Your problems are multi-fold.
First, the WYSIWYG editor is probably giving you a few of the lost paragraph tags. Check the line numbers and track them down to fix them and determine what it is you are doing that make those happen. WYSIWYG editors are still not very perfect.
Your template files has some problems in the
sidebar.php template. The nested list is a common problem in the sidebar and with careful scrutiny, and the WordPress Codex article on Styling Lists with CSS, you can figure that out.
The plugin you are using for Weather has more problems. Turn that off and your problems there will go away. I know a lot of people enjoy that, but honestly, how important is the weather where you are to people in Russia or England reading your site? Do they care? Is your site about the weather? Don't think so? Maybe you don't need to clutter and the time it will take to track down those errors.
Errors in your web pages are kinda like dominos. One lost tag and the rest look borked because the browser is still hunting for that one closed tag. Find that missing part and the rest of the errors will go away.
And avoid using inline styles like the
text-align:center in the DIVs. Set that in your
style.css style sheet in the appropriate DIV reference.
You only have 19 errors. Be thrilled with that. I've seen pages with hundreds of errors - so many, the checker stopped checking. Many of these are caused by the little missing tag in your sidebar. Fix that and test again.