Just some more info
http://ccmc.gsfc.nasa.gov/modelweb/solar/kp.html
Planetary K-index | NOAA / NWS Space Weather Prediction Center
Just FYI, a high KP index can actually wreek havoc with electrical grids, radios, etc. These are another concern. The reason GPS has problems is that the radio signals from the satellites are tiny and in the microvolt range. But.... High KP values can take out satellites in space, take out power grids on the ground, and create big problems with radio signals everywhere. Especially high frequency radio, such as is used in UAV's
The reason that is important is that you Solo uses Radio for GPS AND communication to you. You lose both, and it lands where it is. High KP values makes this a higher likelyhood.
Something to consider...
Not saying don't fly, but if it were me...... I would carefully consider going over water in those circumstances, and I would have a plan B, C, and D for flying. This is exactly why I bought both the Gitterback and the Marco Polo, when I allready have a Spot Trace. The Spot is good anywhere in the world, but it uses satellites for GPS and uplink also... Gitterback is low tech and good for water, and Marco Polo uses direct (900 Mhz) radio that is less suseptable to a high KP. In this case I would use those, and likely leave the Spot at home.
The right tools for the right job.
Just my 2 cents