Forecaster summary - Issued 2018-05-17T00:30:25

The high energy electron flux (greater than 2MeV) at GEO has been at high levels (over 1000pfu) since 14/0625 UTC, in the wake of the high speed stream from coronal hole 93, which has held the corresponding 24-hour fluence well above the Active threshold for longer than anticipated.

A temporary reduction in the electron flux to background levels is likely on day 1 (17 May) due to enhanced geomagnetic activity from the arrival of the high speed stream. Flux levels are then expected to rise again from later day 2 (18 May) once the high speed stream becomes fully established, likely reaching high levels again by day 3 (19 May). 

The corresponding 24-hour electron fluence is expected to remain well above the Active threshold (1e8 integrated pfu) at first on day 1 before falling later in the day and during day 2 in response to the reduced flux, with this likely to fall below the Active threshold for a time. Fluence levels are then expected to rise again during day 3 as flux levels recover, with an increased risk of reaching the Active threshold again. 

The REFM forecast has current and past fluence levels much too low, though above the Active threshold. The forecast for the coming days is broadly correct for day 1 and 2, with a drop in fluence levels anticipated. Thereafter, the expected increase in electron fluence is not well captured.