Weather on the Scottish West Highland Way in March?

Be prepared for any kind of weather in March.

The weather in Scotland can change very quickly, and being caught on the hills with inadequate clothing can be a recipe for disaster, especially if visibility turns bad, bringing the added danger of getting lost.

Scotland Weather - Expect The Unexpected!

Due to this little country's geography, predicting the weather in Scotland can be challenging!

Scottish weather can change abruptly, in fact sometimes you can feel as though you've experienced three (or even all four) seasons in just one day.

One thing that you can usually depend on though... is that it's going to rain at some point.

Western Scotland is generally wetter and milder than the East, in fact palm trees can grow in micro-climates in the south-west.

https://www.hillwalktours.com/walking-hiking-blog/the-weather-on-the-west-highland-way/:

Spring on the West Highland Way: The average temperature in spring depends strongly on your exact location on the route but is normally between 7 and 13 ° C. In March and April snow can still fall and the peaks are often still covered with a white blanket.

https://outdoorscott.com/best-time-year-west-highland-way/:

During April it can be very changeable, feeling like summer one day and winter the next. The rainfall charts illustrate April as the second lowest rainfall month in Scotland, however in Fort William it is the 4th lowest during the year. It should be noted that Fort William has one of the highest amounts of yearly rain in the UK, great for snow in the winter, but not so good for walking.

https://donsnotes.com/places/europe/west-highland-way.html (mirror):

Note from https://donsnotes.com/places/europe/west-highland-way.html that the elevation changes quite a bit too:

Dy	Section	Dist. (mi)	Ascent (ft)
1	Milngavie to Drymen  17x23	12	500
2	Drymen to Balmaha  20x15	8	1,200
3	Balmaha to Rowardennan  20x15	7	1,200
4	Rowardennan to Ardlui Boat dock row-invrsn  12.2x15.6   invrsn - invern  12x13.5	12	1,785
5	Ardlui to Tyndrum  15.5x21	14	1,270
6	Tyndrum to Inveroran Hotel  14x16.5	9	1,225
7	Inveroran Hotel to Kingshouse Hotel  12x21	10	1,700
8	Kingshouse to Kinlochleven  12.2x11	8	1,388
9	Kinlochleven to Fort William  14x16.5	15	2,400
Total		95	12,668

Here's the weather data for Bridge of Orchy. This is the highest altitude major town on the route, but as Franck's answer points out the route does go quite a bit higher. Here's the key quote:

In Bridge of Orchy, during March, snow falls for 11.8 days and regularly aggregates up to 281mm (11.06") of snow.

Also note that the average low at night in March is 0.2 celsius.

From personal experience, I have encountered snow on West Highland Way in first half of March - around Crianlarich area. There wasn't much, but it was definitely snow. Albeit that was some 15 or so years ago. I was told that wasn't common - but happened occasionally.

As others have said, be ready for anything.

I would highly recommend Yr.no for their weather forecasts. They have good short and long range tools and are invariably accurate in that area of Scotland.

That being said, you could get anything. Rain, wind, sleet, snow, sun. Most likely the first 4.