Forecaster summary - Issued 2025-06-17T00:11:25

The high energy (> 2MeV) electron flux observed at GEO by GOES19 has been at mostly moderate levels. However, with the arrival of the HSS from CH57/+, a large southern hemisphere coronal hole, and the limited geomagnetic activity, the Van Allen Belts are most likely charging.

The strength of the connection to this large source region remains uncertain, and the possibility of a glancing blow from a coronal mass ejection (CME) adds further complexity to the forecast. If such an interaction occurs, it could temporarily enhance solar wind speed and pressure, compressing the magnetosphere and pushing electron populations to lower altitudes. This would likely suppress the observed electron flux at geostationary orbit (GEO) for a short time. However, as solar wind conditions relax, the flux would likely increase again later in the period. Confidence in this scenario is low but with speeds expected to remain slightly elevated and perhaps become elevated over the next 24 hours, the electron flux should continue to increase and eventually reach high levels, at least during the diurnal maximum.

The associated electron fluence is currently well below the Active threshold and also below the REFM forecast so any diurnal high flux levels should have limited impact. However, fluence should be on a slight rising trend over the following days, the probabilities more reflecting a lack of confidence rather than a chance of exceeding the Active threshold, due to the reasons mentioned above.