Forecaster summary - Issued 2026-04-18T00:18:44

High energy (>2 MeV) electron flux at GOES19 reached high levels at the diurnal maximum in the last 24 hours, but is currently at moderate levels. With the onset of a HSS through Day 1 the electron flux is expected to decrease to become background to moderate. The fast wind is then likely to cause further charging of the outer radiation belt, but the solar wind pressure is expected to keep the belt compressed below GEO into Day 2 (19 Apr). Through Day 3 (20 Apr) a significant rebound of electron flux is expected to occur.

The associated 24 hour fluence is currently close to the Active (1e8 integrated pfu) threshold. MOSWOC REFM is currently underestimating the observed fluence and is likely to continue to do so in the coming days. The REFM forecast trend, with an increase early through Day 1 is not accepted, as a decrease trend is preferred. The forecast upward trend at the end of the period is reasonable guidance, although a stronger upward trend is preferred, inline with recurrence.

Fluence is expected to initially fall below the Active (1e8 integrated pfu) but with an increasing chance of exceeding the threshold through Days 3 and 4 as geomagnetic activity wanes.