There is really no reason to offer complicated reasons for said rally. After the premarket mark up tingled the microchips of HAL9000, the dollar continues to get hammered and therefore any risk asset on Earth can be bought with impunity. Thousands of PhDs at quant funds across the land deem it so in their collective wisdom, so first grade logic it must be. (Click to enlarge)
The NASDAQ and Russell 2000, coming into the week ahead of the S&P 500, now sit at or just above resistance. The S&P 500 is still 7 points away from reaching the same point, but that's nothing the next premarket rally cannot take care of. Or, if they can hammer the dollar another 0.3% or so, perhaps will be gone by later this afternoon.