Forecaster summary - Issued 2026-05-18T00:15:11

GOES19 >2MeV electron flux was on a rising trend and was predominantly High, peak 6.11e3 pfu at 17/1740 UTC. Electron flux is expected to be largely High through the period, perhaps approaching Very Active through the diurnal maxima.

The associated 24-hour fluence has been on a steady rising trend, becoming Active (1e8 pfu) from 17/1200 UTC, with an observed value of 2.87e8 integrated pfu at 18/0000 UTC. Fluence is expected to continue rising over the next few days as solar wind pressure eases, most likely remaining Active for the remainder of the period. A similar trajectory to REFM is forecast, with a Slight Chance of becoming Very Active. However, confidence decreases through the period due to possible glancing CME effects, which may serve to reduce electron counts at GEO should they arrive between days 1-3 (18-20 May).