La Nina 2017-18 remains biased cool across the eastern half of the equatorial Pacific Ocean to the east of the Dateline. The Nino4 sea surface temperature anomaly (SSTA) region which represents equatorial SSTA near and just east of the Dateline remains in neutral ENSO phase. The Nino34 SSTA is within moderate La Nina criteria while off the northwest coast of South America La Nina is quite strong (Nino3/Nino12).
An evolving cold air mass featuring arctic air is ahead for the northern U.S. and some of this vigorous cold is likely to extend to Northeast Corridor where forecast models indicate piling snows over the next 1-2 weeks. Early January is potentially the second coldest of the past 10 years. Forecast models indicate the cold reverses quickly in 3 weeks. But will it? New stratospheric warming is indicated in 13-15 days and lack of a progressive MJO into the Pacific Ocean will allow the big chill to linger.
An outbreak of arctic air is forecast to move into the northern Plains this weekend and slowly sprawl south and east likely across fresh snow cover. Heading into the New Year the U.S. population weight gas home heating degree day forecast is 258 which is 36 HDD above normal and easily the coldest week of this early winter so far. The cold start to the New Year is not the coldest in recent memory. Early 2014 and 2010 were slightly colder.
An eastward shift of the Madden Julian oscillation from the equatorial Pacific Ocean into the Atlantic in the 6-10 day period coupled with a stratospheric warming event over northern Canada next weekend forces arctic air formation in south-central Canada this weekend released into the West and Central U.S. early next week. The air mass races into Texas moderating south of snow cover nevertheless having quite a cold punch. Eventually, the air mass shifts into the East days 11-15. An expansive U.S. snow cover evolves during the period.