Posted June 19, 2025 | By Matt Reardon, Senior Atmospheric Scientist – Nutrien Ag Solutions

The summer solstice arrives this year on Friday, June 20, marking the longest day of the year in the Northern Hemisphere. At the June solstice the North Pole is oriented as far toward the sun as it will all year, so daylight hours reach their maximum. This celestial event isn’t just an astronomical milestone - it’s an important marker in our North American growing season.

Although the Northern Hemisphere basks in its warmest season around the solstice, Earth is near its farthest point from the sun in early July. Conversely, we are closest to the sun in early January.

Why doesn’t that extra distance cool the summer? Two reasons:

1. Tilt dominates distance. The 23.4° tilt concentrates sunlight on northern latitudes in June and July, creating long days and high sun angles that more than compensate for the weaker solar intensity.
   
   
2. Seasonal heat storage. Land and ocean surfaces in the Northern Hemisphere have been steadily warming since spring, so accumulated heat and extended daylight outweigh the small orbital effect.

Understanding this nuance reminds us that day length and sun angle are the primary drivers of summer warmth and crop development, not Earth–sun distance.

A Turning Point for Soybeans and Other Crops

Soybeans are “short-day” plants. Rather than counting daylight, the plant’s phytochrome system actually measures continuous darkness each night. Once night length exceeds a crop-specific “critical” threshold, hormonal changes trigger the plant to move from vegetative growth into flowering stages. After the solstice, nights begin to lengthen, so soybeans receive the signal to flower sooner rather than later.

Timely flowering sets the stage for a longer seed-fill window, but if cool, cloudy, or excessively wet conditions linger in late June, flowering can be delayed and plants may grow too tall and leafy, diverting resources away from pods.

Around the solstice, we also tend to see a change in atmospheric behavior. Large frontal systems give way to ridges in the jet stream. Around the periphery of those upper-level ridges, ridge-riding thunderstorms dominate summer precipitation budgets in high-production states. This sets up trains of precipitation in some areas while leaving others dry. This shift can quickly amplify drought conditions under persistent ridging patterns while counties with more storm activity receive timely rains and occasional severe weather like the feared summer derecho.

Why Sun Angle Matters

When sunlight arrives at its most direct angle, bare or dry soils absorb more short-wave energy. With less moisture available for evaporation, more of that energy converts directly into sensible heat. That is why late June and early July heat waves are often more damaging than similar events in May or August. Multiple studies using USDA-NASS yield histories and high-resolution weather datasets show that air temperature and rainfall from roughly June 25 to July 20 explain the largest single-month share of final U.S. soybean and corn yield variability:

• Soybeans: July rainfall alone can account for 40–50 % of year-to-year yield swings in the central Corn Belt.
  
  
• Corn: Maximum temperatures above 95 °F or minimums above 72 °F during tasseling can reduce statewide yields.
  
  
• Take-away: Management decisions (irrigation scheduling, foliar protection, late-season nitrogen, or marketing hedges) made during this three-to-four-week stretch carry outsized weight on end-of-year results.

Because this “high-leverage” window follows immediately after the solstice, the quality of medium-range forecasts you receive in late June and early July often makes the difference between proactive risk management and costly surprise.

Our meteorologists will be tracking those forecasts day by day. Subscribe to our YouTube channel and follow @NutrienAgSolutions on social media for timely updates and in-depth analysis as we move through this critical stretch of the growing season.