Don't let winter stop you from riding year round! With a wee bit of thought, you can remain toasty on the trail!
Layers
Alright, you've head this a million times before but it's worth reminding yourself about. The objective here is to trap warm air between the layers of clothing - and it works! There's also the advantage of being able to remove some layers if you get too hot, whilst still having others.
Materials
I'm a huge fan of merino wool. It's unbelievably warm, wicks sweat away quickly and doesn't stink like synthetics! Check out Madison's Isoler Merino sleeveless vest as a first layer. I pair that with a long sleeve merino top which is a super warm, but not bulky, combo. Merino isn't cheap but is worth every penny, in my view. Just make sure it's 100% merino wool - many manufacturers use a blend of merino wool and synthetic fibres to reduce cost.
Wind
The enemy of warmth! It doesn't have to be windy for you to be affected by windchill. Simply riding at speed will create a windchill that can cool you rapidly. Think about how windproof your clothing is and where the wind could get in. A Buff will stop wind getting down your neck and long cuffs on gloves will help with sleeves. See that velcro adjustment on your jacket cuff? Yep, do that up!
Water
So, rain needs no explanation but consider spray from your wheels and the trail. Mudguards do a really great job at keeping the spray off you, leaving you drier and warmer for longer. Waterproof bike shorts aren't cheap and wear out quickly from the gritty mud paste all over your saddle. Get yourself a cheap pair of waterproof overtrousers and cut the legs off at the knee - hey presto! Waterproof shorts! Buy a size up to accommodate knee pads. Chances are, your riding shoes aren't waterproof. Investing in a pair of waterproof socks will keep your feet happy on rainy days. Do remember that if the sock is exposed to the rain/spray (wearing shorts for example), they will start to absorb water and your feet will get damp in the end.
Other stuff
Pack a pair of disposable toe warmers for those days where you lose the feeling in your toes! Simply open the pack to activate them and stick them on top of your toes. They're thin enough to fit in your shoes and provide enough warmth for a full day out. Overshoes aren't just for roadies! Most MTB shoes are designed for other parts of the world with ventilation holes to keep your feet from overheating. That's great for the rare hot day in Scotland, but rubbish for the rest of the year. A pair of overshoes will keep the wind and water off your feet so you can ride for longer. Overshoes are normally designed for clipless pedal shoes but Endura brought out the first flat pedal specific overshoe.
Lastly
Just keep riding! Stop for a blether and you'll quickly cool down so save the chat for the climb back up to the top of the hill.