Wednesday, October 11, 2017

My Winter 2017 2018 outlook


Well it's getting close to that time of year, when thoughts start to shift toward winter, and what might it be like.
One question I've seen a lot is, because our Summer was cool and wet does that mean this winter will be cold and wet?  My answer is sure, there is a chance. But then there is a chance it won't.  For several years, I've looked at the analog data hard; I've never found any direct correlation between a cool summer and a cool winter.

This year I want to start out listing my analog winter seasons. I used these to try an come up with a reasonable idea on how this winter should behave.  

Analog years:

I looked at the years that had a weak La Nina along with a negative QBO.... 1950, 1954, 1956, 1962, 1964,1967, 1970, 1974, 1983, 1988, 1995, 2000, 2005, 2007, and 2011

Analog years ended up being 1952/1953, 1953/1954, 1958/1959,1960/1961, 1962/1963 1964/1965, 1967,1968, 1969/1970, 1970/1971, 1976/1977, 1977/1978, 1979/1980, 1981/1982,1995/1996, 2000/2001 2004/2005, 2006/2007, 2007/2008, 2014/2015.  I gave the seasons in red the most weight, with  1970/1971 and 20006/2007 being double weighted.

The thing that directly impacts our weather is the jet stream. To refresh Y'all, the jet stream is a narrow river of fast moving air that resides above us in the upper atmosphere. There are many jet streams, but the two that effect the Northeast the most are the sub tropical jet and the polar jet.  The polar jet sits around the 500mb level (25,000-30,000 feet), while the subtropical jet is a little higher, around the 300mb to 115mb level (30,000 to 50,000 feet ) During the Summer the polar jet is typically found well to the north in northern Alaska and northern Canada. While the subtropical jet pushes south to near the Gulf Coast.

The wavering of these two jet streams is what causes the day to day variations in our weather. When the polar jet drifts south, we see cooler weather. When the subtropical jet moves north we see warmer weather. 

But our weather is also effected by other teleconnection flows. the El Nino and the Southern Oscillation, the North Atlantic Oscillation. the Quassi-Biennial Oscillation, The Pacific Decadal Oscillation, and others. We also are effected by things like sea surface temperatures, snow and ice extent, and even sun spots. All of these things play a role in how cold and snowy our winter will be.

Sea Surface Temperatures and the El Nino and the Southern Oscillation (ENSO):

There are four regions in the tropical pacific that we track, El Nino region 1+2, 3, 3.4, and 4.


I think Winter 2017-2018 will be more of a negative ENSO or a weak La Nina. The La Nina could get close to moderate, but I rather doubt it. The SST in Nino regions 1,2 3, 3.4 were dropping off fairly quickly. Then there was a warming trend. The last couple of weeks have seen the Nino region start to cool off again. They are currently below normal and are approaching La Nina levels. Because of the up and down cooling most atmospheric indicators have remained ENSO neutral. Winter 2016-2017 was a mix of El Nino and La Nina.

The type, timing and strength of the La Nina will be critical. an east or central based is more favorable for a cold east of the Rockies, compared to a west based event.
Sea Surface temperatures in the northeast Pacific and off the Eastern Seaboard of the U.S.





Currently, sea surface temperatures (SST) in the eastern tropical Pacific are slightly below average. The mid eastern Pacific has seen the biggest departure from average, right now that's about one degree Celsius.  The coolness does extend down a few hundred meters below the surface. We should see the east - central Nino regions will continue to cool . Last winter, regions 1 and 2 got warm, I don't see them getting that warm this winter.   So It seems likely that my idea of a cool  ENSO neutral to weak La Nina seem likely. If we do see a weak La Nina I expect it would reverse back to ENSO neutral for late winter. So a cool neutral or weak La Nina for November into the end of December or so, then we should see the La Nina reverse as we get closer to late winter.

There has been a big change in the ENSO from this Spring compared to now.


Here is a look at the mid-April International Research Institute for Climate and Society (IRI) chart.



Here is a look at the latest International Research Institute for Climate and Society (IRI) chart.




If we do end up with a weak La Nina; I do think the La Nina will be leaning toward the east based idea.






I have to remind you that many other factors are involved besides just the ENSO and La Nina.

The Indian Ocean Dipole is neutral

The Quassi-Biennial Oscillation (QBO):

The QBO started trending easterly back in April. So it looks like a moderate to strong east based QBO is likely. During last year's winter of 2016-2017 we had a La Nina with an west based QBO. So an negative east based QBO would have a completely different impact on our winter. When we have an eastern based QBO we tend to see a warmer stratosphere over the northern polar region, as opposed to a cooler stratosphere when the QBO is west based. Looking at past east based QBO years, the East does tend to see more troughiness.  

The Pacific Decadial Oscillation (PDO):

As it has been for the last few winters, The PDO remains positive. But because of the double La Nina, it is weaker than it was last year. The positive phase of the PDO involves warmer than average water temperatures off the West Coast of North America. The cool negative phase is the opposite.




The PDO has a big impact on where ridging and troughing sets up.  The more positive the PDO the more persistent and deeper the western ridge. I think the PDO will stay a weak positive into the Spring of 2018, where as it would go neutral. Being weaker than last year and the year before that. Will mean the western trough and eastern trough won't be as strong and dominate has they have been. This would have a impact on the storm track and how far south the cold extends.

There are many other teleconnections that I looked at. But I don't want to overwhelm Y'all with all of that data. More or less they support my idea on how winter will turnout.

It is important to remember, how a season turns out is based on a mixture of different teleconnections and other patterns, not the individual teleconnections themselves.

