HUGE Winter 2014-15 Recap: Reasons for Arctic Cold, Snow, Records

I hesitated to post the final details on this past winter until I was pretty darn certain we were finished with snow. Historically, we have always used April 15th (Tax Day) as this magical, non-scientific date that signifies the demarcation between snow and spring.  If you can make it to the 15th, 99 times out of 100 you're good to go.  This winter worked out great in this regard.


Here are the final winter numbers. See my early March post on the metrics we typically use and why we used them.  Many of these graphics compare this winter to last winter and the COLDEST winter ever (1976-77) in northern Ohio.


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Our winter outlook was created by analyzing the global sea surface temperatures in these regions.

Pacific warm and cool pools have shifted since last winter (2013-14). Yet the result was the same:  COLD EAST, MILDER WEST.

The pressure pattern over the Pacific Ocean and North American continent reflected the sea surface temperature pattern:  This pressure configuration was a strong -EPO, -WPO, +PNA set up. It stood firm all winter which locked in the ridge west and trough east for the most part.

Image courtesy: Larry Cosgrove

Negative EPO favors eastern cold. Eastern US Cold periods circled in red

Positive PNA favors eastern cold. Cold periods circled in blue

-WPO favors eastern cold. Cold periods circled in red

Last summer (2014), talk of a strong El Nino faded as a central based El Nino developed called a "Modoki". These central based weak El Nino come in many different flavors. The current El Nino is circled at the top of the graphic below.

These favor below normal temperatures across the eastern US and above normal temperatures across the west.  Ridge west, trough east. 

Our winter forecast was created with weighting certain years in our analog set. Our forecast matched up very close to the overall average temperatures across the US from December through February.

We started off very cold in November partially driven by the Typhoon in the Pacific. It boosted the Gulf of Alaska low which boosted the ridge of warmth in the west which in turn drove cold south across the eastern US.  I wrote about the Typhoon Rule back in November and how we uses that to forecast the November cold.

Overall temperatures across the continental US on November 18th were the coldest since 1976!

The high of 18 degrees on the 18th was the coldest November day since 1958; 4th coldest high temperature in November since the 1870s.  
 
US temperatures rebounded in December after the cold November. We had one SNOWFALL in December which was under an inch. The 3rd lowest total since 1893; lowest since 1931.

By New Year Day, people were wondering where this cold winter was we had outlined in our outlook back in late October. I kept telling people on Facebook and Twitter to be patient. The cold is coming and when it does, it will harsh and similar to the year before.  Guess what happened in January?  The slow turnaround toward ARCTIC COLD began across the eastern US.

By February, the arctic floodgates had opened across the eastern 1/2 of North America. It was ALL-TIME COLDEST February in Cleveland since weather records began in 1871.

Rome, Ohio in the heart of Ashtabula County, due to cold air drainage down the surrounding terrain had a low of -39 degrees!

As the winds dropped, so did the temperatures. The next day, temperatures jumped 65 degrees in 30 hours!

February 14th through the 20th was 5th coldest 7 day stretch in 145 years in Cleveland coming close to matching the arctic cold of 1994.

Remember back a few winter ago when the ski resorts were having a tough time staying open because of the lack of snow and cold? Look at the winter 2012-13 temperature ranks vs the last two winters.

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Coldest winter since 1977-78

Less days above 40...

More days below freezing

 

Arctic cold and clear/calm skies produced huge ranges of temperature.

 Very cold late season morning lows we haven't seen since the early 1960s!

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 We had much more snow in 2013-14 vs this past winter...hard to believe.  If December snowfall would have been closer to average, the last two winter snow totals would have very close.

Days with snow cover of at least ONE INCH. Last winter we had more.

 Peak Lake Erie Ice Cover and Dates.

The Different Faces of Central Pacific El Ninos

A few weeks back, I had an email conversation with Professor Jin-Yi Yu of University of California Irvine.  I ran across his website and 2009 El Nino paper on Central Pacific El Ninos and was looking for some additional information on what the difference is between a Central Based El Nino and a "Modoki" El Nino according to his work. If you remember, the current Central Pacific El Nino was and still is a significant variable in our winter weather outlook. This is what he had to say after I emailed him the sea surface temperature analog composite for January asking him if this was a Modoki pattern we've heard so much about in the media:

"...this SST anomaly pattern is a Central Pacific El Nino pattern,
not a Modoki El Nino pattern. The Modoki pattern requires the warming in
the central Pacific to be flanked by cooling in the eastern Pacific and
western pacific".

This graphic illustrates the differences between both El Ninos. El Nino Modoki on top, Eastern El Nino (typical El Nino) on bottom. Notice the cooler water flanking the relative warmth in the middle of the Pacific near the dateline.

Dr. Yu's 2012 paper summarizes each of the 21 El Nino events since the early 1950s using three El Nino Indices. The El Nino Modoki Index (EMI Method), the basic Nino method using the Nino3/4 sea surface temperature readings and the EP-CP Index derived by Dr. Yu and his colleagues published in his 2012 paper. I highlighted the seven consensus Central Pacific El Nino events across all three indices.

7 Consensus Central Pacific El Ninos (The paper above describes what thresholds are used in identifying EP or CP El Ninos.)

While the list above doesn't identify specific Modoki El Ninos among the Central Pacific El Ninos, checking the average sea surface temperatures starting in September and overlapping each month through February/March, "Modoki type" temperature signatures (cold pockets flanking warmth near dateline) can be seen.  Below are the seven consensus Central Pacific El Ninos in chronological order. Each evolved differently. Each one has central warmth (2009-10 was the warmest). Only 1958-59, 1963-64 and 1977-78 seem to have the strongest "Modoki" signature (cool pockets east and west) by visual inspection.

One other note, notice the warmth along the west coast of North America in 1958-59, 1963-64, 77-78 and partially in 2009-10. Professor Yu shows in this paper that this warmth is connected to the development of the Central Pacific El Nino. The coastal warmth is associated with the North Pacific Oscillation teleconnection.

MODOKI signature present

Weaker MODOKI Signature. Not as strong as 1958-59

Weaker MODOKI Signature

Strong Modoki Signature

Weak MODOKI Signature

Weak MODOKI Signature

Weak MODOKI Signature

What can we say about these seven events?  The central warmth seems to mature in January. The cool pools east and west were firmly established by October in the first four events (1950s through the late 1970s).

What about our current event?

The central warmth us weaker than 2009-10. The coastal warmth is off the charts due to the North Pacific Oscillation index rising to the highest levels ever for November going back 60 years! The cold pools east and west are showing some signs of developing.  As of mid December, the Modoki signature comparing all three sea surface temperature regions to the other seven events is weak.

The next 6 weeks will be critical in determining whether this Central Pacific El Nino will continue to mature into a formidable driver of the early 2015 winter pattern. Based on past analogs, it should.