TRACKING SIBERIA SNOW COVER
Most of the weather model projections over the past 10 days appear to be verifying quite nicely. The REX BLOCK pattern DID develop as forecasted over northern Siberia and it has been a tremendous " positive" development with regard to the buildup of snow cover south of 60° N latitude (the critical aspect of the SAI). In addition the REX BLOCK pattern has also allowed for a significant expansion of the overall snow cover as far west as the Ural mountains so the SCE values are also pretty tough.
Over the past few days the weather models have shown a bit of a break in the pattern which would shut off the snow over central Russia and allows for somewhat warmer temperatures. This depiction of the European Jet stream map valid as of October 28 - 29 show the RIDGE that forms in the jet stream over central Siberia and somewhat warmer temperatures.
However if we look to the actual min and Max forecast temperatures will see that the models do not bring temperatures above -2C for Max readings and overnight min temperatures are still around -7c in central Siberia. This means that the snow cover will not be diminished at all by this brief 2 day warm up.
CLICK ON IMAGE TO SEE FULL SIZE
Here we can see the 13km GFS final forecast valid for the evening of October 31. Again I have drawn in with a black line the approximate value of 60° N latitude so we can see the extent of the snow cover SOUTH of that key benchmark. Of course we don't know the actual figure because we can only judge by the maps
However the official data coming in from the satellite sensors which track the snow cover over the Northern hemisphere and Siberia ...as of October 26.... show a value of 14.5 Million square /km at the end of week 43.
When compared to the all of the other week 43 values since 1966 (which is how far back we have data for Siberian snowfall) OCT 2015 week 43 value of 14.5 million sq km is 16th best out of 50 ? How does this value compare to the last several years of week 43 snowfall coverage in Siberia ?.
WEEK 43 OCT 2014..... 18.66
WEEK 43 OCT 2013..... 15.99
WEEK 43 OCT 2012..... 17.61
WEEK 43 OCT 2011..... 15.91
WEEK 43 OCT 2010..... 14.52
WEEK 43 OCT 2009..... 15.99
WEEK 43 OCT 2008..... 12.31
As you can see the week 43 as of October 2015 is a somewhat below the last few years but still significantly Above Normal when viewed over the past 50 years.
SUMMARY With only 5 days left it is likely that the final OCT 2015 Siberian snowfall cover will be OVER 16 million sq/lm. But it OCT 2015 will end up being in the top 30% of all years since 1966 . This STRONGLY implies that the Arctic Oscillation is LIKELY to stay predominantly in the Negative phase. In addition there s NEW information coming out shortly that supports a strong -NAO for most of this Winter as well . More and more I think that if and when this current El Nino begins to weaken things will turn extreme and probably in the 2nd half of the Winter and all of March 2016
The overall pattern across Siberia continues to evolve into what can only be described as n extremely favorable setup with regard to producing significant snowfall over the the last 12 days of the month.
Of course this is a model PROJECTION but it does show a HUGE shift or change in the snowfall cover between October 18 and October 31. As you can see this is a significant change south of 60° N latitude. -- the thick black line that I have drawn in on both maps.
There has been a major development with regard to the overall pattern and potential for increased snowfall over Siberia.
Looking at the latest model data from Siberia we can see that a exceptionally favorable early winter pattern is developing which is likely to produce significant advances in snow cover over the next 10 to 14 days. In particular the European and the GFS ENSEMBLES both show a very pronounced and powerful looking **REX BLOCK ** developing in the 6 to 10 day over downtown Siberia. The development of this particular pattern in the Middle October is likely to cause a significant enhancement and rapid buildup of snow cover over most of Siberia.
These two images will help understand the concept behind the "REX BLOCK" Jet stream pattern. Usually the Jet stream moves in a west East direction in the northern hemisphere. Sometimes however the pattern can become quite twisted nd convoluted. The term " REX BLOCK" refers to a somewhat unusual Jet stream configuration that consists of a upper Low in the jet stream of the atmosphere which has moved underneath of a large Ridge or DOME of High pressure. What is significant about this particular type of pattern is that it often last for a prolonged period of time and can keep a weather pattern locked in position for an extended period of time as well.
This next image shows the MEAN 500 mb pattern over the next four days. We can see one large powerful trough with a ULL ( Upper level Low closed off at 500 mb Low) centered over northeastern Manchuria and southeastern Siberia that is moving towards the Kamchatka of peninsula ...and a second a large system leaving central Western Russia and moving East through the Urals.
