I'll make an attempt to answer your questions about how the PLB will operate in poor weather and/or poor light-of-sight conditions.

When a 406 MHz PLB is activated it transmits a signal that identifies the PLB (I assume there is a unique ID code).

If you are in a latitude between 70 degrees north & 70 degrees south that signal will be picked up almost immediately by geostationary (GEO) satellites that are positioned at the equator.

If you are not within that 70 degree latitude area - or marginal - that signal can still be picked up by low-Earth orbiting (LEO) satellites. Because LEO satellites have a more narrow view of the Earth it may take some time for one of them to come into "view" of your PLB signal. This potential time delay is longer at the equator and shorter at the poles - up to 1.5 hours. The maximum delay in the United States is about 1 hour.

It is my understanding that transmission of the PLB signal to the GEO and LEO satellites does not require direct line-of-sight, and will do well even in poor weather. The effect of mountains and buildings in blocking the signal will depend on the type and location of the receiving satellite - your mileage may vary there.

Receiving the PLB signal alone is of limited benefit if the system does not know your location.

There are two methods of identifying the location of the PLB signal: GPS and Doppler. The GPS method requires a clear view of the sky, but the Doppler method is more robust and shouldn't be impacted by weather.

GPS:
If your PLB is equipped with a built-in GPS capability, AND you have a reasonably clear view of the sky, AND the GPS has succeeded in locking in on enough GPS satellites to provide position coordinates, then the PLB transmission will include those position coordinates to both the GEO satellites (potentially instantaneous) and the LEO satellites (may be delayed up to 1.5 hours). The accuracy of the GPS position is within about 400 feet.

Historically GPS has required a fairly clear view of the sky, but in the last few years more advanced GPS chipsets can lock onto GPS satellites even without a direct view of the sky (under vegetation, inside buildings, ...). I'm pretty sure all modern PLBs have those more advanced GPS chipsets.

Doppler:
If your PLB is not equipped with a built-in GPS capability, or you do not have a clear view of the sky, your position can still be determined by the LEO satellites using a Doppler effect - though there can be that delay associated with the LEO satellites. The accuracy of the Doppler position is within 1.2 to 3 miles, but averaging about 1.5 miles.

Note that because the GEO satellites are geostationary there is no Doppler effect - they aren't moving relative to your location, so they cannot find your location using this method.

It seems to me that the +/-1.5 miles area is pretty big, but its far far better than no location information at all. At least they will be looking for you nearby.

DO get a PLB that has an onboard GPS capability.

If you activate the PLB, then you'll want to give it as good a view of the sky as you can. If you're in your vehicle, put it outside. If you're in a collapsed building, put it near a window - or an opening if possible. Getting that GPS position means they'll essentially come right to you. Without that GPS position they'll need to search for you which will take more time.

Hopefully that helps,

Ken