2045 HRS EST 29 NOV 2011… STARDATE 201111.29
I am doing it this evening update because several things have changed on some of the afternoon models which deserve comment.
A lot of the speculation in the weather committee both within the energy sector and those on the various whether forms that the winter is in trouble or delayed or not going to be significant has been based primarily on the perception that this winter was going to get off to a bang upstart… in a manner similar to what we saw last winter and in the winter of 2009-10.
Since that clearly is not going to happen…. a lot of the energy meteorologist and private sector weather information providers have been backpedaling on their winter forecast. I am one of them … my DECEMBER 2011 forecast is probably going to be too cold east to the Rockies with respect to a temperatures…. especially in the area were a have the -4° F region. My point however is that once the energy forecasts became known through the weather hobbyist community it caused a corresponding increase in the dissipation and expectations – HYPE. Now that we have all had to backpedal on that …we are seeing the same affect swing the the other way.
For example even though most of the model data over the past 24 hours have a showed a pretty strong -EPO West coast ridge ( +PNA) and downstream trough in the jet stream over the Midwest in the 6-10 day. But the overwhelming amount of consensus forecasting from the various private weather servic’s has been that it is not going to last. In the 11-15 day the +PNA is going to break down.
In other words the -EPO will lose its intensity and the West Coast Ridge will collapse and it will slide back out towards the dateline in the north Pacific . This means of course no flow of cold air into the central and / or eastern Conus and it could even imply a return to -PNA ( West coast trough) which is the pattern we are just now coming out of and which has dominated North America since Halloween.
The reason why these private forecast services have been suggesting that is because the model data was showing that! In other words they are not making this up….
For example here is the 0z 11/29 run of the ECWMF 500 MB for day 9. As you can see the entire West Coast ridge pattern has completely broken down.
So then …the KEY ISSUES are 1) how Long does this cold pattern last?? 2)Does the +PNA pattern break down and do we return to a pattern like we have seen for much of November???
In my opinion the argument that we are going to see a return to a super warm -PNA November like pattern is wrong because it misses how we ended up getting such a warm pattern. It is NOT the had a -PNA pattern and +NAO over north America. There was something at play here.
The super warm November of 2011 was caused in my opinion by the development of a large 500 Low– a POLAR VORTEX — over Siberia which moves across the Bering sea into Alaska during the month. At the same time a Ridge in the North Pacific was trying to expand and push north towards the Aleutian islands and the south coast of Alaska. These two forces cause the Pacific jet stream to “COMPACT” : we could be seen by noting the very strong wind speed velocities at 200 MB during the month of November over the north Pacific. At times the speed were up to 200 knots. This extremely fast Pac jet not only ensure a persistent trough over the West Coast but it also cut off the flow of any sort of cold air getting into central or Southern Canada.
All that being said it should be pointed out that the GEFS– the GFS ensemble– has been much more bullish with a cold pattern for North America. The Tuesday afternoon /12z run of the 11/29 ECMWF the European model change direction dramatically and ends up showing a vastly different pattern the one who showing this morning and one that is much closer to what the GEFS has been showing for the past few days. Even more surprising is that the European ENSEMBLE agrees with with the Operational European and the GFS / GEFS ensemble!
To show you how big the changes are let’s take a look of this first image. There are four maps here…. Both maps on the left side are the Day 9 European model … on the right side are the day 9 GFS model. the TOP are the 0z runs the Bottom maps are the 12z runs. As you can see the European high showed a huge change from 0z to 12z runs.
Now that this sort of BIG Model flio flop is not always a good thing because that sort a big change in model consistency especially with a good model like the European can be troubling. On the other hand the fact that the European is turning towards the GEFS ( GFS ensemble) could be significant.
Here is the 12z 11/29 GEFS at Day 10. I have e highlighted some important features here so that you can see why this map is significant.
By 324 hr the GEFS is showing some changes. The Big west coast Eidge ( the +PNA) has broken down and is moving (retrograding ) west towards the dateline. But also note that the bright red area over the azores at 240 hrs is STILL there at 324 hrs.
This image shows you the day 10 euro from the 12z run 11/30. I have highlighted some features for you to take a look at. Let me be clear– this is not in any way a Major or a Severe arctic outbreak of cold air. This is a good cold (seasonally cold ) early December looking map.
But clearly the most important feature on the European is the development of a strong north Atlantic Ridge in the north central Atlantic which appears to be pushing into Iceland and the southern tip of Greenland. This is not technically a -NAO but by Day 10 it appears to be on its way of becoming one. Again this is a major change in the European model and it does so because the model develops a strong piece of energy — a shortwave– that bombs a surface Low off the Gulf of Maine Coast DEC 7. This Low moves up into southeast Canada which in turn causes the N Atlantic ridge to develop and expand towards Iceland in Greenland.
The 12z European ensemble generally supports the operational European to a large degree. As you can see the model actually does support the north Atlantic Ridge Building towards Iceland / Greenland which quite frankly surprised the hell out of me because I thought the operational European was on its own. In addition the model has slowed down the movement of the West coast ridge sliding back to the west somewhat.
To show you what this looks like at the surface …here is the large scale day 10 European map with 850 mb temps…
and the close up view of Just the CONUS and far southern Canada. As you can see as cold and over the upper Midwest and the Great Lakes it’s pretty darn cold.
Here is the 12z 11/29 run of the GEFS 500 MB height anomalies for the 6-10 day and 11-15 day. As you can see that very strong positive height anomaly along and just off the west coast of Canada in the 6-10 day . IT does slide WEST in the 11-15 day. This causes the cold pattern to relax somewhat but that does not mean we are going to see we turn to the super warm pattern of Nov 2011.
The GEFS does not show a strong north Atlantic Ridge expanding into Greenland and Iceland at day 10 0 or day 13. Instead the model has a very strong “Azores Ridge”. And that has to be watched because it is very possible that the relaxation of the excessively stormy pattern in the northeast North Atlantic will allow this Azores Ridge to expand towards Iceland.
One last point…. The current MJO impulse does not support a prolonged +PNA and true classic -NAO. Most of the MJO models show the current impulse weakening as it moves into phase 4 and 5 and then collapsing or dining in the circle of death. The change from what we saw on Monday and over the weekend…. when the various MJO model forecasts showed a strong MJO impulse. If in fact the trend is correct and the current MJO impulse collapses this COULD allow for a more rapid transition to a new and cold a pattern over North America.