1ST SPECULATION OF WINTER 2016-2017
I suppose the first question that many are going to ask is WHY am I talking about the winter of 2016-17 in the middle of August? It's a fair question I suppose. I am mostly doing this because so far the hurricane season is not been particularly exciting ...but also because there is important new data which has come out recently with regard to how the developing La Nina event is unfolding.
Before we get started we have to understand some basic concepts about La Nina Winters over North America. Generally the consensus is that the stronger the La Nina more likely the winter is to feature warm than normal temperatures for the central and eastern U.S. and below normal snowfall. In general the data does support this but still have been some exceptions.
The first buzz notice about the upcoming Winter probably came about because of the July 1 Japan climate model. This climate model ( which did very well last year for the Winter of 2015-16) ... was forecasting a very weak or nonexistent La Nina for the Autumn of 2016 and Winter of 2016-17. Not surprisingly the temperature forecast for North America was cold for anybody east of the Rockies. However that was the July 1 Japan model which as we can see is based on a nonexistent La Nina with sea surface temperature anomalies (SSTAs) near neutral across the equatorial Pacific.
However the August 1 update has just come out and it is significantly different. As you can see the New Japan, the model now forecasts a weak La Nina event which causes its climate models to have a significantly different solution for the winter with respect to temperatures. And we can see that here.
As you can see the difference between the July 1 in the August 1 Japan climate model is quite significant and it is very heavily depended upon how strong or weak the La Nina is going to become. There are several other climate models we can take a look at.
Here are the Mid JULY IRI climate models and as we can see all the models show colder than normal SSTAs across the equatorial Pacific but only half of these models actually show the water to be cold enough to support a very weak La Nina event. On this image the YELLOW LINE represents the mean of all 26 models and as you can see their minimal weak threshold conditions of La Nina is achieved.
The European ENSO climate model forecast for region 3.4 from early July can be seen here. The updated forecast for August should be out within the week all we can clearly see that the models forecasting the weak La Nina to reach its peak intensity in August or early September then undergo steady weakening as we move into the winter of 2016-17.
Another image we can view is the NMME enso forecast model projections from mid July into the Spring of 2017. This image shows 8 of the main climate models and most the data shows weak La Nina developing during the Autumn but weakening steadily and fairly rapidly throughout the Winter. This would seem to favor a somewhat milder than normal autumn but potentially a colder than normal and stormy of the normal winter for the central and eastern U.S..
Next let's take a look of the Australian models which are somewhat more simplified and easy to read. This image compares the 8 different major climate models at October 2016 and December 2016. Notice that many of the climate models show the La Nina weakening by December 2016. The lone exception to this is the CFS /NWS climate model which shows the La Nina actually holding steady and slightly increasing in DEC 2016 ...and reaching the minimal threshold criteria for a weak La Nina event.
Indeed if we take a look at the American or CFS / NWS enso model we can see that over the past 30 days it has not changed very much an all. Of the 8 Primary climate models forecasters… the CFS shows the strongest possible weak La Nina conditions being achieved by December 2016 at approximately -0.75C. But again the trend is quite clear the after December 2016 the La Nina rapidly breaks down and becomes neutral for the second half of the Winter into the spring of 2017.
We can see the impact of weakening La Nina into Neutral conditions has on the CFS model temperature forecast by comparing the rather warm DEC 2016 with the much colder January 2017. In addition the precipitation maps are also significantly ominous looking for January 2017 with a large area of above normal precipitation stretching from the Deep south into the Ohio Valley and the East Coast where the cold area is situated.
Finally in take a look at the new and improved CA SST analog forecast model which is based in part by into SSTAs along the equatorial Pacific.
This image clearly shows that the cold sea surface temperature anomalies SSTAS will develop across the central portions equatorial Pacific and not off the coast of Peru. This development of the temperature anomalies and the central Pacific is the fur to as a MODOKI enso event. Most MODOKI events which have occur over the past 50 to 75 years have been warm or El Nino events. Cold water / La Nina Modoki events are rare and somewhat difficult to anticipate. The last one was back in the winter of 1995 -96 which of course will get winter weather lovers extremely excited along the East Coast as there were 4 major snowstorms - 2 of which were blizzards . Of course this is just one sample or Datapoint and it's far too risky to simply make that sort of blanket assertion that this winter is going to be like that infamous winter. If this trend continues I am sure there will be a lot more talk regarding the developing La Nina in the central Pacific and what it means for the winter in the western hemisphere.
