Is it normal for my ground mount panels to barely produce anything in winter?

The weather is probably most of it, honestly. Heavy December overcast is not the same as the thin clouds you get in summer. Thick grey cloud can knock a panel down to a couple percent of rated output, and two panels at a couple percent looks exactly like what you're describing: the controller limps along, barely registering anything. Cold boosting voltage helps a bit, but voltage without much light still means low amps, and watts are what matter. Short days also mean you only get a few usable hours even when the sun does show, so the daily totals look brutal compared to what you remember from fall.

That said, there are a couple quick checks before you write off the setup. On your next clear morning, before the sun is up much, look at the panel voltage on the controller. It should read close to the open-circuit voltage printed on the panel label for two panels in series, or close to one panel's rating if they're in parallel. If it's way off from what you expect, you've got a wiring or connection problem. If it reads right, your wiring is fine and it's purely a light issue. Also worth watching: some MPPT controllers need the panel voltage to sit a few volts above battery voltage before they'll even start charging. On a dark day with a 48V bank, a weak array may never clear that threshold, which makes it look worse than it is. Frost or a thin glaze of ice can do a sneaky amount of damage too, even on a steep tilt. Brush it off, wait ten minutes, and see if the numbers jump. One more thing, if the two panels are wired in series, a shadow on one panel from a chimney or a neighbor's bare trees at the low winter sun angle can throttle the whole string. Low winter sun traces a very different path across your yard than the summer sun did. For what it's worth, my winter totals on a similar setup run a small fraction of what the same gear makes in June, and heavy cloud days can be basically zero. If your clear-day midday numbers look reasonable for the array size, you're fine.

Been running a small standalone setup for years and winter expectations are where most folks get burned. I remember checking mine with an ammeter clipped right at the panel leads back in the day, that's how we did it before controllers told you everything. What helped me was keeping a simple log, just amps at the same time each clear day, then compare month to month. If your numbers hold steady on those sunny days you've got nothing to worry about. Also don't underestimate how much a dirty panel costs you, snow residue plus road dust on a ground mount is worse than people think. Give them a good wipe when you brush them.

Following this with interest becuase I'm in a similar boat, just reversed. My little portable panel setup does great all summer running the shed lights, then every winter I convince myself something broke. Last year I dragged it inside twice thinking the charge controller was faulty, and both times it tested fine once spring came back. The sunrise voltage check suggested above is a good idea, I never thought of doing that on purpose. Does snow reflection off snow on the ground around a ground mount actualy help at all, or is that a myth? My neighbor swears his numbers jump after a fresh dump.

One thing that bit me a couple winters back was snow buildup on the low edge of the frame. Even a two inch lip of snow across the bottom of the panel cuts output way more than you'd guess, because the cells at the bottom shade the whole string in series. Mine looked fine from the deck but the numbers were garbage. Now I sweep the bottom edge every time I brush the glass and it made a bigger difference than I expected. Might be worth a look next clear day.

Don't forget your battery state of charge matters too. If the bank's sitting low after a string of grey days, the controller pushes everthing it can into bulk charging and you might be seeing normal numbers without realizing it. Mine sat at like 70% for most of last January and I almost panicked thinking the panels died, but the math just didn't work out with that little array and no sun. I ended up adding a small genset charging session every couple weeks to break even instead of chasing ghosts in the wiring.