If you really want to know the weather history for a location, don't depend on peoples
opinion and stories.
Use the internet for FACTS!
Weather Underground has a great calendar history page where you can view the actual temps and rain or snow days and accumulation for every day of a month and year you select, going back some 20-30 years. If you want to see other cities, such as Anchorage, just go to Anchorage on WU and click on "Calendar".
Here is a link to the September 2018 weather in Delta Junction, AK:
https://www.wunderground.com/calendar/us/ak/big-delta/PABI/date/2018-9
Note that in this most recent Sept, Delta Junction had NO snow and the temps generally with highs in the 50's and low 60's and lows in the 30's and low 40's. Down right chilly, but not too bad, if you are committed to seeing the norther lights.
Also September 2017 looks pretty much the same.
An advantage to this part of Alaska, is that it is an easy drive to leave the state via the Alaska Hwy. Much easier & quicker than leaving from Anchorage.
This is not to say you can't have a winter storm come in and bring some really nasty weather. It is just that your odds of nasty weather are not as great as the common opinion would have you believe.
You do have some exposure to snow and cold on your way down the Alaska hwy, so plan on staying put for a day or few days in some of the towns to wait out the weather.
Additionally you will be far better off, not only on the way back down, but on your whole trip if you can dry camp, i.e park your w/o hookups, running off of your batteries and recharging with the generator. Lots of great places to dry camp and boondock in AK, BC & YT.