11/13/11

STILL ANOTHER LA NINA RIDES IN FOR THE WINTER 2011-12: WILL SHE BE AS TROUBLESOME AS HER SISTERS? (Final)

   AN ACTIVE STORM TRACK...BUT FOR WHAT PART OF THE COUNTRY ?  THAT IS THE QUESTION!
Written by: William R. Deedler, Weather Historian 11/12/2011

Temperatures: 
As the storm track shifts around this winter, look for temperatures to be quite variable but with a decided trend
toward below normal. Selected analogues this winter do suggest a colder than average winter across Southeast
Lower Michigan. A rather strong storm track will ride on an oscillating southwest to northwest jet stream. Once 
again, how much affect the track has on Southeast Lower Michigan, guided by La Nina in conjunction with the
North Atlantic/Arctic Oscillation /NOA, AO/, will play a large part on temperature patterns across the Great Lakes
This pattern seen is very true of our recent La Nina winters and I see no reason to deviate from it. I look for this
winter to be colder than a typical winter seen (and felt;-) the past 30 years (and this is reflective of the new 1981-
2010 normals used). Look for temperatures to average 1.0 to 3.0 degrees below the new normal averages 
(seen in the analogues) for Southeast Lower Michigan.  

Snowfall and Rainfall:
With the variability of the below normal temperatures in many of my analogue winters, snowfall also widely ranged
from well above normal to well below. This would be expected since the variance of temperatures hint at the 
upper patterns and storm tracks Most of the coldest of winters showed less than normal or normal snow as 
the baroclinic zone and subsequent storm track held just south of the region (this also shows up on
precipitation composite maps I ran from CDC).

As with the recent La Nina winters, pinpointing the prevailing storm tracks and exact locations will make all 
the difference in the world in snowfall. Now, we have had some incredibly snowy winters the past decade or 
so with all three cities seeing five of recent winters (since 2000-01) landing in the top snowy winters list
And a more relevant point, the three recent La Nina winters supplied copious amounts of snow to all of 
Southeast Lower Michigan. Will this happen again? This is really a tough question (not to mention; 
a tough act to follow), so I look to the selected analogs I researched this winter for at least part of the 
answer along with recent pattern developments for the other part. As far as the analogues go: there is 
a subtle but definite shift to the higher side of normal /+5.0”/ (rather than above) for snowfall totals over
part of the region with again, higher than normal for other parts. 

Basically, I look for normal to above normal snow and precipitation across Southeast Lower 
Michigan (see particulars in Analogue section)
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A brief intermission about a be'atch of mine
Up on my soapbox about Normals

I might as well get this out from the get-go, the new 30 year winter normal (1981-2010) at Detroit has risen from 27.1 for the 1971-2000 norm to 27.9 (or up 8 tenths) yet the 100 year norm is still close to 26.7. If one is going to use normals (and lets face it, some sort of standard is needed) why not use a normal that has some use to its users. We now have that capacity of climate data needed (and then some) at many climate sites across the US. We are dealing with a planet’s climate, by most accounts, that is at least millions of years old and of course we have no “normal” for that time period (wouldn't that be a trip) but just 30 years? That’s like looking at your life and saying the past few hours (or even minutes) are normal for your entire life…and how many of us could or even would want that? 

Knowledge increases about the cyclical nature of ENSO (prevailing La Nina and El Ninos), the Pacific Decadal Oscillation, the North Atlantic Oscillation /NAO/ (including the Arctic Oscillation), the Atlantic Oscillation /AMO/ (not to mention the Madden Julian Oscillation /MJO/ but this has a much shorter relevant cycle) and how they all work in conjunction and affect our daily, monthly and seasonal weather. Note: I linked a variety of resources which link to others. Many of these Oscillations run on approximately a 70 year total cycle. It would then seem to me most advantageous to develop norms to accommodate these cycles. Therefore, the 70 year cycle (or something close) would be best suited with a moving updated average.  

As an example: The past full cycle for ENSO (the prevailing periods of El Nino's and La Nina's combined), the PDO and NAO

Expanding further on this “normal” idea for our winter outlook, it is interesting to note that the 100 year winter mean temperature for Detroit is approximately 26.7 degrees with a one standard deviation spread of 3.5 degrees either side of that 26.7. Statistically speaking, based on this data the temperatures could average as low 23.2 degrees or as high as 30.2 and still be considered within a “normal” range of the mean.  Basically, this just supports the idea that winter temperatures in these parts, by nature, have a wide statistical range.
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Ok Ok Ok....Back to the Outlook

The Macroscale:

Discussion
Another interesting and challenging winter is ahead of us with many main weather features: La Nina, 
NAO, AO, PDO, MJO, and AMO working together (and apart) to bring Southeast Lower Michigan a fairly
busy winter.

