weather in May

The key word here is 'layer' and be prepared for anything. You will most certainly want some type of waterproof jacket. Mornings and evenings will most likely be cool but will warm up during the day. Cannot guarantee that the weather will be suitable for shorts but then again you never know. It will must certainly be cooler than what you experience in NC! Oh - while I never carried an umbrella when I lived in the Pacific NW, I am never without my brolley here!

I have been to London 4 times. Once in march, 3 times in july or august. Rained every visit, ( which were all about a week or so long) except the visit in March when it sleeted (wet snow).
There were some nicer days mind you, but if staying for a week expect to hit some rain period, you might not but that would be the exception not the rule. Rain jacket and something warm to layer underneath( I bring a fleece ) .. for anytime of year. I always pack a small umbrella( I don't like putting on hats) . Remember when it rains if feels cooler with the damp. This all said, you may hit some nicer weather, but don't expect it to be hot and sunny, if you get some of that its a total freakish bonus. I would not pack shorts. Really I wouldn't.

The nice thing about May/June in London, and elsewhere, is that daylight hours are at their longest and the parks and gardens are a fresh green and full of flowers. Echo advice re layering as we usually expect some warm periods in May/June. Historically among the driest months of the year but who knows these days. 2012, after a dry first four months with little rain and drought warnings, turned into one of the wettest years on record!

Layering is essential. We had mostly wonderful weather in May, but it can also be cold and very rainy. Start with a good water-proof rain shell. Ideally something with a hood and long enough to cover your bottom in a downpour. Under that have a couple of warm items you can wear one at a time or together if it's really cold. A wool sweater and a medium weight zip up fleece, as an example (try to pick ones that aren't too bulky, so they don't take up your whole bag). I normally pack five tops, some combination of t-shirts and button up shirts. They allow me to dress up or down and layer a t-shirt under a nicer shirt when it's cold. I add a few casual slacks (mix and match to fifteen outfits), these should be quick-drying so they don't stay wet if you get caught in a downpour. My wife usually packs one pant, one capri and one skirt - adjusted a little to the expected weather. Bring comfortable shoes that can shed some rain, waterproof is nice. I like Costco's hiking socks, they're mostly merino wool, sturdy and not expensive. They keep your feet warm and dry quickly - avoid cotton socks.

Our first day in England was June 8 last year. We were in Bath, and we enjoyed the walking tour of the city recommended in a Rick Steves book. However, it was so rainy, windy and cold, I spent 40 minutes in Bath before that walk started looking around for a stocking cap as my ears were so darn cold. And I'm from Wisconsin and am used to cold weather. That being said, the balance of our 10-day visit we had more normal weather, including several days of sun and some days with just a passing shower. This really doesn't help you at all but it is fun for me remembering our trip!