7/2/15: Crop and Pest Report Forecast

Here is my take on the next week and a peak into July:

The July 2 through July 8 Weather Forecast

Although the persistent smoke plume over the eastern part of North Dakota into much of Minnesota earlier this week suppressed the temperatures by several degrees and therefore, lowered the potential growing degree days (GDDs) by 10 to 20 degrees, the past week still finished with slightly above average temperatures in the east and well above average in western North Dakota.  These warmer temperatures were associated with a strong ridge of high pressure that was centered over the northern Rocky Mountains over the past several days.  That ridge is slowly shifting westward and by early next week it is projected to be centered over the Gulf of Alaska (Figure 1).  That subtle shift west will mean that North Dakota and western Minnesota will transition into a cooler weather pattern after the Independence Day weekend.

Figure 1:  Projected 500 mb heights and anomalies for 00Z July 7, 2015
Figure 1: Projected 500 mb heights and anomalies for 00Z July 7, 2015 from ECMWF WMO-Essential

That change will begin on Sunday (July 5) with a cold frontal passage.  Although there will be other days with some thunderstorms (today, (Thursday) for example), that transition to cooler air on Sunday will be the day when much of the observed precipitation falls in the next week.  Behind the front, Monday through Wednesday should record well below average temperatures, meaning fewer GDDs this week, plus, that cool air in combination with the Sunday precipitation, will likely mean low level relative humidity levels will be frequently high from Sunday through Wednesday (Figure 2).

Figure 2.  Projected Hours of RH of 85% or Higher
Figure 2. Projected Hours of RH of 85% or Higher

Projected GDDs, base 34°, 44° and 50° for the period July 2 through July 8, 2015 are presented in Figure 3.  With the cooler weather moving through the area at some point on Sunday, a higher percentage of these numbers will occur today through Independence Day than what is anticipated for early next week.

Figure 3.  Estimated Growing Degree Days for the period from July 2 to July 8
Figure 3. Estimated Growing Degree Days for the period from July 2 to July 8

 

The rest of the month: The month of June finished with temperatures from 1 to 3 degrees above average.  It may have seemed cool, but overall, it would be considered a mild month.  The cool down next week may be a persistent pattern in July.  Clearly not every week will be cooler than normal, but there are several indications that July as a whole may finish with slightly below average temperatures instead of the slightly above average temperatures recorded last month.  Summer precipitation projections are always difficult because of the wide variations in rain totals in thunderstorms, but with a dominate flow from the northwest foreseen more often than not in July, near normal precipitation, overall, would be favored in that type of pattern.

 

Figure 4:  Temperature Anomalies for  June 2015
Figure 4: Temperature Anomalies for June 2015

Daryl Ritchison, Meteorologist / Assistant State Climatologist

Twitter: @darylritchison