There isn't a clear catalyst for the improved sentiment in markets and fall in the US dollar but they've come at the same time. S&P 500 futures are now up 20 point and commodity currencies are leading the charge against the dollar.
The loonie is particularly strong today after a jump in oil prices in Texas on the shutdown of the Keystone pipeline due to a leak. I think that's the wrong takeaway because the pipeline transports oil from north to south and is likely to further exacerbate the huge discounts ($30) in Canadian crude.
In any case, it's not just the loonie as AUD, NZD and GBP make solid moves against the US dollar. Cable is nearing the high from late yesterday:
Another spot I'm watching closely today is gold. It's up $5 after the latest dip in the US dollar in what would be the third day of gains.