Below average temperatures lingering in the Northeast this past weekend are not extreme but are several degrees colder than models forecast as arctic air typically erodes slowly.  Warming in the wake of last week’s intense arctic air outbreak will continue to be limited through the 1^st half of this coming week by snow and/or ice events models forecast across the northern U.S. and as far south as the southern Appalachians as several milder Pacific storms eject east of the Rockies. More importantly a strong midweek storm exiting the East Coast is forecast to tap into the coldest arctic airmass yet in Canada virtually ensuring plummeting late week temperatures across the Eastern 3^rd of the country extending deep into the Southeast and Florida at 15° below average intensity or greater by this weekend (Dec 21-22).  Unlike most arctic air outbreaks observed since Thanksgiving a less intense glancing blow of cold air spilling into the central U.S. will only produce slightly below average temperatures across Texas. Milder temperatures in the central-southern Plains are related to much warmer model shifts across Western North America  generating several days of record warmth across the Desert Southwest (near 80°) during the latter half of this week. Longer range implications of strong Western warming scouring arctic air out of western Canada extend milder flow across the Eastern half of the U.S. potentially producing the longest stretch of above average temperatures yet this winter between the end of December into early January. Latest 30-day MWA ensemble runs also latched onto this warmer 11-15 day signal, but still sharply cool the Eastern U.S. below average much of January starting early in the 2^nd week of the month. In support latest CFSv2 model mean January forecasts continue to trend colder favoring predominance of seasonal to below average midwinter temperatures east of the Rockies.