The overall fall pattern is unfolding as predicted back in August with a largely warm September and start to October with cold end. Also, as expected, the pattern is shifting and November overall is looking milder and wetter for the East while the trough repositions back over the West as the indexes flip.
Based on all current and projected conditions in the ENSO index, NAO/PNA/AO indexes, Sea surface temperatures, low solar cycle and various long range modelling.. I believe the upcoming US winter should be colder than normal and considerably colder than it was during December and January last year.
Here is the current from the ECMWF looking 10 days out from now and you can see a rather zonal or west-east flow with cold to the north and warmth to the south. This is the setup I expect to see towards mid-month but before we get there, storminess will connect with cold to bring a series of cold, snowy shots into the West while ridging and warmer weather dominates the East.
The 8-14 days Climate Prediction Center forecast shows a cold West, warm East.
Here’s the CFSv2 November forecast
Current Sea Surface Temperatures
Water temperatures can play a crucial role in feeding back to the atmosphere and
Below are the forecasted SST’s through the upcoming winter from the CFSv2 and Jamstec models.
SST’s are important when it comes to atmospheric feedback as you know and it’s interesting when looking at the forecasted Dec-Feb global SST’s. While both CFSv2 and Jamstec models agree on the North Atlantic tripole of warm-cold-warm supporting a Greenland block, they disagree on SST’s over the equatorial Pacific. The CFSv2 shows a centrally positioned El Nino signal which supports a cold signal for the US while Jamstec is more neutral.
This disagreement is very clear in it’s forecasted temperatures over the continent. While modelling bounces from warm to cold almost daily, the Jamstec shows a warm winter for NA.
Here’s the Jamstec for the Dec-Feb period.
The CFSv2 has been all over the place when it comes to warm and cold but interestingly the CFS is persistent in the high latitude blocking, supportive of the warm SST’s extending from the North Pacific and Atlantic up into the Arctic.
In terms of the ENSO, I believe it’s either going to stay neutral through most of this winter or it will go into a slightly warm El Nino state with warmth out over the central Pacific. Warmth nearer to South America would support a warmer US winter. Models show the central based Nino.
NAO/PNA & AO
As expected, the NAO/AO is positive and with a slightly negative PNA, the next 2-4 weeks should support an initial Western trough/eastern ridge then a flattening out but look out for significant building of cold over the arctic as well as Canada.
History and projection of the NAO/AO and PNA via GFS ensemble.
Check out the below chart which shows the temperature response across the United States dependant upon NAO/AO indexes verses ENSO type.
Bare in mind I’m going for a -NAO/AO winter with neutral (La Nada) to weak central Pacific based El Nino.
Arctic Sea Ice Extent Greater Than Recent Years
Because of the more extensive arctic sea ice compared to the last 4-6 years, this should support a larger, stronger reservoir of cold air. The current +AO will continue to allow this building but look out once the index flips once again.
Check out the comparison in N Asia snow cover compared to this time last year. This too supports a larger, stronger reservoir of cold.
As for solar activity, well it peaked in the current ‘weak’ cycle 24 and is now heading for the minimal. While not as low as back around 2009-10, it far less than in 2011-12 when the winter was warm. Oh wait, when the sun was at it’s quietest in some 100 years was that winter (2009-10) not very cold winter over the US, Europe and East Asia? Hummm. The trend is downward and heading for those levels and I believe that is something worth considering for this winter as low solar activity along with warm SST’s support more high latitude blocking.
As for volcanic activity. It’s been on the increase up across Alaska with a few eruptions here as well as across northern Russia. These high latitude ejections, along with low solar and warm SST’s also encourage high latitude blocking.
Here’s an image capturing an eruption of Kamchatka in Russia. It’s likely that only the bigger eruptions which spew ash and other materials up into the higher atmosphere, have effect on weather patterns but volcanic activity cannot be overlooked.
So how does all the above constitute a cold winter for the United States?
While the trend in the NAO/AO supports the return of negative later down the road, it’s the warm waters and where they’re positioned as well as the low solar cycle and recent volcanic activity which backs up both me and the CFS idea of substantial high latitude/N Atlantic blocking this winter.
The key is exactly where those ridges setup. Right now I believe we’ll get two strong positives 1) up the West Coast of NA and the other over the Davis Straits between Canada and Greenland with a connection of the two over the top. This should at some point either mid or late December, all but empty the arctic into the Lower 48 as well as Europe.
Here’s the CFS 500mb heights
I believe December could bring the first real blast of winter both in terms of snow and arctic cold. This deep trough and arctic air mass may drop into the West or Plains before migrating east. It’s very tough to say exactly when this will hit and whether it comes in a progressive nature in the form of a series of clipper-like upper disturbances.
My suspicion is that between December 10-17th may be the period to watch.
December temperature anomalies
Here’s the CFS 500mb heights.
The model shows a classic blocking setup over the pole with major stratospheric warming event either mid or late December which leads to a major cold spell into early or mid-January. An arctic blast which the Plains, Midwest and East hasn’t seen since 2009, perhaps even extending back to 2004. This should be a cold which holds for a prolonged 2 weeks or more and we could see one or two significant East Coast snowstorms just as the motherlode of cold drops into the heart of the nation.
January may end milder with the final 10 days seeing a thaw.
CFS January temperatures
Here’s the CFS 500mb heights.
February may start mild but more cold is sure to dive south once again.