What is Driving Our Not-so-Cold Winter?

We've grown accustomed to cold and snowy starts to winter.  The last two have featured rounds of cold and snow with steady snow cover. This winter hasn't behaved like her predecessors.  Why the change?  wasn't La Nina supposed to drive this winter's cold?  Not so fast.

The answers lie within several regions of the northern hemisphere and the indices that describe their behavior. Here are the regions and their parent indices in no particular order.  I'll explain what each index measures and describe the impact each index has on our weather here in northern Ohio.

ARCTIC (ARCTIC OSCILLATION) "AO"
NORTH ATLANTIC (NORTH ATLANTIC OSCILLATION) "NAO"
EASTERN PACIFIC (PACIFIC-NORTH AMERICAN OSCILLATION) "PNA"
TROPICAL PACIFIC (EL NINO OR LA NINA)

We'll describe each teleconnect and show how each plays a role in our weather patterns across the Great Lakes and northern Ohio. It gets complicated so I've tried to keep the technical explanations to a minimum.



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The Arctic Oscillation (AO) is a measure of the opposing pressure patterns of the mid-latitudes (across Canada and US) and the polar north.

When the index is POSITIVE, high pressure over the US and Canada drive storm tracks farther north keeping temperatures above normal across the eastern US (see left side of graphic above). When it is NEGATIVE (see right), the pressure tends to be lower across the US and Canada with higher pressure over the polar region. This causes storm tracks to come from the northwest ushering in colder than normal air.

The North Atlantic Oscillation (NAO), the AO's cousin, describes the pressure changes between low pressure over Iceland and the semi-permanent high over the Azores (eastern Atlantic).

Both of these teleconnections play direct role in how much and to what degree the cold air/storm track and intensity becomes in winter across the eastern US and Ohio.  The lower or more negative the AO and NAO levels, the more frequent and deeper the cold air.

The problem is that these pressure variations are incredibly random and very difficult to predict much further than a week ahead of time. This is why we refer to these as "wild cards".

I plotted the average AO and NAO levels for the Novembers and Decembers since 1991.

The last 3 winters had AO/NAO levels well below zero. See how the NAO and AO run hand in hand. When the AO goes down, the NAO follows. Notice below how many days (graph below) over the last two early winters the AO/NAO were well below zero

The pressures over the arctic were alot higher, the pressure/storm tracks across the Great Lakes were much lower, the cold air much colder. The shades of blue show temperatures below normal across Ohio and the  eastern US.

The pattern resulted in snows like  this...

This year, we count only 9 days with AO levels below zero! Not many at all.

Yet this year, the levels were very high. The highest levels in decades! What did this do? It kept the polar jet stream strong and consistant which keeps the cold air locked up north.  The pressure tendencies in the north Atlantic were such that it steered the storm tracks well north of Ohio.  All of this kept unseasonable temperatures for November and December. 

I plotted the average November and December combined temperatures for each year since 1991 on the AO/NAO plot. Notice that the warmer periods match up well with the higher levels of the
AO/NAO; colder periods for the lower AO/NAO levels.

The Pacific Ocean has also played a pivotal role in our pattern this year. TWO OTHER INDICES were very good guides on this milder pattern. The first is the PACIFIC-NORTH AMERICAN OSCILLATION. Its the general pressure pattern over this area shaded in red.

The higher the pressure pattern, the stronger the ridge over the western US and Canada, the stronger the trough/cold air over the US. This, unlike the other indices, means that lower than average pressure was centered over the western US/Canada and higher than average pressure was over the eastern US.

This winter, the PNA has been mainly negative.

The ocean temperatures in the tropical Pacific have been below average since last fall. This below normal ocean sea surface temperature pattern is a classic LA NINA PATTERN.

This change in ocean temperatures buckels the jet stream across North America which alters the storm tracks so that they come from the northwest. Last winter, we had more than 9 cold front-type snows from Canada. This year, ONLY TWO!

How does this LA NINA compare to others that share similar characteristics (time of peak/length of duration)? Use like to use the MEI Index because it factors in PRESSURE DIFFERENCE, WINDS, AIR TEMPERATURE, CLOUD COVER and SEA SURFACE TEMPERATURES in the tropical Pacific Ocean. Here is a graph that plots this LA NINA event to the others that compare favorably. Notice that it is similar to the three year LA NINA back in the early/mid 1970s.

How can we summarize what has happened so far?

• While the LA NINA pattern was present last winter allowing for clipper snows from Canada, the ARCTIC/NORTH ATLANTIC PATTERN continued to drive the cold air south reinforcing the La Nina storm track.  

• This year, the LA NINA is present yet the ARCTIC/NORTH ATLANTIC CONNECTION is noticably absent.  So instead of reinforcing the colder air/northwesterly storm tracks, it shifted the storm track more south featuring above normal rain (7+ inches for Cleveland in November and December).The ridge over Ohio and the east coast pushed snow producing CLIPPER SYSTEMS north and the temperatures higher.   

