Dakota Wesleyan University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dakota Wesleyan University Observatory clear sky chart from 2005-11-06 to 2026-07-31.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	10% 7% 3 7% 4 4 4 4 5% 7% 44%	146483
	Night	9% 7% 3 7% 4 4 4 4 5% 7% 46%	143872
Transparency	Day	38% 6% 13% 25% 15% 2	141160
	Night	37% 5% 14% 26% 16% 2	140208
Seeing	Day	14% 9% 31% 30% 13% 2	18371
	Night	12% 8% 34% 34% 10% 1	28215

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	8% 13% 5% 14% 8% 6% 6% 4 4 5% 26%	4720
	11th to 20th	Day	4 9% 5% 13% 8% 7% 7% 4 6% 7% 30%	4740
	21st to end	Day	5% 9% 5% 10% 7% 6% 6% 4 5% 6% 37%	5598
February	1st to 10th	Day	9% 13% 4 9% 7% 6% 6% 4 4 6% 32%	1890
	11th to 20th	Day	7% 8% 5% 10% 6% 5% 6% 3 5% 7% 37%	1939
	21st to end	Day	8% 9% 4 9% 5% 5% 6% 3 6% 7% 38%	1730
March	1st to 10th	Day	9% 8% 3 8% 4 4 3 2 4 6% 49%	4728
	11th to 20th	Day	7% 6% 2 5% 4 4 4 4 5% 9% 50%	5090
	21st to end	Day	20% 11% 3 11% 5% 5% 4 4 5% 6% 26%	5585
April	1st to 10th	Day	16% 8% 2 6% 4 3 4 4 6% 7% 39%	2415
	11th to 20th	Day	17% 9% 3 7% 4 4 3 3 6% 6% 38%	2699
	21st to end	Day	18% 9% 3 5% 4 4 3 3 5% 7% 39%	2730
May	1st to 10th	Day	8% 4 2 5% 4 4 4 4 6% 7% 52%	7655
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 5% 6% 48%	7627
	21st to end	Day	18% 7% 3 6% 4 4 4 3 5% 7% 39%	8828
June	1st to 10th	Day	11% 4 2 5% 4 3 4 3 6% 9% 48%	3150
	11th to 20th	Day	11% 6% 1 5% 4 3 5% 4 7% 8% 46%	3150
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 8% 50%	3150
July	1st to 10th	Day	9% 4 2 5% 4 4 5% 4 7% 8% 49%	6634
	11th to 20th	Day	8% 4 2 5% 3 4 3 3 5% 8% 54%	6480
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 6% 10% 48%	6748
August	1st to 10th	Day	8% 6% 2 7% 5% 5% 5% 4 7% 9% 43%	5801
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 5% 9% 45%	5821
	21st to end	Day	8% 5% 2 6% 3 3 3 3 5% 6% 56%	6490
September	1st to 10th	Day	10% 6% 2 4 3 3 3 3 5% 6% 55%	2301
	11th to 20th	Day	8% 5% 1 5% 3 3 3 3 5% 7% 56%	2200
	21st to end	Day	12% 4 2 4 3 3 2 2 5% 6% 57%	2200
October	1st to 10th	Day	8% 4 1 3 3 2 3 3 4 5% 65%	3442
	11th to 20th	Day	9% 5% 1 5% 3 4 4 3 5% 6% 56%	3240
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 5% 7% 45%	3263
November	1st to 10th	Day	9% 7% 3 6% 4 3 4 4 6% 8% 47%	1853
	11th to 20th	Day	6% 7% 3 9% 5% 4 4 4 5% 7% 47%	1841
	21st to end	Day	8% 9% 3 8% 4 4 4 4 4 7% 44%	1680
December	1st to 10th	Day	5% 9% 4 10% 7% 7% 6% 4 5% 6% 37%	2690
	11th to 20th	Day	8% 11% 5% 10% 5% 5% 5% 4 6% 8% 34%	2729
	21st to end	Day	15% 9% 4 12% 7% 4 4 3 5% 6% 31%	3646
January	1st to 10th	Night	5% 10% 5% 13% 9% 7% 6% 5% 6% 6% 28%	8201
	11th to 20th	Night	3 8% 4 10% 7% 6% 7% 5% 8% 8% 35%	8250
	21st to end	Night	3 7% 4 11% 5% 5% 5% 4 6% 6% 44%	8613
February	1st to 10th	Night	9% 11% 4 9% 5% 5% 6% 4 5% 6% 35%	2730
	11th to 20th	Night	7% 10% 3 8% 5% 4 5% 4 6% 6% 40%	2585
