GPS Satellites are not geostationary or geosynchronous. Throughout a 24 hour period, some drop lower on the horizon or even go entirely below the horizon affecting the numbers of satellites pool your device has to choose where to get position data from. As well, throughout the year the number visible to your location may vary significantly. I've always heard the further north you are the less gps satellites you will have available to you particularly during the winter. I suppose since this was told to me, perhaps they may have closed some coverage gaps.

You can always go to satellite tracking websites and filter out for just GPS, GLONASS or what ever you desire and see what should be in the sky over you for any particular time, date and position. This is one I used recently..... https://in-the-sky.org/satmap_radar.php
Be sure to select your satellite types and check your location.

But yes, precip of any sort, foliage--especially wet foliage, shadowing by terrain and buildings, even your body and rf interference can affect your signal.