Access denied for weather sites

I access a couple weather sites many times a day. About once a week I get the "Access Denied" message shown below. That message is for wunderground.com, and I almost always get the same thing for weather.com at the same time. No other sites I visit experience this issue. While this is occurring, I can always open the site on Safari. And the issue always goes away on it's own usually after several minutes. I've cleared cookies and data for those sites and that doesn't clear it up...only waiting a few minutes works. Does anyone have any thoughts on what might be going on? 'Access Denied You don't have permission to access "http://www.wunderground.com/weather/us/ia/cedar-rapids" on this server. Reference #18.8aa03b17.1786700537.30ccea5b https://errors.edgesuite.net/18.8aa03b17.1786700537.30ccea5b'