Florida Freeze

On February 19th, arctic air moved into the eastern US:

Hard freeze warnings went to Daytona Beach, freeze warnings went to near West Palm Beach, and a wind chill advisory was issued for Miami:

Numerous low temperature records were set on Feb 20th, and many by a wide margin:
                              new       old
Location               record   record    year
Marquette                -26       -15     1966
Detroit                     -12       -8       1934
Cincinnati                -12      -7        1885
Pittsburgh                 -10      -2       1968
NYC Central Park       2          7       1950
Washington DC          5          8       1896
Charleston                18       22      1968
Macon                      18       21      1958
Jacksonville              24       28      1958
Vero Beach               30       35      1958
West Palm Beach      38       42      1958
Naples                      36       39      1960
Key West                  49       52      1958

The low of -10 at Pittsburgh was the lowest temperature this late in the season since records began in 1871.

Central Plains Temperature Inversion

This morning, Chinook winds produced 850 temperatures over 20C across the Central Plains:

With cold, stable air still in place at ground level, a temperature inversion of over 20C (36F) was present in the Central Plains. At North Platte, NE, the temperature increased by 20C only about 200 meters above ground level: