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Mid to Long Range Discussion ~ 2023


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 While we're waiting on the 0Z runs for the potential Feb 12th snow, I'm going to go back to the much longer range in this post, specifically related to the upcoming SSW. 
 Check out the tweet below, which is a reason to closely follow Arctic stratospheric progs of the EPS (including weeklies), GEFS, and others. The strat, after a SSW, is more predictable than the upper tropospheric pattern starting with day 5 and is much more predictable by day 15 in the Arctic. Note the lighter colors (lower correlation) in the lower levels meaning more difficulty.

 From this, one can infer that the models tend to have a very hard time predicting AO/NAO indices and other possible downward reflections into the Arctic troposphere after an SSW, despite the SSW, itself, being highly predictable. Look at day 23, for example. Whereas the strat above 100 mb still has an impressive anomaly correlation of 0.6 to 0.8, the upper troposphere (300 mb) has already plunged to under 0.2! So, keep this in mind as regards the extended models getting a good handle on where our sensible wx may go late this month. It is very highly unpredictable at this point in time even though the strat is much more predictable. So, expect a lot of change on the models as we get closer.

 From the same Twitter thread: "... so even though the winter stratosphere is relatively predictable, the models can't effectively translate that skill down to the surface. Nevertheless, the *potential* predictability linked to the stratosphere is good reason for following these forecasts closely."

 Or put another way by Dr. Simon Lee:

 "The stratosphere can be extremely predictable -- particularly after SSWs -- but both model deficiencies *and* unrelated tropospheric noise means this doesn't perfectly translate to tropospheric skill."



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Just now, Sandstorm94 said:

Probably is under that bowling ball ULL... They generate their own cold air so you can not go by the surface temps shown

Sent from my SM-S102DL using Tapatalk

I'm aware but the upper low has to be closed and quite strong for it to puke snow with this airmass 

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Overnight runs aren't necessarily all that great. Yes, models are currently converging towards an ideal track and evolution of The ULL. But not only is this very much subject to change, but the Euro shows, how even a pretty good outcome, which is like, 90% of the way to the GFS, just doesn't get the job done. Also the 0Z GFS tracked like 50 miles more inland which pushes the piedmont out of the good banding. 50 miles further east and you get something more like the Euro. It's delicate to say the least and we have at least 48 hours before we can really know what's going to happen.

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14 minutes ago, msuwx said:

Folks complaining about the overnight runs must not have been paying attention this winter. At least it's something.

Yea really don’t have a single complaint considering I myself haven’t seen accumulating snowfall for freakin ever. Worst case scenario favored climo spots score. Best case the ULL bowling ball allows a whole bunch to cash in. 

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