La Nina is Back!

A change from El Nino to La Nina occurred in the fall of 2010, and a moderate to strong La Nina formed throughout the winter of 2010-2011. La Nina conditions returned to the equatorial Pacific Ocean as the 2011-2012 winter season began.

The official winter prognosis for the United States has been released by the Climate Prediction Center (CPC). So, what exactly does this imply for the states of Northern Indiana, Southwest Lower Michigan, and Northwest Ohio? Please continue reading for further details…

What is La Nina?

Periodically, the equatorial Pacific’s center and east-central regions experience a cooling known as La Nina. Although La Nina periods tend to occur every 3–5 years, this pattern can sometimes persist for several years. In the El Nino/Southern Oscillation (ENSO) cycle, La Nina is the chilly phase.

Late this summer, as negative temperature anomalies returned to the equatorial Pacific Ocean, there were signals of a rebound of La Nina, which had decreased during the spring and early summer of 2016. The latest official forecast from the Climate Prediction Center (CPC) predicts that this La Nina will strengthen and linger into the early Spring of 2012. This is in line with the predictions of several computer models.

The tropical rain patterns from Indonesia to the west coast of South America are influenced by temperature shifts in the Pacific Ocean during a La Nina event. Worldwide climates are impacted by shifts in tropical rainfall patterns. The winter months, when the jet stream is at its fiercest over the United States, are typically the most severe for these effects.

A wave-like jet stream flow through the United States and Canada is characteristic of wintertime La Nina events, leading to colder and stormier-than-average temperatures in the North and warmer and less stormy-than-average conditions in the South. The weather in the Midwest is often warmer and drier in the fall and rainier in the winter. Our weather is influenced by a wide variety of complex factors in the atmosphere and oceans.

Following are images depicting temperature, precipitation, and snowfall anomalies in CONUS based on historical La Nina episodes dating back to 1950. An anomaly map and a frequency map make up both sides of every picture. Calculated anomaly from all prior events is displayed on the anomaly map. The right-hand frequency map depicts the typical occurrence of these outliers.

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How La Nia may impact winter weather in the U.S. : NPR. https://t.co/q9xA1HGJfO The climate pattern known as La Nia generally brings winters that are drier and warmer than usual across the southern… #ClimateChange #GreatLakes #PacificNorthwest #Pacificocean #UnitedStates

— Igor Os (@IgorOs6) November 14, 2021

The likelihood that the anomaly will happen again increases as its frequency rises. Composite maps appear on top, trending maps in the middle, and hybrid maps at the bottom. This link provides a more in-depth description of these maps. Images on the left are from meteorological winter (December–February) while those on the far right are from the beginning of meteorological spring (January–March) (late winter into early spring).

You can see that the temperature anomalies around here are very near to zero, but the negative anomalies are located only a little way to the northwest. This reflects the fact that some La Nina years are warmer than average while others are colder.

Generally speaking, our region experiences wetter-than-average precipitation and snowfall anomalies as winter turns into early spring. Keep in mind that these forecasts only take into account the effects of previous La Nina episodes and not any other factors that may operate with or against this pattern. In the next parts, we will examine two of the more well-known events.

Arctic and North Atlantic Oscillations

The weather in the continental United States (CONUS) is correlated with conditions in the Arctic and North Atlantic Ocean, according to studies conducted over the previous several years. The Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) are two names given to these weather patterns (NAO).

The Arctic Oscillation (AO) describes the ebb and flow of air pressure in the Arctic’s high latitudes. The AO is said to be in a negative phase when there is high pressure over the northern polar region and low pressure in the middle latitudes. In its positive phase, this pattern exhibits a reversal. During the negative phase, the jetstream weakens, allowing the very cold arctic air to be pushed southward by high pressure in the polar region.

This causes the air to plummet southward into the central and eastern United States. The winds that accompany the polar jet stream are zonal and localized to the northern hemisphere during the positive phase. Because of this, the extremely cold air in the polar regions is virtually “bottled up.” You can observe the AO phases in the following diagram. You may get more details about the AO at

The North Atlantic Oscillation (NAO) is analogous to the Arctic Oscillation (AO), but it is a measurement of the atmospheric sea level pressure differential between the Icelandic low (also known as the arctic low) and the Azores high (also known as the subtropical high). When the NAO is in its positive phase, both the Azore’s high and the Icelandic low are more intense than usual. Because of this, the pressure difference between them grows.

