https://www.uavforecast.com/#/faq

Q. What is the Kp index, and why does it matter?

The Kp index measures geomagnetic disruption caused by solar activity, on a scale from 0 (calm) to 9 (major storm). Anything at or below 3 or 4 is usually safe for flying. The higher the Kp index, the more likely you are to have diffulties getting an accurate GPS lock.

Solar activity interferes with GPS signals in two ways, both due to disruptions in the ionosphere:

• It decreases the signal-to-noise ratio and affects carrier frequency, causing the receiver to lose lock on some satellites. Instead of 9 satellites, you might lock only 6, or the number might fluctuate from second to second.
• It changes the propagation delay through the ionosphere, making GPS positioning inaccurate even if the receiver has all satellites locked.
  

Even during a major storm, the extent to which you see these problems will depend on many other factors. One major factor is your latitude: ionospheric disturbances are worse at high and equatorial latitudes, and less noticeable at mid latitudes. Another factor is the time of day: most disturbances occur in the evening between the hours of 8pm and midnight. The effects also vary; sometimes everything will be fine, while at other times you'll lose lock completely for a few seconds or even a minute, or appear to have a lock but the position will actually be wrong by hundreds of feet.

The storms can also interfere with radio control signals, or with electronics of your aircraft.

In general it's better to play it safe during solar storms, even though most of the time you won't notice any issues. Happy flying!

For a nice research paper demonstrating the effect of solar activity on GPS, read Impacts of ionospheric scintillations on GPS receivers intended for equatorial aviation applications by Groves et. al.

I use Kittyhawk(app) and noticed the Kp on their start screen.  Thoughts?

Q. What is the Kp index, and why does it matter?
A. Despite what UAV Forecast have told you, the Kp index does not matter.

It's just another one of the myths spread by drone forums.
No drone flyer has had a flight incident that could be attributed to a high Kp Index.

Labroides Posted at 3-24 19:19
Q. What is the Kp index, and why does it matter?
A. Despite what UAV Forecast have told you, the Kp index does not matter.

Really? What makes you say that?

Ex Machina Posted at 3-25 05:46
Really? What makes you say that?

Six years of studying the facts and observing the tendency for these forums to spread myths to the uninformed.
A proper understanding of GPS and how drones work.
And a complete lack of evidence of any drone incident where high Kp Index has caused a single drone flyer any trouble.

Labroides Posted at 3-25 13:49
Six years of studying the facts and observing the tendency for these forums to spread myths to the uninformed.
A proper understanding of GPS and how drones work.
And a complete lack of evidence of any drone incident where high Kp Index has caused a single drone flyer any trouble.

Huh, do you have any links you can share on why the KP index doesn't matter? I take your points about myth propagation and finger pointing.

Ex Machina Posted at 3-25 17:19
Huh, do you have any links you can share on why the KP index doesn't matter? I take your points about myth propagation and finger pointing.

Has anyone ever seen a single incident of high Kp Index affecting drone flights?
I've been looking out for any for 6 years and as far as I'm aware there haven't been any.
Just lots of myth spreading.

If it was a real issue, the day it happens, you'd expect plenty of flyers to be affected, but still none have been reported.
The next high Kp Index flight incident reported, will be the first ever.

Ex Machina Posted at 3-25 17:19
Huh, do you have any links you can share on why the KP index doesn't matter? I take your points about myth propagation and finger pointing.

Here's a link with some info from someone that knows a bit more about the topic than the myth spreaders:
http://www.phantompilots.com/vie ... mp;p=331319#p331319

How many times do we get a KP over 5 when you're not lockated near north- or south-pole. Even when I was in Iceland, the highest KP I experienced was 3. Hoped for a 5 to see the northern lights. I flew without problems with a KP 3. A very high KP however will affect all electronic and electrical systems, so also our drones. The sun activity has also a cycle. Until now the activity was low. It should rise rom this year, 2020, on.

But still, how many wil have a KP higher than 4 or 5 in their area ?

https://www.spaceweatherlive.com/en/help/the-kp-index

That is also why in aviation they use radiation hardened parts. It's a serious business.
It just takes one bit for everything to go awry.

Labroides Posted at 3-25 17:33
Here's a link with some info from someone that knows a bit more about the topic than the myth spreaders:
http://www.phantompilots.com/viewtopic.php?f=4&t=35796&p=331319#p331319

It is very rare for the KP to be above 4, but it does happen and it will affect GPS reception.

https://www.swpc.noaa.gov/impacts/space-weather-and-gps-systems

grahamjohnson10 Posted at 3-26 06:06
It is very rare for the KP to be above 4, but it does happen and it will affect GPS reception.

https://www.swpc.noaa.gov/impacts/space-weather-and-gps-systems

It is very rare for the KP to be above 4, but it does happen and it will affect GPS reception.
And it still won't make any difference to drone flyers

Check this video out
https://bit.ly/UAV-Forecast-Kp-Index