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What a Difference a Year Makes!

By: Christopher C. Burt, 8:41 PM GMT on March 21, 2013

What a Difference a Year Makes!

On this date (March 21st) last year the anomalous ‘summer in March’ heat wave reached its peak intensity with all-time record high temperatures observed across most of the upper Great Lakes and New England. This year it’s an entirely different story. Here is a brief recap comparing the temperatures and snow cover then and now.

On March 21, 2012 Fort Wayne, Indiana recorded its warmest March temperature on record with an 87°F (30.6°C) reading. On March 21, 2013 the city measured a low of 11°F (-11.7°C), a record low for the date (previous record was 12° in 1960). The daily temperature average was some +32°F above normal for the date in 2012 and -20°F below normal in 2013.

The unseasonably cold air this year has mostly affected the northern Plains and upper Midwest but not so much New England (so far) thus the temperature differences between 2012 and 2013 have been most pronounced in the upper Plains and Great Lakes. For instance, Bismarck, North Dakota recorded a record high of 81°F (27.2°C) on March 16, 2012 compared to a high of just 19°F (-7.2°C) on the same date this year, an amazing 62°F difference. Milwaukee, Wisconsin experienced the same spread of temperatures on March 20th when the city recorded a high of 83°F (28.3°C) in 2012 and a high of 21°F (-6.1°C) this year that day. Chicago had a high of 85° (29.4°C) on the 20th last year but just 26°F (-3.3°C) this year. International Falls, Minnesota saw the greatest spread between departures from normal year-on-year of any site I’ve identified so far: On March 17, 2012 the temperature averaged +40F above normal (a high of 77°F/25°C and low of 52°F/11.1°C) while March 17, 2013 was -27°F below normal (with a high of 22°F/-5.6°C and a low of -28°F/-33.3°C). A difference of some 67°F! If we compare what the high was last year to the low this year on the 17th we see a spread of 105°F! In general the temperatures the past few days have averaged 40-50°F colder than they were last year at this time for most of the upper Midwest.

The reason for this anomaly is a complete reversal of the prevailing jet stream this month compared to this month last year. In March 2012 a stubborn and pronounced high-pressure ridge dominated the eastern half of the country:

The prevailing weather pattern during the last half of March 2012.

Whereas this year just the opposite has been occurring; a persistent trough over the East with the jet stream sweeping deep to the south across the eastern half of the nation allowing cold arctic air to dig into the northern tier of the East and Midwest:

Although this graphic of the upper air flow and jet stream is just for March 20th, it illustrates what the dominant pattern has been for the U.S. over the past week or so.

Big difference in snow cover as well

Spring flowers push their way through an icy cover this year in Hampton, Connecticut. Last year at this time the flowers were in full bloom with temperatures in the 80°s. Photo by ‘hamptonite’ for wundergorund.com

Just as anomalous as the temperatures have been year-on-year, so has the snow cover. In fact heavy snow has buried portions of the Northeast this week Houlton, Maine saw a 17.5” accumulation on Tuesday and Wednesday (March 19-20) while just last year the city recorded its all-time March record high of 79°F (26.1°C) on March 21st. Bangor, Maine had 9.6” this week; last year it hit 84° (28.9°C) at this time. Lake-effect snowfall has buried portions of upstate New York under two feet of snow the past couple of days. Last year it was 82° in Buffalo on March 21st and 77°F (25.0°C) at Saranac Lake in the Adirondack Mountains. It was -14°F (-25.6°C) at Saranac Lake on March 18th this year with deep snow.

A comparison of snow depths on March 21st for 2012 and 2013 in both the Northern Great Lakes and Northeast. In 2013 the Northeast had 97.1% snow coverage compared to 18.4% last year on this date. In the Northern Great Lakes the difference is even starker with a 92.2% coverage this year compared to 0.6% last year on this date.

Christopher C. Burt
Weather Historian

Extreme Weather Temperature Snow

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

Thanks Chris for the outstanding blog entry..
What a difference a year makes..
The variability of the Jet Stream is wild..
Those temperature records are eye-opening for sure..
Forecasting even 3 days out right now seems to be a challenge..
Thanks again..

The climate prediction center has a nice site where you can make US temperature and anomaly plots.
I did some from 3/20/2012 for 7 days.
The entire Midwest had mean temperature anomalies of more than 20 degrees F.
That is crazy.

Temperature Analysis
20 degree anomalies are not uncommon there. It's like a great big highway for air to move north and south.
weatherhistorian has created a new entry.