Mortgage rates rose gently today. Most mortgage borrowers (and many mortgage professionals, for that matter) wouldn't be aware of slightly more alarming risks lurking underneath the surface. Those risks involve the broader bond market from which mortgage-related bonds take their directional cues.
More simply put, if US Treasuries are improving, mortgage-backed bonds tend to improve as well. The level of correlation varies though. For nearly all of 2018, mortgages weren't improving as quickly as the most widely-used rate benchmark: 10yr Treasury yields. That began to change recently--especially when 10yr yields began moving higher 3 weeks ago. During that time, we've seen moderate moves higher in 10yr yields met with modest moves higher in mortgage rates. Today was another one of those days.
The underlying risk is that the moderate moves in Treasuries are adding up and potentially crossing dangerous lines. Mortgage rates aren't any worse than they were at last week's highs, but Treasuries are as high as they've been in more than 3 weeks. If they go much higher, they'll be breaking some important ceilings that investors might treat as harbingers of additional momentum. The net effect would be additional increases in mortgage rates. Even if those wouldn't be keeping pace with the weakness in Treasuries, they still wouldn't be pleasant.