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Winter 2022/23 Medium/Long Range Discussion


Chicago Storm
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Pretty incredible agreement on an extreme 5-day mean pattern on all 3 ensembles 5-10 days out (December 16-21)...and this point, that's unlikely to significantly change:

Euro ensemble:

603113557_EPS5-10.thumb.png.352fe5ce2942e014365da6000cf3fd85.png

GFS ensemble:

361668276_GEFS5-10.thumb.png.e7a3864e4a11bc1f130ddcb0aa37608b.png

Canadian ensemble:

1563274062_GEPS5-10.thumb.png.69b16c8bf97a446b8e21d4f1eaa56301.png

All three have a huge ridge over the northeast Pacific and Alaska extending to the north pole, facilitating prolonged and robust cross-polar flow. Plus, a west-based -NAO persists. 

Sub-tropical jet looks fairly active, thanks to a ton of momentum getting added to the Pacific jet stream over the next week or so (this also contributes to the huge ridge into Alaska). Suppression is a concern, but this is definitely a robust clipper pattern too with such amplified flow out of Canada. And, if we can get sufficient wave spacing and a shortwave can amplify, the blocking does support amplified, slow-moving systems across the central and eastern CONUS...but again, would need proper wave spacing or else we'll get more numerous but more suppressed systems in the sub-tropical jet. Because this is a La Nina there will be a gradient with frequent systems somewhere, likely south of the entire region at times, but when blocking relaxes or if a stronger shortwave in the subtropical jet comes along it could shift north at times. 

Regardless of how much it does or doesn't snow, much of the CONUS will be cold to very cold in the lead-up to and then through the holidays. Severe cold will pour into the northern Rockies and Plains at times, with large pieces of that coming east. Really is hard to draw up a better pattern for Arctic air outbreaks, and at least some snow potential appears to exist. 

A couple important things happening teleconnection wise in the near future...first, a huge Siberian high descends into eastern Asia later this week. A strong "positive" east Asian mountain torque, which will add significantly to the Pacific jet stream:

eps_mslpa_global_fh0-240.thumb.gif.b9b51c889633e5cbb75517d916c94d27.gif

Note how shortly after the huge high descends out of Siberia, the Rossby wave train amplifies significantly over the Pacific, allowing the huge ridge to pop into Alaska. It does not hurt that the MJO is becoming more coherent and moving into the western Pacific after mid-December:

eps_chi200_global_fh-24-240.thumb.gif.e6e211041d5ad67b6f41c9868026df90.gif

This also adds to the Pacific jet...looking at the op Euro, note how early on in the loop there's some enhancement to the Pacific jet from the first little high descending over East Asia. This begins amping ridging towards Alaska. Then, the larger high descends and convection increases over the western Pacific, adding a ton of momentum to the jet and causing the ridge to amplify in a huge way over the eastern Pacific:

ecmwf_uv250_global_fh0-240.thumb.gif.49d362b3d77b7a05800f0eba4672d246.gif

Long story short, the north Pacific ridge has had a propensity to amplify this fall and is about to do so in its most significant fashion yet over the next 5-10 days...this will lead to a pattern very supportive of extreme cold into the northern Rockies and Plains, with cold anomalies dominating most of the CONUS before and during the holidays. Snow potential will inevitably come and it's possible the sub-tropical jet has some activity, but some uncertainty lingers regarding more significant snowstorm potential. 

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