Nares is either blocked by an arch - usually in Kane Basin, otherwise in the Lincoln Sea - or exporting ice throughout the winter. There is a near-constant current down the strait, and the pressure of the trans-polar drift helps push ice into the funnel.
Indeed, years where an arch fails to form are relatively rare, and the export effect is not negligible as this is the thickest ice in the Arctic. However, I seem to recall I once estimated the total volume and it came to some tens of km3 over the winter, so not a make-or-break factor. We can discuss this further in the Nares thread.