This Winter forecast has already undergone some significant changes. When I initially began the Winter 2016-17 outlook during the middle of October, I was significantly more "bullish" on the overall winter than I am now. The appearance and persistent position of the Polar Vortex (PV) in Siberia and the enhanced Pacific jet stream over the past few weeks are somewhat troubling signs. That being said I am not bearish or fading (to use trading terms) the winter of 2016-17 especially over the central and eastern CONUS. But the appearance of these two important factors in November along with some strange behavior by the QB0, do have me somewhat concerned with respect to WHEN the winter pattern is going to setup and how severe it may or may not be. What you will not see in this winter forecast are predictions for snow fall amounts. In dealing with seasonal forecast it is hard enough to figure things out without having a guess about snowfall amounts for particular cities / regions. I know a lot of TVmets do this sort of thing as do some private forecasters, but here at WxRisk.com,we do not BS. If you want to skip all the science (I dont know WHY anyone would want to do such a thing but there are some freaks out) use the other link, or scroll down to the end of this report. However, it is our view that doing the science and going through the steps is as important as coming up with the right answer. A lot of people don't understand this as the emphasis in our culture is on getting the right answer. For example If I forecast the winter pattern based upon the number of socks in my dresser draw and the forecast turns out to be correct it doesn't mean my technique was scientifically based and/ or it can be used in the future.
Winter of 2015-16 was an exceptionally mild winter over most of the country because of the super powerful El Nino event. The month of December 2016 may have been one of the warmest Decembers on records especially east of Mississippi River. The super El Nino event has faded but there is still some residual warmth left in the atmosphere. Even though there was a massive snowstorm on the East Coast at the end of January 2016, most of the country saw below normal snowfall as well.
The main issue for this winter will be a weak La Nina event but even that presents a lot of uncertainty as to whether not it is going to continue through the Winter or fade to neutral conditions as we begin the heart of the Winter. Perhaps the biggest dilemma of the winter -especially for the first half - is the appearance / position of the polar vortex (PV) centered not in western hemisphere but over in Siberia on the Russian side of the Arctic circle. Having the PV in that location is a very bad sign for those hoping for an early start of the winter over any portion of North America. KEY FEATURES The weak La Nina event - generally a neutral or favorable factor over the central and eastern U.S. with regard to running either an average or above normal and temperatures running either average or below normal The near record snowpack over Siberia in October 2016 which is spread rapidly westward into central and Western Russia over the past two weeks. - a favorable factor over the central and eastern U.S. with regard to running either an average or above normal and temperatures running either average or below normal The strong indications for high latitude blocking patterns - a favorable factor over the central and eastern U.S. with regard to running either an average or above normal and temperatures running either Below Normal or much below normal The weakening and decreasing amount of solar activity - generally a neutral or favorable factor over the central and eastern U.S. with regard to running either an average or above normal and temperatures running either average or below normal The development of a large pool of warm ocean water temperature anomalies in the northern Pacific. - favorable factor over the central and eastern U.S. with regard to running either an average or above normal and temperatures running either average or below normal
NEGATIVE FACTORS The early season development of a the POLAR VORTEX (PV) overnorthern Siberia and locking into that position. This can be considered to be a unfavorable, if not hostile factor, with regard to seeing either average or above normal snowfall. Temperatures will likely run either average or Above normal for the central and eastern U.S as long as the PV stays in Siberia. This is considered to be a positive factor however for the western third of the CONUS with respect to Above Normal precipitation and Below normal temps. That being said it needs to be kept in mind that it is still mid November and the odds significantly favor the PV shifting from its current position in northern Siberia. The very strong enhanced Pacific jet which is dominating the northern hemisphere pattern - this can be considered to be a unfavorable if not hostile factor with regard to seeing either average or above normal snowfall for the central and eastern U.S.. Temperatures will likely run either average or Above normal for the central and eastern U.S as long as Pacific jet continues to be enhanced. In the weather biz, this is often call the Pacific Jet firehose. This is considered to be a positive factor however for the western third of the CONUS with respect to Above Normal precipitation and Below normal temps. But again it is still early and the odds significantly favor strong Pacific jet stream breaking down and allowing for a significant change in the pattern at some point during the winter season. DETAILED DISCUSSION The weak La Nina event These two images show comparison between the global sea surface temperature anomalies (SSTA) from DEC 2015 and early November 2016. The most important feature of course is along the equatorial Pacific or the large area of above normal sea surface temperature anomalies can be clearly seen. The contrast with the area of below Normal Sea surface temperatures in the current November 2016 map is quite striking.
