Switzerland early May

You can't trust a weather forecast this far out. When we travel in the Alps, we plan two itineraries-- good weather (mountain scenery) and bad weather (cities-- museums, churches, palaces etc) and then alternate as the weather dictates.

Day trips: rail to Jungfraujoch & Kleinescheidegg (walk over to the cliff & watch avalanches on the North Face of the Eiger;
Lauterbrunnen Valley: Waterfalls, cable cars to scenic views. Trümmelbach Falls-- a waterfalls inside a cave.
Road trip: 3 Passes Tour

Lucerne and surrounding area is beautiful and weather should not stop u from taking ferry rides to mt pilatus or other lovely spots on the lake. But the suggestion for L. Valley is a good one, if weather is gd easy access tontrams and train up the mtn.

Weather forecast for the next 2 days - probably right.
Weather forecast for the next 3-7 days - possibly correct.
Anything after that, you are just looking at averages for previous years.

I don't know where you come from, but first week in May is nearly 2 months away, no way weather forecasts are valid that far in advance.
May should be mostly good weather, do not alter your plans.

Once stayed in Murren in mid-may. Had three days of perfect weather: mid 70s perfectly visibility, on the fourth day and overnight snow storm dumped six inches of snow. So be prepared for anything.

Something else to consider is that May is between seasons, so mountain villages like Wengen and Murren will be like ghost towns. A lot of the hotels, shops, and restaurants will be closed until June. In addition lots of the trails above the tree line will be still be snowed in from winter and closed-off.

Thanks all! Since my son is so young we’re not planning on doing too many hikes but was still hoping to be in the mountains for short hikes or just walk around some of the towns. We’re definitely ok being spontaneous based off of weather-I just can’t figure out if we should stay in Lucerne for that reason then—how long does it take to get from Lucerne to wengen or Mürren? Is it too far and we should gamble w weather and plan a few days in wengen or murren and the other 2-3 in Lucerne?
we’ll have a car as we’re driving from Austria but I was thinking drop it off in Zurich and just use trains in Switzerland-would you all agree?
Thanks again!

how long does it take to get from Lucerne to wengen or Mürren?

Luzern to Mürren: 2h52
Of which Luzern to Interlaken 1h49 + 10 minutes between trains + Interlaken to Mürren: 53 minutes.
Look up train times on the SBB website: https://www.sbb.ch/en/

should gamble w weather and plan a few days in wengen or murren and the other 2-3 in Lucerne?

That is usually a good mix. 3 day Wengen/Mürren + 2 in Luzern. Luzern is an old town + lake, so different, but still with sight of the mountains, plus boats on the lake, plus 3 local mountains to go up (Titlis, Rigi and Pilatus)
360° panorama of Luzern: http://tour.luzern.com/360/en/

Edit:

we’ll have a car as we’re driving from Austria but I was thinking drop it off in Zurich and just use trains in Switzerland-would you all agree?

Yes, trains better. You cannot drive to Mürren or Wengen, no roads, just trains and walking. That is one reason why they are so kid-friendly.

BUT, where were you planning on dropping off the car?
Hiring a car in one country (Austria) and returning it in another (Switzerland) is usually very expensive.
Do not assume hotels (for example in Luzern) have parking. Often they do not, or it is chargeable.

Above comments about weather prediction are great.

Here's my personal comment. Discard if you want: I'm going to be in Switzerland from May 1 to May 8. I too want sunshine. My daughter lives in Switzerland and snapchats me sunny gorgeous pics all the time (but not every day is sunny). So I went to a historical weather site that said for our dates, "cloud, cloud, cloud1" My other trip to Switzerland was in December and almost every day was cloudy, which I expected. This trip, though, I want the Instagram pictures! I asked my Swiss son-in-law what his favourite month was, and he says "May!" Apparently because the weather is getting really nice. I know his snapchats from last May were spectacular (Lucerne region). Crossing fingers . . .