Oct 14 (Wed), Oct 17 (Sat), Oct 26 (Mon), Nov 4 (Wed), Nov 13 (Fri), Nov 22 (Sun).
The time it takes for a Coronal Mass Ejection (CME) to reach the Earth depends on several factors, such as the speed of the CME, the density of the solar wind, and the position of the Earth relative to the Sun. On average, a CME can take anywhere from 1 to 5 days to reach the Earth: fast CMEs (speeds > 1000 km/s) 1-2 days, average CMEs (speeds ~500-1000 km/s) 2-3 days, and slow CMEs (speeds < 500 km/s) 3-5 days.
Geomagnetic disturbances (higher Ap) are hypothesized to subtly impair collective mood and raise risk aversion. Traders and investors may then misattribute that gloom to economic prospects rather than space weather, so elevated Ap tends to precede weaker S&P 500 returns and trend reversals by a short lag of a few calendar days.
The Ap Index (used in NOAA's 45- and 27-day forecasts) is the linear counterpart of the quasi-logarithmic Kp Index (used in NOAA's 3-day forecast). Each 3-hour Kp value converts to an equivalent amplitude via a fixed table (Kp 0→0, 1→3, 2→7, 3→15, 4→27, 5→48, 6→80, 7→140, 8→240, 9→400); the daily Ap is the average of those eight 3-hour values. The two indices therefore track the same geomagnetic activity on different scales.
The Ap Index (used in NOAA's 45- and 27-day forecasts) is the linear counterpart of the quasi-logarithmic Kp Index (used in NOAA's 3-day forecast). Each 3-hour Kp value converts to an equivalent amplitude via a fixed table (Kp 0→0, 1→3, 2→7, 3→15, 4→27, 5→48, 6→80, 7→140, 8→240, 9→400); the daily Ap is the average of those eight 3-hour values. The two indices therefore track the same geomagnetic activity on different scales.
NOAA's latest 3-day forecast above shows a peak Kp of 5 (equivalent Ap ≈ 48) on Tuesday, October 13, between 06:00 and 09:00 UTC (2:00–5:00 a.m. ET). Shifting that interval forward by three calendar days points to Friday, October 16; a four-day shift points to Saturday. This suggests another S&P 500 low may arrive by the end of the trading week.
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