Tennessee Weather Forum

Weather Forecasting and Discussion => Winter Weather => Topic started by: schneitzeit on July 31, 2020, 10:05:17 PM

Title: Long Range Discussion: Winter 2020-2021
Post by: schneitzeit on July 31, 2020, 10:05:17 PM
We're four months from meteorological winter, and winter lovers nation-wide are apt to discuss what to expect this season.

So, let's talk about it.

La Niņa is expected to develop during the autumn months[1], though we're not entirely confident in that just yet as we are currently in an ENSO-neutral pattern. La Niņa events typically feature increased precipitation for the Tennessee and Ohio River Valleys, and commonly bring warmer than normal temperatures.

Last winter, we were stable in a weak/moderate El Niņo. You can see the trends since 2008 here (credit to NOAA):


Another factor to examine is the North Atlantic Oscillation (NAO). This phenomenon is indicated by the pressure discrepancy between the subpolar and subtropical latitudes (on a map, Greenland and the Azores). A +NAO typically results in warmer than normal temperatures in the Eastern U.S. We witnessed this last year [2]:


Yet another factor to analyze is the Madden-Julian Oscillation. This eastward-moving tropical convective system is classified into eight different phases, and it status affects our temperature and precipitation anomalies on a weekly basis. The MJO often traverses the Indo-Pacific Warm Pool every 30-60 days. [3] Take a look, for instance, at the phases of the MJO and their effect on our temperature during the winter months:


More importantly, however, the MJO is more of a short-range tool, as it varies on a weekly basis. So one really couldn't use the status of the MJO for a long-range forecast, if I am not mistaken. But it's yet another tool that helps an amateur weather enthusiast like myself gauge the climate as we descend into the cooler months.

I have simplified a tremendously complex process, and the best insight we have at the present time is probably our seasonal La Niņa Watch. But I hope I have invited amiable discussion, and here's to, hopefully, a better winter than the recent ones our state as a whole has experienced. I know statistics just don't work this way, but let's be honest, we're past due for a decent winter.


[1] https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml

Title: Re: Long Range Discussion: Winter 2020-2021
Post by: snowdog on July 31, 2020, 11:15:50 PM
Well, for better or worse, you now carry the burden of winter on your shoulders. May God have mercy on your soul.
Title: Re: Long Range Discussion: Winter 2020-2021
Post by: BRUCE on August 01, 2020, 08:24:10 AM
way early still... but I am going out. on a limb here, I am going with a warmer than average winter...
Title: Re: Long Range Discussion: Winter 2020-2021
Post by: StormNine on August 01, 2020, 10:42:28 AM


We are passed due for a colder and snowier winter and typically a La-Nina should mean an active northern stream although with a SE Ridge, but other factors may dominate the ENSO which looks to be a fairly weak La-Nina.  Just like the MJO and the strong Polar Vortex dominated the El-Nino last winter and the MJO and -PNA dominated the El-Nino in 2018-19. 

With the unusual warmth in the Maritime area/Indian Ocean that is still a strong signal for MJO phases 4-6 the least favorable phases.  Add the very warm Gulf of Mexico/Atlantic Ocean plus the tendacy for a La-Nina to have a ridge component plus recent trends/climate change then I just don't see how you can forecast anything but warmer than average. We at times are still struggling with that pesky ridge off the west coast of Alaska.

In order for us to get below-average we are going to need a strongly -NAO/-AO (we haven't seen a -NAO since 2012-13 and we will likely need a 2010-11 style NAO/AO combo or a super strong -EPO/+PNA with a weaker polar vortex-like 2013-14, 2014-15, or that late Dec/Early January period of 2017-18).

It isn't impossible for us to have a colder/snowier than normal winter but more things are on team warms side than team cools side.   
Title: Re: Long Range Discussion: Winter 2020-2021
Post by: StormNine on August 01, 2020, 10:48:28 AM
Early Analogs:

There may be some hope that December may be at least around average instead of a blowtorch like we are used to but either January and/or February go above to even way above average just on an analog approach.