National Weather Service Weather Forecast Office

      With the first half of October going down with bouts of snow and unseasonably cold temperatures, many are probably wondering what is in store for the upcoming winter?  The answer to this question likely lies in the equatorial Pacific Ocean, where anomalously warm waters have been building up into this fall setting the stage for an El Niño this winter.

 

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 What is El Niño?

 

El Niño is the warm phase of the El Niño Southern Oscillation (ENSO), with the cold phase known as La Niña.  An El Niño occurs when the waters in the central equatorial Pacific Ocean become warmer than normal.  It is officially declared when the 3-month average sea surface temperature departure in the central Pacific exceeds +0.5^o C (currently is near +1.0^o C).  El Niño conditions recur approximately every 3 to 7 years and typically stay around for 6 months to a year, though on occasion they have lasted as long as 2 years.  The impacts of an El Niño are mostly felt during the winter months, with Minnesota and Wisconsin tending to have above normal temperatures with below normal snowfall. However total precipitation (all types) does not have a strong signal one way or the other with an El Niño.  For more educational information on El Niño and its impacts, see the Climate Prediction Center's (CPC) educational page.

With the warmer ocean temperatures, thunderstorm activity shifts from Southeast Asia into the central Pacific Ocean.  This impacts the upper level jet streams, with the southern jet becoming more active, while the northern jet is suppressed and shifts north.  The impact on the changes to the northern jet in an El Niño winter is to decrease the number of Alberta Clipper type systems seen and decrease instances of arctic air outbreaks.  The combination of the two is what results in typically seeing above normal temperatures with below normal snowfall.

 

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 Where do we stand now with the El Niño and what do we expect?

 

Current Sea Surface Temperature (SST) Departures

Note the positive temperature anomalies (warmer than normal waters) in the highlighted area.  This large area of +1^o C to +2^o C anomalies is the evidence of the current El Niño.  This puts this El Niño into the moderate strength El Niño, with the final maximum departure expected to end up near +1.3^o C.

 

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 What does a moderate El Niño mean for this winter?

 

To answer this question, we went back in the historical data to find when previous moderate El Niños with SST anomalies between +1.2^o C to +1.8^o C (where this El Niño is expected to end up) occurred.  Since 1950 (when accurate SST data in the central Pacific became available) there have been 6 such El Niños that impacted 7 winters (there was one prolonged El Niño that lasted from the 1986-87 winter through the 1987-88 winter).  For these winters, total seasonal snowfall and the average winter temperature (average temperature for the months of December, January, and February) for our 3 main climate locations (MSP, EAU, and STC) were compared to the normal for each site.  The results can be found in the following three tables.

MSP Seasonal Snowfall and Winter Temperature for Moderate El Niños 

Season	Season Snow (125 year ave is 45.6”)	DJF Ave Temp (o F)	Temp Departure (o F)
2002-03	35.0	19.1	+1.8
1994-95	29.6	20.7	+3.4
1991-92	84.1	23.7	+6.4
1987-88	42.4	16.4	-0.9
1986-87	17.4	25.8	+8.5
1965-66	36.1	15.9	-1.4
1957-58	21.2	21.1	+3.8
Average for all years	38.0	20.4	+3.1

EAU Seasonal Snowfall and Winter Temperature for Moderate El Niños 

Season	Season Snow (112 year ave is 49.9”)	DJF Ave Temp (o F)	Temp Departure (o F)
2002-03	32.2	17.2	+1.2
1994-95	42.2	19.5	+3.5
1991-92	52.3	22.5	+6.5
1987-88	32.3	15.2	-0.8
1986-87	23.4	23.5	+7.5
1965-66	34.3	14.4	-1.6
1957-58	25.3	17.2	+1.2
Average for all years	34.6	18.5	+2.5

STC Seasonal Snowfall and Winter Temperature for Moderate El Niños 

Season	Season Snow (110 year ave is 41.8”)	DJF Ave Temp (o F)	Temp Departure (o F)
2002-03	31.7	15.6	+1.9
1994-95	46.7	15.6	+1.9
1991-92	54.5	20.2	+6.5
1987-88	32.1	12.8	-0.9
1986-87	16.7	22.2	+8.5
1965-66	25.5	11.7	-2.0
1957-58	24.8	17.0	+3.3
Average for all years	33.1	16.4	+2.7

Some notes on the tables above:

• The large snowfall in 1991-92 at MSP was due in large part to the Halloween blizzard, followed by another large snow storm near Thanksgiving, for December through March, snowfall was below normal.
• At all 3 locations, the average temperature for the month of December was above normal for every winter listed.  Even the bitterly cold winter of 1965-66 (when the average temperature at STC for January was  -1.4^o C!) had an above normal December temperature.
• Temperatures in January and February showed much more variability, with some of the winters having below normal temperatures for one or both of the months.
• For years where snowfall was above normal, this was largely aided by a couple of significant early season (Oct/Nov) snowfalls.

 

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 What is the current winter outlook?

Read more about the official NOAA Winter Outlook

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