Solar Activity:

This Winter will feature low solar activity. There is a correlation between winter temperatures and sun spot activity.  Years with  low solar activity tend to run colder with more of a negative AO and negative NAO, than winters with high solar activity. Winter's that experience low solar activity also tend to see higher increases of higher latitude blocking around Greenland and Iceland. Which is good if you like colder weather.

Here are a couple of charts that show how all of this characteristically works out .


Here are a few images that show  Ap solar activity and NAO index values.



Here is one from, International Climate and Environmental Change and Assessment Project (ICECAP).




You can see there is a coloration between solar activity and the NAO and AO

When we have negative NAO and AO index values we tend to see more outbreaks of cold air moving out of Canada do to blocking over Greenland.

The Hurricane Season:

This year we have seen a lot of low pressure over North America. This happened when prevailing high pressure set up in the Atlantic. We have seen a lot of high pressure over eastern Canada into the Northeast. So with lower pressure over the Southeast into Caribbean and Gulf land falling tropical cyclones were going to be a given.

I have found that there is a weak association between Atlantic and Pacific tropical activity and winter snowfall.  It all comes down to Accumulated Cyclone Energy (ACE). ACE measures the strength and duration of individual tropical cyclones.

As of Hurricane Olivia this seasons ACE sits at 212. An average year has an ACE of 111. OK but how does this impact our winter? The atmosphere is always seeking a balance. When I looked back at years that had above average ACE. The years that came up were 1950, 1969, 1980, 1989, 1995, 1996, 1998, 1999, ,2000, 2001, 2003, 2004, 2005, 2008, 2010, 2011,  2012. Over 60% of the time, When ACE was above average, the Northeast saw above average snowfall overall, while the Southeast saw below average snowfall overall.


 The ACE data set is small. so finding meaning from extrapolated data is hard.  I don't claim to have found the only answer, because other issues could be involved. But I believe further research should be done in this area. There is also a correlation between ACE and the AMO, which I won't go into too.  

Going into Winter: 

October, November, and into the first part of December will see temperature swings back and forth. That doesn't mean we won't see cold, it just means it won't be really long lasting or widespread. We could see a decent cold outbreak in a couple of weeks. But I do expect to see some early season snows end of October or November, especially in the Snow Belts and higher elevations of New York State and Northern New England. 

The real winter cold will most likely hold off until January. Making January, February, into March feeling the most winter-like. Mid to late winter should see more longer lasting cold in the Great Lakes and Northeast.

So, October is going to be very transitory in nature. The overall temperatures in October will be above average. The Northeast has been very dry the last three to four weeks. But Nate is going to bring some much needed rain. So precipitation wise October will end up close to average. November will see the pattern go back and forth, so again we should end up with overall temperatures being above average. Unless we see another tropical system, It will also be rather dry, (unless we see something tropical).

December should see temperatures average to slightly above average.

Northern Hemisphere snowpack:

Snow has been falling in Siberia and we've had a few early season snowfalls in the Rockies into Montana. The models are bullish on the idea of snow in Siberia into China over the next two months.

Here is a look at the snow and ice extent.




With snows flying in Siberia, the more snowpack there is in Siberia and northern Canada, the better the chance for high latitude blocking.  So there is a good chance for negative NAO and a negative AO.   

Wild Cards:

Pacific Jet. for winter 2016-2017 we had a zonal (west to east) flow due to a strong Pacific jet. This is the main reason for the warmth  and wild swings we saw. There is a chance we could see a strong pacific jet again this winter.

There would be cold air in Canada and into the middle of the CONUS (Continental U.S.). depending on how the polar jet acts it could overwhelm the pattern during the last half of winter.  

Blocking, How much we see and where it sets up is as of yet, a little unclear. But I don't think the warmth of this fall will last all the way through winter 2017-2018.

Summary:

Where the prevalent ridge sets up will be key, as to where the core of the cold sets up. I do expect to see some level of a southeastern ridge. But I don't think it will be as prevalent as last winter. why? Because I think we will see more Greenland Blocking than we saw last Winter.

While the core of the winter cold looks to setup in the Great lakes into the Plains. The Northeast and Mid Atlantic can expect a chilly winter especially from mid winter to end of winter. 

The Southeast is going to see a very warm Winter, that combined with cold air invading the Rockies into the Great Lakes, will allow for plenty of opportunities for wintertime precipitation.  Blocking is going to be a wildcard for winter 2017-2018. But it looks to setup so that the Midwest and Great Lakes will be quite cold, with the Northeast not getting quite that cold. The analogs I looked at, show the storm track should be fairly active. So I don't think snowfall will be all that bad here in the Northeast into the northern Mid Atlantic. An active clipper and Colorado Low storm track will bring many chances for lake effect snows downwind of  Lakes Erie and Ontario. But, the water temperatures in the Great Lakes are warmer than last winter, so unless we can get some really cold air toward the end of November, lake effect snow  could be less than last year.

Temperatures:

Temperature profiles in the Northeast are going to be very tricky this winter. This year we will have an east based La Nina. Typically La Nina winters tend to be colder in the Northwest, Central US, and the Great Lakes. The Southeast tends to be quite warm. The Northeast and the Mid Atlantic tend to be in-between somewhere. The strongest widespread cold will be mid it late winter. November will feature some cold . But, I don't expect to see  longer lasting cold for the first third of winter. But January thru March have the potential to be cold.

Here are my temperature ideas.



Precipitation:

During an La Nina, the typical precipitation pattern sets up as above average over the Northeast. So, snowfall and mixed events for much of New York State and northern New England should be above average. With the Pennsylvania, southern New England, and  Mid Atlantic seeing  average to slightly above average, there is a bigger risk for mixed events in the Mid Atlantic region. The relatively warm waters off the East Coast could allow for a few bigger snowstorm events.

Here are my Northeast snowfall Ideas.



If I have any changes to make, I will post on that around mid November.