First thoughts for autumn 2021 and could winter 2021-2022 be cold in the Northeast.

 

La Nina faded and ended this past spring. Well, quite a few months ago, I talked about the idea of a resurgence of La Nina in the eastern and central equatorial Pacific. As time goes on, that idea is becoming more and more likely. The Climate Prediction Center, which is part of the National Oceanic and Atmospheric Administration has issued a La Nina Watch for late autumn and this coming winter.

 

When we look at the Sea Surface Temperature (SST) anomalies in the equatorial Pacific; there is no doubt that the water conditions are getting cooler once again. Right now, the SSTs east of the Dateline are on the neutral cooler side. But as we approach winter 2021-2022, the SST should become cooler. This will be especially true in the Central tropical Pacific. There are two types of El Nino: The most common is the classic east based La Nina. Less common is the central based Modoki La Nina. Both of these have an impact on our weather here in the Northeast.  The idea of La Nina returning is going to have implications on not only the 2nd half of the Atlantic hurricane season; but also, on autumn 2021 and winter 2021-2022. 

 So, what exactly is La Nina?

 The El Nino-Southern Oscillation (ENSO) is a cyclical climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean. As with all teleconnections the ENSO has three phases. El Nino involves warmer-than-average SST. La Nina is when SST are colder-than-average. The third phase called ENSO-neutral (sometimes referred to as La Nada), this is when SST in the central and eastern Pacific are considered average.

As such, its sea surface temperature (SST) pattern has a tremendous influence on all weather and climate around the world and the more anomalous the sea surface temperatures, the more the impact can be on the atmosphere around the world.

El Nino: characterized by a positive ONI greater than or equal to +0.5ºC.

La Nina: characterized by a negative ONI less than or equal to -0.5ºC.

By historical standards, to be classified as a full-fledged El Nino or La Nina episode, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons.

The equatorial Pacific is divided into 4 regions: Nino 1+2. Nino 3, Nino 3.4, and Nino 4. The CPC considers El Nino or La Nina conditions to be present when the monthly Nino3.4 OISST departures meet or exceed +/- 0.5ºC along with consistent atmospheric features. These anomalies must also be forecasted to persist for 3 consecutive months.

Here is a look at the current Nino region and subsurface values.

 

 The El Nino - Southern Oscillation (ENSO) and Southern Oscillation Index (SOI):

The SOI is an index used to indicate the development and intensity of El Nino or La Nina events. This is calculated using the pressure differences between Darwin and Tahiti. These pressure differences effect the strength of the Pacific equatorial trade winds.  Negative values favor El Nino, while positive values favor La Nina.

SOI values for 25 Jul, 2021

Average SOI for last 30 days    15.03

Average SOI for last 90 days    6.47

Daily contribution to SOI calculation 15.94

 

The SOI Turned Positive on June 29 with a daily value of positive 0.77. One day later on June 30 it had surged to 10.75. However, that value quickly was eclipsed. Other than July 5 and 6, the entire month of May so far has been very strongly positive. In a similar trend, the 30-day SOI value pasted into La Nina territory (plus 7.0 or higher) on July 10 at positive 7.41. Since then, the 30-day SOI was at positive 15.03. The SOI jump during July is occurring at almost the same point it happened a year ago, in July 2020.

 So, there is little doubt, that we’re quickly moving into a La Nina.  

The Oceans and Seas cover around 71% of the Earth’s surface. The Pacific Ocean makes up around 30% of that. Since the Oceans absorb hold most of the energy available to the global climate system; it should be no surprise that the ENSO has such a huge impact on global temperatures and precipitation patterns.   

As I said above, La Nina is a natural climate pattern that is marked by cooler-than-average ocean water in the central Pacific Ocean. It is one of the main drivers of weather in the United States and around the world, especially during the late fall, winter and early spring.

The latest model projections.

 

 Implications:

The strength, longevity, and placement of La Nina plays a role in how it will influence winter weather patterns.

