Models are used for guidance! In times like these with so many changes occurring they tend to flip flop with models.  The late November snow storm for some/rainstorm for others was predicted by the medium to long range models to be a lake cutter.  Through using tropical forcing and the observations I knew that the threat for a significant model would shift eastward and it did.  If the models are right and it does not get as COLD as we originally thought it still is a huge improvement from last winter we just miss out on the arctic stuff.

Since we are on the topic of models lets knock this out of the way first and see where we stand in today's 12z run from the GFS mean and Euro:

Above are the day 7-10 Euro and GFS Ensemble means

A few things stand out here:

1) The very strong PAC Jet giving everyone nightmares of last winter with the positive WPO look.  This does not make a lot of sense given where he are headed with the pattern.  The GFS is better here with higher heights heading into the GOA instead of a deepening trough.  

2) The area circled on the European with a question mark is a trough extending into the Caspian Sea.  This will not be a feature we have to worry about like last winter as the stratosphere is showing signs of very cold temperatures invading this part of the Globe.  This would lead to a signature closer to the GFS with a strong Caspian ridge.  

3) The shifting and decreasing stratosphere temperatures across the Polar areas really questions the intensity of the PV over NE Siberia into the Arctic Ocean.  

Now here are the stratosphere temps:

Notice the cooling of the warm Stratosphere around our Polar vortex and the increasing cold pool of air extending westward across our polar areas.  The warming continues to invade the CONUS which would suggest colder air/troughiness.  

Well the stratosphere supports a colder look to the pattern what else:

The MJO entering phase 1 has been agreed upon from many models and ensemble members :

A phase 1 is being showed by both the European and the Euro ensembles and the GFS op and Ensembles. A phase 1 in December looks like this:

Now weather is not textbook like this, but we can see the general pattern for a phase 1 in December and we can take a lot away from this image as we go forward in the next 10-15 days.  The PNA on this image will most likely not materialize for an extended period of time :( sorry, but the deep troughiness extending into the Eastern US could bring a very interesting set up.  A pulse amplification around the time of the next big storm system around the 19th could also be very interesting.  

The area across South America into Mexico is an area we will be watching closely as strong upward motion of the phase 1 favors convection in the areas outlines.  We can already see a phase 1 look but the variablity of tropical convection elsewhere is leading to a weak signal.  A kevin wave that has been progressing across the equatorial pacific will continue to warm the waters in the eastern Pacific just in time for the phase 1 which could allow an impressive breakout for convection given the projected signal of the MJO impulse. This supports (as shown above) a deeper trough in the Eastern US.

Southern Oscillation Index:

You can see from the map above that pressures have been dropping over Tahiti and the latest values of the SOI are very impressive with a noticeable decrease over the last few days.  We are seeing values below -30! That is something that has not happened in a while and this noticeable shift should send a pattern amplification to the US around the 15-18th.  

***********DEC 10th value nears -50!

Mountain Torque and Global AAM

As we discussed in my last blog significant negative AAM anomalies will be marching poleward and be in place for the 15th which is right on schedule.  But another thing I noticed is the EastAsian MT is the exact opposite of last winter and the consistent negative values will continue to act to disrupt any vortex/low heights that try to develop in the GOA. Latest image you can see the E Asia MT head towards neutral but another significant drop is likely given the GWO phase and tropical forcing and current frictional torque indications.  

Conclusion:

The pattern change is coming!  You will be able to feel it shortly after December 15th I promise! The argument right now is it won't be arctic cold it will just be cold.  Given the unfavorable setup showing up on the ensembles and models that we showed above they STILL show a lot of cold air despite the unfavorable look and this is related to our snow cover being well above average.   The 12z Euro Ensembles for day15 has cold air over us and has been showing this for a while.  This is the BIG difference from last winter because the cold air is already here and with the PV not in a favorable spot and a rather zonal flow across the CONUS we see these numbers:

- Models are changing and showing us a return to below average temperatures for the second half.  It will not be arctic cold but it will feel like winter. If models adjust to the thinking I laid out above these temperatures will be colder.

- December 19th storm threat as shown by the European to go into the Ohio Valley needs to be watched.  In terms of our slow pattern change process to the cold arctic air this is a good track.  But with the things I outlined above we could sneak another Northeast snow event in here which would make many of you very happy!

- January is going to be very cold.  Is the pattern change getting pushed back? NO   Is the arctic air getting pushed back? Yes

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