Here is the long awaited North American update, with extensive analysis in the climate drivers section towards the bottom. Also includes model analysis….
Per EC Weeklies, Labrador and Aleutian ridging hold a low over NW North America stretching down to the SE US. This would to bring snow and cold to the Central and Eastern US.
A similar setup, but ridging to the south reduces impacts towards the north of the US, with Canadian troughing remaining.
Ridging increases over most of the US, with Northern troughing pushed towards and into Canada. Aleutian ridging starts to move towards Canada, and a low grows south of the Aleutians.
-EPO ridging builds, reducing snowfall for Western US, but increasing it for NE US, driven by ridging building to the west and south, and laid out by the North Pacific low.
The Aleutian Low continues to strengthen, and so does -EPO ridging. Troughing is restricted to the NE US and Atlantic Canada/Quebec towards Greenland, and just off the SW US.
CFS above shows the present MJO pulse, weakening into Phase 7/8, reducing the influence of the tropical wave. However it’s weaker, yet present impact still carries to the Atlantic. CFS notes hospitable tropical conditions for the long term in the Central/Eastern Pacific region, which may work well for the Eastern US.
However the opposite pulse through Maritime Continent will mean that there is unlikely to be another lap of the MJO around for quite sometime into February. Once the MJO signal fades, it is unlikely that we will have a strong tropical influence besides the lack of convection over Maritime Continent. This is probably not going to mean a sustained pattern change, and looks to more of a continuation to the up and down nature of the climate this year.
EPS-46 still shows that base state in the Western Indian Ocean (albeit slowly weakening in late Feb and early March), unlike CFS. It shows the same Maritime Continent conditions, but for a shorter period. EPS shows some sort of Phase 3-4-5-6 progression fo the tropical signal in Mid February. This is more likely to work out for the Western US, particularly with those earlier phases California.
The GWO (above) (represents extratropical impacts) is currently going through an abnormally positive orbit through GWO Phases 6 & 7. This has firmly established stronger momentum in a global context. The question is whether this is a once-off, or the sign of a new phase in terms of atmospheric conditions globally.
The vast majority of momentum has been added into the tropics, by the very strong recent MJO pulse. That addition of momentum has now subsided with the strong Frictional Torque back to neutral.
You can see above in the NH, the positive momentum in the poles and the negative momentum in the extratropics. Ideally IMO this would be reversed. The poleward mild +AAM deposits are just adding to a +AO state, which is benefitting the PNW/BC in terms of snowfall, and not so much for the Eastern US.
Strong mountain torque is expected to be sustained for a decent period of time, currently sustained by +MTs in North America and the Andes, and soon to be controlled by a strong +EAMT driven from the last few days of Jan into the early days of Feb. This is going to sink lots more momentum into the Pacific basin. We should see the impacts of this in the 5th-20th of February period.
So what I’d argue for is a change from the existing pattern that benefits the PNW/BC, towards one on the Western US that benefits the SW and California more for mid-February. I’d also argue that the mid-February period is likely to have elevated cold and snowfall risks for the Eastern US. This is all due to a jet extension of the North Pacific jet at it’s peak 7-10 days after the +EAMT event. We are also seeing some medium term trends of heading towards more equator-ward movement for the jet stream.
The one other block in this puzzle, the Arctic Oscillation threatens to dampen the impacts of this tropical to extratropical momentum transport.
EPS refuses to change its AO base state at all, as above. CFS also remains positive until late February, for a decent dip into the negatives during early-mid March.
In terms of the stratosphere, we have some decent wave-1 amplitudes coming through, leading us to this signal in 10 days:
As you can see this struggles to make much of a dent on the SPV, other than the typical slow demise, that does little towards changing the AO pattern. There’s still a chance of a SSW later in Feb or even March, but each day and each forecast that goes on reduces those chances.
- PNW/BC/Northern Rockies to remain good for the next fortnight, reducing in the second week of Feb.
- California/the SW/Southern Rockies to improve for the latter half of February (maybe a bit earlier)
- Eastern US expected to improve for the last 15-20 days of February (2nd-3rd weeks of Feb, possibly into the 4th week) IMO.
- These impacts may be reduced/weakened by Arctic influence, etc.
Thanks so much for reading. I hoped you enjoyed reading it.
Disclaimer: There is low skill asssociated with using long range model forecasts to find snow systems.
Thanks again for reading this North American long range snow forecast, follow me on Twitter @longrangesnow and subscribe to my email list by clicking on the tab on the main header above.