Curious WSPRs

It's often, perhaps even usually the case that when there is a reasonable geomagnetic disturbance, unusual openings occur on HF.

There was a disturbance in the past 24 hours, and this led to interesting spots by OH6BG, who appears to be a very recent entrant into the world of WSPR.  

The early, ~15UT drop-off of my signal to him was difficult to match with any field data.  The field was at that stage fairly quiet, and about three hours away from the onset of disturbed conditions.  In fact, the best match with any field changes seems to be with Alaska, although a minor change was also then happening at Jan Meyen and northern Greenland (see last trace 'jan' and 'sco' stations, respectively).  

The traces from Norway, Finland and Iceland do not appear to show any significant deviations that would explain the 15UT effect.

OH6BG hearing my 0.2W, 14MHz WSPR signal (vertical delta loop), 19-20 April 2021.  Long horizontal section is period of non-reception.

Magnetometry (Z component) for (in red, top trace, 'ded'), Deadhorse, Alaska. 

OH6BG was confirmed as listening throughout the period, and checking against M7WBY confirmed the same effect at ~15UT:

The return of reception of both my and M7WBY's signal at OH6BG around 00UT is when the field was undergoing a final, sharp burst of disturbances:

Greeland (East) magnetometer line, showing disturbances either side of 00UT, notably at 'hov' (Faroes), and 'lrv' (Iceland).