Outerwear for January in Amsterdam?

For actual, day-by-day, historical weather statistics for Amsterdam in January, go to timeanddate.com. It has data going back at least ten years and allows you to see the full range of what you might experience rather than just averages. I've linked to January 2019's data; you should go back at least three years--five would be better.

I don't travel to Europe in the winter, but I'm sure others will contribute experience-based suggestions.

Where else are you going?

I don't travel to Europe without a waterproof jacket under which I can layer shirts/puffy vest/jacket for warmth. I've not been in January since uhhh, Gerald Ford was in office, lol. I needed waterproof then.

Amsterdam in January is more likely to be rainy than snowy so I would look at bringing something light and waterproof. I have a North Face jacket that folds up into its hood and takes up very little space, it also unfolds completely crease free, couple this with several layers to provide warmth/coolness as and when required and it's a much better choice than lugging a heavy woollen coat around.

Like Pam, I don't travel without my waterproof rain jacket which goes over a down puffer jacket. Currently in Budapest wearing a water resistant Gore Tex down parka over a fleece layer over a wool sweater over 32° Warm l/s shirt. 32° Warm thermal layer under my outer pants. Hat, gloves, muffler, wool socks.
You may have to make the final coat decision the day before you leave based on a 5-day forecast. And, of course, based on how much you plan to be outside.

Expect temps between low 40- to low 50-
I prefer a poncho to a rain coat as it covers you completely including a back pack or purse/shopping bags . There are thin poncho's that are very thin ( disposable i.m.o.) and just slip in your pocket.. Bought one at WM for $1- Never had to use it b/c June 15-28 2019 while I was there with the grand kids there was no rain !

I track Amsterdam weather these days now that my daughter lives there; I visited in December 2018 and plan to go next month for another short visit so right now I’m watching the weather quite closely. Prepare for rain, but also wind - and depending on what you are used to at home, the cool, damp, windy weather can chill you to the bone especially if you are outside for hours. So I would take the water-resistant jacket AND the umbrella AND the warm inner layers. And think about waterproof boots or shoes, as well.

Like Kathleen says prepare for rain and wind! It has not been that cold if you just look at the thermometer but the (strong) winds combined with the pervasive humidity can make it feel quite chilly. I suggest bringing layers : sweater, vests, rainproof coat and scarf.

Water resistant and layers like a turtle neck or thermal and flannel over that; not the wool coat.

Thank you all so much - this information and your thoughts are very appreciated. Definitely not bringing the wooly! Will bring my lighter jacket, puffy vest and other various layers as well as hat, earmuffs, gloves, scarf and umbrella. And also going to spray my footwear again. This will be so fun! I'm really looking forward to being there this time of year and catching the tail end of the Amsterdam Light Festival and next Saturday is National Tulip Day - here comes spring! hahaha!