Top of the stairs are some icy elemental critters. Combat duly formed. Things going reasonably well for the party until a second wave of smaller elemental nasties start coming up the stairs. The combat rages across the ground and first floors, Cythor thinks the new elemental creatures are the same colour as the frozen blue flames in the gruond floor fireplaces. Checking these out reveals that the fireplaces have activated and become portals to the elemental plane of ice. A combination of arcana checks by Cythor and some dextrous manipulation of moving parts by Erithan allows all 4 portals to be closed and the nasties beaten.
On up to the top of the tower, where an icy gem is suspended in mid-air. Touching it triggers an elemental creature called the Heart of Winter to emerge. Fairly nasty fight but lots of daily powers are enough to kill the elemental.
As it dies, the gem shatters and the elemental forces causing the snow, and the encasement of the tower are broken. The weather begins to turn back to normal and the harvest is saved. Hurrah!