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Pattern December to Remember

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MichaelJ said:
To sum up the teleconnections on the 12Z runs, All have a strongly negative NAO/AO and a less negative EPO. The WPO is negative to neutral and the PNA stays strongly negative. The surprising thing to me is how close to the same forecast are for the CMC and the ECMWF, haven't seen this much before. Here are the CMC and Euro on the NAO
1639828800-30yWGvUaCwkgrb2.png
1639785600-iHGxP095EI0grb2.png

Here is the AO for CMC and ECMWF
1639785600-O5LJl7WNf4Ygrb2.png



1639828800-u15vWsCx07Ygrb2.png

A striking correlation.
Click to expand...

Thanks for posting these, which give me hope for a cold dominated pattern to eventually get here, especially if the PNA at least gets close to neutral.

So, the EPS/CMC mean has the AO getting down to a -4, which if accurate would imply a peak perhaps down to near -4.5 to -5 like the controls have. GEFS is similar with mean down to near -3.5.

For whatever reason, unlike the AO, WxBell maps have always inflated NAO by factor of ~~1.7 vs what is commonly followed (NCEP). You can tell by looking at today and the next few days and comparing to the GEFS runs per NCEP. NCEP has todays actual at -0.87 vs the WxBell Euro near -1.5. WxBell shows a forecast peak near -3.1 on EPS/CMC. The record NCEP met winter peak is only -2.5, which was on 12/22/1978. (OTOH, WxBell AO is ~the same as NCEP’s AO.) But even after reducing the WxBell -NAO peak of -3.1 to get it in line with NCEP, I still get -1.8, which is not much lower than the NCEP GEFS peak forecast near -1.6 and would still mean a very strong -NAO. The last met winter day with a -NAO that strong was way back on 1/4/2011, when it was -1.9. With an implied EPS/CMC mean peak near -1.8 and a GEFS mean peak near -1.6, a -2.0 peak wouldn’t at all be surprising thus maybe getting to the levels of 2010-11.

So, in summary, today’s ensemble forecasts imply to me a shot at a late Dec -AO peak of -5 and -NAO peak of -2. That combo would be very high up on the strong -AO/-NAO scale if verified.
 
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