7/9/15: Crop and Pest Report Forecast

 If you do not subscribe to the Crop and Pest Report that is issued weekly by NDSU, below is a copy of my contribution this week:

The July 9 through July 15 Weather Forecast

The weather during the next week with have both positive and negative components.  One postive will be a return to much warmer temperatures.  After several days with below to well below normal temperatures, maximums are expected to be in the 80s during this period with some portions of western North Dakota probably recording some lower 90s on occasion.   The warmer weather will be associated with a transition of the upper-level wind from the northwest to a more westerly direction, often referred to as a zonal flow. This shift in the mean wind flow should also, at least temporarily, lessen the likelihood of smoke from forest fires in Canada impacting the region.  By early next week the upper-level wind is expected to have a slight southwesterly component (Figure 1) that often leads to an elevated risk of heavier precipitation.

Monday 500 mb
Figure 1. Projected 500 mb (~18,000 feet) Heights / Anomalies for July 14. Wind flow is generally parallel to the black lines. Red=above average. Blue=below average. Use by permission of Weatherbell Analytics (WMO-Essential ECMWF)

 

With the upper-level wind flow west or southwesterly during this period, the low pressure centers attached to this storm track will have the ability to advect low level moisture from the Gulf of Mexico into the Northern Plains.  This in turn will add a negative element to the weather in the next 7 (plus) days.  Dew points are expected to be in the 60s to around 70° frequently beginning this weekend into much of next week.  This will be especially true in central and eastern North Dakota through much of Minnesota.  This higher low-level moisture will keep overnight minimums mild, but also create conditions for a high number of hours when relative humidity will be above 85% (Figure 2).  Plus, the high dew points will increase the risk of heavy overnight dew development on crops adding to this increased risk for fungal growth.

 

Projected Hours of RH of 85% or Higher at 5 feet from July 9 through July 15, 2015
Figure 2:  Projected Hours of RH of 85% or Higher at 5 feet from July 9-15, 2015

With these higher atmospheric moisture levels, any thunderstorms that do form will have a greater probability of producing localized heavy downpours (1 inch or more).  The best time frame for thunderstorm development will be from Saturday through Tuesday mainly during the late afternoon and evening hours.  These storms are expected to be hit and miss on most days, but a high percentage of the region will record rainfall during this period with several days of possible development.

Projected Growing Degree Days (GDDs), base 34°, 44° and 50° for the period July 9 through July 15, 2015 are presented in Figure 2.  Although maximum temperatures will be slightly above average, it will be the minimums that will be the more significant factor in the increased GDDs expected this period.  Looking beyond the next 7 days, there are several atmospheric factors that would indicate that our region will transition to a cooler pattern for the second half of the month.

Figure 3.  Projected Growing Degree Days (units) from July 9-15, 2015
Figure 3. Projected Growing Degree Days (units) from July 9-15, 2015

 

Daryl Ritchison