25 degrees warmer overnight and predicted long run suck

Depends on what my goals are. If I have some upcoming races down the road where I know I'll be dealing with similar conditions I look at it as an opportunity to adapt my body to these temps. If that is the case I'll adjust my pace according to RPE and plan on drinking more fluids.

If I just want to get a quality run in and I don't want my quality/pace to suffer because of the heat, I'll rearrange my schedule for an evening or early morning run.

yep that's what i did this morning...embraced the suckage. it was really humid and my pace dropped a minute slower than I expected but that weather is coming, like it or not for me.

Yes, it's coming for sure. I'm guessing your location is Mississippi? Yeah, that sounds hot like SC.

I was just reading yesterday about slowing pace by :30/mile for every 5 degrees above 60, I think it was. Yikes, that's a lot of slow!

If you were somewhere less humid, I'd say wait till it's dark.  Here, the sun goes down, and temperatures drop 20F.  On the other hand, 80F + 20% RH is great to run in.

However, growing up in Michigan, I know that's not an option.  It'll still suck, and just be dark.

If I did this where I live I would never finish the run. 

+ work on your tan, shirtless run this afternoon for me.

+1 to that. I just got back from parading my white chest around the neighborhood.

Also, I can't believe its May and we're already whining about the weather...

when things happen unexpectedly, like weather, I look at it as,"What would I do on race day?" I don't think one should change their workout because of things out of their control, like weather.

There is a very hard road race in Syracuse in May, hilly as all get out called the mountain goat. It was mild coming up to the race and everyone trained in 30-60 degrees... race day was 90+ and humid.

Well you could go for a shorter easier run alright, but I just went out for a short 5K walk and came back at about the level of saturation as after my 10K run yesterday  right now we are showing 84 with the humidex of  91 that's a pretty big switch from yesterdays 62 with the  humidity and this weeks mid 50's temps that we have had. I might go out for a run but I probably wouldn't go for a long run , even being fairly fit, too much of a change in to short a time frame for my old body to adjust too on such short notice. I am about 100 miles from you straight across  to the east so we pretty much share the same systems. If I did go long I would sure be going easy and watching hydration very carefully .

No kidding!  But if last winter's warmer temps are any indication, this summer's gonna be awful.  Lotsa water, lotsa electrolytes.  Worst part is trying to stop sweating when you get back to work...