Crop and Pest Report Forecast 7/21/16

Although some of the warmest temperatures of the summer have been recorded in the past couple of days and today and for some locations even Friday having 90° plus potential, the generally trend this week will be for cooler rather than warmer temperatures.  This transition to cooler temperatures will have two noticeable impacts.  The first will be a high likeihood of thunderstorms, probably widespread over much of North Dakota on Friday into Saturday.   After that system exits, cooler and drier air will advect into the northern plains.  That will bring the second notable feature of the next seven days;  fewer hours with high relative humidity (Figure 1).   It appears that most locations will record between 10-20 fewer hours where relative humidity values are above 85% during this period than were recorded during the past week.

Even with a transition to cooler, but far from cool, temperatures, the number of growing degrees days (GDDs) are expected to be greater than in the past week (Figure 2).  Although it has been quite warm these past couple of days, it was cool of course for several days before this brief “heat wave” started.  Therefore, expected GDDs this week will be slightly higher than the previous seven days, plus, once we get into this weekend into next week, the temperatures will be at a more optimal level for good plant development without worries of heat stress.  It appears that minimums will mostly be around 60° or in the 60s with maximums in the low to middle 80s.

Beyond this seven day period, current indications are that temperatures near normal, or even slightly below will continue through the first part of August.  This period of “normal” temperatures looks to be occurring not only in our region, but throughout much of the north central part of the lower 48 states, including Iowa, Illinois and Indiana.  Higher heat will likely return in August, but the next 10 days does not show any signs of high heat returning once we get through this weekend.

Figure 1. Relative Humidity Hours



Figure 2. Growing Degree Day Projection


Daryl Ritchison