The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or 
Here is a graph to show you how fast the NAO and EPO changed and how when their values changed the country saw a major pattern change (Notice the negative anamolies in the 1st half of December followed by the positive anamolies throughout late December and Jan).... This shows the importance of these two indexes.
It has been proven that it is hard to keep the EPO in a strong state (positive or negative) for an exteneded period of time. However, the record breaking low QBO over the past month enhanced the Pacific jet allowing for the EPO to stay very positive for a long time (its now been 6 weeks) which has in turn been filtering the warm Pacific air into the US all of January. Because of this, I have had an admittingly strong warm bias over the past few weeks in regards to our overall pattern and storms (with good reason). However, things are now changing...
Two days ago, the NAO went negative for the first time since mid-December. With the negative NAO causing the Polar Vortex to move out of Greenland, and into a more favorable position in Central Canada/Alaska, we are seeing pattern change starting to take place. The reason the negative NAO hasnt flooded the US with extreme cold over the past week is because of the EPO. This index has arguably been the index that has had the greatest effect on the US so far this winter. The EPO is currently still in a raging positive state. With this staying very positive, we arent going to see any record cold at least in the short term. So you may ask... What can cause this index to drop or even go negative?
Since the raging Pacific jet has kept this index so high over the past month, the Pacific jet would have to weaken for a short period of time in order for the EPO to drop. As seen by the MJO chart that I am about to post, the Pacific jet is now allowing for a very strong wave to come across the west Pacific which means that the Pacific jet is currently in a relaxed state! We are no longer seeing record negative QBO numbers.
This has 2 major implications on what we will soon see in early to mid Feb....
1. The EPO should become a lot less positive, and eventually negative as the MJO passes through a stage that could enhance EPO cooling. Also, climatology says that the EPO cant stay raging positive for much longer. This soon to be drop is starting to come up very well on the MRF index model shown by the CDC's site....
<a href="http://imageshack.us" target="_blank"><img width="650" class="attach" src="http://img221.imageshack.us/img221/7239/119974pl.gif" border='0' alt="User posted image" />
</a>
2. It has been proven that if strong, the MJO passing through phases 8-1-2 correlates to a very negative NAO setting up. Since the MJO wave looks to stay strong as it passes through these phases, the NAO should continue to drop and reach a severely negative stage by Feb 1st. Again, the index models are picking up on this....
The EPO and NAO both becoming negative by Feb 5th will allow for cold weather to flood into the US. A negative EPO correlates more with cold in the Upper Midwest, GL's., and NW. A negative NAO correlates more with cold temps in the East and rest of the Midwest. Togeather, there are severely negative anamolies all across the US. We saw this in early December.
Not that we have proven that there is going to be cold in this timeframe, we just have to look at what part of the country will see the most cold from this.
In January 2006, the PDO averaged out to have a POSITIVE anamoly for the month. Data (I have been doing a lot of research on this PNA/PDO correlation, and I will soon post my findings) suggests that 76% of the time, a POSITIVE PNA is found in the month following one which the PDO was postive.
This means that we can now expect a positive PNA to occur during the month of February. I originally had a theory about the SOI impacting the PNA, but that theory has proven false upon further research. As seen here, the CDC's climate index models are now showing an incredible positive PNA setting up by the Feb 5th timeframe....
What a +PNA does is it puts a strong trough over the East while ridging the West. With the NAO and EPO both negative like they were in early December, the eastern 1/2 of the country could see severe cold when all this sets up by around Feb 5th.
With this cold pattern will come lot of surpressed storms, several snow shots for the MA and SE, and bitterly cold air throughout most of the country (with the exception of the west).
By Feb 15th, the MJO will enter a phase favorable for a positive NAO to develop, and with the Pacific Jet gaining strength once again, the pattern should change back to seasonal if not eventually warm again across the country.
Lets hope I get some...
