Shadow Plane conditions

[Lanathar]

Is the shadow plane inherently cold ?
The srd says no. However I am playing a module where the is a shadow plane based prison where it cold enough to force fortitude saves

My players will want to make knowledge planes checks before entering. I don’t want to cheat them out of potentially valid info

[Pizza Lord]

It is not inherently cold any more than the Prime Material Plane is inherently cold. There may be places that are hotter or colder than normal. The Shadow Plane is linked to the Material one, so the Shadow Plane Antarctica or North Pole is going to be cold. Most places will probably have shifting weather (the seasons or their effects may be skewed or not as dramatic), for instance, the sun probably isn't as hot in the Shadow Plane, but a Shadow Plane volcanic field or hot spring in a snow plain is going to be warmer than normal. A Shadow Plane desert is probably not quite as hot during the day, but will get freezing at night like a normal one.

Overall, I would say that temperature-wise, it will probably be a bit chillier, due to the 'shade', but not in an inherently cold manner, other than in places that would already be cold in the Prime Material Plane. So if your prison is on a glacier in the Shadow Plane, then it's going to be cold. If their knowledge of the prison and its location are known (through Knowledge checks)... then knowing it's either on a glacier, in a floating iceberg, or in some anomalous well of Shadowy freezing air would be common sense to figure out it's cold.

[Lanathar]

Ok. It is just the module has the particular sub dimension as cold and I am sure my player's are not going to be prepared for it.

There is a chance they just succumb to the cold rather than the villains. It might speed them up!

[Pizza Lord]

A 'sub-dimension' is probably another. Kind of like how different levels of Hell or Layers of the Abyss could be inferno environments or freezing cold, those probably would count as having a certain designator and obviously anyone researching them should find that out, even though the Abyss or Hell wouldn't normally have a cold classification.