Forecaster summary - Issued 2021-05-17T00:24:46

High energy electron flux (greater than 2MeV) as measured by GOES-16 at GEO is currently at background and expected to persist at this level day 1 (17th), before erratic enhancements occur as a result of the arrival of any fast wind and potential CME effects later day 1 or early day 2. Although any geomagnetic activity and fast wind arrivals could bring periods of observed flux dropping out, due to Van Allen belt compression. A more notable enhancement is then likely on day 3 (19th) or into day 4 (20th), however, as a result of the arrival of the fast wind of CH59. High flux is likely by the end of the period. 

The associated fluence is also expected to rise in response, but likely remaining below the Active threshold until at least day 4 (20th), although there is a slight chance of rising above before this. This increasing trend is indicated by REFM, however persistence is currently giving poor guidance beyond T+24, so forecast values beyond this period should only be used cautiously.