The question has been asked, "Why does wifi or RF signal strength vary so much?"
Often when in one location, with seemingly nothing changing, signals can appear to drift in and outline the wind. What causes this? It can be very extreme, some networks can appear from nowhere with strong signals, and then seemingly disappear without a trace.
There are two effects at play. The signal itself varies with attenuation and other effects such as reflection and diffraction. But that's usually smoother than the kind of variation you are describing (and that all Wi-Fi users are used to in real life).
The fault here is with the second source of variation, that is interference. Wi-Fi and radio frequency bands are crowded with signals, everyone interfering with each other. Some signals may come from other places and users, some may come from external sources like microwave ovens. A slight shift in position may unsettle the delicate balance in the combinations of signals that your antenna is receiving. So the signal that your decoder is retrieving after a lot of signal processing may vary a lot, and very suddenly, due to the ever present (but wildly varying) interference.
Whenever someone travels this stretch of Orchard Lake Road, it seems that the cellphone signal-strength seems to wildly vary from very-weak, to very-strong. It has been this way for years.