During the great reloading supply shortage of 08-10, I ended up buying several powders that were not my normal varieties. These powders subsequently languished in my Texas garage. Do any of you have reliable information regarding the shelf-life of powder that has been stored in a non-temperature controlled location? For the most part, these containers never have been opened, but they've been subject to temp variations between 30 degrees fahrenheit and 100 degrees fahrenheit for up to 5 years. Any advise appreciated.

If the powders were of recent manufacture when you obtained them chances are they are still in perfect condition. Most powders are incredibly stable and maintain original specs even when subjected to quite wide environmental variation as you describe. However, provisos are whether the powders have remained sealed against moisture and whether the powders were not prone to deterioration in their particular storage circumstances. The only way to know for sure is to open each container and check.
I have some powders in good storage that are older than me and are still in great condition. I was recently shown some recovered powder more than 100 years old that exhibited no indications of breakdown and is currently being used in handloaded ammo. The only storage failure I ever experienced was with 1 lb. of Vithavuori N140 that was about 15 years old. I noticed the closed container was slightly bulged. I carefully removed the cap and a small puff of dust erupted. Smelling the powder was unpleasant and stung my nostrils. Some powder flakes were sort of an orange colour. Obviously this powder had gone off and was promptly dumped.
If you check yours and find anything like this dispose of it immediately. Any sound powders should look a uniform dark grey to black colour and have a tolerable typical powder odour.

I had a couple cans of powder that were “in between”

Stored “outdoors” for a while.

Cans looked fine.

Smelled like acetone.

When poured out of the can, had a red dust appearance with the kernels. Some erosion on the inside of the can.

They became expensive fertilizer.

I think that this was rust inside the can, and while the powder might have been fine, it’s not worth the risk.

In my mind, if the powder has anything off- smell, texture, color- I’d toss it.

I started storing it inside since then.

Except for the occasional batch of powder which is defective it is difficult to treat powder so adversely that it deteriorates in five years. One of my very best and most dependable powders is some original surplus 4831 which is over 70 years old. The cartridges for both calibers that my son and I used on a trip to Africa a few years ago were loaded exclusively with that surplus 4831, so as that illustrates, I have total confidence in it. By the way, some of it was stored in an non-climate controlled Texas garage for several years.

Powder which is deteriorating often exhibits a coating of rust-red fine dust on it. This is NOT from rust inside the can, but a chemical result of powder break-down.

I routinely use powder from WW2 and 25 year old powder is new to me.
Five years is nothing.
If it smells like ether, it is good. If it smells like acid, it is bad. Red dust with an acid smell is bad.
Ball powder is different; no smell.
Black powder lasts Forever.
Stone already said it; shoot it.

I store mine in my outdoor shop in Texas! I am not very far from the coast. With plastic cans the only powder to go "bad" was Vithavouri. Not sure how old it actually was but it turned to a solid black puck! Varget always smells even brand new!

Thanks, everyone, for your sage advise. the containers that previously had been opened smell like ether, so I'm going to go ahead and start using them up. I'll report back if anything goes desparately wrong with the reloads