Good Sunday evening to everyone,
It appears that the start of 2025 is going to include a visit from Ol’ Man Winter!
The buzz of a significant cold outbreak and possible southern snow is going around the ranks of social media. We would like to take a moment to lay out some of the parameters that we are looking at that suggests not only cold weather but snow opportunities could be materializing over the next two weeks.
Favorable Global Teleconnections
Year-round we look at several teleconnections and oscillations to see what may be in the works 10-20 days ahead of time. In the winter, we are always looking at the Northern Atlantic Oscillation (NAO) along with the Pacific-North America (PNA) teleconnection. Each feature plays an important role.
First, with the PNA we are looking at how the jet stream may orient itself in the Pacific. The importance in this is for a + PNA setup where the origin or winds are coming from the arctic and polar regions rather than a fast, zonal Pacific flow (-PNA) which floods milder air across the country mixing out any cold that might be in place.
As we look into the first half of January, it appears that a substantial +PNA will take hold. The PNA will peak around January 10 at a 2-3 above standard deviation. What this means in laymen’s term is a lot of northwest winds flooding air into the country. This allows shortwaves to dig far south and help spawn areas of low pressure across the Southern US
At the same time the North Atlantic Oscillation (NAO) will peak at about 2x below standard deviation. A -NAO pattern supports blocking across NW Atlantic over to Greenland which for us in the United States prevents surface lows from cutting west of the Appalachians. For southern snow lovers you want to see a suppressed storm track. The -NAO looks to peak around Jan 7th and holds firm through the 10th before slowly rising.
The final global parameter is the Madden-Julian Oscillation (MJO) which has eight different phases. The MJO is a measurement of enhanced upward motion in the atmosphere across various sections of the globe. During the hurricane season we look at this for enhanced tropical systems and the same concept applies to winter weather as areas of low pressure are in more favorable environments. The current MJO which we have circled it leaving phase-7 and over the next two-plus weeks will move into phase-8 and phase-1. Those two latter phases are suggestive of extra lift in the Western Hemisphere. A normal MJO rotation takes about 60 days to complete. If you look back at how late this past hurricane season persisted, it was due to being in phases 8,1,2 in late October and into November. So, in essence we are due to re-enter those favorable areas in early January.
So, in review over the next 2-3 weeks, the US is going to enter into favorable phases of the NAO, PNA and MJO…and on top of that, it will occur around the coldest time of the year in terms of climatology. It’s been a long time since all three parameters have fallen into place in the heart of winter.
Does model output fit global parameters?
If you look at the main computer model guidance used to predict weather 7-14 days out, we are seeing signs of a pattern that fully supports the global parameters being indicated.
All signs are leading toward this upcoming week (Dec 30 – Jan 5) being a time of transition. We will have mild relatively days coming up but once we get to Thursday, a gradual stepdown to below normal temperatures begins. Below is a look at the wind pattern at 10,000 ft along with temperatures at around 5,000 ft. By the end of this upcoming week a ridge will be developing along the west coast which signifies the +PNA. That will shove cold air from northern latitudes into the United States. Meanwhile, a blocking pattern forms near Greenland, signifying the -NAO.
Once we get into the second week of January we have an intensifying west coast ridge (+PNA) while the Greenland block holds firm (-NAO). All of this is ongoing as the MJO are running through phases 8 and 1. During the timeframe the coldest temperature anomalies in the entire Northern Hemisphere are centered over the Ohio Valley and Appalachians.
Summary and Conclusion
The players are coming to the table to create a potentially active first half of January 2025. The strength of cold looks to be more certain as the 500/850 mb maps are matching up and just looking at the surface output from the model ensembles, we are going to have a prolonged stretch of daytime highs in the range of 10-15 degrees below normal.
For comparison sake, the average high temperature across the North Carolina foothills are in the 46-48 degree range during the heart of winter. Just do the math and you can see how cold it will likely be.
As far as the snow potential goes, no forecast can be nailed down a week out but just taking into the account of all three global parameters, there’s a belief that a synoptic winter weather event will be a case of “when rather than if it will happen”. One thing we can say with confidence is that a synoptic event is very unlikely over the next seven days. After Jan 5, all options are definitely on the table. Below is our current forecast for the next 10 days.
Stay tuned with us throughout the upcoming week as any potential threats down the road may become a bit more clear.