 Tropical Atlantic:

 The idea of a returning La Nina for the 2^nd half of the hurricane season. Indicates the likelihood of an increase in Atlantic hurricane activity. This ties into the hurricane outlook I released a couple of months ago.  La Nina weakens the wind shear over the Gulf of Mexico, Caribbean and tropical Atlantic, which enables aids in the ability for tropical cyclones to develop and intensify. There is no change in my thoughts I released with my Atlantic hurricane outlook.

 Fall 2021:

 Temperatures have been generally above average for much of the Northeast and Middle Atlantic for the first half of summer. The pattern that has been driving this warmth looks to persist into the fall, which will generally lead to above-average temperatures for much of the region.

  

Historically La Nina falls, tend to be warmer and drier than normal while winters tend to be wetter than normal. However, there are also many other complicated factors in the atmosphere and oceans that can also impact our weather patterns.

Temperatures will be the farthest above average from the Southern and Central Plains into the Great Lakes and much of the Northeast.

When I consider the pattern that is in place and how it looks to evolve. I come to the following conclusions.

Looking at the month of August as a whole suggests a slightly above average month (+1.0°F to +3.0°F) using long term climate models and seasonal/global observation trends.

Widespread overall above-average temperatures are anticipated as meteorological fall starts in September. These above-average conditions are likely it stick around for the entire month across the Northeast and northern Mid Atlantic.

For October, warmer-than-average temperatures are likely across New England into Eastern New York State, with the rest of New York State, Pennsylvania, into the Mid Atlantic seeing general temperatures around seasonal averages.

During November most of the region should see temperatures close to seasonal. But for Southeast Pennsylvania, New Jersey, Maryland, Delaware looks for overall temperatures to be above average.

As far as precipitation September and October should see the pattern return to seasonal average across the Northeast and Mid-Atlantic. Right now, November looks to see regional precipitation amounts fall to below average levels.

Before July, we were very dry here in the Northeast and Mid-Atlantic. But with the well above monthly average rainfall for July drought conditions have greatly reversed. This should help this falls foliage outlook, allowing for more in the way of vibrant color. But that will greatly depend on the early autumn weather patterns.

  

Possible look for Winter 2021-2022 at first blush:

 

I’ve seen some outlets posting detailed winter outlooks. Although it's several months away yet, some have been wondering what I think about winter 2021-2022. I’m not going to go into a lot of detail. Frankly that would be irresponsible as there is no way to know with any kind of accuracy how everything is going to come together.  But there are a few hints in the pattern and teleconnections that are interesting.  There for I will talk a little about what these little signs could indicate.    

 

When we’re in La Nina it favors the build-up of colder than normal air over Alaska and western Canada.

 

When we’re in La Nina, New England, Most of New York State into northern Pennsylvania along with the Upper Midwest tend to see colder than average temperatures. Likewise, the Southeast and Mid-Atlantic tend to see warmer-than-average temperatures during a La Nina winter.  This is especially true for the Great Lakes into New England during the second half of the winter season.

When we look at similar years with the same general conditions.

I’ve talked about the cold May to busy Atlantic hurricane season and cold Decembers and generally cold overall winters correlation. When we add in years that were around a La Nina Modoki, we see the Decembers tend to be quite cold, with January becoming warm overall with Februarys becoming overall seasonally average.   El Nino Modoki’s tend to be snowy. La Nina winters do seem to be a little less snowy.

So overall based on the Idea of La Nina along with the cold May, this winter looks to be overall generally colder, with what looks to be overall snowfall amounts around seasonal average.

 But we have to remember there are other ocean and atmosphere cycles and teleconnections like the Quasi-Biennial Oscillation (QBO), Eastern Pacific Oscillation (EPO), Arctic Oscillation (AO), North Atlantic Oscillation (NAO), and many others, that are also factors in how the winter season generally turns out. I won’t know how all of those things will work into the winter equation for a while yet.   

Well, that’s it. Please give me feed back on what you think. And as always, feel free to ask me any questions y’all might have. If you like what you see, please share.

 Images are from Tropical Tidbits, Australia Bureau of Meteorology, NOAA Physical Science Laboratory, international research institute, and Tropical Tidbits.

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