Azzy
ᚳᚣᚾᛖᚹᚢᛚᚠ (He/Him)
Right? There were some legitimate complaints along with a bit of nitpicking (including some of my own), but there was also proposals to rectify these issues. But then came the hipsters who decided to tear down the entire adventure, the developers, and WotC for the the same kind of over-the-top "up to eleven"ism that is all too common in genre fiction. G.R.R. Martin, who has been brought up in this very thread for also having multi-year long X-treme winters in his fiction doesn't get denigrated for writing "slop" or being the downfall of his oeuvre (instead he gets a nice book deal where he laugh at deadlines and has his work made into TV shows).Remember when this was about the content, and how some people want to amend it, and not some kind of personal thing? sigh.

One of the nitpicks that is brought up is that two years of winter would have a dramatic effect on the setting. This is absolutely true, and the adventure even acknowledges this in passing:
This prolonged winter, which has gone on for more than two years, threatens to doom not just the flickering lights of civilization known as Ten-Towns but also the indigenous flora and fauna that need sunlight and the change of seasons to survive.
I have not read enough of the adventure yet to see if it goes into any further detail to address the ramifications of the two-year winter aside from one-offs like:
FUEL SOURCES
The folk of Ten-Towns don't have a lot of options when it comes to keeping warm. People from Good Mead, Lonelywood, and Termalame burn wood salvaged from nearby forests to heat their houses. In the other towns of lcewind Dale, wood is too precious a commodity to burn, so whale oil is used in lamps and small stoves around which townsfolk huddle for warmth.
Ten-Towners buy their whale oil from whalers who live on the shores of the Sea of Moving Ice. Whaling is thus a lucrative (if inherently dangerous) business in lcewmd Dale.
If we want to keep the two-years of winter as the book outlines rather than abbreviating it to be a much more recent onset of Überwinterung der endlosen Nacht (forgive my Google translation, but hyperbolic terms are more fun in German), we could instead split the difference with the OP and interpret it that "Auril's everlasting winter" (or "Aurils ewiger Winter", for more Google German—hopefully a native German-speaking poster can come in and skewer these translations and berate me soundly) started simply as the failure of normal winter to properly give way to spring, and has since slowly getting colder while also having the days get incrementally shorter as Auril fights uphill against the turning of the seasons, the daylight, and power of the gods that preside over them. As she invests more and more of her power each night, her magics slowly overwhelm the nature of things until several months ago (or whenever the DM feels is appropriate) "Der Winter, der Dungeonmeister Angst macht" (okay, I'll stop with that, now) reached its current state.
Sure, it's still not realistic and it still has issues as to how exactly that would affect the communities, flora, and fauna of IWD, but it's a starting place.
Temperatures. During Auril's everlasting winter, the average temperature in lcewind Dale is -49 degrees Fahrenheit (-45 degrees Celsius). Wind chill can lower these temperatures by as much as 80 degrees.
As Jasper and I pointed out, probably the most egregious thing that's been brought up is the temperatures, wind chill, and wind speeds needed to cause such wind chills. Since this is a magically-induced ever-winter created by an intermediate goddess in a fit of pique, let's see what IWD is normally like: In the 2e supplement, The North: Guide to the Savage Frontier*, the climate of the Frozenfar is described thus:
Arctic Climate
Arctic climate conditions dominate Icewind Dale and the Sea of Endless Ice, bringing bitterly cold winters with lows of -40° F and highs rarely exceeding 30° F. Summer brings warm days of 70° F or more, but with lows that can drop to 11-19° F. Stiff breezes off the Trackless Sea create bitter wind chills by as much as 10-20° F. Winter snowfall is heavy enough to regenerate the glacier mass dominating the Utter North. This translates to about 20-50 inches of snow accumulation each winter, but no more than a few inches each snowfall. The rest of the year, drier weather prevails.
Arctic climate conditions dominate Icewind Dale and the Sea of Endless Ice, bringing bitterly cold winters with lows of -40° F and highs rarely exceeding 30° F. Summer brings warm days of 70° F or more, but with lows that can drop to 11-19° F. Stiff breezes off the Trackless Sea create bitter wind chills by as much as 10-20° F. Winter snowfall is heavy enough to regenerate the glacier mass dominating the Utter North. This translates to about 20-50 inches of snow accumulation each winter, but no more than a few inches each snowfall. The rest of the year, drier weather prevails.
I would have thought something more along the lines of a subarctic climate, predominantly taiga (with the trees growing sparse to nonexistent away from the lakes) and tundra, but maybe they just mangled the term "arctic climate". Looking for a roughly comparable real-world equivalent in terms of climate and biome, I propose Happy Valley-Goose Bay in Newfoundland and Labrador, Canada rather than Greenland, however (the choice absolutely had nothing to do with it having an awesome name).
In comparison to the climate data we were given in The North, here's how Happy Valley-Goose Bay shapes up: Summers have an average high/low of 67℉ (19.4℃)/47.2℉ (8.4℃), with a record high/low of 100.0℉ (37.8℃)/24.4℉ (-4.2℃). Winters have an average high/low of 13.4℉ (-10.3℃)/-4.3℉ (-20.2℃), with a record high/low of 52.1℉ (11.2℃)/-37℉ (-38.3℃).
IWD seems to roughly fall in line with HVGB if you read between the numbers. Though, since it gives extremes rather than averages, it seems to paint a more radical picture than what might actually be experienced. Given that bias, it's little wonder that when these were used as a baseline from which to turn up to 11 for Auril's X-treme Winter (which should be unnaturally cold in comparison to IWD's normal winters), the results were X-treme². Still, giving -49℉ (-45℃) as the average for Auril's Winter Special isn't out of bounds (I would have stuck with ICD's mundane extreme of -40℉/-40℃ as the new average instead, but whatever). If that's the new average, what about the new low (because now need to reach a new low...

But what about that wind chill that makes it feel -80℉ (-44.4℃) colder that is apparently caused by 245 mph (394 km/h) sustained wind speeds (which is just shy of the real-world world record for highest wind speed (254 mph (408 km/h) at Barrow Island, Austrailia in 1996)? Yeah, that's gotta go.
So, let's look at blizzards. Since my Google-Fu is strong, I discovered that, to be categorized as a "blizzard" (al least in the US), a snowstorm has to have sustained winds or frequent gusts of 35 mph (56 km/h) or more. A "severe" blizzard has sustained winds/frequent gusts in excess of 45 mph (72 km/h). Let's turn that up a bit and say that the worsts blizzards produced by Auril's Halitosis have 90 mph (145 km/h).
Now, let's take the adventure's temperature average of -49℉ (-45℃), subtract 18℉ (10℃) to determe the coldest it's going to get during this stage of Auril's Escapades, resulting in -67℉ (-55℃). Armed with that and the X-Treme blizzard's 90 mph (145 km/h) winds, we plug the numbers into a wind chill calculator to get a wind chill of -136℉ (-93℃). This is colder than the -129℉ (-90℃) that's in the adventure, but now we've clarified that this is the absolute, most extreme weather that the characters are going to run into. If we stick with book's average of -49℉ (-45℃) and use an "average" blizzard with 35 mph (56 km/h), we get an "average" wind chill of -93℉ (-70℃) during a blizzard.
I spent way too long doing research on this, but I was having fun.
*Look at what they're wearing on the cover of that book, @jasper. This is why it only takes a DC 10 Con save—they're being simulationist to AD&D cover art!

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