If you've ever watched a survival show where campers set up pots and pans tied on a string to sound an alarm for approaching bears, etc., then the upcoming chart will make lots of sense.  10yr Treasury yields--the best benchmark for domestic interest rate momentum--set up their own sort of defensive perimeter yesterday.  They did this by opening significantly lower than the previous session's entire trading range.  This is an uncommon move, and one that most market participants view as significant.

If 10yr trading happens to fill this gap any time soon, it wouldn't necessarily indicate the end of the long term rally, but it's more likely to result in at least a temporary ebb in the recently intense positive momentum.  The longer yields are able to hold underneath, the more legitimate the rally becomes, even if yields don't continue to stampede lower.  In other words, between 2.20 (Tuesday's close) and 2.28 is a fine range to consolidate longer-term gains.

Bond markets can watch this trip wire against the backdrop of the week's only big-ticket economic data: today's 8:30am Retail Sales.  In short, we're merely tuning in for a few minutes to see if anything has changed about economic data not having an impact on bond trading.  Once that's confirmed, it will be right back to watching technical levels and waiting for tradeflows to manifest themselves (i.e. watching for big trades and the resulting market reaction). 

In addition to tradeflow momentum, other market movers include stocks, European bond markets, and even headlines (Ebola and Fed policy).

As for the extrapolation from Treasuries to MBS, the latter would actually benefit from some tempered weakness in bond markets.  MBS don't like to move too far too fast, so the more we can level-off without giving up too much ground, the more MBS can get caught back up with their recent level of performance vs Treasuries.