Crop and Pest Report, July 30 Edition

Climatological averages in the Northern Plains where highly variable weather is the true normal, tend to have little meaning when dealing with short term weather forecasting and clearly do not represent what should be expected on any given day.  Yet, this next week, at least temperature wise, both minimums and maximums are projected to be near those 30 year averages.  This will mean a lot of days with daily maximums in the low to middle 80s with morning minimums in the upper 50s to the lower 60s.  There will of course be the normal day to day subtle variations but overall, the frequent weather swings so common in recent weeks appear to be taking at least a brief break.

The mean upper-level wind flow that had been from the southwest for much of the last week, that not only brought periodic thunderstorm events, but also many days with high dew points, has now transitioned to a more northwesterly flow.   This will mean the next week will tend to be drier both in the sense of rainfall and also in low level atmospheric moisture content.   Thunderstorms look spotty and light until perhaps the middle of next week (Figure 1) and dew point temperatures will be frequently below 60°.

Figure 1.  Precipitation Anomalies through August 5, 2015
Figure 1. Precipitation Anomalies through August 5, 2015

With dew points generally low, relative humidity (RH) levels in turn will also trend lower for most of the next 7 days.  Therefore, RH values will above 85% for fewer hours this week and mostly only during the traditional period in the early morning.  Plus, during the other periods of the day the RH of the air will often be below 50% creating minimal disease stress on susceptible crops during this forecast period.

The projected Growing Degree Days (GDDs), base 34°, 44° and 50° for the period July 30 through August 5, 2015 are presented in Figure 2 and the number of hours where the relative humidity is expected to be at or above 85% can be found in Figure 3.


Figure 2
Figure 3