This image shows a comparison of the subsurface conditions along the equatorial Pacific across the various ENSO regions. The cold water is fairly deep underneath the surface but it is not particularly intense and is rather indicative of a weak La Nina event. This next image shows the current plots of the various ENSO regions along the equatorial Pacific. Notice that over the past 30 days only the region known as ENSO 3.4 has been close to the minimum threshold for weak La Nina conditions.
So the question now becomes what happens to this weak La Nina event as we move into the winter months.? Most of Model data suggests that the current weak La Nina is going to break down and dissipate early in the winter and that most of the winter will see near neutral conditions. Other data suggests that the weak La Nina will hold on for most of the winter only dissipating in February 2017. So let's consider the two possibilities.
LA NINA DISSIPATES IN DECEMBER 2016 If we take a look at all the seasons where there has ben a weak La Nina in the Autumn which dissipated during the Winter months we come up the following analog years. 1962-63 1983-84 1996-1997 2005-06 2008-09 2013-14 The first map shows the overall pattern for those winter analogs and we can see a persistent deep trough covering most of the central and eastern CONSU that favors a cold and potentially stormy winter pattern. In addition most of western and central Europe also appears to be quite cold and stormy. This sort of pattern supports strong blocking across the arctic regions, especially over Greenland and Scandinavia as well as the Bering Sea. If we break this down month by month, we see that the Jet stream patterns remain quite impressive with a massive deep longwave trough over the central and eastern portions of the CONUS as well as western/ central Europe. The analog of Winters that featured weak La Nina in Autumn that dissipated in the Winter suggests that the Month of February could be particularly cold and stormy for the eastern half of the CONUS. This map shows temperatures and precipitation for the selected analog years. Notice that the lower Plains look to be fairly dry. However temperatures are quite cold relative to normal over all the Midwest and the interior portions of the East Coast.
Taking a look at the temperatures and precipitation for December, January and February it appears that December is particularly cold and wet especially along the East Coast and quite cold over the upper Midwest and much of Canada. According to this analog, January features large areas of below normal temperatures across all the Midwest and most of the East Coast with near normal or slightly below normal precipitation. Over the lower Plains and the Delta region, it appears to be somewhat drier than normal. February appears to show the large area of cold temperatures diminishing and much of the lower Midwest and portions of the East Coast turning somewhat drier than normal.
WEAK LA NINA LASTS THROUGH THE WINTER Now let's take a look at what happens if the weak La Nina event stays on through the heart of the winter. The analog years are the winter of 1950-51 1954-55 1964-65 1967-68 1971-72 1984-85 1995-96 2011-12. This image shows the overall large scale pattern over the northern hemisphere for those analog years. As you can see the pattern features a deep and persistent trough over Western Canada into the Rockies and the upper Plains. The RIDGE position is not on the West Coast, but over eastern Pacific Ocean which is not favorable for winter weather lovers over the eastern U.S. In addition, notice that there is some sort of Ridge over far southern Greenland and central north Atlantic. This is often mistaken as a Greenland block or a negative phase of the NAO. However to call this feature a Greenland block or -NAO would be a serious mistake. This kind of positive Height anomaly supports a North Atlantic THUMB Ridge which is not the classic / Greenland block -NAO. In the overall sense this sort of pattern would support a favorable winter pattern for the Rockies Upper Plains and Midwest but not the East Coast. It is not a terrible pattern for winter weather lovers over the eastern US --just not ideal. As you can see temperatures run below Normal over the northern 25% of the country with temperature actually above normal over the Deep South. Precipitation is near normal everywhere.
That being said the weak La Nina analog years 1950-51 1954-55 1964-65 1967-68, 1971-72, 1984-85, 1995-96,2011-12 is a pretty mixed collection of very different types the winters. If we take a look at these weak La Nina Winters with a little more focus, we notice that many of these years were actually winters which featured prolonged La Nina events that had been going on for over year and some of these analogs La Nina events were are actually much stronger at one point in the cycle. So not all of these weak La Nina analog years are good matches to the current situation. If we keep in mind that we have come out of a fairly strong El Nino event from last winter,which finally ended in the Spring of 2016, with near neutral conditions for the Summer of 2016,.which have now developed into weak La Nina conditions in the Autumn, we find three close analog matches.: The winters of 1954-55, 1964-65, and 1995-96. This image shows the overall large scale hemispheric pattern for those three analog winters. It is similar to the previous analog which featured all the winters that had weak La Nina events but with one major change. The north Atlantic thumb ridge appears to be much stronger and much larger and could now be considered a legitimate Greenland block /-NAO feature.