ENSO - La Nina

Geeze, another La Nina ?? (We can’t get rid of the…)

Let’s spend a little time in this outlook talking about our brand new La Nina. Checking out the very 
latest(11/7/11) Pacific water temperatures in Nino 1+2, 3 and 4 (Fig-1a, b, c, d & e), shows the 
distinctive and fairly steady cooling of the areas of the Pacific Ocean since the summer used in 
determining the pattern. For scientific purposes, Nino 3.4 is used to determine officially, whether or 
not a La Nina is in effect. I also included the ENSO graph back to 1950. The latest as of 11/07 
weekly SST departures below normal are:

                       Niño 4      -0.5ºC
                       Niño 3.4   -0.9ºC
                       Niño 3      -1.0ºC
                       Niño 1+2  -0.9ºC

The temperature in Nino 3.4 has slipped to 0.9C below normal in early November which indicates La Nina conditions exist. La Nina “conditions” are considered to be occurring when the SST departure of area Nino 3.4 
are at/below -0.5C along with La Nina-type atmospheric conditions. To officially be classified as a "full-fledged"
La Nina, the temperature must average at/or below -0.5C for a period of at least 5 consecutive overlapping
3-month seasons

While areas 3.4 and 3 continue to cool, it is interesting to note area 1.2 actually has hovered between normal
and just below normal (for now) as La Nina subtlety becomes more east-centrally based rather than just east 
(the cooler below average waters meander west with time). I believe the La Nina is beginning to mature and
according to the latest models (fig 1- e) should peak roughly within a month of Christmas-time or holiday season. 
For a more in depth look/summary of the model predictions head over to International Research Institute /IRI/.

  Fig - 1a 

     ENSO Regions 
    1b 
  
                                                                       Latest SST Plot of Regions

 BTW, here is an up to date sweet animation from CPC of the on-going La Nina 

1c/d

                                   
                                     My estimation of dominant ENSO trend since 1950 
                                     
            1e

                                                   
Southern Oscillation Index /SOI/

The monthly Southern Oscillation Index /SOI/ reading for October  (Fig-2 and not to be confused with
the La Nina SST) came in at +9.7 while the past 30 days has averaged +10.8 (as of 11/8/11)
The Southern Oscillation Index is explained here and is displayed on the following chart up to 1950 
and after 1950. Here, the latest values are updated daily. We’ll get back to this in our analogue
discussion.


Those above numbers would be 0.97 and 1.08, respectively on the SOI Tahiti - Darwin graph scale below.                                                       
          Fig - 2

  
The Ever Elusive NAO/AO

The other main ingredient in this winter’s weather (like any other) is of course, the trend of the North Atlantic Oscillation/Arctic Oscillation throughout the winter. Of course, this is the biggest challenge to the forecast and potentially, has the biggest bust potential. While trends with La Ninas and El Ninos are seen (and these are not always consistent, either) the NAO is highly elusive and generally trends are seen only a week or two out. Generally, our colder winters in the study reflect a predominately negative NAO. The winter of 1903-04 in our La Nina list below was a brutal winter with cold and snow. This remains our coldest winter to date on record since 1874 at Detroit. In long term trend of the NAO (Fig 3 a,b) clearly shows the oscillations long and short term from positive to negative and back to mainly positive, to neutral (early - mid 2000s) and since, predominately negative. The near term (autumn, 3c) has been neutral to positive reflecting the recent mild weather but what of the projected? Seems as though the model ensembles are having a bit of trouble. That's not the first time that erratic pattern has been seen and sometimes that happens around a notable change, we'll just have to keep an eye on it.

                                                                                 Fig - 3a
  3 b 

3 c 
NAO recently and short term forecast
                                         
Pacific Decadal Oscillation (PDO)                           

The Pacific  The Pacific Decadal Oscillation (PDO) is the long-term ocean fluctuation of the Pacific Ocean. The PDO waxes and wanes approximately every 30 to 35 years. Many scientists (including myself) think we have just entered the “cool” phase (Fig-4a,b) of the PDO. The cool phase is characterized by a cool wedge of lower than normal sea-surface heights/ocean temperatures in the eastern Pacific and a warm horseshoe pattern of higher than normal sea-surface heights connecting the north. The last time the PDO trended into the negative phase was back in the mid 1940s, lasting into the late 1970s. There is good evidence that during the cooler phase, La Nina’s tend to be more commonplace (as in our recent La Nina & PDO pictured below in 2008) and tend to last longer with multiple occurrences. Compare the pattern likenesses of the ENSO, PDO and NAO trace/phases of the mid 1940s/early 50s into the late 70s. It will be interesting to see how our winter patterns continue to unfold the next decade or two and if they continue to resemble those of the 1950s-70s. As of October 2011, the negative PDO index dropped down slightly in Oct 2011 with PDO @ -1.5.
                         
