A Cool August: Implications for Corn Belt Harvest Weather

(CORN) (ZCU25) (ZCZ25) (ZSU25) (ZSX25) (SOYB) (TAGS) (DBA) 

“A Cool August: Implications for Corn Belt Harvest Weather”

by Jim Roemer - Meteorologist - Commodity Trading Advisor - Principal, Best Weather Inc. & Climate Predict - Publisher, Weather Wealth Newsletter

Edited by Scott Mathews

• Weekend Report - August 22-24, 2025

The Eastern Pacific Oscillation (EPO) index is a meteorological indicator used to track variations in the strength and location of the eastern Pacific jet stream. When the EPO index goes negative, it signifies a particular atmospheric pattern.  I began talking about this last April when I had a bearish summer attitude in grains and predicted generally big Midwest corn and soybean crops.

You can download a free issue of WeatherWealth from a month ago when I predicted a negative EPO and the earlier bear market in grains (and most recently natural gas)

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Using the EPO index and other climatic variables to predict corn belt weather works best when we have an “El Niño neutral” phase. 

The weather in the tropics (when La Niña or El Niño is present) usually has a greater influence on Midwest grain yields. Not this summer.

Here's what causes the EPO index to go negative:

• Formation of an Alaskan ridge: The key factor in a negative EPO is the development of a strong high-pressure ridge over Alaska and the Gulf of Alaska.

  Image Source: ClimatePredict (a BestWeather, Inc. company)

• Weakening of the eastern Pacific jet stream: This Alaskan ridge disrupts the usual flow of the jet stream, weakening it and potentially creating a split flow pattern.

• Encourages a northwesterly flow from Canada: The ridge effectively redirects the jet stream, forcing it further north and then down into the interior of North America. This cooler Midwest weather is ideal for August soybean yield development. Though there are a few dry areas in the Delta and northeastern soybean belt—but it is not a major nationwide issue.

• This negative EPO pattern has a significant impact on North American weather, often associated with a cooler summer. If it persists into November and December, eventually natural gas prices would bottom. But not right now.

• Warmer than normal temperatures in Alaska and the Western US, especially the Southwest, due to the northward deflection of the air flow around the ridge. This is aggravating the extreme wild fires out west again.

Image Source: NASA

What does a negative EPO imply for October corn belt harvest weather?

Image Source: ClimatePredict (available for free to all WeatherWealth subscribers)

Looking at my in-house weather forecast program used by farmers and commodity traders around the world, I look at what happens when the summer EPO is mostly negative (warm block over Alaska) when accompanied by an “El Niño neutral” event.

 

The red stars (above) indicate those teleconnections. In addition, the Nino34 region in the western Tropical Pacific has a cool scale (2-4) that may suggest a weak La Niña forms later this year. This could (eventually) take the bearishness out of grains with some potential crop issues  this winter (Argentina's summer).

Nino12 represents warm water temperatures near Peru.  I'll be watching this west (cool), east (warm) temperature gradient for analyzing weather influencing multiple commodities and crop patterns around the world.

Image Sources: TropicalTidbits.com and USDA

BOTTOM LINE: 

Generally decent autumn harvest weather may mean the potential for new lows in corn and soybeans in a month or two. 

However, demand is now picking up, and there are bullish seasonal tendencies for the next few weeks prior to harvest. In addition, there are questions as to whether the USDA was too high in their yield productions for corn and soybeans recently.
 

Cooling at Nino4 could result in some potential South American crop issues for the 2025-26 crop if it strengthens more.  I will address this and trading ideas in grains, etc. for WeatherWealth subscribers. Does a farmer hedge more grains or not?

Thanks For Your Interest In Commodity Weather!!!

Jim Roemer, Scott Mathews, and the BestWeather Team

Mr. Roemer owns Best Weather Inc., offering weather-related blogs for commodity traders and farmers. He is also a co-founder of Climate Predict, a detailed long-range global weather forecast tool. As one of the first meteorologists to become an NFA registered Commodity Trading Advisor, he has worked with major hedge funds, Midwest farmers, and individual traders for over 35 years. With a special emphasis on interpreting market psychology, coupled with his short and long-term trend forecasting in grains, softs, and the energy markets, he commands a unique standing among advisors in the commodity risk management industry.