My players primarily operate in and around the Sword Coast. I have only really used weather a few times. I considered everything south of the Spine of the World to be temperate. The players are heading up to Icewind Dale from the city of Waterdeep.
After reading Frostburn one more time, I set out to find a list of Forgotten Realms cities or locations and their climate.
After going through every edition I own, I finally found a reference in ADnD's The North: The Wilderness:
Beyond the Spine of the World, arctic conditions prevail. From the Spine to Waterdeep, subarctic weather is found. The coastal areas as far north as Port Llast are temperate climates…
Have I overlooked or missed something? If not, does this information seem about right to you for a 3.5 campaign?
Best Answer
The Spine of the World for a truly arctic climate, but still fairly harsh until you get to the lower Dessarin valley.
The 3.5e Forgotten Realms Campaign Setting Book states the following on page 78 under the Climate section and beneath the heading "The Northwest":
The book does not contain a climate map, nor a table giving specific temperature ranges for each month, but this detailed textual description gives a fairly comprehensive 3.5e account of what the weather at the Northern end of the Sword Coast is like.