• The cooler than normal Pacific water temps off of the coast of California and Alaska kept the cold and storminess further west (NEGATIVE PNA SHOWN EARLIER) while further enhancing theridge of dry/milder weather across the Great Lakes

How about snow totals comparing this year through January 12th to the last two winter? MUCH LOWER

How will these TELECONNECTIONS change in the weeks ahead?  More on that later after this rare round of snow moves through. :)

What About this 2011-12 La Nina...Is it Different from Last Year?

I created an animated Sea Surface Temperature map comparing last year from early October 2010 to early January 2011. Notice the streak of blue and purple in the middle of the map. That's the classic La Nina signature. Also, check out the warm pocket in the northwestern Pacific and the cooler water to the east of it. THE WARM POCKET SEEMS WEAK... 

This year, the La Nina signature doesn't seem as strong. Perhaps more importantly, THE WARM POCKET IN THE WESTERN PACIFIC IS STRONGER although it is showing signs of fluctuating.

The weaker La Nina and the strength and position of the warm pool in the western Pacific, I believe, have played a large role in the storm paths across the US and over Ohio.  Last year, we had prolonged cold.  This year, only one day below freezing in December. 

La Nina is peaking which means that other factors will come into play in the months ahead. Will we be able to get the Christmas decoration down due to the snow and cold? Will sledding at Virginia Kendall Park in Peninsula we possible?  Will we see more of the grass than snow cover? More later this week

Where is the Lake Erie Ice? Will it freeze over this winter?

Living in Cleveland, Ohio, the lake just to our north plays a major role in our wintry weather. Lake effect snow especially early on in the season can produce more than 24 inches of snow in a very short time. The relatively warm water of Lake Erie (temps between 40 and 50 degrees) in November and early December provide a surplus of moisture necessary for the creation of full blown lake effect events. All that is needed is cold air.  This winter trough the end of December, we haven't had much.  The absence of cold air keeps the lake free of ice. 

All of this begs the question:  Will Lake Erie freeze over this year?

Go back to last winter when we had 18 of 31 days in December with temps in the 20s. The lake water temperature went from 45 degrees on December 1st to 33 degrees on December 24th. The ice cover for December 20th looked like this: 

RED indicated 80%+ ice cover. Notice the open water in white.

January of 2011 continued with temperatures below averages with 20 of 31 days in the 20s or colder. Ice development on the lakes tends to lag several weeks after the cold air starts.  Here is the ice cover map on January 2nd.

The ice started to develop further east

Now the ice cover map for January 17th, only 15 days later.

80% ice cover spread across most of the lake

Finally, the ice map for January 27th.

80% to 100% ice cover over much of the lake

 

How about this year? Temperatures in December of 2011 stayed well above normal. Only one day had a high BELOW FREEZING! The lack of ice on lake erie isn't that surprising.

Ice cover for December 20th

How about January 2nd? A little bit of ice over the western basin where the water is shallow indicated with the light blue color.

Even the ice coverage is less than 10%

How about the rest of the month? We are running way behind in ice development. Below is the actual satellite photo of the open water of Lake Erie on December 26th.  The white on the right is cloud cover

A two week arctic outbreak would be needed to drop the lake water temperature to 33 degrees. The current temp is 39 degrees!  Remember last year, we fell below 39 on December 9th! It would take some time for the water temp to fall to 32-33 degrees before widespread ice would form.  I just don't see this happening. Maybe 50% coverage by early February. If it doesn't happen by early February, the water temps will start to climb. Even last year, the water temp was in the upper 30s by the end of February and above 40 by March 13th.

All of this means that when it does get cold even for a day or two, lake effect snow will be more common and might last into February and March. Whereas last year, lake effect snow ended in mid January. 

Just our luck.

First Lake Effect Event for Northern Ohio

We ring in the new year with our first lake effect event here in Northern Ohio at least a month late. The classic snowbelt areas are below with a more westerly wind.

Late today, winds shift and come out of the NORTHWEST wind and push lake effect bands south into areas that don't typically receive lake effect snow.

Total snowfall accumulations through noon Tuesday are as follows. Remember that lake effect can flare up without warning depending on the winds and the elevation. Higher elevations in southern Cuyahoga and northern Medina counties can "squeeze" out more snow. Keep this in mind if you are driving along I-71 or I-77 in these spots.

Northeastern Ohio's First Widespread Snow

As of 8AM Tuesday morning, the rain has spread throughout most of northern Ohio. Some reports of sleet/snow near Vermilion and Lorain.  Temperatures are still not super-cold although they are slowly falling out west.  This marks the last southern/panhandle storm system for a while. The transition to a more progressive/clipper-like pattern this week and into the first week of 2012.

When will the rain/sleet transition over to ALL snow?  Here is the map for noon today and then 6PM today.

ALL of northeastern Ohio will seen 1-3" of snow by sundown.  Additional accumulations with the following lake effect overnight tonight brings the amounts to this...

Is Winter Finally Coming? Our Changing Pattern in January

THE PATTERN IS BEGINNING TO SHIFT BACK TO A CLASSIC WINTER ONE.  IN FACT, LOOKING AT THE MOST RECENT PROJECTIONS FOR NEXT WEEK AND BEYOND, THE FLOW IS SETTING UP TO BE EXACTLY HOW I THOUGHT THE WINTER WOULD START BACK IN LATE NOVEMBER. 