	21st to end	Night	8% 8% 3 7% 5% 5% 4 4 6% 7% 44%	2076
March	1st to 10th	Night	9% 8% 3 6% 4 3 4 3 5% 6% 49%	5359
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 9% 52%	5090
	21st to end	Night	15% 11% 3 7% 4 4 4 3 5% 7% 36%	5588
April	1st to 10th	Night	14% 8% 2 6% 4 4 4 5% 4 7% 41%	2203
	11th to 20th	Night	15% 7% 3 5% 4 3 3 3 5% 7% 44%	1869
	21st to end	Night	16% 8% 2 6% 3 4 4 4 6% 6% 41%	1890
May	1st to 10th	Night	10% 4 1 5% 4 4 4 3 6% 7% 52%	5292
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 7% 53%	5265
	21st to end	Night	17% 6% 3 6% 4 5% 5% 3 5% 8% 38%	5343
June	1st to 10th	Night	8% 4 1 4 4 3 3 4 6% 8% 55%	1470
	11th to 20th	Night	9% 4 2 4 4 3 4 3 6% 10% 50%	1470
	21st to end	Night	8% 4 1 4 3 3 4 3 5% 9% 56%	1470
July	1st to 10th	Night	7% 3 2 4 3 4 4 4 6% 10% 53%	3546
	11th to 20th	Night	7% 4 2 5% 3 3 3 3 5% 7% 58%	3720
	21st to end	Night	5% 3 2 5% 3 3 4 4 7% 11% 54%	4333
August	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 4 7% 10% 45%	4011
	11th to 20th	Night	8% 4 2 5% 4 4 5% 3 6% 9% 51%	4028
	21st to end	Night	6% 4 2 5% 3 4 4 4 5% 8% 55%	4487
September	1st to 10th	Night	9% 3 2 3 3 3 3 3 4 6% 61%	2095
	11th to 20th	Night	7% 4 2 4 3 3 4 3 6% 7% 58%	2200
	21st to end	Night	8% 5% 2 3 3 3 3 3 4 6% 60%	2200
October	1st to 10th	Night	9% 3 1 3 2 2 2 2 3 5% 69%	3704
	11th to 20th	Night	9% 5% 1 4 2 2 2 3 5% 8% 58%	3899
	21st to end	Night	10% 6% 2 6% 4 4 4 3 6% 8% 47%	4533
November	1st to 10th	Night	8% 5% 2 6% 3 4 4 4 5% 7% 52%	2665
	11th to 20th	Night	7% 7% 3 8% 5% 3 4 3 6% 6% 47%	2777
	21st to end	Night	7% 8% 3 6% 4 3 4 4 6% 7% 48%	2940
December	1st to 10th	Night	5% 7% 4 9% 6% 5% 5% 3 5% 6% 47%	4720
	11th to 20th	Night	7% 11% 4 9% 6% 6% 5% 4 5% 7% 38%	5681
	21st to end	Night	15% 10% 4 11% 5% 4 4 3 5% 6% 33%	7569

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	60% 6% 13% 15% 6%	4723
	11th to 20th	Day	51% 4 13% 17% 14%	4740
	21st to end	Day	46% 6% 17% 21% 11%	5598
February	1st to 10th	Day	54% 6% 14% 17% 9%	1890
	11th to 20th	Day	46% 6% 13% 22% 11% 2	1948
	21st to end	Day	45% 7% 14% 21% 12% 2	1730
March	1st to 10th	Day	38% 4 10% 31% 15% 2	4728
	11th to 20th	Day	31% 5% 10% 31% 21% 2	5090
	21st to end	Day	57% 7% 14% 17% 4 1	5585
April	1st to 10th	Day	43% 5% 13% 25% 12% 1	2415
	11th to 20th	Day	45% 6% 11% 22% 14% 3	2702
	21st to end	Day	45% 6% 11% 25% 12%	2730
May	1st to 10th	Day	28% 6% 9% 29% 27% 1	7655
	11th to 20th	Day	37% 5% 9% 21% 20% 8%	7631
	21st to end	Day	44% 6% 11% 25% 13% 1	8829
June	1st to 10th	Day	32% 7% 16% 31% 12% 2	3150
	11th to 20th	Day	34% 7% 15% 26% 16% 2	3150
	21st to end	Day	30% 7% 16% 29% 15% 3	3150
July	1st to 10th	Day	30% 7% 18% 31% 12% 1	6566
	11th to 20th	Day	28% 6% 13% 32% 18% 3	6405
	21st to end	Day	30% 8% 18% 26% 16% 2	6559
August	1st to 10th	Day	33% 6% 15% 28% 14% 3	4220
