It looks pretty simple to me, in fact.When there's a sudden rush for the door, the flight to quality is to the T-Bill, the T-Bill and then the T-Bill. Under nearly all circumstances is has the market breadth to be able to soak up countless zillions of dollars at any given moment. But when nerves turn to outright panic and there's a overwhelming demand for the 3 month T-Bill, it's like 25 fat guys trying to squeeze through the same door at the same time. The result is that flight to quality money can't get parked in the T-Bill quickly enough the yield drops and drops and drops and the fat money looks for an alterative place to hide.
That alternative is gold. To the utter chagrin of the goldbugs, it has to be said that gold is very much second choice as a safety buy and is only used in extremis situation like mid March and Wednesday 17th (two days ago). The plain vanilla fact of the matter is that the gold market is too small to be able to efficiently carry the amount of money that moves around the world market. We saw that Wednesday when the sudden overwhelming demand for gold made it spike the hardest since 1999. It wasn't the end of the fiat dollar or any other such nonsense dreamed up by the tinfoil hatters, it was "just" an extreme case of more buyers than sellers.
Therefore it makes plenty of sense to watch the yield in the three month T-Bill tomorrow. If the yield rises it means there is plenty of room for any frightened money to go and hide there. Therefore it won't be needing gold. If the 3 month yield drops even closer to zero then the panic is on again and we can expect gold to react accordingly.