                     Fig - 4a 

 
                                          
                                                                                         4b



Microscale discussion 

Let's get right to it...

2011-12 Analogue Winters

Researching locally as far back as the late 1800s, I have a full set of analogues, composite maps and storm tracks for the winter with 16 at Detroit and 14 at both Flint and Saginaw. Most of the winters in the analogues followed the similar sequence of events recently observed over the Eastern Pacific during the past few seasons
a waxing and waning of La Ninas, several at or close to the timing of our present La Nina. It’s not surprising the current dominant La Nina(s) pattern has been somewhat unusual in recent decades (between the 1980s and mid 2000s) when El Ninos and Neutral patterns held sway. Just by looking at the cyclical nature of these guys (ENSO, PDO and NAO and others) is that any surprise? The last time we left the cool or negative biases of these cycles was in the 1970s. This predominant La Nina (and multi-La Nina) pattern we are now experiencing was last seen in the early to mid 1970s time frame and extended back into the early 1950s. Therefore and surmising: the majority of analogues in the study are those just recently experienced, several between the 1950s-70s and then way back into the late 1800s to the early1900s.

The solar cycles (S) are also included with this simplistic legend and rough timing of cycle estimates. Why include the solar cycle? I guess my answer (and question) is: why not? It may have little significance on a winter season most times but what about when the solar sunspot activity is at a lull or on the low side, like the past few years (though it is now beginning to increase). It’s a well known fact that the earth cooled during very extensive lulls in sun spot activity such as the Maunder Minimum. What effects do changes in solar energy have on planetary or geostrophic wind patterns continue to be debated. This is a “hotly” (pardon the pun) debated subject across the globe especially in Europe where new research papers released this year ignited more chatter. A Google search on this topic yields some wide ranging results and opinions. In my Winter Outlook, a majority of the analogue La Nina winters occurred on the lower side of the solar cycle. Below is the legend I devised for the solar cycle timing in each La Nina winter.  

Symbol                       Solar Cycle Meaning____________________________
     -             At the high of the solar cycle or completely opposite of current cycle
     +             At the lower half of solar cycle
     ++           Near current cycle either declining or rising  
   +++        At or near current cycle and rising


           DETROIT

                                                                            FLINT

                                                                        SAGINAW   
             
 
 Local Comparisons/Results: 
 
Many of our earlier winters (before 1950) indicate colder than normal temperatures across Southeast Lower Michigan. In the later years (after 1950), generally more of a mixed picture is seen though the recent trend has returned to the below normal dominance. In any event, a rather strong cold biased results when all are averaged 
and ironically, all three locations average right around 2 degrees below the new 1981-2010 normals. In many of
my previous Outlooks, when the majority of the analogues pointed in one direction that was the direction to take. Though there have been a few occasions where the trend was not my friend. If I was intuitive (or lucky enough ;-) to recognize that beforehand, I went against the trend (like this past summer for a start). While the temperature trend has usually been a fairly good prognosticator for the season, the departure magnitude has been less reliable.

In this particular event, I feel we will average below normal putting a range of -1.0 to -3.0 (I bring this up again in the storm track portion of the Outlook).

 Season snowfall totals were all over the board, which really isn’t surprising if one considers the vivacious jet stream and storm tracks associated with these years - where just a variation of 50 miles or so can make all the difference in the world. Two of the most obvious trends in the analogues are the snowier winters recently and the snowier locations over the northern two thirds of Southeast Michigan. This area extended from Detroit's northern suburbs, northward across the Flint and Port Huron areas into the Thumb Region and Saginaw Valley. Saginaw's average snowfall was a whopping 14.4" above normal because there are plenty of (9 out of 14 ) snowy winters here. As one travels south, the snowier winters are still strong but lose some of their numbers with six at both Flint and Detroit. Closer to normal snowfalls prevailed on average at both of these locations though they were still on the high side (I elaborate on this further in the storm track section).
I look for normal to above normal snowfalls with a decided preference toward above normal for the northern two thirds of the region.

Worst of the winter 

Temperatures

The coldest part of the winter relative to normal in the analogues was generally mid to/or late winter. I really hope this does not play out and this is wrong because that would be some cold weather since our coldest normals are mid to late winter (and think of the heating bills, I'd rather not;-). 

