Historical Climate Extremes give hints on what an El Niño year could mean for Chesapeake Bay

El Niño: what is it and why do we care?

smileBy now, you have probably heard that we have a strong El Niño this year and that this unseasonable warm December is likely related to it.

In fact, the media is already calling this “The Godzilla of El Niños” or “The Christmas Grinch” who stole our chance at a white Christmas.

El Niño years occur when a warmer-than-average band of ocean water develops in the central to east-central Pacific Ocean. This “warm” phase is part of the entity named the El Niño Southern Oscillation (Figure 1).

Figure 1: The warming (El Niño) and cooling (La Niña) anomaly in the east central Pacific attributed to the El Niño Southern Oscillation. Credit (http://iri.columbia.edu/news/eight-misconceptions-about-el-nino/)

Figure 1: The warm (El Niño) and cool (La Niña) anomaly in the east central Pacific attributed to the El Niño Southern Oscillation. Credit

Essentially, the sea surface temperatures increase enough to affect pressure patterns, which consequentially affects global weather patterns. A strong El Niño often changes the normal trade wind strength and direction in the Pacific, which consequentially changes regional precipitation and temperature.

Every El Niño is different and will affect the United States in different ways.

This strong El Niño will likely continue to get a lot of buzz since it can affect the global socioeconomic stability by increasing the probability of droughts and flooding in certain regions.

Figure 2: The expected general wintertime El Niño pattern in North America. Credit (https://www.climate.gov/news-features/blogs/enso/united-states-el-ni%C3%B1o-impacts-0)

Figure 2: The  general wintertime El Niño pattern in North America. Credit

But what does this warming anomaly all the way in the Pacific mean for us here in the Chesapeake Bay region? Unfortunately, the east coast Mid-Atlantic region is “in-between” the zones of probable weather (Figure 2).

This is where we come in! We can use our historical extreme climate data to give hints at potential patterns specific to our area. This analysis is not a forecast, but does give an insight on what we might expect this winter.

What does our extreme climate data suggest: Annual

El Niño had no significant relationships with our annual indices (Figure 3). This demonstrates to me that El Niño’s effects on weather are seasonal! And this is no surprise. In general, El Niño’s affects are strongest in the fall and winter.

But wait! There’s more!

This year is complicated since we also have a positive North Atlantic Oscillation, or NAO! Using our data, it is evident that a positive NAO generally results in fewer Frost Days and Icing Days. In other words, less days below freezing!

It also suggests that we will have a longer Growing Season Length, supporting the potential for a more mild cold season!

Figure 3: This Corplot shows only the statistically significant relationships using our ~115 years of historical data in the Chesapeake Bay region. The number in each box is the strength of that relationship, so the closer it is to +1/-1, the stronger the relationship. Blue indicates a negative trend and red a positive trend.

Figure 3: This Corplot shows only the statistically significant relationships using our ~115 years of historical data in the Chesapeake Bay region. The number in each box is the strength of that relationship, so the closer it is to +1/-1, the stronger the relationship. Blue indicates a negative trend and red a positive trend.

What does our extreme climate data suggest: Winter?

Table 1: The 4 teleconnection indices represented in our analysis.

Table 1: The 4 teleconnection indices represented in our analysis.

Most analyses I’ve read have generalized a strong El Niño to be attributed to a warmer and wetter winter. But this is for the seasonal average temperatures and our study looks a extremes.

There is a negative correlation to the winter season TNn index, which is the seasonal absolute coldest temperature. This infers that under a strong El Niño year, that winter coldest temperature reached may be even colder. This does not say we will have a cold winter, rather, we have a chance at having at least one really cold day.

This one is quite complex!

Final Thoughts

st_thompson_statistics_fOut of my own curiosity, I’ve been reading the literature on El Niño weather affects to figure out what I should expect this winter. I ended up becoming overwhelmed: most of the general weather patterns are to the North and South of Chesapeake Bay, leaving Maryland and Virginia in a giant question mark.

This exercise gives me a hint that the extreme cold events could be even colder. This does not mean we will have a cold winter, but we have an increased likelihood to have at least one day this winter when hot cocoa will be required!

Also, the non-relationship with the Rx1day index (largest single day precipitation event) could suggest that a massive one day snowfall is neither more nor less likely than an average year.

More reading for me!

PS: This is a interesting read on climate change vs El Niño!

 

Kari Pohl

About Kari Pohl

I am a post-doctoral researcher at NOAA and the University of Maryland (Center for Environmental Science at Horn Point Laboratory). My work investigates how climate variability and extremes affect the diverse ecosystems in Chesapeake Bay. I received a Ph.D. in oceanography from the University of Rhode Island (2014) and received a B.S. in Environmental Science and a B.A. in Chemistry from Roger Williams University (2009). When I am not busy being a scientist, my hobbies include running, watching (and often yelling at) the Boston Bruins, and taking photos of my cat.
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