This was posted maybe 4 or 5 years ago.
Here is a post from a user that works in the industry also. I tend to side on his wisdom. Others may not.
"A little primer on geomagnetic storms and GPS.
A geomagnetic storm is when a shock wave from a solar flare smacks into the earth's magnetic field, which triggers a lot of disturbances in our ionosphere due to a wiggling magnetic field and increasing the electron density. Huge geomagnetic storms (K index 8-9) are rare. The triggering flare has to be huge (an M or X class flare), located near the center of the sun to directly strike the earth, and one that produces a strong coronal mass ejection (CME) - or the shock wave. The CME usually takes about 3 days to strike the earth following the flare. If conditions are right, it can trigger a major geomagnetic storm which usually has a duration of several hours.
During a major geomagnetic storm, GPS signals from the satellite to our UAV's GPS receivers gets bent by the increased electron density, which increases the path length and introduces position errors. The disturbed ionosphere can also cause degraded signal-to-noise problems, meaning your receiver may loose lock on one or more birds. Also, the bending of signals can also cause "phase slips, which can also cause the receiver to temporarily loose lock on the GPS, taking a few seconds to tens of seconds to relock on the dropped satellite.
Scientific experiments done during strong geomagnetic storms shows the bending of the path length can cause up to about 30M (100 foot) errors in position at mid-latitudes (like the US/Europe and Australia), and slightly worse near the equator. Again, this is during a MAJOR geomagnetic storm of K=8 or 9. Thus, I would expect no effects to a UAV below K=7.I have flown in K7 with no ill effects.
With K=8 or 9, I would expect the following effects to a UAV:
A position error of around 100 feet would not normally be catastrophic. The position error is not going to make your UAV fly a mile away; just 100 feet or so. This would only affect your RTH position and landing point. It might skew the onboard compass off a few degrees, but probably not noticeable. If you're still tracking 6+ satellites, just bring it home (assuming you even notice anything).
With poor signal-to-noise or phase slips, the UAV GPS receiver will loose lock and drop into the manual mode. Bring it home in manual mode.
Again, I wouldn't expect any effects until a MAJOR K=8 or 9 geomagnetic storm, and nothing that is going to cause the UAV to not know where it is more than a 100 feet in error (not a fly away). Go here to see what the K index and general space weather is:
Homepage | NOAA / NWS Space Weather Prediction Center These are the guys that measure things every hour.
Do not listen to warnings issued by the major news media. Every flare lately seems to be an end-of-the-world news story, and furthermore, a solar flare means a POSSIBLE geomagnetic storm 3 days later, not right after the flare.
We have enough to worry about to keep our UAV's flying safe from proper calibration, good batteries, pre-flight check-out, and the various things that can go wrong (a weak ESC, smacking into a tree, loosing LOS, etc.). The geomagnetic storm concern doesn't even make the top 10, in my opinion. Let's focus our worries and concern elsewhere."