Storms/Snowfall

Boy, this sure is a loaded phase ("worst of the winter") because a lot of us storm and snow lovers think of this as the "best of the winter" (except when I had to drive to work ;-).  The ranges of snow each month is extraordinary with some ranges two to nearly three feet. Just in February alone: Detroit ( 2.6" to 31.7" ), Flint (1.5" to 31.4") and Saginaw ( 3.7" to 34.2"). This handily shows this incredible range of snowfalls. Really, the only thing I can gather here is that these set of winter's seemed to be more back-end loaded with the worst of the winter coming the second half. Another, but more subtle trend shows the worst coming early and again late in the winter or a "U" shaped winter.

COMPOSITE MAPS OF ANALOGUE WINTER YEARS

Below are the composite maps for the analogue years in the local study. Remember these maps average what happened over the region and do not take into account any recent trend observed over the region. They are only a “guidance tool” to past similar type La Nina winters.



       La Nina affects on the Jet Stream



The above spliced maps contain the standard affects of La Nina on the Winter Jet Stream against my analogue years. The positive meters/sec (m/sec) areas denote the above average wind speed at the 500 MB meridian wind and resultant jets. Thus, the positive values over the north Pacific extending northeast and southeast while interacting & phasing with the Polar/Arctic jets were the dominant and typical pattern seen during these analogue winters. This correlates well with the standard, as it should. In addition, note the somewhat higher than average wind of the sub-tropical jet stream extending from the Pacific into the southern US - another piece of the puzzle for storm development and phasing this winter.The large dark purple and -m/sec area show the huge below normal area of winds and heights circulating around a deep polar vortex. The strongest of the jet is on the far perimeter of the circulation. Finally, I certainly would be remiss if I didn't mention the very impressive strong wind cores where the jets phase to our east, out over the northern Atlantic region including Greenland. Combine that map with the 500 MB heights for the analogue years (shown in the map below for Nov-Mar) reveals some very impressive low heights (low pressure/trough) over Canada and high heights (high pressure/ridges) over the north/central Pacific and northern Atlantic which charge up some screaming jets between the two opposing anomalies. This favors an active storm track and will likely lead to some notable blocking patterns this winter across the northern hemisphere!





STORM TRACKS

Jet axis holds keys to this winter


 The interaction between La Nina influenced Pacific jet stream and the North Atlantic Oscillation will hold the key to this winter’s storm tracks and what type of storms develop over the country. Also, the interaction of the jets whether it be by phasing or split flow will, to a large extent, layout a pattern.


I indicated on the map below where the phasing regions will most likely to occur: one, along the Arctic/Polar jet headline for the northern Pacific and the Polar/Arctic jet axis and two, either or both of those two jets with the sub-tropical jet. These are likely to merge out over the Central  & Southern Plains. These above scenarios give precedence to the Alberta Clipper or Saskatchewan Screamer Low, the Colorado Low and Texas Panhandle/Hooker Low which will all bring precipitation to the region. Also I indicated on the map, a west/east arrow from west-central Canada to the Quebec/New England region. I expect this 500 MB low to dance across Canadian region as usual, the only difference being this winter she may find more partners than typical over Southwest Canada.

A third area of phasing also is likely over the Ohio Valley into New England. This will be one of the major wild cards this winter as to snowfall amounts in S E Mich. This is not as clear cut as the past few La Nina winters. As mentioned above, the northern areas of Southeast Lower Michigan had higher amounts of snow relative to normal in the analogues than the south. In my mind, two main reasons can account for this. First being: the storm track that rides up from the Southern Plains area crosses over or near Southeast Lower Michigan rather than south of the region and thus, the majority of the snow rides further north with it (this would also open up the door for more mixed precipitation). Second, our Ohio Valley snow machine is either less pronounced this winter OR parks further south. 

I mentioned the "sling-shot" pattern in my earlier discussion in regard to the jet stream. Plain and simple, by looking at the storm track map you can see how the Arctic/Polar jet prefers to take a dive southward (southeast or even southwest) to the lee of the southern Rocky Mountains in these analogue winters. This in turn, loads the storm "sling-shot "and shoots it east northeast toward the Great Lakes and then "somebody gets stung in the....";-).  Who gets stung remains to be seen as the pattern evolves. If the storms ride further north than expected, this could also botch up the temperature forecast too with the upper level ridge holding stronger in the Southeast.




Well, that's pretty well covers what we are up against this winter.  I will discuss some of the things I mentioned in the Outlook as the winter evolves.

Constructive comments or thoughts on the outlook are welcome.I noticed I have a good number of  viewers from outside the U.S. I'd like to heard from you too.  I wonder how you came across my blog? 

Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian

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