Friday, November 04, 2011

Could We Receive 15" of Snow By Christmas?

"Another La Nina Winter" has been the catch-phrase among meteorologists as they unveil their Winter Weather Outlooks. Scour the internet and you'll find La Nina as the focal point of every outlook from California to the Carolinas.  La Nina--and to the other extreme--El Nino are terms that describe the changing ocean temperatures in the Pacific.  El Nino is warmer ocean temps and La Nina is colder.

While La Nina/El Nino describes the ocean temps, it doesn't paint a good picture of how the colder or warmer ocean temps are affecting the atmosphere ABOVE the ocean. Luckily, there is one index or number that describes the many elements of the La Ninas and El Ninos that ultimately effect our weather in the US and here in Ohio. This index is called the MULTIVARIATE INDEX or MEI.

The variables are combined to form the MEI:  Sea-level pressure, all directional components of the surface wind, sea surface temperature, surface air temperature and total cloudiness fraction of the sky.

Basically, its a great tool to describe the "NINAS" of all shapes and sizes. Below is the plot of the MEI numbers since 1950. La Nina years--like the one we are entering--are below zero while El Nino years are above zero.  Notice last year's La Nina in the lower right.

What does this have to do with whether or not we see snow in Cleveland before Christmas? Take a look at the list of strongest La Nina Novembers and Decembers since 1950 according to the MEI and the snow totals for each and the average over those years by the end of December.  (The blue years are closer matches to this year than the others)

        NOV/DEC  SEASON TOTALS                                
1955     18.5"            54.2"         
1973     17.1"            58.5"             
1975     18.7"            54.4"            
2010     12.7"            59.8"          
1988     19.6"            54.8"           
1950     34.0"            77.2"   (Thanksgiving Storm) 
1970     11.2"            51.4"             
1999     11.9"            60.1"          
2007     10.7"            77.2"   (March 8th Blizzard: 15-20"+) 
1954     11.8"            49.3"    

 AVG:    16.6"

The November and December snow totals since 1950 in years like this year are fairly consistent. Here are the totals plotted on the MEI graph. The numbers below the zero line are La Nina years.

For comparison, below is the strongest El Nino Novembers and Decembers per the MEI with snow totals. Notice the relatively weak snow years (the one outlier is 2002)


1982      8.5"             38.0"
1997    19.3"             34.0"
1972    13.3"             68.5"
1991    12.9"             65.7"
1987    17.4"             71.3"
1965      4.4"             37.3"
1957    10.0"             31.1"
1994      1.0"             43.6"
1986      4.2"             55.8"
2002    28.5"             95.7" (Christmas Day Snow)

AVG    11.9"
What does this tell about this year's early winter from now until after Christmas?

1.  We typically get more November/December snows during strong La Ninas than during strong El Ninos. 
 The difference is noticeable. Look at 1994!

2.  If the LA NINA factor stays prominent, expect around
16 inches of snow by New Years Eve!!!

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