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
Station	J	F	M	A	M	J	J	A	S	O	N	D	Year
Bismarck	55	56	60	59	62	62	76	73	65	61	46	48	62%
Bismarck	*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
Station	Sky	J	F	M	A	M	J	J	A	S	O	N	D	Year
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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