Delta T forecast website now available for Minnesota

This article was written by Rob Proulx, Extension ag technology and grain systems specialist, North Dakota State University. Delta T might not be a familiar concept to those outside of the more arid western Minnesota; read on to see why this metric might be one to pay attention to, particularly when spray timing corresponds with conditions of high temperatures and low relative humidity.

The ‘ND Delta T’ forecast website is currently available for the 2026 season and now includes maps for Minnesota. To access this site, go to ndawn.info, then navigate to Agriculture, Ag Tools, Delta-T Forecast (Figure 1).

 

Figure 1. Navigating to the Delta T forecast site through NDAWN.info.

Delta T describes the evaporative capacity of the ambient air – the higher the value, the drier the air and the greater its evaporative capacity. When Delta T values exceed 14 °F, excessive spray droplet desiccation and spray deposit evaporation may result in reduced herbicide efficacy. Impacts will be most noticeable when using Fine or Medium spray qualities, and glufosinate (Liberty) is the active ingredient most likely to be negatively impacted by elevated Delta T.

For North Dakota and Minnesota, the ND Delta T website displays:

• a map of current Delta T (from NDAWN/MAWN)
• maps of forecasted maximum Delta T for the current day and the next 5 days thereafter
• maps of historical Delta T values dating back to late March
• a table of the current day's hourly forecasted Delta T from 6 am to 6 pm 

The About page provides additional background information and explains my reasoning for the site. Briefly, I intend for the website to assist applicators in:

1. planning for days when Delta T is forecasted to reach the caution or unsuitable ranges, so they can appropriately schedule sensitive sprays
2. fostering a mindset where they (i) think proactively about spray weather conditions, so they (ii) check NDAWN repeatedly when spraying, and (iii) adjust operations according to changing conditions.
3. using historical Delta T maps as a resource when troubleshooting instances of poor pesticide efficacy.

The 2025 version of the site was well-received, and I am excited to expand its 2026 coverage to mirror that of the Minnesota Ag Weather Network. Please direct any feedback to Rob Proulx at rob.proulx@ndsu.edu.