For the final Crop and Pest Report of 2015, instead of analyzing the weather for the next week, I thought I would summarize how similar patterns, both atmospherically and oceanically did in the past (analogs) to what is occurring globally at this time. Both spring and autumn are the most difficult seaons to project because the atmosphere is transitioning away from the yearly extreme season of summer and/or winter. Weather patterns are ever changing, but atmospheric patterns are a bit more likely to not alter widely during the warm and cold seasons as they do in the interim seasons. This autumn like many others is expected to jump from from strong positive to negative temperatures anomalies and in between these periods being the timeframe for the higher probability of widespread precipitation to occur.
The temperature and precipitation this region experience in the next 6 months will likely be influenced to some degree by the El Nino currently occurring in the equatorial Pacific Ocean. Too often this one influence is over emphasized and as a reminder there are many variables even under a strong El Nino that will and do influence long term trends in the atmosphere. The projections for the next few months are what occurred during analog years where ocean patterns (Figure 1) as well as other atmospheric variables were close to what is presently occurring around the world.
Based on comparable years in the past, with some of those years double weighted based on stronger similarities to current global conditions (strong El Nino, positive Pacific Decadal Oscillation, etc.), the 91 days from September 1 through November 30 favor a near normal temperature finish with above average precipitation especially across northern North Dakota and northwestern Minnesota in particular. Of course, “normal” in our climate means the average of many extremes, therefore, a month by month analog summation is given in Figures 2 through 9.
In quick summation, the analogs used suggest:
September being close to or a bit below average for temperatures, wetter than average north. The Labor Day weekend rains which brought widespread heavier rain to northern North Dakota are some indication that the past analogs for the month are a good match for this year. Not suggested in the graphics, but the first widespread frost risk may occur around September 20-22. October, near average temperatures, but wet, especially the first half of the month. November leaning cooler than average east, touch warmer in the west, with near average precipitation. As a bonus month, the past analogs suggest a very mild December (by our standards) with near average precipitation. I will continue to give updates on my blog, www.ndsu.edu/ndawnblog for those that are interested.
As a reminder, these are based on analogs and other techniques and does not necessarily constitute a forecast but instead gives a perspective to what occurred in the past that may give hints to the weather patterns coming up this autumn.