Here's the HRRR forecast of 600mb RH. Watch how the coastal fires up at the end of the run and circulations form near this gradient on the water vapor loop between WV and NJ. This is why PHL is such a tough call. I picked 600mb because this is in the DGZ. pic.twitter.com/hXjyW6fv0y

— Anthony Masiello (@antmasiello) February 1, 2021