This image represents the upper air maps for the heart of the Winter DEC JAN FEB. The model implies significant Ridging or a positive height anomaly --a blocking pattern over North Central Canada. This could qualify as a -AO (arctic oscillation) feature. In the second half to winter we see very pronounced trough centered over the East Coast and the Great Lakes along with indications of a significant RIDGE over Northern Alaska into the arctic region supplying the cold air. But the pattern APPEARS to turn more favorable for cold/ snow over the eastern US in the 2nd half of the Winter
If we take a look at temperatures and precipitation we see that early in the Winter only the East Coast looks to be fairly wet and cold. But in the second half of the Winter JFM the temperature anomaly maps show a large area of much below normal temperatures east the Rockies covering all the Midwest and the East Coast.
So at this point it APPEARS that most of the climate models are predicting a weak La Nina event OR a non event with SSTAs that have below normal where temperatures but not cold enough to qualify as a weak La Nina. Going back since 1950 there are six Winters that featured similar conditions in the equatorial Pacific. Those analog years are the winters of 1954-55... 1964-65... 1974-75... 1995-96... 2000-01 and 2011-12.
These two images show what the temperatures and precipitation was like for those winters. Notice that the cold as temperatures over all appeared to be centered over the Pacific Northwest into the northern Rockies and the Upper Plains... and there appears to be a small area of slightly in milder than normal temperatures from Virginia too Louisiana.
If we look at the large scale hemispheric pattern for these winters... we can see some interesting features here as well. Obviously there is a huge negative anomaly -- the dark purple - over Northwest Canada which extends south nto the Rockies. There is a strong positive anomaly in the Eastern Pacific Ocean but it does not extend to the west coast. We also see a strong positive anomaly - A RIDGE or a BLOCK- over southern Greenland and over the north central portion of Siberia along the arctic region. This sort of mapa is NOT an ideal map for big winter storms for the East Coast but it is also not a terrible map either. It's a very good map for winter lovers located in for the Midwest and the Plains states.
However as we saw from the CA SSTA - constructed analog from forecasted SSTAs - it appears that the second half to winter could be significantly colder and stormy are than the first half. Indeed that does seem to be the trend over the last few winters.
Taking a look of the second half of the winter... we see a colder stormy overall pattern. The positive height anomaly or block over Greenland appears to be much stronger and extremely intense but we also have a strong negative anomaly or deep trough over the western half of the country. To the south there is weak ridge located over Florida and the Bahamas. This sort of pattern argues for winter storms coming out of Texas and the lower Plains and tracking in a ENE direction. The pattern seems be very similar to the extremely active winter we saw in 2012-2013 which saw numerous small to moderate winter storms affecting much of the country but very few large powerful ones.
Focusing more on southern Canada and the US ...the temperature forecast for the second half to winter fronm these 6 analogs shows more impressive cold pushing deeper into the country from Canada and the mild temperature anomaly looking very weak along the Southeast US coast. And the precipitation anomaly also looks promising for the eastern US with a large area of above normal precipitation running from the delta into Virginia and up to Pennsylvania and the Ohio Valley. This is somewhat similar to what the latest version of the CFS model is showing.
Finally let me conclude by adding a few remarks. First this essay should be viewed as informed speculation and NOT as a post an actual winter forecast. So please keep that in mind. On other concerning factor is a course whether not the La Nina develops in the central equatorial Pacific or the eastern Pacific off the coast of Peru. The former would represent a special type of El Nino event known as a Modoki ....which is generally much more favorable colder and stormy than normal winters for the central and eastern U.S. So far this La Nina has underperformed it we compare its current status over the last several weeks to how the various climate models forecasted this La Nina to develop. This tells me that the odds of the La Nina reaching "moderate" criteria is quite small and there is a very good chance that this La Nina may only briefly reach the technical threshold for a weak La Nina this autumn before weakening.