Mürren in mid August

You won't need anything too elaborate. Even though it's usually cooler in the mountains, the weather in August is still usually quite warm, even at Mürren's altitude. And if you're hiking, once you start moving, the exercise will probably raise your body temperature significantly. Even the mountain summits usually aren't particularly cold in August, except perhaps at night. Quite windy, though.

I would recommend a water resistant light windbreaker with a hood (not waterproof, or else you'll burn up from not being able to vent), and a pair of outdoor pants, something like this. Maybe bring a light sweatshirt or sweater in case it gets a little cool at night or in the morning. If you plan an excursion to the Jungfraujoch or Piz Gloria, it wouldn't be unreasonable to pack a scarf and light pair of gloves, although checking the conditions on the day you ascend will provide an indication if you need them.

"Will the rain likely be mountain drizzle or heavy downpour?" Either, or. If it's just a drizzle, you can usually still hike, although your views will white-out. It can be dangerous hiking in heavy rain, so if you see reports of a heavy storm in the forecast, it's best just to find another activity for the day, preferably, indoors.

Overall, put it in this perspective. You're not headed to winter-like conditions in the summer. At the coldest during the day, likely something similar to mid-spring. Don't be surprised if temperatures rise well above 30° C.

I can comment on late Sept/early Oct weather - the day we spent in Murren we sat there soaking up the sun wearing tshirts and a light summer jacket later in the afternoon. I actually brought lightweight long underwear for Switzerland, thinking it'd be cold...lets just say, it came in handy for pj's since that was the only time I wore it. We had some folks from Bern take us on a hike down a 'mountain' (well, a ski hill - I don't know the name of it, but there was a lovely lake at the bottom) - this was early Oct...my feet got so warm in my boots I had to take them off to let them cool down, and a tshirt was fine...(mind you, I'm from Nova Scotia, so anything in the low to mid-twenties (celcius wise, I think that's in the high 60's Fahrenheit wise) is warm for me.)

Thanks Tom, and Nicole..... It was sort of what I figured.... I just wasn't sure about the temps (we're from Hawaii, so we don't want to buy clothes we'll never use again.. We're both looking forward to this trip.

Perhaps a good analogy would be Hawaii Volcanoes National Park. I recall temperatures being rather mild during the day and cool at night where I stayed at Kilauea Military Camp, but things warmed up considerably after driving down to the sea along Chain of Craters Road. That's about the difference you can expect to feel between, for example, a non-Alpine area of Switzerland and Mürren.

Don't you ever need rain jackets in Hawaii? Even if you don't, souldn't one be useful for when you visit the mainland?

You do not need "warm clothes" like heavy ski jackets or wool coats for Switzerland in August. But it can be cool in evenings and on mountaintops. The trick is layering. Take one long-sleeved teeshirt or lightweight pullover sweater, and a micro fleece zip jacket. Layer both under the rain jacket for the coldest conditions. You will want the lightweight micro fleece jacket for walking to dinner in the evening anyway. You can find these on discount websites like Sierra Trading Post or REI Outlet.

thanks Sasha.. I like your idea of layering, I just need to do some research on what's available. We travel pretty light and we will be spending a month in Southern Germany and the Salzkammergut in Austria prior to Switzerland. My thoughts about rain gear is rain coat vs rain jacket. At home it usually rains at night and during the day I don't like rain coats because they are too hot.

Tom, thanks for the analogy of Volcano. That gives me more perspective than just numbers on a thermometer.

You can always buy what you need there. Then, you know exactly the conditions.

You absolutely do not need a raincoat, just a rain jacket. Something like this:

http://www.sierratradingpost.com/marmot-precip-jacket-waterproof-for-women~p~2283c/?filterString=womens-rain-jackets~d~599%2Fspecdataor~jacket%20features%3Bnon-insulated%2F&colorFamily=50

This is a Marmot Precip waterproof/breathable rain jacket, very lightweight and packble, for $75. On the website you can find rain jackets for half that, but they may not be as durable. If you will be in Germany and Austria for a month before Switzerland I can guarantee that you will need a rain jacket at some point. Thisis a good one, available in many colors.

Just add the micro fleece zip jacket, which you should find for $50 or less, and you are ready for whatever the Alps produce, as far as tourist activities. Not for an all-day hike acros glaciers and high passes, but that is not your interest anyway.

I buy my jackets in neutral colors or black and make them double as evening wraps.