Forecaster summary - Issued 2025-06-04T00:25:02

The >2MeV electron flux observed at GEO by GOES-19 has been suppressed over the last three days by the recent CME arrivals, resulting in mainly Background to Moderate flux and only occasional High flux being observed. However the extended period of above elevated, peaking at exceptional, solar winds, alongside the strong geomagnetic response has likely both compressed and charged the outer Van Allen Belt at lower orbits. As solar winds ease, this enhanced flux is expected to expand outward, increasing the flux at GEO through day 1 (04 Jun), likely becoming more persistently High, and then continuing day 2 (05 Jun). 

Confidence is reduced however, with the potential for further CME influences. The first of these, on day 1 (04 Jun) is very low confidence, as this may have already arrived, and the second is likely to only give a glancing impact on day 3 (06 Jun). Any such arrival is likely to result in the observed flux falling to background.

The associated 24 hour fluence is expected to rise alongside the increased flux, likely becoming Active (greater than 1e8 pfu) later day 1 and day 2 (04-05 Jun). Confidence for this to continue then fades later in the period. This rising trend is suggested by REFM, however this is currently underestimating the forecast during the T+24 period.