When the NAO is in its negative phase, the pressure gradient between the Azore’s high and the Icelandic low is smaller. In the eastern CONUS, warmer-than-average temperatures are connected with the positive phase, while cooler-than-average temperatures characterize the negative phase. A schematic of the NAO phases is provided below. You may learn more about the NAO here.

Despite the AOs and NAOs’ shown influence on weather across the CONUS, they are only reliably forecastable for up to two weeks in advance. Since the AO and NAO changes occur on a considerably shorter time scale than La Nina, their effects can either amplify or dampen the circumstances generally associated with a La Nina. Cold air can be brought to the CONUS when both the AO and NAO are in their negative phases. A big snowstorm could occur if these phases coincide with a powerful storm system developed in a La Nina cycle. There may be less cold air and possibly more liquid precipitation if the AO and NAO are in a positive phase when a storm system starts. Predicting the winter weather in the central and eastern United States is challenging for many reasons, including these complex relationships.

Here are graphics depicting the continental United States (CONUS) during the AO’s positive (AO+), neutral (AON), and negative (AO-) phases, respectively, in terms of temperature and precipitation anomalies. Images on the left are from December through February, while those on the right are from January through March. For much of the central and eastern CONUS, temperature anomalies are seen to be positive when the AO is positive.

Many of these locations also show negative temperature anomalies when the AO is negative. The effects on precipitation are not as widespread as those on temperatures, but in locations where La Nina tends to generate above-average precipitation, such as the Ohio and Lower Mississippi Valley regions, there is a trend toward less precipitation in a negative AO pattern.

These contrasting tendencies add fuel to the uncertainty surrounding winter precipitation forecasts. However, the negative precipitation anomalies associated with the negative AO in our area are typically countered by the powerful and moisture-rich La Nina systems that are typical of this time of year.

Climate Prediction Center’s Outlook

The scientists at the Climate Prediction Center (CPC) use data sets, computer models, and other research tools to forecast temperatures and precipitation on weekly, monthly, and seasonal timeframes. Current predictions for this Winter are depicted here (December, January, and February). Currently, Northern Indiana, Southwest Lower Michigan, and Northwest Ohio have a 50/50 chance of normal, above, or below normal temperatures and a higher than normal likelihood of above normal precipitation this winter. These maps depict the likelihood that these conditions will arise; they do not represent absolute certainty. The precipitation map is thus not indicative of the likelihood of snowfall or the volume of snowfall, but only precipitation. Weaker than usual winter temperatures in the northern CONUS may result from an AO or NAO flipping to positivity for an extended period, as discussed above. But if they stay negative for a while, it might be a very chilly winter in the north.

These indices have been on the negative side for the past few winters, and some studies predict they may remain there for a while. As a reminder, in the winter, the location and type of precipitation that falls are heavily dependent on how and where storms develop and move over the Midwest. During a La Nina winter, the storms are more likely to form in the Ohio River Valley than in other parts of the country. Because of this, our area is usually on the far northern edge of winter storms.

Local Study

After reviewing the national-scale research and the CPC’s winter forecast, a local study was conducted to investigate the effects of previous La Nina episodes on the area. There have been 14 La Nina events recorded since 1950.

These results cannot, on their own, predict what would happen during the present La Nina phase due to a restricted dataset and local climate variability; however, the tendencies are worthwhile to note. Fort Wayne and South Bend’s monthly average temperatures, rainfall, and snowfall were recorded for each occurrence. The following graphs depict the overall deviation from the average for all La Nina events.

Fort Wayne

During La Nina events, March, May, and November were colder than average in Fort Wayne, but all other months were warmer than average. January, February, May, August, and October all saw above-average precipitation, while the other months were drier than usual. The months of January, February, April, and October–December saw below-average snowfall, while March saw above-average amounts.

South Bend

In general, South Bend was warmer than normal during La Nina years, except for February, March, and May. It rained more than usual in January, February, April, August, and October, and less than usual in the other months. The months of January, February, and November saw below-average snowfall, while March, May, and October saw above-average snowfall.

Winter 2010-2011 Recap

Due to a moderate to strong La Nina phase, the winter of 2010-2011 was cooler and drier than usual, yet snowfall was above normal in both Fort Wayne and South Bend. The winter of 2010-2011 demonstrates why one should not extrapolate precipitation predictions to infer probable snowfall quantities.

