El Nino is coming back...what does that mean for Winter?

Being that this has been one of the coolest summers on record thus far, the last thing you may want to think about is winter and it being 5 months away. However, we have good news for you…it appears as though this winter will be above normal temperature-wise and drier/less snowy. This doesn’t mean that we won’t have any snow and that temperatures won’t plummet at times, but these harsh conditions likely won’t happen as much.

So, what is leading forecasters to think this? Two words: El Nino. One of the main long-term forecasting tools that meteorologists and climatologists look at are water temperature patterns along the equator in the Pacific Ocean. Fishermen off of the Peruvian coast noticed that in certain years when water temperatures were unusually warmer and fish would be scarcer due to salinity levels in the water. They named these periods El Nino, which means Little Boy or Christ child in Spanish, because of the tendency of this phenomenon to arrive around Christmas. Researchers have found that these warm periods come in cycles of about every 2 to 3 years with the unusually colder periods named La Nina. Here’s an example of how the weather pattern along the Equator shifts during an El Nino:

December - February Normal Conditions

During normal conditions, most of the convection along the equator remains further east near Papua New Guinea and Australia. As the tradewinds along the equator weaken, the waters further east start to warm and the convection shifts eastward and leave the region near Australia dry.

December - February El Nino Conditions

Over the past two winters, conditions over the equatorial Pacific have transitioned from La Nina in 2007-08 to Neutral conditions in the winter of 2008-09. The Climate Prediction Center declares the onset of an El Nino episode when the 3-month average sea-surface temperature departure exceeds 0.5 degrees Celcius in the east-central equatorial Pacific, also known as the Nino 3.4 zone.

Nino Regions

The Climate Prediction Center is forecasting for El Nino conditions to be met for the three month period of May-June-July and continue into the winter. Here is the latest observed Sea Surface Temperatures (SST) along the equator in the Pacific as well as the SST Anomalies showing the warming pattern.

Observed Sea Surface Temperature/Anomalies

SST Anomalies

The forecast into the winter is for a weak to moderately strong El Nino to persist into early next year. So, what does this mean for us in the Chicagoland region? Using data going back to 1950 on previous El Nino years, the trend is for our winters across the upper Midwest and northern Plains to be warmer than normal as well as drier and there being less snow. As always, Mother Nature sometimes has a mind of her own with some of these El Nino winters actually being some of the coldest and snowiest on record. However, with the overall trend mainly being warmer and drier, the Climate Prediction Center has gone with a similar forecast for this winter. As for this fall, there isn’t as much of a signal for how the developing El Nino will shape our weather with an almost even split of below normal, near normal and above normal seasons in terms of temperatures, precipitation and snow. The following are data from previous El Nino years at Chicago and Rockford (bolded data indicates data in the Top 10 warmest/coldest, wettest/driest, or snowiest/least snowiest seasons) along with the general trends expected during El Nino seasons and CPC’s forecast.

CHICAGO

Year	Fall Average Temps	Fall Precip	Fall Snow	Winter Average Temps	Winter Precip	Winter Snow
1951	50.3	11.76	14.3	28.6	5.38	43.6
1957	52.1	6.95	2.4	26.9	3.40	16.2
1963	59.1	4.46	0.0	25.4	2.41	16.8
1965	53.7	8.37	0.0	27.5	7.32	20.9
1968	54.7	8.73	0.8	26.9	6.33	21.9
1969	52.8	6.81	3.8	24.2	3.86	44.7
1972	50.8	12.55	6.3	28.0	7.52	20.0
1976	48.6	5.04	0.9	19.0	2.30	42.7
1977	52.7	13.50	6.3	19.1	5.68	71.2
1982	51.5	9.98	0.4	30.2	11.28	16.0
1986	52.2	12.28	3.8	30.1	3.75	17.7
1987	52.1	5.30	1.1	24.9	6.94	39.6
1991	50.7	13.46	1.2	30.6	3.97	14.5
1994	55.3	8.02	0.0	28.4	5.23	20.5
1997	51.3	5.92	3.3	33.2	5.87	18.1
2002	51.6	4.36	4.7	25.0	2.48	13.8
2004	54.7	7.39	5.1	28.6	7.34	31.1
2006	51.4	13.54	0.7	26.6	6.51	29.6
Norm:	51.7	8.99	2.1	25.5	5.81	28.3
Above: 6	Above: 7	Above: 7	Above: 7	Above: 4	Above: 5
Near: 7	Near: 6	Near: 7	Near: 7	Near: 7	Near: 2
Below: 5	Below: 5	Below: 4	Below: 4	Below: 7	Below: 11

ROCKFORD

Year	Fall Average Temps	Fall Precip	Fall Snow	Winter Average Temps	Winter Precip	Winter Snow
1951	47.6	11.39	14.7	25.0	3.30	30.8
1957	49.2	5.86	1.3	22.6	3.89	15.5
1963	56.4	7.33	0.0	21.8	2.26	17.1
1965	51.4	12.97	0.1	23.2	6.46	16.8
1968	51.4	10.82	4.5	23.8	5.21	14.3
1969	49.9	11.64	0.6	19.7	2.27	29.6
1972	49.6	12.19	4.5	24.9	5.60	16.0
1976	44.4	3.71	4.5	14.7	1.62	18.9
1977	49.6	8.80	7.3	14.5	3.12	40.2
1982	51.1	10.61	0.0	29.2	5.65	18.6
1986	50.0	13.45	5.0	27.8	2.41	11.5
1987	49.7	5.77	0.6	21.7	7.02	40.3
1991	49.3	13.60	0.7	29.0	4.12	20.0
1994	52.9	9.59	0.0	24.8	3.17	29.9
1997	49.8	4.45	No Data	30.1	4.64	No Data
2002	49.8	5.19	2.7	23.2	1.28	8.0
2004	53.1	5.83	5.3	26.0	5.45	23.7
2006	50.0	9.12	0.1	24.3	4.76	33.2
Norm:	50.3	8.67	2.7	24.4	4.81	29.0
Above: 6	Above: 8	Above: 7	Above: 8	Above: 3	Above: 2
Near: 5	Near: 4	Near: 2	Near: 6	Near: 6	Near: 6
Below: 7	Below: 6	Below: 8	Below: 4	Below: 9	Below: 9