microconvergence zones?

always figured it was basically differences in air currents around microlandforms, and structures, trees etc.

Unless all the snow in one weather event falls straight down, a house will have a major effect on the surrounding snow depths, as will a parked vehicle. Your rain gauge is likely far enough from the roof so that drops of rain are not bouncing off it and landing in the gauge.

The recent snow in Portland was in the form of showers and 1/4 mile (5 blocks) could easily see a 2- or 3:1 difference in snow depth.

For the first 2 or 3 inches, deck railings or fence tops can be accurate since they are a very small target. Past this depth, the snow tends to slough off, resulting in an uneven depth.

I was kinda thinking along the same lines. I took measurements both in open spaces, as open as it gets in town at any rate, and on the deck railing and the chaise lounge for comparisons, and everything in my yard, deck, railing, chair, driveway, lawn was right around 12". There was no wind to speak of so that may have contributed to the consistency. And this snow was incredibly dry and powdery, so maybe that's why it piled up on the narrow deck railing to same depth as on the ground. I didn't expect it to be the same.

But the park down the street had way more snow than me, and people nearer the park reported upwards of 16" of snow, just a few blocks away from me. Kids trying to sled on it in the park were just sinking. No fun.

So it must have snowed a lot more since your original measurements of 18 January. Seems like the snow totals are actually converging, ratio-wise.

Taking several measurements around your house and averaging is a good method.