Climate change without elevation

Well, the tundra region is pretty flat so what you need to do is have a sign along your right-of-way with the notice "Welcome to the Arctic - Now Crossing the Arctic Circle" and then make sure the snow effect travels in an arc across part of the corner of the layout.  On the other side have another sign by the tracks which says " Now Leaving the Arctic - Come Back Soon"  This will solve your snow problem and because it is tundra you will save money on the cost of tree installation.

I would not do it in the space you have allocated for your new layout.

Michael,

the only way I have seen it done effectively is to have a very distinctive view block, where it is obvious the train has traveled to a different region.  I think the best way is to have a backdrop down the middle of a table or an around the walls layout.  if I can think of where I have seen photos of this done effectivly, I will post them.

Otherwise, I would agree with Brian that summer and winter right beside each other would look strange.

I'd put up a new table for the new scene and "travel" to this new area via long bridge.  then you can drop the height of the new table a little to add a little elevation

Acadia National Park, 1500 ft above sea level is above tree line.  It gets cold quick.  They talk about all those little evergreens under your feet being very old.

That was my primary concern.

Hmm, well the easy answer is the least fulfilling: Its your layout, do what you want!

Of course I cringe when I hear that non-answer, but I figured it needed to come out.

Next, as said a view block, you could have a narrow foot of a mountain popping out that the train tunnels through, and voila!  On the other side it's SNOW!! 

Another thought, try having a small transition zone.  Maybe right side of layout is summery, middle bit is more fall colors, left corner or so is SNOOOOOW!! 

I know you have all those trees, are they evergreens?  Maybe some are oaks, etc, and some cans of orange and red paint will make their leaves change colors quick.

It's a lot to cram into a relatively small space, but if you want it bad enough you'll make it happen.  Personally I think the mountain spur with tunnel makes a good transition.  Think of it as The Wall from Game of Thrones.

Disney does it effectively. You walk from one land to the next without being shocked by the transition. But from an aerial view, how can one ease the transition? Place something at the transition that draws the eye, like a line of the large winter trees. By the time the eye moves to the train or past the trees to the winter area, it will seem ok.

A bridge or tunnel without elevation will do the same for the train. Viewer will follow train to bridge, see train on bridge and refocus to new season on exit.

here's some play on Lionel's 1957 Catalogue track plan.

I like the idea of a dogbone or an "L" shaped layout with one end in winter the other in summer and transition in between.