Solar activity was moderate. The largest flare of the period was an optically uncorrelated M1 at 17/2157 UTC. EIT imagery suggests the source of this flare to be returning Region 9393, which has been newly numbered as Region 9433 (N15E74). Old Region 9415 (L=360) produced a C2 flare, CME, Type II sweep, and 570 sfu tenflare at 18/0215 UTC. The region was almost 25 degrees beyond the West limb at the time, which likely masked the full strength of the x-ray flare. New Region 9432 (N09E21) was also numbered today.

Solar activity is expected to be predominantly low with a chance for an isolated M flare from Region 9433.

The geomagnetic field has been quiet to minor storm, with severe storm conditions at high latitudes. An interplanetary shock passed the ACE spacecraft at 18/0005 UTC; subsequently the Boulder magnetometer registered a 50 nT sudden impulse at 18/0048 UTC. This shock was likely associated with the X14/2B on 15 April. Greater than 10 MeV and greater than 100 MeV proton events began at 18/0315 UTC and 18/0255 UTC respectively, most likely associated with the activity from old Region 9415 discussed in Part IA. The greater than 10 MeV protons reached a peak of 321 pfu at 18/1045 UTC, while the greater than 100 MeV protons reached 12 pfu at 18/0600 UTC. The Thule neutron monitor measured a ground level event between 18/0242 UTC and 18/0914 UTC; a polar cap absorption (PCA) event began at 18/0425 UTC and remains in progress. Values for the greater than 2 MeV electrons at geosynchronous orbit were not reported due to sensor contamination by the proton event.

The geomagnetic field is expected to be quiet to active on day one of the forecast period, dropping to quiet to unsettled on days two and three. The proton events and PCA are expected to end on day one.

  Pozorováno       18 Apr 132
  Předpovězeno   19 Apr-21 Apr  135/145/155
  90 denní průměr        18 Apr 165

  Pozorováno Afr/Ap 17 Apr  004/007
  Odhadovaný     Afr/Ap 18 Apr  028/050
  Předpovězeno    Afr/Ap 19 Apr-21 Apr  012/015-010/015-005/010