Sunday, 6 January 2013

Winter Comeback On The Way

Their is some very interesting weather to talk about this morning! First let's take a look at the latest ECMWF forecast for the MJO. Notice the eastward propagation through phases 4,5 and 6 which line up nicely with our January thaw that I believe is coming to an end by the 18-23 of january. This lines up well with the MJO wave which is entering phase 7 which  favors eastern cold by the 18th. The UKMET ensembles have a similar outcome and are basically in line with the european albeit more amplified.
Paul Roundy's OLR site goes out a little bit further into the long range. From now until the 18th we can see the MJO transitioning from phase 6 to 7 but it gets really interesting from the 19th to 26th when the MJO propagates into phases 8 and 1. During this time period the stratospheric warming event begins to push arctic air into the mid latitudes. This is one reason why I believe the cold will eventually progress eastwards after the 20th of january.
Phases 8 and 1 of the MJO look like this in January:
Phase 8
Phase 1



 Quite a battle will be going on from the 16th to 25th as the arctic air is pressing against the southeast ridge. A baroclinic zone will set up across the appalachians, interior northeast, eastern great lakes and the coastal plain. With a SE ridge and east based blocking in place most storms will take more of an inland track but some east coast storms are very possible.

500mb height field shows the blocking connecting over the pole and a stormy pattern for the interior


 Now let me explain some of the other players on the field. A very important observation is the current  SOI drop caused by the eastward propagation of a kelvin wave in the pacific. This is yet another sign that will help to transport very cold air into north america which is in line with the MJO and SSW events. Daily contribution to the SOI is well negative. This drop in the SOI will force a compensation across north america which will help flip the pattern to colder.


Another interesting player on the field is the extreme amount of blocking that is forecast to take place. It looks like the ECMWF and GFS are showing what should happen given the physical drivers on the field which i have displayed for you guys. The 06z GFS OP is pumping two strong ridges, one across alaska and another across eastern greenland. These ridges connect over the top which really allows the cold air to penetrate the east. An event like this is called a cross polar flow pattern which means that the jet stream extends so far north that it can pull siberian air(extremely cold air) well south into the north american weather pattern. The GFS shows this type of setup with a deep trough over the central and eastern u.s. Keep in mind this is a run of the operational past 240 hours out so caution is warranted. The ensembles have a less amplified solution which is common this far out.  The CPF event continues for several days as the PV collapses southwards after the 20th.



The european OP is moving towards the GEFS:
The NAO responds:
As you can see current observations from the tropics, stratosphere, indices and now the modelling are all pointing towards a huge change in the overall North American weather pattern. Don't put away the shovels just yet the second half of winter is going to be a wild ride!




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