friday, according to Yahoo Finance AlphaSpace analysis. The index appears set to start the week under this level based on premarket trading action on Monday.

The 50-day moving average is one of the most widely watched technical indicators on Wall Street, calculated simply by averaging a stock or market's closing price over the past 50 trading days and plotting it as a continuously updated line on a chart. It gives investors a real-time snapshot of a stock or market's medium-term price trend.

Read more: How to protect your money during turmoil, stock market volatility

When a stock or market is trading above the 50-day moving average, it is generally considered to be in a healthy uptrend, signaling that buying momentum is stronger than selling pressure. A stock or market trading below that line is often viewed as technically weak and vulnerable to further downside.

The reason: The stock market has experienced heightened

Fuente original: Yahoo Finance (https://finance.yahoo.com/markets/article/the-sp-500-just-sent-a-warning-signal-to-investors-121007971.html)