The temperature patterns show much colder conditions across the Great Lakes and the Northeast U.S. While the lower Plains and the Southwestern states stay fairly mild. Precipitation appears to be above normal over the Middle Atlantic region and the Pacific Northwest.
The near record snowpack over Siberia in October 2016 The data from October 2016 shows that the Siberian snow cover was extensive and near record. In fact it came in as the third greatest snow cover for the month of October over Siberia on record. The reason why this is important is because the expansion of the snow cover especially south of 60 N latitude in the month of October, seems to have some sort of correlation to development of blocking patterns in the Jet stream over the Arctic region. This in turn ends up impacting the weather patterns over all of North America especially in the second half of the Winter into early Spring. The technical name for this phenomenon is called the Siberian Advance Index or SAI.
There are of course exceptions to this. Last winter for example we have the raging super El Nino so even though the snow cover was fairly extensive for the month of October 2015 over Siberia, the SAI had little impact. In addition the extensive or geographical size of the snow cover in Siberia was also extreme during the month of October 2016. This aspect of the snow cover in Siberia is known as the Snow Cover Extent or SCE. It does not get as much attention as the SAI but the SCE in out view is quite important. One can have what would seems to have a favorable overall hemispheric pattern which appears deliver cold air and winter storms for the central and eastern portions of the CONUS. But if the supply of cold air coming from Siberia is weak, the cross polar flow from Siberia across the Arctic region into Canada can become problem for setting up the classic winter storms (which require a large supply of Polar or Arctic air).
So in summary both the SAI and SCE numbers and correlations are very strong positive with respect to the potential for this winter over the central and eastern U.S.. The strong indications for high latitude blocking patterns AO/ Arctic Oscillation The Arctic Oscillation is a climate index or major weather pattern (atmospheric circulation ) that plays a huge role in weather pattern over the entire northern Hemisphere. The AO's impact is especially significant from October to April. The AO has so-called positive and negative phases. When the Arctic Oscillation is in the negative phase, cold Arctic air masses tend to plunge southward and into the U.S., spawning snowstorms and leading to colder than average conditions. This is because a Negative AO will a weaker PV (Polar Vortex) OR several mid size PV OR a PV that is strong but displaced well to the south. A positive phase for Arctic Oscillation, by contrast, tends to mean warmer than average weather with less snow for the eastern U.S. This is because a Positive AO means large strong PV over the Arctic regions / and or Greenland which locks up he cold to the north and prevents the northern jet stream from merging with the southern jet stream (it is this phasing or merging of the 2 Jet streams that create big winters storms). Research has long established that the phase of the Arctic Oscillation during the month of October is often a indicator of what phase the AO is more likely to average during the course of the winter months of DJF. There is some uncertainty as to why this is the case but the data is pretty strong that there seems to be some sort a correlation. Assuming this is correct, if we take a look of the Arctic Oscillation over the past 5 months, we see a very strong and noticeable dip in the AO into the Negative phase during the month of October. The Arctic Oscillation can vary considerably on short timescales, such as within a single month or from one month to the next, and the causes of its variability aren t entirely known. It was largely positive during the winter of
2007-8, which followed the previous sea ice record low, and then turned record negative during the winter of 2009-10, during which the infamous Snowmageddon blizzard occurred along the East Coast. It was then largely negative during the winter of 2010-11, and positive to weakly negative last winter, which was the mildest winter on record for the U.S. The weakening and decreasing amount of solar activity Research and actual observations have shown that weak or low solar activity tends to be correlated with frequent blocking pattern in the Jet stream at the high-latitudes. Currently the Sun is now experiencing one of the weakest solar cycles (#24) in more than a century. Moreover as you can see from this image the already weak solar cycle is headed rapidly towards the next solar Min - usually the least active time in a given cycle. If we take a closer look at this sun cycle chart will see something quite significant. Notice that the solar / Sun minimum occurred in 1984-1985 1995-6 2009-10 or all winters which featured extreme cold and some serious snow storms across portions of the Midwest and the East Coast. In particular the winters of 1995-96 and the winter of 2009-10 featured major East Coast and Midwest snow storms that set records for seasonal snowfall and many areas. This also has some significance for the future winters as it looks like the Sun will be reaching a strong negative solar minimum in the winter of 2019-20.
