Weather in April

We were there in April and drove around. I would advise wearing layers; topping off with a wet weather layer. A ski jacket might be too bulky; I did have a puffy jacket that could be packed small. My pullover heavy fleece top was the most useful. You don't need hiking boots; just water resistant oxford style shoes. Or very lightweight all weather boots . Wear knit caps and a wool neckscarf (good souvenir in your tartan). We did have some snow flurries when we were there but mostly just some scattered showers. Good time to hit the pub.

April Weather in Edinburgh:
Average high temperatures: 53 degrees F.
Average low temperatures: 40 degrees F.
Average days with precipitation: 9 days
Total precipitation: 1.6 inches
Average sunshine per day: 4.7 hours (out of 24 hours)

Sounds as if it's an overcast month that's pretty cool. The weather really doesn't turn until June, but even then it never gets very warm that far north.

Here are links to the UK Regional Climate:

Eastern Scotland: climate

This describes the main features of the climate of Eastern Scotland,
comprising the Borders, the Lothians, Falkirk, Clackmannanshire, Fife
and the former regions of Tayside and Grampian.

This region includes the cities of Edinburgh, Dundee and Aberdeen
From chart of Edinburgh mean daily temperatures for April:
Extreme Max High +22.5C
Mean Max High +12C
Mean Max Low *5C
Extreme Min Low -5C

Mean monthly rain 40 mm

Western Scotland Climate

There are several large towns in the region, but the only city is
Glasgow (UK's fourth largest), which has several substantial towns
surrounding it. The largest of the islands is Mull.

Northern Scotland climate

This describes the main features of the climate of Northern Scotland,
comprising Highland Region, the Western Isles, Orkney and Shetland.

I was in Scotland in May of 2015, in the cities and in the highlands and on one of the islands. You can expect cool temps and rain, rain, rain! I wore a lightweight water repellent long jacket (holds in heat!) and waterproof (sprayed) Ecco hiking boots. Underneath I usually wore a long-sleeved cotton knit shirt and a sleeveless fleece vest that I could easily remove it I felt too warm. I also had gloves and a hat. Layering is the key. Scotland is so beautiful! Have a great trip!
Lisa

Check the long range weather forecast on the BBC or Met Office websites just before you leave. This week, Scotland has been 10 degrees warmer than London at times, but that is unusual.

It's not so much the temperature that is relevant as the strength and direction of the wind. The west coast is usually wetter and windier than the east.

Layers and a waterproof outer coat are key. I would take a ski jacket, most probably.

Thanks for all your suggestions. I'm going to skip the bulky ski jacket and go with layers and enough waterproof stuff. I'll throw in my heavy, old turtleneck shirt just in case (hardly ever use in San Franciso).

Living in Colorado for my entire life, and living and working outdoors. I'd highly recommend that you skip any COTTON items of clothing and take with you lightweight Merino Wool, or any synthetic that wicks moisture.

A good rain jacket is highly advised as well.

And as other advise, plan to layer. Easy to remove layers if needed.

I'm going to Scotland in March, so one month earlier than you...my clothing will be all wool, but lightweight. Will be packing a hat, waterproof gloves, scarf, wool socks, a fleece jacket, and my lightweight packable down jacket. Probably will invest in a cheap poncho for when we are outdoors in the Highlands, just as a back up....and I'll bring a compact umbrella for use in Edinburgh and Glasgow while sightseeing.

On my feet will be waterproof insulated footwear (I have some Lowa winter boots).

As long as I'm dry, and my core is warm, the holiday will be enjoyable. I don't want to waste time and money purchasing extra clothing while I'm there...!!

Enjoy your trip. We sure are looking forward to ours...