Altiwind shows the current Kp index from NOAA's Space Weather Prediction Center, adjusts it for where you are on the planet, and turns it into one plain line: "GPS: normal" or "GPS: may be degraded".
What Kp measures
Kp is a planetary index of geomagnetic disturbance on a scale from 0 to 9, issued for every 3-hour period. Kp 5 and above counts as a geomagnetic storm on NOAA's scale, from G1 at Kp 5 up to G5 at Kp 9. Storms disturb the ionosphere, the layer of charged gas that satellite signals pass through, and that can add error to your drone's position.
What it really means for your drone
Drone forums often treat Kp 5 as a reason to stay home. The real picture is calmer. According to NOAA SWPC, single-frequency GPS is typically accurate to about a metre or less in calm conditions, and a severe storm can push errors to tens of metres or more. Those large effects mostly happen at high latitudes, though major storms can reach mid latitudes too. Near the magnetic equator, the ionosphere can also cause signal problems just after sunset, which has little to do with Kp.
So GPS errors at high Kp are real, but at mid latitudes in a moderate storm they are usually modest. If the app says "GPS: may be degraded", fly with a bit more attention: watch the satellite count, look out for drift while hovering, keep the drone in sight and be ready to fly without position hold. The guide on Kp index myths and facts covers the forum claims one by one.
Latitude weighting
The same Kp means different things in Tromsø and in Athens, so Altiwind adjusts it by your geomagnetic latitude. That is latitude measured from Earth's magnetic axis, which is tilted towards Canada, so North America sits magnetically further north than Europe at the same map latitude.
| Geomagnetic latitude | Adjustment | Roughly |
|---|---|---|
| 60° and above | +1 | Auroral zone: northern Scandinavia, Alaska |
| 50° to 60° | 0 | The UK, much of Germany, southern Canada |
| 40° to 50° | −1 | Much of southern Europe and the central US |
| Below 40° | −2 | The southern US and lower latitudes |
The adjusted value drives everything else. At an adjusted Kp of 4 or less the app shows "GPS: normal"; from 5 it shows "GPS: may be degraded". In the go/no-go score, an adjusted Kp of 4 or less is "Within your limits", 5–6 is "Marginal" and 7 or more is "Outside your limits".
Example
NOAA reports Kp 6, a G2 storm.
- London (0): adjusted Kp 6. "GPS: may be degraded", Kp chip "Marginal".
- Madrid (−1): adjusted Kp 5. Still "GPS: may be degraded" and "Marginal".
- Athens (−2): adjusted Kp 4. "GPS: normal", "Within your limits".
Kp now
Altiwind shows the latest observed Kp, adjusted for your spot, with the GPS line and the Kp reason chip.
For a quick look without the app, the Kp index tool shows the current value.
FAQ
Should I cancel my flight when Kp is 5?
Not automatically. At mid latitudes a moderate storm usually has a modest effect on GPS. Altiwind marks it "Marginal" so you know to watch for drift and a low satellite count, and you decide from there.
Why does Altiwind say "GPS: normal" when Kp is 5?
Because of latitude weighting. If you are below 50° geomagnetic latitude, Kp 5 is adjusted down to 4 or less, and storms of that size rarely cause trouble that far from the auroral zone.
Where does the Kp data come from?
From the NOAA Space Weather Prediction Center: the observed Kp for now.
Does Kp affect the weather?
No. Kp is about the magnetic field and the ionosphere, not wind or rain. It sits in Altiwind next to the weather checks because it affects how well your drone knows where it is.