Autumn is right around the corner, and similar to the winter season ahead, long-range oceanic and atmospheric signals can provide clues for what we might expect in terms of weather patterns as the seasons change.

Meteorological autumn in the Northern Hemisphere is defined as the period from September 1 to November 30. During this 3-month period, a progressive decrease in average temperatures and daylight hours occurs, though back-and-forth fluctuations in temperature are common during this transition from summer to winter.

Autumn is also considered by many to be the most beautiful season, due to comfortable temperatures, frequent stretches of stable and sunny weather, and of course, the fall foliage. 

However, inclement weather can also occur during the fall, with extremes ranging from wildfires to hurricanes to severe weather, and from cold and rainy conditions to early-season snow events.

El Nino Continues to Strengthen

As discussed in our Winter Forecast Preview that we published last week, we are heading into a very strong, or "super", El Nino with well-above-average sea surface temperature in the Eastern and Central Equatorial Pacific Ocean

As El Nino continues to strengthen, this will likely be a key player in fall weather patterns this year.

We also examined these other factors into our outlook for the fall:

• El Nino sea surface temperature distributions in the Equatorial Pacific, with this year being a more east-based El Nino, though significant warmth is expected in both eastern and central areas.
• Sea surface temperature distributions in the North Pacific Ocean, Atlantic Ocean, and Gulf of Mexico.
• Quasi-biennial Oscillation (QBO) – A measure of upper level trade win patterns in the tropics, for which we are currently entering a westerly phase
• Hurricane Season – Influences of El Nino on Atlantic and Pacific tropical activity, and how this could impact North American fall weather.
• North American Monsoon – A active late monsoon season expected in the Southwest U.S. in September.

2026-2027 Winter Forecast Preview

Could Upcoming Super El Nino Be Strongest Ever?

Fall 2026 Seasonal Outlook:

For the three-month period from September to November as a whole, our outlook favors above-normal precipitation across the Southwest and much of the Western Central U.S. with below-normal precipitation favored across central and northern portions of British Columbia. 

In the East, our outlook favors above-normal precipitation across parts of the Southeast from the Florida Panhandle to the Carolinas, while below-normal precipitation is favored from Northern Michigan to Ontario to Quebec, mainly north of the St. Lawrence River. 

In terms of temperature, our outlook favors above-average warmth for the three-month period as a whole across much of the Central U.S. and Central Canada, with equal chances of above or below normal temperatures across the Rockies, West Coast, Southwest, Southeast, and East Coast. 

Monthly Signals Based on Historic Analogs

We examined weighted historical analog years in producing this outlook, along with predictive tools based on our own modeling and from global seasonal weather models. 

When looking at the weighted historical analogs and breaking it out by month, we found some interesting signals that indicate how the seasonal progression could play out, in terms of dominant weather patterns during past years with similar ocean/atmosphere signals to this one.

Here is the monthly breakdown...

September:

Historical analogs favor a trough-dominant signal along the West Coast during September, which would favor above-average precipitation and near to below-average temperatures west of the Continental Divide. We see similar support from some of the more reliable seasonal models, such as the European Model.

This type of setup could potentially signal some cool-season like low pressure systems moving into the West, while we are also seeing signs of an active late season monsoon across the Southwest and Southern Rockies.

A wild card factor in the West is tropical activity in the Eastern Pacific. El Nino tends to favor above average tropical activity in this region, and the remnants of tropical storms and hurricanes can ocassionally reach the Western U.S. at this time of year, bringing substantial rain to some areas. 

Along the eastern side of the Divide in the Rockies and adjacent plains, we see a warmer signal with mixed signals in terms of above or below normal precipitation. 

The blue arrow in the map below indicates the favored storm track based on these weighted analogs.

Across the East, analogs favor a ridge-dominant pattern over the Great lakes and Northeast with a slight troughing signal over the Southeast and Mid-Atlantic. 

Overall, the warmest signal is across the Central U.S. and Central Canada during September, while the East has more of a neutral temperature signal (can go either way). Seasonal models are more bullish on September warmth in the East compared to our analogs, for what it's worth. 

The analogs also favor below-average precipitation from the Midwest into the Southeast, while New England has a wetter signal compared to the rest of the East. 

El Nino tends to favor a quiet Atlantic hurricane season, so this likely plays at least some role in the drier signal for the Southeast, though tropical storms and hurricanes are still possible even if the overall season is below average, and this always presents a wild card at this time of year. 

October:

We start to see more of a classic cool season El Nino signature emerge in October when looking at historical analogs, with a troughing signal becoming more dominant across the Southern U.S. and a ridging signal across the Northern U.S. and Canada.

Precipitation signals seem to be more mixed/neutral across most of the Western U.S. as we gradually transition from a summer pattern to a more winter-like pattern, but we do see a slight wet signal along the east side of the Continental Divide.

It's not unusual during strong El Nino Octobers for cut-off low pressure systems to track across the Southwest with winds shifting to easterly east of the Continental Divide. If these systems pull in cold enough air from the north, they can lead to October snow events in the Front Range and eastern portions of the Rockies. Something to keep an eye on this fall...

Further east, we see a wetter signal across the Great Plains into Texas during October based on historical analogs, with mixed signals across the Southeast (neutral to wetter in most areas). However, we see a stronger dry signal from the Mid-Atlantic to New England. 

Seasonal weather models (ECMWF and NMME in particular) are a bit wetter overall for the East compared to our analogs.

In terms of temperature, we see a warmer signal across the Pacific Northwest, Northern Rockies, and Upper Midwest with neutral signals elsewhere.

November:

The El Nino signal really begins to flex during November based on historical analogs, with a trough-dominant signal emerging over the Southwest along with an active southerly storm track that favors above average precipitiation from the Southwest to the Southeast. 

We also tend to see a signal for above average snow in New Mexico and Colorado (including the Front Range) during El Nino Novembers.

We also see a colder signal (relative to average) across much of the Southwest and West Central U.S. during November, even though as we note in our winter forecast, the core of the winter season is favored to be warmer than normal for much of the West. 

A ridging signal is more prominent across the Pacific Northwest during November, based on historic analogs, which tends to favor below-average precipitation, though the temperature signal is less clear.

In the Northeast, we see a ridging signal, but not necessarily a dry signal, presumably from coastal storms spinning up at times in response to the active southern storm track. 

We also see a warm signal (above average temperatures) for the entire East during November analogs.

The Midwest has a neutral/mixed signal in terms of temperature, while precipitation generally is favored to be above-average in November.

Seasonal Forecast Caveats:

These signals are interesting to examine and can give us some clues on what may be more or less likely this fall, and during the individual months as the seasons gradually shift from summer to winter.

Keep in mind that every year is unique, and while past strong and east-based El Ninos exhibit some similarities when looking at the big picture, there will always be year-to-year variations and sub-seasonal factors that are not anticipated months or even weeks in advance. 

Thanks so much for reading!

Alan Smith