Fort Wayne- Low temperatures were the norm from December through February in Fort Wayne. In December, the average temperature was 5.3 degrees below normal, in January it was 3.1 degrees, and in February it was 1.8 degrees below normal. The average temperature for the winter will be 3.4% lower than usual as a result. January and December precipitation were also lower than usual (1.69″ below in December and 0.25″ below in January). Precipitation levels in February were well above average ” (1.27″ above normal).

Winter precipitation was 0.67 standard deviations below average “. While rain was below average, snowfall totals were much above average in all three months. Both December’s and January’s snowfall totals were more than double the average. With 18.3 inches of snowfall (or 10.7 inches more than average), February ended as the second snowiest month on record. The 45.3-inch snowfall total was 19.5 inches above average and made this winter the third snowiest on record.

South Bend — South Bend saw temperatures that were below average for the winter months of December, January, and February. In December, the average temperature was -4 degrees below normal, in January it was -2 degrees, and in February it was -1 degrees. The average temperature during the winter was 2.7 degrees below average. Both December (1.25″ below normal) and January’s precipitation were below average (0.11″ below normal). Precipitation levels were above average in February (1.53″ above normal).

An abnormally low 0.17 inches of precipitation fell over the winter. While rain was below average, snowfall totals were much above average in all three months. This December had an abnormally high amount of snowfall, 4.4 inches more than average. The 53.8-inch snowfall in January was 30.6 inches more than average. This is the second snowiest January on record, after January 1978.

February saw a whopping 10.0 inches of snow, well over average. This winter was the second snowiest on record, with a total of 102.9 inches, 45 inches above the long-term average. The only other winters to record 100 or more inches of snow were 1977–1978 and 1981–1982.

Winter 2011-2012 Recap

From the beginning of the 2011-2012 winter season through February 25th, temperatures were above average and precipitation was above average due to a weak to moderate La Nina phase. However, snowfall was below average in both Fort Wayne and South Bend. The 2011-2012 winter season, like the previous one, demonstrates the fallacy of assuming a certain quantity of snowfall based on a forecast of precipitation.

Fort Wayne (through February 25) —Fort Wayne experienced warmer-than-average temperatures throughout the winter months of December, January, and February. In December, the average temperature was 6.0 degrees F above normal, in January it was 4.7 degrees, and so far in February, it is 4.6 degrees. This results in an increase of 4.0 degrees above average during the winter season.

Both December and January saw precipitation levels that were above average (1.00″ above in December and 0.83″ above in January). Precipitation levels in February have been well below average thus far (0.35″ below normal). We received 1.48 inches more rain than usual this winter.

January’s snowfall was above average compared to the previous year, while December’s was below average by 1.9 inches and February’s by 0.7 inches (4.5″ above normal). Through February 25th, a total of 27.5 inches of snow had fallen for the season, 1.2 inches more than average.

South Bend (through February 25) — The temperatures in South Bend were above average from December through February. In December, the average temperature was 6.3 degrees above normal, in January it was 5.0 degrees, and so far in February, it is 4.0 degrees. We had a winter where temperatures were, on average, five degrees warmer than usual.

Both December (0.01″ above normal) and January’s precipitation were likewise above average (0.68″ above normal). Precipitation levels in February thus far have been well below average (0.24″ below normal). The total amount of rain that fell during winter was 0.45 inches higher than average.

There was an above-average amount of rain, but below-average amounts of snow in December and February and above-average amounts in January. From December to January, snowfall was 11.6 inches below normal, 14.4 inches above normal, and 4.7 inches below normal for February. A total of 49.7 inches of snow fell throughout the season, which was 3.2% lower than average.

So why is this winter so different from last year’s if La Nina conditions have been present for the past two winters? Although the reasons for the variances are difficult to pin down, they may be related to the previously discussed Arctic Oscillation (AO) and North Atlantic Oscillation (NAO). Cold air can be brought to the CONUS when both the AO and NAO are in their negative phases.

A big snowstorm could occur if these phases coincide with a powerful storm system developed in a La Nina cycle. There may be less cold air and possibly more liquid precipitation if the AO and NAO are in a positive phase when a storm system starts. This is what has caused this winter, as cold air has been trapped in the north of Canada. Last winter, while both the AO and NAO were in their negative phases, cold air was able to penetrate the region, resulting in more snowfall than liquid precipitation.