The development of a large pool of warm ocean water temperature anomalies in the northern Pacific. Besides the weak La Nina there is another important feature in the Northern Pacific Ocean that deserves considerable attention. The severe historic winter of 2013-14 was totally and completely under forecasted by CPC (Climate Prediction Center) and by most if not all private forecasters. The driving factor in that surprisingly severe and cold winter was a development of a large pool of warm sea surface temperature anomalies (SSTAs) in the Gulf of Alaska and the northeast Pacific Ocean. This feature helped to bring about a somewhat rare and not well known weather pattern in the jet stream known as the +TNH or positive phase of the Tropical Northern Hemisphere pattern. This pattern is frequently confused with the much better known jet stream pattern known as +PNA. This image shows the development of a large pool of extremely warm SSTAs in the northeastern Pacific that appear in October 2013. This feature persisted right through the winter... and into most of 2014. Indeed this feature what actually contributed to the colder than normal and fairly stormy winter of 2014-15. All that being said let's focus on what is going on in the northern Pacific in October and November 2016. This map from beginning of October 2016 showed that another large pool of exceptionally warm SSTAs had developed over the Northeast Pacific Ocean in and around the Gulf of Alaska. This is very similar to we saw in the Autumn of 2013. This has led to some speculation from some forecasters that the pattern may be a repeat of the severe winter of 2013-14. That assumption has some validity to it but that assumes that the large pool of warm SSTAs in the northeast Pacific does not fade and that it last into the winter months.
The problem is that because of the overall pattern across the Pacific Ocean over the last 30 days, the large pool of warm sea surface temperatures in the northeast Pacific weakened considerably. The strong Pacific jet stream and a series of major systems moving across the northern Pacific Ocean has caused "upwelling" which is turns has severely weakened this large pool of warm sea surface temperatures. These two images show that changes over the last 30days - from mid October to mid November. Over the last 30 days we can see that the warm waters over the northeast Pacific have almost completely diminished.
If the overall pattern begins to change across the northern Pacific over the next two or three weeks, it is still possible that the pool of warm SSTAs will hang on and even Re-intensify as we move into the heart of the winter. If this were to happen it would greatly enhance the probability of a colder than normal and snowier than normal winter for portions of the central and eastern U.S.. Obviously this variable is going to be very important to watch over the next few weeks. The early season development of a the POLAR VORTEX (PV) over northern Siberia and locking into that position - The very strong enhanced Pacific jet which is dominating the northern hemisphere pattern It is hard to overstate how critically important the position of the PV being located over Siberia is with respect to the overall winter pattern to the northern hemisphere pattern in general and the western hemisphere pattern specifically. For those looking for an early start to the winter having the PV situated in eastern Siberia is thee kiss of death. Here is why 1. First it pulls all the arctic air out of the northern regions of Canada and the arctic region itself. The numerous stories which have appeared in the media recently about the exceptional warmth relative to normal over the
arctic region is in part attributable to the unusual position of the Polar Vortex that is currently located in Siberia. 2. Having the PV in eastern Siberia ensures that the Pacific jet that leaves China and Japan will streak across the Northern Pacific Ocean with enhanced with velocities and intensity. This image shows the impact of the deep PV over in Siberia is having on the Pacific jet stream. This image shows that the civic jet stream has been running at 200 knots or 250+ mph. It is Extremely difficult to get the overall pattern to shift / change when the jet stream is that zonal and that fast. Indeed the enhanced and powerful Pacific jet slamming into the West coast of North America is the primary reason why the area from British Columbia to central California have seen a barrage of powerful weather systems that have brought much above and extreme much above precipitation to that area over the past 45 days. 3. The enhanced zonal Pacific jet stream overwhelms Southern Canada with mild air as well as most of the U.S.. Temperatures consistently run above normal and the snow cover over the southern half of Canada can be greatly diminished. In fact last week most of the snow cover over southern Canada had completely disappeared because of the extreme warm (relative to normal). And without the early season snow cover in southern Canada,even cold air outbreaks when they do occur, have a lot less staying power over the CONUS. 4. The zonal and enhance Pacific jet stream means that it is impossible to get any sort of RIDGE to form over the West coast of Canada. And without that RIDGE...there is no mechanism to deliver cold air into the central and eastern portions of the CONUS
All that being said, we believe that the Polar Vortex will eventually move from its current location in eastern Siberia back into the arctic region. In doing so it will lead to a chain of events that will bring in a more typical winter like pattern for the western hemisphere. However, this could be a fairly long process. First, if and when the PV leaves eastern Siberia and moves back into the Arctic region... the depleted sea ice will have to regenerate. Next, the cold air over Northern Canada will have to move southward establishing snow cover over South central Canada. 3 rd, the pattern will have to shift so that the Pacific jet breaks down but and a RIDGE becomes established over western Canada. Only when all three of these items have developed, will the pattern turn back to a seasonal early winter pattern.