Forecaster summary - Issued 2021-09-24T00:18:21

The high energy electron forecast (greater than 2MeV) is highly uncertain, but overall is expected to show an increasing trend over the coming four days, with an increasing risk of Active integrated fluence being reached by day 3 (26th). However, confidence is low regarding the forecast, as more prolonged spells of enhanced geomagnetic activity could offset the general increase in high energy electrons that are expected to arrive under the influence of the two HSS. Persistence methods of forecasting are likely to be of very limited use in the period, as during the previous rotation CH03 was not present, CH05 was smaller and a CME arrived to contaminate the geomagnetic signature of the rotation. Therefore the Met Office REFM model is not expected to offer useful guidance.