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Climate of North Dakota

Sunshine and Cloudiness


North Dakota receives a higher percentage of possible sunshine and more hours of sunshine annually than any state on the Canadian border with the exception of Eastern Montana which receives about the same amount. On an annual basis, North Dakota receives 58 to 62 percent of total possible sunshine (Table 9). July is the sunniest month when approximately three-fourths of the possible sunshine is recorded, while November is the poorest month for sunshine when only 40 to 46 percent of possible sunshine is registered. The amount of possible sunshine increases 11 to 14 percentage points from June to July, remaining high through August. Annually, North Dakota registers about 2,600 hours of sunshine in the east to more than 2,800 hours of sunshine in the west. Roughly 25 percent of the total hours of sunshine occur in July and August, and this is a large contributing factor to North Dakota's beautiful summer season.

Table 9. Percent of possible sunshine by months and for year at four locations and average solar radiation (langleys) at Bismarck.

Station Month Year
J F M A M J J A S O N D
Bismarck 55 56 60 59 62 62 76 73 65 61 46 48 62%
*159 248 357 431 536 571 607 522 384 269 159 124 364
Devils Lake 53 60 59 60 60 62 71 67 59 56 44 45 59%
Fargo 50 59 59 58 58 58 71 68 59 57 40 44 58%
Williston 51 56 65 58 61 62 76 75 66 61 45 51 62%
*Solar radiation data.

Sunshine is not only measured by the duration of actual sunshine, but also by an evaluation of the intensity of the sun's rays. This evaluation is called solar radiation and is an energy measurement which is expressed in langleys (a langley is one gram-calorie per square centimeter). Annually, North Dakota averages 350 to 370 langleys of solar radiation per day, which like the percentage of possible sunshine is higher than any state on the Canadian border with the exception of eastern Montana which receives about the same amount. As would be expected, the greatest amount of solar radiational energy is received in June and July and least in December. In June and July, more solar energy impinges on the earth's surface in North Dakota than in any state east of North Dakota. The high energy input is another important factor contributing to the successful agriculture carried on in North Dakota despite its relatively short growing season.

More days average out to be cloudy than clear or partly cloudy over the course of a year (Table 10). The most cloudy days occur from late fall to early spring. The number of clear days is about the same for all months from November through June. In July the number of clear days sharply increases and remains at about the same level through August, before becoming somewhat fewer in September and October. As a generality, it can be said that July and August will record about twice as many clear days as during any other months of the year, while the number of cloudy days in July and August will only be half as many as for other months of the year.

Table 10. Average number of clear days (C), partly cloudy days (PC), and cloudy days (CY) between sunrise and sunset at four locations. Sky cover is expressed in a range of 0 for no clouds to 10 for complete sky cover. A clear day is based on a daytime average cloudiness of 0 to 3, partly cloudy day from 4 to 7, and cloudy days from 8 to 10.

Station Sky MONTH Year
J F M A M J J A S O N D
Bismarck C 7 5 5 6 6 7 12 12 10 10 6 7 93
PC 8 8 9 9 11 10 12 11 9 8 7 6 108
CY 16 15 17 15 14 13 7 8 11 13 17 18 164
Devils Lake C 8 8 7 9 9 9 13 13 11 10 7 8 112
PC 8 8 10 9 10 11 11 10 9 8 8 7 109
CY 15 12 14 12 12 10 7 8 10 13 15 16 144
Fargo C 6 7 5 6 7 6 11 11 9 10 5 6 89
PC 8 7 9 9 10 11 13 12 9 8 7 8 111
CY 17 14 17 15 14 13 7 8 12 13 18 17 165
Williston C 5 5 8 5 5 6 12 13 10 10 6 6 91
PC 10 7 8 10 12 10 12 10 8 8 9 8 112
CY 16 16 15 15 14 14 7 8 12 13 15 17 162


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