Forecaster summary - Issued 2026-04-17T00:21:09

High energy (>2 MeV) electron flux at GOES19 reached high levels at the diurnal maximum in the last 24 hours. Flux is likely to remain moderate to diurnally high until the fast wind from CH42/- arrives either late Day 1 or early Day 2 (17-18 Apr) with the anticipated strong wind speeds and increase in geomagnetic activity expected to cause a flux dropout. The fast wind is then likely to cause further charging of the outer radiation belt, but the solar wind pressure is expected to keep the belt compressed below GEO into Day 3 (19 Apr). Through Day 4 (20 Apr) a significant rebound of electron flux is expected to occur.

The associated 24 hour fluence is now below the Active (1e8 integrated pfu) threshold and is currently at a lower level compared to 24 hours ago. MOSWOC REFM is currently underestimating the observed fluence and is likely to continue to do so in the coming days. The strong downward trend in recurrence values on Day 1 (17 Apr) was tied to CME activity for the equivalent period in March and is not a good guide for the timing of any decrease in the upcoming period. However, the upward forecast trend at the end of the forecast period is accepted as good guidance, but with the stronger upward trend as indicated by recurrence preferred. 

Fluence is expected to initially remain below the Active (1e8 integrated pfu) but with an increasing chance of exceeding the threshold through Days 3 and 4 as geomagnetic activity wanes.