I just wrote a post about my favorite EDC handgun. That being said I also have a second favorite EDC handgun due to the weather here in Colorado. Nine months out of the year I wear my Glock 30, but during the mid-summer months (June, July & August) it gets warm here and I use a smaller, more compact handgun so it conceals better with the thinner clothes that I wear. Here are some things you need to consider during warmer weather.
A Smaller Handgun Works Well
In the summertime the weather is warmer so we tend to wear less clothing, thus a smaller handgun works better. These guns will be lighter, less bulky, may carry fewer rounds in the cylinder or chamber, and will be easier to conceal. Again whether you carry a j-frame revolver or a small compact automatic, it will make things easier in warmer weather.
Change in Cooler Clothing
As warm weather shows up in the summer, we shed the flannel shirts, sweatshirts, jackets, etc. And replace them with t-shirts & shorts, etc. That being said, your heavy cover garments tend to get put in storage until next Fall. It is very important to me to always keep my firearm covered, not allowing it to “print” or be seen. In case you do not know, “printing” is when the outline of at least some part of a handgun is seen through the cover garment. Moving to a smaller handgun, in a good concealment holster will help it not to print. No matter how hot it is, I always use a cover garment. It might be a short-sleeved shirt, unbuttoned and untucked but it is always over my t-shirt. I do not trust a t-shirt to cover my handgun.
Leather Is Not The Best In The Summer
Summer heat tends to make things sweat and leather holsters are no exception. If your handgun is stainless steel then you do not have much to worry about. But if it is a blued finish then sweating in a leather holster can cause rust on your gun. That is why I always use a Kydex holster, then sweating is not an issue.
Off-Body Carry
While I usually always carry my handgun on my body, there may be some times that off-body carry might work. In the summertime when things are hot and sweaty, that is one of those times. Whether you use a fanny pack, backpack or purse, it can be done. You just need to watch when you take off that piece of gear, what do you do with it. It is important that someone else does not take it from you. Vertx packs are a very good way to carry off-body, they have a whole line of packs that can be used this way.
I use the Vertx Dead Letter Sling Pack when I need to carry off-body and it works great for me. See the product review I did on the pack if you are interested, click here.
What I Use In The Summer
As I told you the Glock 30 is my normal concealed carry handgun during most of the year. But when the heat gets the better of me and I need something smaller, I carry the Glock 26. 
This is a great compact handgun, very accurate, lightweight but easy to handle. I have added a Pierce grip extension on the bottom of the magazine to aid in better control of the firearm. Getting my little finger on the bottom of the grip gives me better control of the handgun, but it does not negatively affect the concealment. I use a Comp-Tac Infidel IWB holster for this handgun and place it at the 8:00 position on my left hip.
Final Comments
I think it is important to have both a Summer and Fall/Winter/Spring setup when you carry concealed. It takes a little bit of planning upfront but it is so much easier knowing what you are going to do as the year goes on. 
As you can see by this picture, the Glock 30 is on the bottom and the Glock 26 is on top. The Glock 26 is both shorter and thinner and the grip is also smaller. This makes it more concealable and it is easier to carry in the summer months.
The Glock 26 is a great little gun, having the Pierce grip extension on this gun gives me a full-hand grip on this small handgun and that helps my accuracy. I also added an adjustable rear sight which makes my G26 shoot much better. I really like my baby Glock, it conceals very well and is a joy to shoot. Whether you like Glocks or not, that is your decision, but consider the idea of a different concealed carry option for the summer! It will give you many more options when the weather gets hotter.
If you have any questions about this post or anything related to Everyday Carry (EDC), feel free to leave a comment below and I will be happy to get back to you.
All the best,
Larry
Founder of EDC Essentials