It's a lot more complicated than just "going north equals less harsh summers and more harsh winters." The continental U.S. is subdivided into four distinct regions: the Northeast, which includes New England and the mid-Atlantic states (New York, Pensylvania, New Jersey, etc), the Midwest, which includes the north central states (Illinois, Ohio, Michigan, etc), the South, which includes the south Atlantic and south central states (Texas, Georgia, North Carolina, etc), and the West, which includes the mountain and pacific states (California, Washington, Arizona, etc). These four regions with 48 states between them (50 if you include Alaska and Hawaii) cover 25 degrees of latitude and 60 degrees of longitude. That is huge, making the U.S. one of the largest countries on the planet by land area.

I bring all this up because the ocean has a stabilizing effect on temperatures around the year. It's not necessarily about how far north or south you go that determines how harsh the seasons are, it's about how far you can get from a significant body of water. The Atlantic and Pacific Oceans and the Great Lakes are basically massive heat batteries. They keep the states close to them cool during the summer and warm during the winter. When you live very far inland, you don't have that heat battery to stabilize temperatures, so you can expect harsher temperature swings throughout the year. It certainly doesn't help matters that the U.S. is bisected by two mountain ranges: the Rocky Mountains in the west, and the Appalachian Mountains in the east. These keep the wind from blowing air from the oceans a significant distance inland, and thus, we have even more extreme seasons. Fun fact, by the way: it's because of this phenomenon that the U.S. gets the most tornadoes per year.

What I can tell you is which cities have the harshest summers and winters. For harshest summer in the U.S, my vote is Miami. Yes, it can be pretty comfortable some of the year, but it's a tropical climate with a monsoon season (or as it's known more generally in the U.S, hurricane season). Temperatures tend to average 84 degrees Fahrenheit during the summer, and with humidity averaging out at 73 percent year-round, summers in Miami can be pretty miserable. Las Vegas may get hotter, but it's so dry that your sweat can cool you down as it evaporates off your skin. In Miami, the humidity will drive you inside eventually if the heat doesn't. For harshest winter, Anchorage is definitely up there. Subzero temperatures for 7 months of the year are already pretty bad, but add in 12+ inches of snow per month and short periods where the sun is above the horizon, and it's just depressing. Boston is a close second for me: the temperatures may not drop as low as Anchorage, but it's prone to snowstorms that can completely bury the city under a foot of the stuff, sometimes even more.