	11th to 20th	Day	43% 7% 15% 24% 10% 1	4210
	21st to end	Day	27% 6% 18% 28% 18% 3	4674
September	1st to 10th	Day	30% 5% 12% 31% 19% 3	2301
	11th to 20th	Day	28% 5% 16% 33% 17% 1	2200
	21st to end	Day	29% 5% 10% 32% 22% 3	2200
October	1st to 10th	Day	23% 4 9% 26% 34% 4	3442
	11th to 20th	Day	31% 4 11% 31% 20% 3	3240
	21st to end	Day	39% 5% 12% 23% 20% 2	3263
November	1st to 10th	Day	35% 6% 18% 26% 13% 3	1853
	11th to 20th	Day	37% 5% 16% 27% 13% 2	1841
	21st to end	Day	40% 5% 15% 27% 12% 1	1680
December	1st to 10th	Day	46% 7% 16% 22% 7% 1	2690
	11th to 20th	Day	48% 6% 19% 20% 7%	2726
	21st to end	Day	54% 5% 14% 22% 5%	3646
January	1st to 10th	Night	55% 6% 13% 17% 8% 1	8202
	11th to 20th	Night	44% 5% 15% 20% 14%	8250
	21st to end	Night	39% 6% 16% 25% 13%	8613
February	1st to 10th	Night	47% 7% 15% 19% 11% 1	2730
	11th to 20th	Night	42% 5% 14% 22% 14% 3	2586
	21st to end	Night	38% 5% 14% 25% 13% 4	2076
March	1st to 10th	Night	35% 5% 11% 29% 19% 2	5359
	11th to 20th	Night	30% 4 10% 30% 23% 2	5090
	21st to end	Night	48% 6% 13% 24% 8% 1	5588
April	1st to 10th	Night	42% 6% 13% 26% 12% 1	2203
	11th to 20th	Night	40% 6% 10% 24% 19% 2	1869
	21st to end	Night	42% 6% 12% 25% 14% 2	1890
May	1st to 10th	Night	29% 6% 11% 29% 23% 3	5293
	11th to 20th	Night	32% 4 10% 19% 26% 8%	5266
	21st to end	Night	43% 7% 12% 25% 13% 1	5345
June	1st to 10th	Night	27% 7% 16% 28% 19% 4	1470
	11th to 20th	Night	29% 6% 16% 22% 22% 4	1470
	21st to end	Night	25% 6% 16% 31% 20% 3	1470
July	1st to 10th	Night	27% 6% 19% 33% 13% 3	3506
	11th to 20th	Night	26% 6% 10% 36% 18% 4	3672
	21st to end	Night	24% 7% 21% 29% 17% 2	4210
August	1st to 10th	Night	31% 7% 17% 29% 14% 2	2916
	11th to 20th	Night	33% 7% 15% 30% 13% 2	2915
	21st to end	Night	26% 6% 17% 25% 21% 4	3234
September	1st to 10th	Night	24% 4 16% 29% 23% 4	2095
	11th to 20th	Night	25% 6% 15% 33% 19% 2	2200
	21st to end	Night	26% 4 9% 31% 27% 3	2200
October	1st to 10th	Night	20% 2 6% 21% 45% 6%	3704
	11th to 20th	Night	25% 3 11% 32% 23% 6%	3899
	21st to end	Night	35% 4 13% 26% 19% 1	4533
November	1st to 10th	Night	32% 4 14% 26% 20% 4	2665
	11th to 20th	Night	36% 5% 15% 24% 17% 2	2777
	21st to end	Night	35% 4 16% 28% 15% 1	2940
December	1st to 10th	Night	39% 5% 15% 31% 10% 1	4720
	11th to 20th	Night	46% 6% 18% 24% 7%	5683
	21st to end	Night	53% 4 14% 22% 6%	7569

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	15% 11% 28% 32% 13% 1	330
	11th to 20th	Day	12% 16% 36% 27% 7% 2	330
	21st to end	Day	15% 9% 39% 23% 10% 2	363
February	1st to 10th	Day	11% 18% 40% 26% 4 1	330
	11th to 20th	Day	13% 12% 40% 24% 9% 2	330
	21st to end	Day	14% 13% 38% 30% 4	273
March	1st to 10th	Day	14% 14% 39% 27% 5% 1	330
	11th to 20th	Day	17% 10% 36% 23% 12% 2	330
	21st to end	Day	25% 11% 32% 23% 7% 2	363
April	1st to 10th	Day	25% 17% 34% 20% 4	435
	11th to 20th	Day	24% 15% 31% 23% 6%	740
