Forecaster summary - Issued 2024-04-24T00:11:35

High energy electron flux as observed by GOES16 rose to persistent Moderate levels during 22 Apr, likely as a result of the recent CME arrival and HSS onset that had been observed on previous days. As solar winds likely continue to slowly ease, any charging that has occurred at lower L-shells is expected to become increasingly relevant at GEO, with the observed flux increasingly likely peaking at High levels during diurnal maxima into days 1 and 2 (24-25 Apr). This is only moderate confidence however, as the arrival of any CMEs and associated geomagnetic activity may help to modulate the observed flux, and any more notable arrivals have the potential to drop values back towards Background. Expected HSS influence by days 3 and 4 (26-27 Apr) will also likely bring a similar reduction in flux values back towards Background to Moderate levels.

The associated 24 hour electron fluence is thus expected to continue on a generally upward trend in the near term, as indicated by Met Office REFM output, which looks to be providing reasonable guidance in the absence of any CME arrivals, but likely under-estimating peak values. This will give a increasing chance of reaching the Active threshold by day 2 (25 Apr), although this potential will reduce should any dropout from any CME arrival occur and remains only moderate confidence, and reduces by the end of the period given potential HSS influence.