Rebecca's, 2023 fall outlook

September 1st marks the beginning of meteorological fall. The meteorological fall covers three months, from September to November. This is the transition season from the warmest part of the year to the coldest part. So, for this reason, it can be quite dynamic. But the vast majority of people follow what it says on the Calendar. This is called astronomical fall (or the fall equinox) which starts on Sept. 23 this year.

The summer solstice occurs when the sun is directly over the Tropic of Cancer.  For every place north of the Tropic of Cancer, the sun is at its highest point in the sky and this is the longest day and shortest night of the year. The winter solstice occurs when the sun is directly over the Tropic of Capricorn and marks the shortest day and longest night of the year

During the equinox, the sun crosses the plane of Earth's equator, making nighttime and daytime (roughly) equal length all over the world. After the Spring equinox, the days begin to get longer as the summer solstice gets closer. After the fall equinox, the days begin to get shorter as the winter solstice gets closer.

But regardless of which definition you follow fall is about sweaters, pumpkin spiced lattes and the beautiful colors associated with the changing leaves.

This outlook will be based on meteorological fall.

 Keep in mind a seasonal outlook is an overall three-month trend. Weather forecasts are about the weather expected over the next few days. While seasonal outlooks say something about likely conditions averaged over the next few months. Seasonal forecasts provide information about these long-term averages.

When I do a seasonal outlook. I try to compile observational weather data from around the globe, I take these teleconnections and compare that against historical weather data, that are called analogues.  All of these metrics and data elements are used to come up with an overall idea for the coming season.  Based on that data, and many other factors including long range computer guidance… let’s take a look at how fall 2023 may be like.  Due to conflicting signals, I have a lower confidence in this outlook, than is typical for me.

 

Let’s look at….

A look at the current global Sea Surface Temperatures (SST) anomalies.   

 

The global SST forecast through October.

Images courtesy of the Australian Bureau of Meteorology.

The Pacific…

El Nino

This year’s El Nino started earlier than the average on the climatical schedule. Typically, El Nino starts in late summer or early fall. So, it has a lot of time to grow stronger over the fall. El Nino’s impact here in the Northeast in the summer and fall are hard to quantify, but most times, normally El Nino hits hardest in December through February, but given that this El Nino is one to two months early mean that we could see some impacts this fall.

During El Nino, on average the eastern CONUS sees cooler temperatures and drier than average conditions during the Summer.

 

Sea Surface Temperatures (SST) in the tropical Pacific are exceeding El Nino thresholds. Looking at the data, the El Nino is still rapidly intensifying

The current SST anomaly in the Nino 3.4 region (where El Nino is measured) is +0.865°C. So, we’re in a moderate El Nino

 

SST consolidation Nino 3.4 image courtesy of Tropical Tidbits.

The strength of an El Nino is determined by how much above average the water temperatures are in the Nino 3.4 region. The stronger the El Nino the greater it’s impacts. I posted in the blog, about what is a Super El Nino which you can find here.

Water temperatures 0.5ºC above average = Weak El Nino

Water temperatures 1.0ºC above average = Moderate El Nino

Water temperatures 1.5ºC above average = Strong El Nino

Water Temperatures of 2.0+ above average = Super El Nino

The Atmosphere in the Northern Hemisphere (NH) is farther along with coupling with the developing El Nino, than the Southern Hemisphere (SH), but the SH should come into line over the next few weeks. The dynamics are complicated, but essentially, we have to look at the Sea Surface Temperatures along the equator and also how the atmosphere is changing as a result of those warm SSTs.  

As the process continues, the El Nino will become very strong over the next couple of months, with water temperatures becoming well above average in the Nino 3.4 region (where El Nino is measured).  The SST could end up +2.5°C or more by the time we make it into the heart of Fall and through the coming winter.

 

 Monthly sea surface temperature anomalies for the NINO3.4 region image courtesy of the Australian Bureau of Meteorology.

