The Matanuska River Valley is known for one thing in the winter. Cold. The frigid arctic air makes its way down from the interior and settles into the Mat Valley. In the dead of winter, temperatures can easily fall to -20 F. Daytime temperatures in December and January usually only make it into the single digits. To make matters worse, the wind can sometimes be incessant which only helps to drop the mercury even further. Typically, the best time to visit these areas is in the late season when the rivers are still solid, the daylight returns, and the ice climbs turn to hero ice.