Today’s Cheviot climate is best described as fickle. On most days it’s almost always colder and windier than you expect when starting out from the valleys, and the unexpected rain shower is a feature of many walks. On northern and protected slopes, snow can lie well into May.
The climate in the area has always fluctuated. After the last Ice Age, and a cold snap lasting nearly 1000 years from around 10900 BC, the climate gradually got warmer, eventually settling at temperatures slightly above those of the 20th century. But from the late Bronze Age and through the Iron Age, things gradually got colder and wetter. There were warmer periods around the time of the Roman occupation and again in the late Middle Ages (the Medieval Warm Period). This probably encouraged upland settlement and farming until about 1300 AD, but then the Little Ice Age cut in (you’re probably getting hang of this now). Human-induced warming has more recently changed the climate again, although on the Border Ridge in March you may think it hasn’t.