The second image is the European ensemble valid for the 6-10 day period taking us to October 20. The REX BLOCK ck pattern is clearly shown but I have highlighted the key features. Let's be clear about this -- what we are looking at is a massive REX BLOCK which has developed over the Siberia region of Asia. The ENSEMBLE mean shows enormous and very enhanced powerful RIDGE on the north coast of Asia that builds into the Asian side of the Arctic circle. Underneath and we have two large 500 mb closed Low that cover all of central and eastern Siberia. It's hard to imagine a more ideal pattern for the middle of October with respect to producing significant accumulating snow fall at a rapid pace
Over the past 15 years Dr Judah Cohen of AER Inc has found a proven strong relationship exists between the build up of snowfall over Siberia and winter weather patterns that tend dominate the cold season in North America ( DJFM)
In general there are 5 key or major atmospheric patterns or " teleconnections" that dominate the Jet stream patterns over the western Hemisphere and North America They are
AO ( Arctic Oscillation )
NAO (North American Oscillation)
EPO (eastern Pacific Oscillation)
PNA (Pacific North American pattern)
WPO (Western Pacific Oscillation)
These key 5 teleconnections are always there and can be in the " negative "... "Neutral" ....or "Positive" phases. They exist whether there is El Nino or La Nina (of course these 5 key teleconnections are affected by a Weak Moderate or Strong El Nino/ La Nina event). Similarly the 5 key teleconnections are always there regardless of the intensity or phase of the MJO. But the MJO Intensity and Phases can/ do enhance these key 5 teleconnections.
Just after 2000 Dr Cohen found that a rapid build up of snow cover in Siberia in October impacts the AO - Arctic Oscillation- by forcing the AO into the predominantly Negative phase. When the AO is negative weather patterns turn colder and stormier (more snow) over the central / eastern portions of the CONUS and in Europe.
Dr Cohen developed two different ways of measuring the snow cover in October over Siberia. Th e FIRST e method is called thee SCE- SNOW COVER EXTENT and is mainly is focused on the amount of area over Siberia which is covered by snowfall (from the Urals mountains in central Russia to the far eastern Pacific coast of Siberia). The SCE has a connection to the buildup of cold air in Siberia which can have a significant impact on the amount of cold air that crosses over the North Pole and moves into central and northern Canada during the winter months. Generally speaking the larger the SCE number is bigger ....the supply of cold air will be available over Siberia and the Arctic regions for later in the Winter season.
The second and more reliable method is called the SAI which stands for SNOW ADAVANCE INDEX and it measures the advance of the snow from the 60° North Latitude line SOUTH towards the equator in the month of October over Siberia. At the end of October the data is look at ... the SAI calculated and released to the weather community.
Last winter the October 31 value was a second highest of all time and after December 2014, the winter of 2014-15 turned quite cold and stormy for much of the eastern U.S. However even though Dr Cohen's SAI values strongly indicated that the AO would turn negative for last winter... it did not in fact do so. Last winter was one of the rare instances where the SAI fail to correctly predict the dominant phase of the AO (arctic oscillation)
This LINK clearly shows HOW and WHY tracking the snow in Siberia on OCT dramatically improves the overall season forecast .
Most of the time however... the SAI values in October correctly forecasts the intensity and the dominant phase of the Arctic Oscillation for the upcoming winter. For example in October of 2013... October 2012 as well as 2010 and 2009 the SAI values Siberia - values were very high. And not surprisingly all of those winters (2009-10 2010-11 2012-13 2013-14 ) all turned out to be colder than normal and significantly snowier than normal for much of the central and eastern portions of the CONUS. And many of those winters have prolonged and rather strong negative arctic oscillation phase
Thus during the autumn season- specifically the month of October -the snow cover in Siberia is heavily focused on by meteorologists who wish to make a accurate and seasonal winter forecast. This is why issuing early season winter forecast in September and August is absolute pointless and a complete waste of time.
Last year the snow cover got off to a very early and aggressive start but the last few days of October 2014 turned a mild and small amounts of the snow cover in Siberia was actually wiped out.
This year so far ... as of 7 OCT 2015 ....the snow cover is off to slow start. Remember the KEY aspect to the SAI and snowfall in Ocotober over Siberia is to see how how far south the snow Advance SOUTH of 60 degrees north latitude by OCT 31 (and to a lessor degree now much of Siberia and central Russia is covered by OCT 31-- the SCE)
The models are showing a significant increase in snow cover over the next two weeks. The European and the GFS models are in pretty strong agreement about this. Both of these models are show a new powerful system coming out of the Urals and tracking into western and central Siberia after October 10. We can see the significant shift or expansion of the snow cover on the GFS ensemble snowfall forecast. This image compares the current ACTUAL snow total as of October 7 with the forecast projection 13 days out valid October 20. Again I have superimposed the black line to show the approximate position of the 60° N latitude line. As you can see there is a significant increase over the next two weeks.
Of course this is a model projection and not get a fact and we don't know what the last 10 days October looks like either .