Tomorrow's October CPI report could jolt markets in a big way if expectations are not met. Here's what to expect, according to JPMorgan

• The October consumer price index report could spark big moves in the stock market on Thursday, according to JPMorgan.
• The bank ran a scenario analysis and said a big miss or beat could move the S&P 500 up or down as much as 6%.
• Economists expect the CPI report to show a year-over-year increase of 7.9%, a decline from September's 8.2% reading.

Following the midterm elections, investors have shifted their focus to Thursday's October consumer price index report, and it could jolt markets in a big way depending on the data, according to JPMorgan.

The bank's trading desk ran a scenario analysis of where it expects the S&P 500 to trade depending on the CPI report. Economists surveyed by Bloomberg expect it to show a year-over-year headline inflation increase of 7.9%, which would be a decline from September's 8.2% reading.

JPMorgan also sees a 7.9% reading as the most likely scenario, ascribing a 40% probability for the outcome, and that would be good news for investors as the bank expects the S&P 500 to rise as much as 1.5%.

"I think bonds, and thus stocks, take this as a small positive since it meets expectations and does not reprice yields higher," JPMorgan's Ellen Wang and Andrew Tyler wrote. Any improvement in inflation from last month would give investors some confidence that the Fed may be closer to a slowdown in its rate-hike cycle.

But things would get dicey quick if October's CPI report comes in above expectations, with the bank expecting a 30% chance that headline CPI prints 8.1% to 8.3%. The S&P 500 could fall between 2% and 3% if that scenario plays out tomorrow.

The least likely scenario happening, according to JPMorgan, is a huge beat or miss in the October CPI report. At a 5% chance of happening on each side of the spectrum, the bank expects the S&P 500 to soar or crash as much as 6% if October's CPI print is below 7.6% or above 8.4%, respectively.

"Seeing a stepdown in inflation of this magnitude likely pulls the 10-Year yield below 4% (currently 4.158%) and triggers a sharp rally in stocks. This may also reset the yield curve lower with terminal rate expectations falling under 5%," JPMorgan said about its most-bullish scenario.

One Wall Street analyst anticipating a below-consensus CPI reading is Fundstrat's Tom Lee, who wrote in a Monday note that medical insurance and falling car prices could put downward pressure on the inflation print.

The October report "could be as much [as] a 'game changer' as 'hot' August CPI derailed S&P 500," he said.

Whatever happens, investors should expect another bout of volatility heading into the end of the week in anticipation of tomorrow's CPI report.