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?