My 2020 Fall Outlook

 

The days are getting shorter, and the leaves on some of the trees are starting to change. Fall kicks off on Tuesday September 22, at 9:30 am, EDT. But if any of Y’all are waiting for those comfortable fall daytime temperatures and those cool crisp fall nights; You might want to get comfy, because those kinds of conditions aren’t going to show up for a while, at least in a long-lasting matter.

Over the last four to five years, fall has arrived late, with summer like temperatures hanging around through September. That trend is looking to include this September as well.

There is no doubt that the entire Northeast and Mid-Atlantic have been hot this summer. In fact, much of the CONUS into Canada has been very warm.

 

The El Nino Southern Osculation (ENSO)

The ENSO is going to be one of the major factors driving the fall pattern. The Madden Julian Oscillation (MJO) is going to be another big factor.

The ENSO has a warm (positive) phase El Nino and a cool (negative) phase La Nina.

La Nina is when the East-Central equatorial Pacific is cooler than average. NOAA currently has an enhanced La Nina watch in effect.  With an La Nina looking increasingly likely we can expect to see both short and long-term major impacts in the Northeast and Mid-Atlantic.

In the Northern Tier of the CONUS, La Nina tends to bring a cooler and more active storm pattern. This is due to the Polar Jet staying a little farther north. This is especially true during the winter. But how much La Nina will impact the Northeast will depend on its strength and severity, so the effect for this fall into winter is going to be varied.

 Sea Surface Temperatures (SSTs)

While Equatorial Pacific SSTs anomalies continue to cool slowly but neutral El Niño/Southern Oscillation (ENSO) conditions still exist though I expect to see NOAA declare La Nina by this fall.  Those SST warm SST in the Gulf of Alaska, will bring a change later this fall as well. By promoting more in the way of ridging in the West and more in the way of troughing in the Midwest into the East. The SSTs in the Atlantic are also mostly above average, with the SST along the East Coast well above average.

Years that match up with the current global SST pattern are: 2010, 2013, 2017, and 1970. With 2017 being the closest analog.

 Why has it been so hot?

It's not unusual for the Northeast to see hot temperatures and humid air during the summertime. For the last 4 to 5 months, we’ve been in the same general pattern, while stagnant atmospheric patterns are also not uncommon, the length of this current pattern isn’t unheard of but it is more unusual.

 There are several reasons for the hot and humid conditions we’ve had since June. El Nino began to develop in the fall of 2018, during the first 6 months of 2019 we were in an El Nino Modoki (which is when the warm SST and enhanced rainfall is around the date line, and not in the eastern Pacific closer to Peru. During the 2^nd half of 2019 the El Nino Modoki ended and over winter of 2019-2020 we were in ENSO neutral (which is neither El Nino or La Nina).  Neutral ENSO conditions continued during Spring into Summer 2020. Then during the Summer 2020 we began the change to La Nina.  I’ve been saying on my Facebook weather pages, that we’re now rapidly approaching La Nina conditions in the Pacific.   A large change in ocean surface temperature from west to east over late Fall through Winter, can be a sign that the following summer will be hot. We went from a Modoki to near La Nina conditions in short order. This allowed for strong high pressure over North America, which combined with the influence from the developing La Nina. Causing a dome of heat over the eastern 2/3rds of the CONUS.  

Another reason is those much warmer than average SST off the East Coast. They have helped boost the daytime temperatures, and especially the overnight lows. You can blame all that extra water vapor for that.

The Madden Julian Oscillation (MJO)

This Summer the MJO has been mainly propagating through phases 8, 1, and 2. MJO phases 8 and 1 typically place more in the way of troughing in the Gulf of Alaska and ridging across the eastern 2/3rds of North America.  During hurricane season phases 1 and 2 are when conditions in the Atlantic Basin are most favorable. They also favor higher heights and ridging over the Northeast. This is another reason we’ve been warm over the summer. It is also the reason for all the tropical activity in the Atlantic Basin. We saw the MJO in the tropical active phases as the MJO traveled through phases 8 and 1, which resulted in Marco and Major Hurricane Laura in the Gulf of Mexico.

 OK what about Fall into Winter 2020?

Over the fall we should be in La Nina, with the MJO circulating into a more amplified phases 3,4, and 5. This setup will be with us as we transition through Fall into winter 2020-2021.

September, I continue to think we will see hotter than average temperatures overall. The first half of the month could feature more 90+ degree days for some of us. During the 2^nd half of the month the odds for those kinds of temperatures does fall off with respect to seasonal averages.

October, the month as a whole should also see overall above average temperatures. But as we get into the 2^nd half the overall trend should be slightly cooler, but still most likely slightly above average with respect to seasonal averages.

Here is a look at the SST and surface temperature anomalies from the 4 years I’ve indicated as analogs.

Current 2020

 

2017

 

2013

 

2010

 

1970

 

 

2020 has seen the MJO act similar to what it did in 2010

So here is a blend of temperature anomalies for 2017 and 2010

 

As far as precipitation, that is going to be difficult to ascertain. But with the pattern as it is. The Mid Atlantic and Northeast are still extra susceptible to tropical impacts.  So, I think overall precipitation will end up average to above average by the end of November.

Snow will be later than normal in showing up. But with the La Nina induced storm track, if we see any polar or arctic outbreaks, those down wind of Lake Erie and Lake Ontario could end up with some lake effect snow out of it.  

Combining the idea of a La Nina Fall and Winter, the MJO wanting to stay in those warm phases, along with those warm waters off the East Coast. The idea of a warm Fall and potentially warm winter is a good bet IMO. For October and November, the La Nina could create an active storm track across the Midwest, Great Lakes into at least part of the Northeast.  All of this will make many across our region feel like they’re on a rollercoaster as we move though Fall. Over the late Fall into the winter the MJO is going to want to try and stay in Phases 3,4, and 5. Which isn’t the greatest news if you don’t like warmer winters. The Mid Atlantic tends to not see tons of snow during La Nina winters. But things can and most likely will change between now and December. 

 

I will be working on my winter outlook over the next 4 weeks. As I have in past years I will most likely release it in 3 parts…..