THE COMPUTER PROJECTIONS WERE HAVING A HARD TIME LOCKING INTO THE NOVEMBER/DECEMBER PATTERN BECAUSE THE FLOW WASN'T A TYPICAL EARLY WINTER ONE. 

IT REACTED AS IF IT WAS AND PRODUCED RESULTS THAT SHOWED THE COLD AIR TO BE WAY TO STRONG.  NOW, THE COMPUTER PROJECTIONS ARE COMING INTO BETTER ALIGNMENT. EITHER THEY ARE PICKING UP ON THE CHANGING CONDITIONS IN THE SHORT-TERM OR THEY ARE ARE PICKING UP ON THE SHIFTS IN THE GLOBAL, LONG WAVE, LONG TERM PATTERN.  I THINK THE LATTER OF THE TWO BEHAVIORS FITS BEST. LET ME SHOW YOU WHAT I MEAN.

TODAY CURRENT MAP SHOWS THIS "CUT-OFF" LOW COMPLETELY SEPARATE FROM THE MAIN FLOW OF AIR TO THE NORTH.  THIS "CUT-OFF" HAS SAT OVER THE SW FOR WEEKS WITHOUT MUCH MOVEMENT.  THE PROJECTIONS HAVEN'T HANDLED THIS FEATURE VERY WELL.  OFTEN TIMES, IT'LL MOVE THE LOW SLIGHTLY MORE WEST BY SHOWING BURSTS OF COLD AIR OVER NORTHERN OHIO WHICH NEVER HAPPEN.  

NOW FAST-FORWARD AHEAD TO RIGHT AFTER THE FIRST OF THE YEAR.  THE LONG TERM PROJECTIONS SHOW THE "CUT-OFF" COMPLETELY ABSORBED INTO THE FLOW.  A SURE SIGN THAT THE NORTHERN STORM TRACK IS BEGINNING TO EXERT ITS DOMINANCE ON THE WEATHER ACROSS THE GREAT LAKES AND OHIO.  THIS ALL MEANS MORE SMALL, FREQUENT SNOWS WITH SUBSEQUENT LAKE EFFECT SNOW.

REMEMBER THE ARCTIC OSCILLATION AND NORTH ATLANTIC OSCILLATIONS?  THEY SEEM TO BE TRENDING LOWER. THIS POINTS TO A STRONGER NW FLOW WITH MORE FREQUENT COLD BURSTS LASTING A FEW DAYS AT A TIME. THE LEVELS AREN'T POINTING AS LOW AND AS COLD AS LAST WINTER BUT ITS A TREND DOWN NONETHELESS.

WHAT WE WILL NEED TO LOOK AT CLOSELY IS THE ARCTIC OSCILLATION IN THE MIDDLE OF JANUARY.   IF A MAJOR COLD AIR OUTBREAK WERE TO OCCUR, THE ARCTIC WILL SHOW SIGNS OF IT AND THE "AO" WILL NOSEDIVE LIKE LAST YEAR AND IN 2009.

Arctic levels dropped VERY low in December

2010 arctic levels drove temps well below normal early in the winter

REMEMBER:  SINCE 1950, 15 OF THOSE 60 NOVEMBERS AND DECEMBERS HAVE HAD LESS THAN 10 INCHES OF SNOW.  THAT'S 25!  THE JANUARY'S THAT FOLLOWED AVERAGED 14 INCHES OF SNOW FOR NORTHERN OHIO (NOT COUNTING LAKE EFFECT AREAS). 
 
THAT IS THE EXACT AMOUNT THAT MY COMPOSITE SHOWED LAST WEEK! 

I GUARANTEE SNOW FOR JANUARY WITH MORE FREQUENT COLD SPELLS. SNOWS WILL BE ALBERTA CLIPPER IN ORIGIN. 

THE LAKE IS STILL WIDE OPEN AND I DON'T THINK IT WILL FREEZE THIS YEAR. THIS MEANS THAT ANY COLD AIR WHICH FOLLOWS THESE CLIPPERS FROM THE NORTHWEST WILL SURELY CREATE LAKE EFFECT SNOWS.

WINTER-LIKE TEMPS ARE CLOSER THAN WE THINK!

Volcanoes: A Year in Pictures

2011 was a year of extremes both in the weather and geology.  I ran across some great pictures posted on theatlantic.com back on December 16th highlighting the eruptions of some of the world's most active and INACTIVE (until recently) volcanoes. (Credits: Reuters, AFP, USGS, Getty Images, AP)

Here they are in no particular order:

Volcano, Hawaii

Southern Argentina

Vatnajokull, Iceland

Grímsvötn volcano

Indonesia's North Sulawesi province

Kilauea Volcano, Hawaii

Mount Bromo, Indonesia

Mount Etna, Sicily

Puyehue Volcano, Southern Chile

Miyazaki and Kagoshima prefectures, Southern Japan

Kilauea Volcano, Hawaii