Iran a factor in the timing of Fed QE

Any oil shock resulting from an strike on Iran would widen the trade deficits of net oil consuming countries like the US that import more than then they produce (US Energy Information Administration).

This negative terms of trade and income shock would force net oil consuming countries to depreciate their currencies in order to create a more positive non-oil trade balance.

Relative depreciation against oil exporting countries tends not to occur as the latter typically use the extra income from higher oil prices to build up reserves, thereby preventing the appreciation of their currencies (European Central Bank, June 2012)

In addition, a Middle-East conflict would intensify safe haven flows into US treasuries, strengthening the dollar and further necessitating depreciation to redress the trade imbalance.

If as some analysts argue QE is an instrument of currency manipulation to cheapen the dollar, and the announcement of previous rounds does correlate with periods of dollar depreciation (see chart below), an oil shock resulting from a US-Israeli strike on Iran will likely precipitate or accelerate QE by the Federal Reserve.