Richard,
first of all I assume you are talking about the Alpine Pass Route as described in the Cicerone guide. In another thread you have been talking about the Via Alpina and therefore I am not quite sure what trail you want to hike.
(http://www.cicerone.co.uk/product/detail.cfm/book/405/title/Alpine-Pass-Route)
I have hiked the Alpine Pass Route almost completely but only in weekend long sections. I have also hiked the PCT.
I did a bit of internet research for you as there is tons of stuff on hiking in the Alps – but it is all in German. Generally early June is considered the very earliest date for doing any high alpine stuff in the Alps. Most guidebooks recommend July to avoid any snow risk. You face the same problem in the Alps as you do in the Sierras. It all depends on the year! I remember hiking the highest part of the APR (Hohtuerlipass: 2.800 m) early July and there was absolutely no trace of snow left.
I found a comparison of snow conditions in the Alps for late May/early June on a German hiking website and there are tremendous differences. One year (2003) was basically snow free under 2.400 m early June – and you only go twice above that altitude in the APR. But in 2009 almost everything was still covered in snow above 2.200 m END of June! Unfortunately, this winter is a very hard one in Europe and therefore I would expect a lot of snow. But you will only know what to expect by May… it all depends on how much more snow falls and how warm spring is. Here you can see recent snow depths in the Swiss Alps in English:
http://www.slf.ch/lawineninfo/zusatzinfos/wt-daten/wt_tabellarisch_EN
There is a incredibly resourceful website about hiking in Switzerland and parts of it are in English: http://www.wandersite.ch
Click on the English flag and you will get to the English content. I did not have enough time to do a lot of research there but maybe you come across more detailed information. The APR is described in great detail in English.
I have hiked the APR directly after the PCT. The PCT is a piece of cake compared to the APR. Except for the snow problem hiking in the Sierras is dead easy and the grade is never very steep. Expect much more technical stuff in the Alps. I remember some incredibly steep and slippery slopes – much more difficult than the PCT. (I am not taking further complications by snow into this consideration).
But on the other side you have a lot of alternative trails in the Alps. Most Americans picture the Alps like the Rockies or Sierras, but keep in mind that the Alps serve as a recreational area for a much bigger number of people and therefore many more trails exist in the Alps than in the American mountains. Even the APR is not high altitude all the time. You could either hike in lower elevation or flip-flop around the snow areas. Your choices of hiking in the Alps are almost limitless – so if the APR does not work out, you can just hike another lower trail. Also public transport goes everywhere in Switzerland so that a mini-flip-flop is not difficult.
Also browse http://www.wandersite.ch – they describe literally a hundred different long-distance trails in Switzerland including a lot that are much lower. To be on the safe side I personally would suggest the Jurahoehenweg, which takes about 2 weeks and stays well below 2.000 m.
You can also contact me via PM if you have further questions or need help in translating from German.
Christine aka German Tourist