Technical Update - Sell-off yesterday in US Equities indicates an ugly autumn. S&P 500 and Nasdaq could drop 15-20% from current levels

But that might not be the exhaustion of the down trend. If the RSI on the weekly chart closes below its lower rising trendline and below 40, it supports the bearish picture. A bearish picture that would strongly indicate S&P 500 could drop to around 3,200 going in to Q4 i.e., the lower range of the consolidation area from Q4 2020 and the 0.618 Fibonacci retracement of the 2020-2022 bull market.
It is also the 1.618 projection of the Q3 correction.
Expect a correction around the 3,636-3,509 area before next push lower. A possible scenario is illustrated by arrows on the chart. 
To reverse this bearish picture S&P 500 needs to close above 4,325.

Nasdaq 100 sell-off closed yesterday a few cents below the 0.618 retracement and support at around 12,046.  A move below last weeks low at 11,928 is likely to fuel the selling pressure and push Nasdaq 100 to test June lows at 11,037.
RSI closed yesterday below 40 supporting the bearish view.

‘On the weekly chart RSI is currently below its lower rising trendline. If closing the week below and below the 40 threshold it will support the bearish picture unfolding. A bearish picture that can take Nasdaq 100 to test the key support at 10,768, close to the 0.618 retracement level at 10,589. However, the bearish trend could take Nasdaq much lower. A close below 10,589 could further fuel a sell-off down around 9K.

To reverse this bearish outlook a close above 13,721 is needed. 9,378 is 1,618 projection of the Q3 correction and close to the 0.764 retracement of the 2020-2022 bull market.