I was at the Alaska NRHS convention last week and I am still smiling. Definitely the best RR convention most of us ever attended, or probably ever will attend. I shot several hundred pictures and dozens of videos (mostly runby).
Alaska RR was very gracious to us, including numerous run-bys in very scenic locations and Wednesday tours of their Anchorage station, shops, yard and operations center. Regarding the weather, it was cool but generally favorable. Sunday was sunny for the North Pole trip out of Fairbanks; Monday (Fairbanks to Denali) was mostly sunny and clear; Tuesday (Denali to Anchorage) was overcast but dry; Wednesday was overcast with a few sprinkles but we were inside anyway; Thursday (Anchorage to Seward) was sunny with broken clouds (and absolutely stunning scenery); Friday (Anchorage terminal, Palmer, Potter) was sunny and clear with unlimited visibility i.e. Mt. McKinley visible from Anchorage; Saturday was cloudy with some showers and we did get pretty wet during the photo stop at Whittier.
I encourage you to ride the Denali Star and the Coastal Classic trains, in Gold Star class, as soon as you have the opportunity. The Coastal Classic (Anchorage to Seward) is the real gem.