	21st to end	Day	25% 11% 28% 25% 9% 2	750
May	1st to 10th	Day	16% 12% 31% 27% 12% 2	753
	11th to 20th	Day	21% 9% 26% 25% 15% 3	775
	21st to end	Day	18% 7% 30% 30% 12% 3	844
June	1st to 10th	Day	9% 8% 26% 34% 17% 6%	780
	11th to 20th	Day	14% 8% 34% 29% 13% 2	780
	21st to end	Day	12% 6% 30% 36% 15% 2	780
July	1st to 10th	Day	6% 4 22% 39% 23% 6%	771
	11th to 20th	Day	6% 3 29% 40% 20% 2	768
	21st to end	Day	7% 3 25% 43% 19% 3	845
August	1st to 10th	Day	10% 4 24% 39% 21% 3	726
	11th to 20th	Day	9% 3 25% 38% 20% 5%	715
	21st to end	Day	8% 4 27% 38% 20% 2	803
September	1st to 10th	Day	11% 7% 29% 32% 17% 4	431
	11th to 20th	Day	11% 6% 33% 31% 16% 4	330
	21st to end	Day	14% 10% 30% 26% 16% 4	330
October	1st to 10th	Day	17% 7% 28% 30% 14% 3	330
	11th to 20th	Day	18% 10% 37% 24% 8% 2	330
	21st to end	Day	18% 15% 34% 23% 9% 1	363
November	1st to 10th	Day	21% 12% 31% 27% 9% 2	330
	11th to 20th	Day	12% 15% 41% 24% 8% 1	330
	21st to end	Day	16% 16% 32% 26% 10% 1	330
December	1st to 10th	Day	12% 8% 39% 28% 11% 1	330
	11th to 20th	Day	14% 16% 39% 26% 5%	330
	21st to end	Day	20% 11% 37% 26% 6% 1	363
January	1st to 10th	Night	11% 10% 37% 33% 8% 1	1050
	11th to 20th	Night	10% 13% 37% 32% 7% 1	1050
	21st to end	Night	12% 9% 39% 31% 8% 1	1155
February	1st to 10th	Night	14% 11% 38% 30% 6%	1050
	11th to 20th	Night	12% 11% 38% 32% 7%	951
	21st to end	Night	12% 10% 38% 31% 8% 1	692
March	1st to 10th	Night	15% 8% 40% 32% 5%	783
	11th to 20th	Night	16% 9% 38% 30% 6%	630
	21st to end	Night	19% 8% 38% 28% 8%	693
April	1st to 10th	Night	19% 12% 39% 27% 3	630
	11th to 20th	Night	20% 12% 34% 27% 7%	623
	21st to end	Night	19% 10% 35% 28% 7%	630
May	1st to 10th	Night	15% 8% 34% 30% 13%	630
	11th to 20th	Night	17% 7% 32% 32% 12%	621
	21st to end	Night	16% 5% 33% 35% 10%	683
June	1st to 10th	Night	8% 6% 31% 37% 17% 1	630
	11th to 20th	Night	10% 6% 33% 41% 11%	630
	21st to end	Night	8% 5% 30% 46% 12%	630
July	1st to 10th	Night	7% 2 22% 47% 22%	615
	11th to 20th	Night	5% 2 28% 50% 14% 1	612
	21st to end	Night	4 2 29% 50% 14% 1	687
August	1st to 10th	Night	8% 3 24% 48% 18%	597
	11th to 20th	Night	7% 2 27% 41% 22% 1	594
	21st to end	Night	7% 2 28% 45% 17% 1	660
September	1st to 10th	Night	9% 5% 27% 43% 15% 2	600
	11th to 20th	Night	8% 4 34% 39% 12% 2	600
	21st to end	Night	9% 7% 34% 33% 15% 2	600
October	1st to 10th	Night	16% 8% 34% 30% 11% 1	662
	11th to 20th	Night	18% 9% 34% 31% 8% 1	800
	21st to end	Night	16% 11% 34% 30% 8%	1047
November	1st to 10th	Night	10% 9% 37% 34% 8% 1	1025
	11th to 20th	Night	11% 10% 38% 31% 9% 1	1050
	21st to end	Night	10% 9% 37% 35% 9%	1050
December	1st to 10th	Night	13% 12% 38% 30% 8%	1050
	11th to 20th	Night	14% 10% 33% 35% 7%	1050
	21st to end	Night	19% 11% 35% 28% 7%	1155

Page generated at 2026-07-28 02:25:24. Version ac07

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