Sunday, 6 October 2013

Late Winter Stratospheric Warming Likely

Warm SST's between 180W and 120E has been helping strengthen the MJO wave in phases 5-7 over the last 3 weeks. This, combined with a strengthening GOA cool pool and confused atlantic tripole has helped develop a very warm pattern in the eastern part of the CONUS.
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Upward motion has generally been strongest in octants 5-1 of the MJO over the summer months. With a similar tropical pacific SST configuration continuing this means that this overall MJO setup should stay fairly consistent unless pattern drivers shift. Long range modelling such as the cfsv2 and ecmwf have been showing a warm pool developing in the central tropical pacific by late fall/early winter. If this setup forms then the MJO will tend to focus more towards the cold winter phases 7-1 as opposed to 5-7 which we are seeing right now. The question continues... can we see this shift occur.
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Another important shift we need to see is a cooling of SST's south of newfoundland and nova scotia. This has been very unfavourable for a -NAO pattern and has been causing heights to rebound very quickly along the eastern seaboard. Good news is that solar activity is expected to drop off and indications are pointing towards a pattern change by late october with a more favourable pattern for blocking. Siberian snow cover continues to remain well above normal but it is important to note that we want to see an increase in snow cover south of 60N according to an updated paper from Cohen et al.

Confidence continues to stay high with regards to a warm DEC in the east with a wet and cool pattern in the west. Analogs and modelling continue to stay in decent agreement. In sharp contrast, JAN-March looks increasingly interesting across the eastern CONUS. Looking back at +QBO, Low Solar and neutral ENSO years (85-86,90-91, 80-81 and 01-02) I found that in all cases their have been at least one late winter stratospheric warming event. With the expected warming ENSO state things could get very interesting in late winter and early spring if warmth can work its way down to 500mb. With an overall state of low solar continuing, this winter should be no different then the analog years with late winter EAMT events helping disrupt the upper stratospheric vortex. 

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