Arctic air flooding the entire eastern half of the U.S. during the Thanksgiving Holiday weekend producing the coldest temperatures in nearly 50 years (since 1976) is slowly moderating closer to normal early this week, but widespread double-digit below average temperatures are far from over during the 1^st half of December. The latter half of this week (Dec 5-7) is certain to feature another pure arctic air outbreak emanating from Siberia extending all the way to the Gulf and East Coasts. Unlike last week the core of coldest arctic air is forecast to focus more directly into the Eastern 3^rd of the U.S. sparing the northern Plains from repeat of extreme single digit high temperatures and overnight lows in the negative teens (25°-30° below average). Now that arrival of the next intense arctic air outbreak is within the short range models are shifting colder across the Midwest and East in forecasts valid at the end of this workweek (15° below average or more), but still may not be cold (or snowy) enough into the 1^st half of next week (Dec 8-11). Meanwhile most of the West continues to slowly warm 5°-10° above average before all extended range models allude to the next fundamental pattern shift mid December establishing lower amplitude flow across North America. In response all 11-15 day model forecasts are closer to seasonal temperatures across the vast majority of the U.S. but are considered too warm across in the Midwest and East as low level arctic air typically moderates slower than models forecast favoring persistence of at least slightly below average temperatures. Still most of the latter half of December is almost certain to be substantially milder across the Midwest and East (warmest in the Southeast) than the frigid start to winter. However, 30-day MWA ensemble forecasts shift noticeably colder during the final weekend of the month (Dec 28-29), potentially marking onset of the next prolonged period of below average temperatures between the Rockies and East Coast through early January.