Analysts at BBH note that the US Dollar Index climbed to its highest level since December 19 at 104.85 with markets returning from holidays. 

Euro trading at lowest level since December 12

"With little in the way of new fundamental developments, this appears to be largely a technical move magnified by skewed positioning as dollar shorts get stopped out. A break above 104.893 would set up a test of the December 7 high near 105.822. "

"The euro is trading at the lowest level since December 12 and has retraced nearly half of the late November-mid-December rally.  A break below $1.0460 is needed to set up test of the November 30 low near $1.0290."

"Sterling is leading this move lower in the foreign currencies and is already testing its November 30 low near $1.19.  A break below would set up a test of the November 21 low near $1.1780."

"USD/JPY broke below the August 2 low near 130.40 to trade as low as 129.50 today before reversing on broad-based dollar gains. That break sets up a test of the May low near 126.35."