Temps will be anywhere from mid to upper 70s to mid 90s. Today it was 85, tomorrow forecasted at 71. Nights will still be a little chilly, anywhere between 40s and 60s.

The biggest difference between here and Mississippi is how much less humid it will be. The heat here is very 'straight up': if the sun is shining on you, it's hot. If the wind is blowing, or you're in the shade, it's not hot. It doesn't feel like you're breathing in a hot cup of soup all the time; it's one of the things I like best about stepping out of the airport here compared to somewhere else like Florida or Philadelphia.

Make sure you bring lots of sunscreen if you can; even if it won't be as hot necessarily as it would be in Mississippi, you can and will get burned (although most of us are so happy to see the sun we don't care).

On that note, precipitation. One of the cliches of the Pacific Northwest is that it's rainy and miserable all year long. One of the best kept secrets of the Pacific Northwest is that the 60 days of sunshine in the summer are absolutely stunning. You may get a few showers here and there during the month you're here, but probably not something that will last more than a day or so. So, bring a jacket and tuck it in your backpack.

As for bugs, you'll primarily have to worry about mosquitos, but I would imagine they probably aren't half as bad as what you're used to; no mosquito nets necessary. I also have never heard of anyone having a tick problem (I think my dog had one once, maybe, but I was young and I don't remember very well), so Lyme disease shouldn't be a problem.

As for snow, you shouldn't have anything to worry about, depending on how high up you are in the Cascades; there may still be snow on the ground at really high elevations, but I can never remember snow falling during the summer even up on Mt. Rainier.

That's pretty much it. Let me know if you have any more questions

Source: Lived here my whole life and I'm also a fellow backpacker.