Mortgage rates couldn't fall forever, it seems.

This week, for the first time since mid-June, the 30-year fixed rate mortgage rate climbed on a week-over-week basis, moving 6 basis points to 3.55%, on average, nationwide.

According to Freddie Mac, 3.55 percent is the highest average rate at which the benchmark product has been offered in close to 4 weeks.

The Freddie Mac published mortgage rate is available for prime borrowers willing to pay a full set of closing costs plus an accompanying 0.7 discount points.

Discount points are a one-time, upfront mortgage loan fee to be paid at closing where 1 discount point is equal to one percent of your loan size. In this way, a Nashville home buyer who pays one discount point at closing will be responsible for an additional $1,000 in closing costs per $100,000 borrowed.

However, although Freddie Mac says that the average mortgage rate is 3.55%, not everyone who applies for a conforming mortgage will get access to that rate. This is because Freddie Mac's published rates are the ones offered to "prime" borrowers, the definition of which often includes :

• Top-rated credit scores, typically 740 or higher
• Verifiable income using two year's of tax returns 
• Home equity of at least 25%

Borrowers not meeting the above criteria should expect slightly higher mortgage rates and/or discount points. In some cases, such as when an applicant's credit score is below 680, mortgage rates may be higher by as much as 0.500%.

Although mortgage rates are up this week, though, the impact on home affordability is muted. Mortgage payments rose just $3 per month per $100,000 borrowed this week as compared to last week. 3.55% remains the third-lowest Freddie Mac rate of all-time.

Mortgage rates remain unpredictable and there's no guarantee for low rates to last forever -- much less through August. If today's mortgage rates meet your needs, therefore, consider locking something in.