"the cold season" or "the cold, rainy season." This refers to the time of year when it is cold and unpleasant and difficult to travel.
# such as has not been
"greater than there has ever been." This describes how great and terrible the tribulation will be. There has never been a tribulation as terrible as this one will be.
# no, nor ever will be again
"and greater than there will ever be again" or "and after that tribulation, there will never again be a tribulation like it"
# had shortened the days
"had shortened the time." It may be helpful to specify which "days" are referred to. AT: "had reduced the days of suffering" or "had shortened the time of suffering" (See: [[rc://en/ta/man/translate/figs-explicit]])
# no flesh would be saved
The word "flesh" refers to people, and "saved" refers to physical salvation. AT: "no one would be saved" or "everyone would die" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
The phrase "those whom he chose" means the same thing as "the elect." Together, they emphasize that God chose these people. (See: [[rc://en/ta/man/translate/figs-doublet]])