Does bad weather affect GPS accuracy on a hike?

The short answer

A GPS fix comes from timing radio signals broadcast by satellites, and the frequency those signals use passes through cloud, rain and fog with very little loss. A storm overhead does not meaningfully weaken the signal reaching a phone the way a solid obstruction does — a rock wall, a building, a thick tree canopy. On the ground, the line a phone draws through a rainstorm should look about the same as the line it would have drawn in sunshine, for the same walk.

That is not the same as saying weather touches nothing. It changes three things indirectly: the barometric elevation reading, how long the battery lasts, and how much a wet forest canopy scatters a signal that was already weakened by the trees. None of those three is what people usually mean when they ask whether bad weather affects GPS.

Why clouds and rain barely touch a GPS signal

It helps to separate two different things that both get called a "signal": visible light and radio. A cloudy sky blocks sunlight because water droplets scatter visible light heavily, which is why an overcast day looks grey rather than blue. GPS satellites do not broadcast light. They broadcast radio waves at a frequency chosen, among other reasons, because it passes through the atmosphere — clouds, rain and ordinary humidity included — with very little absorption. The satellite is not blocked the way the sun looks blocked; the receiver simply is not listening on a wavelength that clouds interfere with much.

This is genuinely counter-intuitive, because plenty of other familiar systems do struggle in rain. Some satellite television and satellite internet services use much higher frequencies that rain noticeably weakens — the effect even has a name, rain fade — and heavy weather really can degrade those. GPS sits in a different, lower part of the spectrum that is far less sensitive to water in the air, so an intuition built from one system does not transfer cleanly to the other.

What weather actually changes

The barometric elevation reading

Phones that include a barometric pressure sensor use it, alongside GPS, to smooth out elevation. That sensor is genuinely weather-sensitive, because it works by measuring air pressure, and air pressure changes with the weather independently of how high you actually are. A front moving through while you are on a long walk can shift the apparent elevation by a real amount even though you never changed altitude. This is a real weather effect — it belongs to the elevation reading, not to the GPS position line.

Battery life in the cold

Cold weather that often arrives with a storm affects the phone itself rather than the satellite signal. A battery loses usable capacity at low temperatures, so a phone can appear to lose charge unusually fast on a cold, wet day. That is a property of the battery, not of GPS reception, and keeping the phone somewhere warmer than an outer pocket helps.

Wet leaves under tree cover

Under a forest canopy specifically, rain does make a measurable difference, because wet foliage scatters and weakens a passing signal more than dry foliage does. That effect only shows up where trees are already involved — the canopy is doing the work, and rain makes an existing obstruction somewhat worse. Open sky does not become a problem on its own just because it is raining.

Where the confusion comes from

Two habits of thought get carried over from other parts of daily life. One is the visual metaphor built into the phrase "satellite signal" itself — it is easy to picture a beam that a cloud gets in the way of, even though nothing about the actual radio path resembles that. The other is genuine experience with a mobile network struggling in bad weather, usually for reasons that have nothing to do with rain hitting the signal directly — more people indoors and on the network during a storm, or a local infrastructure issue — which gets attributed to the weather itself.

GPS and the mobile network are separate systems that happen to live in the same phone, and they respond to the world differently. One listens to satellites and mostly ignores the weather. The other depends on ground infrastructure and can be affected by all kinds of things that happen to correlate with bad weather, without rain-on-signal being the actual cause in either case.

What TrailCam does

TrailCam records a route in the background regardless of what the sky is doing, because GPS reception is not the thing weather interferes with. The distance, pace and elevation profile it reports afterward come from the same points whether the ground underfoot was dry or soaked, and the whole route can be exported afterward as GPX 1.1 or CSV. It is free to download.