It doesn't usually get that cold on Mauna Kea, it feels very cold because the air is very thin and you can get altitude sickness easily, but the temperature barely changes throughout the seasons on top of Mauna Kea.
I'm very surprised by the temperature extremes in the US; even the coldest parts of Scotland have 'only' reached -27.2°C, despite being farther north than the entire contiguous US.
The biggest factor in Scotland's climate are the Gulf Stream and Jet Stream, which bring warmer water and air "that far" north.
The interior of the US, on the other hand, gets the opposite effect from the Jet Stream, which sometimes dips as far south as Texas, pulling cold arctic air down over the prairie states pushing their temperatures well below freezing.
Kind of amazed Florida has gotten that cold. Its highest point is only 105m above sea level, no part of it is far from the sea, and much of it is adjacent to a shallow, warm, tropical sea in the form of the Caribbean. Almost all of the state is south of 30°N. So there are none of the factors that typically permit temperatures significantly below 0°C: no elevation, no high latitude, no continentality.
Much of northern Florida doesn't benefit from ocean effect because it's not on the peninsula, so they reach freezing temperatures every year. I do agree though, -2 is extremely surprising
The interior of the US, on the other hand, gets the opposite effect from the Jet Stream, which sometimes dips as far south as Texas, pulling cold arctic air down over the prairie states pushing their temperatures well below freezing.