Market Weather

How to read the weather

Each scene is one trading day for the 500 most-traded US stocks, every session since 2004. The sky comes from one number: of the stocks that moved, the share that rose.

• Sunny. More than 70% rose: a broad advance.

• Fair. 58% to 70% rose.

• Foggy. 42% to 58% rose: a split day, with neither side in charge.

• Showers. 30% to 42% rose.

• Stormy. Under 30% rose: a broad sell-off.

• Windy. Stocks moved in lockstep: their average correlation over the past month ran well above its level for the past year. Wind clears fog, so a split day with wind is simply windy.

• Rainbow. A breadth thrust: a rare surge of broad buying over ten sessions (Zweig, breakaway or 50-day thrust).

• Sun shower. New 52-week highs and new lows both widened at once: a split tape.

The flag on the tallest tower hangs limp on a calm day and streams out in the wind. The ticker band runs the day’s numbers.

It describes the day that closed. It is not a forecast.

Every session of 2012. Pick a day to see its weather.

• Sunny63
• Fair34
• Foggy59
• Showers37
• Stormy57
• Windy days0

The stormiest and sunniest days since 2004