 

A majority of the Global climate models are calling for SST in the equatorial Pacific to be at least 2.0ºC above average. So at least a strong El Nino is a good bet.

 

Image courtesy of the Australian Bureau of Meteorology.

 

Typically, during strong El Nino’s there is a persistent extended Pacific Jet Stream with an amplified storm track.

 

The Atlantic…

It’s a fact that most of the tropical and subtropical Atlantic are at or near record warm SST for this time of year.

 

 

images courtesy of Tropical Tidbits.

The super-hot Atlantic Basin Sea Surface Temperatures (SST) are going to be a big wild card, not only for the hurricane season, but also for the fall pattern. It remains to be seen how the very warm Atlantic will counter the impact of a moderate or strong El Nino, for that reason there are no great analogs for this fall

We have never seen a moderate to strong El Nino with Atlantic SST this war. Most other years with a very warm Atlantic either had neutral ENSO or La Nina.

These temperatures could correlate to warmer temperatures for parts of the CONUS.

 Other teleconnections...

Madden Julian Oscillation (MJO)

The NAO is currently weak it looks to stay weak for the next 7-10 days, then it should head more toward negative …leads to a blocky pattern

The Pacific North American Pattern (PNA)

PNA positive Associated with troughing in the Aleutian Islands and ridging in western Canada leading to more of a NW flow.

Atlantic Oscillation (AO)

AO negative means a slower hemispheric flow due to that higher latitude blocking

 The current pattern...

Is being driven by convection in the Pacific, which has the trough dominating in the Aleutians leading to a ridge over the western CONUS into western Canada as well as the overall troughing in the east.   

This is why we’ve seen all these stronger cold fronts dropping out of Canada and moving through the Northeast, driving out the warmer temperatures and high humidity. Then after a few days of cooler less humid air, we warm back up for a couple of days.  This back and forth looks to continue through at least the end of August

 

Month by Month…

 September

For temperatures:

The current active pattern with troughs dropping in out of Canada looks to basically continue. 

After a possible warm start, I’m leaning toward western PA, NYS and NE ending up average to slightly below average overall. While Western Pennsylvania into Maryland and Delaware ending up average to slightly above average

For precipitation:

I’m leaning toward the entire region ending up above average overall.

 

October

We should end up with ridging out west with more low pressure troughing over the Northeast

For temperatures:

I’m leaning toward the entire region seeing generally average temperatures overall.

For precipitation:

I’m leaning toward the entire region seeing generally being average overall.  With more of an active storm track over the Plains extending into the Great Lakes.

November

Based on how the pattern looks to go, November should feature above average heights over the Northwest US and Western Canada. This should lead to pronounced troughing over the Northeast. By November the El Nino should be quite strong 

For temperatures: 

I’m leaning toward the entire region ending up below average overall.

For precipitation:

I’m leaning toward far eastern Pennsylvania, New York State, New England into Maryland, Delaware and New Jersey above average overall. With the rest of Pennsylvania and Western Maryland well above average overall.

With the below average temperatures and above average precipitation, it could be a recipe for a few bouts of snow during November.

 

Frost freeze...

The date at which the first freezing temperature (32°F or less) is measured can occur at various times and locations in the United States. Year-to-year variability is expected due to various factors.

 

 Climatological date of median first 32 F freeze.

 image courtesy of US Dept of Commerce.

 Western New York State and Western Pennsylvania could see an earlier start to the frost/freeze season, with the rest of the region being closer to the climatological average.

 For mid to end of October given this idea of general troughing setting up, we should see parts of the Northeast see some snow events.

For November … an active jet stream, pulling moisture out of the Gulf into the Northeast, along with more in the way of colder conditions. I think most of the region will have a good chance of several mixed events and seeing at least one larger snow event, Maryland and Delaware, the odds for a larger snow event are rather low.

Breakdown...

But generally, this fall should be more in the way of wet than is typical.

Well, that’s it. I hope you enjoyed reading this outlook. I’m always grateful to be one of your trusted weather sources.