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 2025-03-27.

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% 5% 4 4 3 5% 7% 44%	112458
	Night	9% 7% 3 7% 4 4 4 4 5% 7% 46%	115632
Transparency	Day	39% 6% 14% 25% 14% 2	112207
	Night	37% 5% 14% 25% 16% 2	115473
Seeing	Day	14% 9% 30% 31% 14% 2	16374
	Night	13% 8% 34% 35% 10% 1	26476

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	9% 11% 4 16% 9% 7% 7% 4 4 5% 24%	3638
	11th to 20th	Day	5% 10% 5% 13% 8% 6% 7% 4 7% 7% 30%	3640
	21st to end	Day	4 9% 5% 11% 6% 5% 5% 4 5% 6% 40%	4326
February	1st to 10th	Day	10% 12% 4 9% 7% 6% 6% 4 5% 6% 32%	1800
	11th to 20th	Day	7% 9% 5% 10% 6% 5% 5% 3 6% 7% 36%	1844
	21st to end	Day	8% 9% 4 9% 5% 5% 6% 3 6% 7% 38%	1650
March	1st to 10th	Day	9% 10% 3 8% 4 4 3 2 4 7% 45%	3319
	11th to 20th	Day	8% 7% 3 6% 4 4 4 4 5% 8% 47%	3590
	21st to end	Day	22% 11% 4 11% 5% 4 4 3 5% 6% 25%	3880
April	1st to 10th	Day	15% 7% 2 7% 5% 3 4 4 6% 8% 40%	2185
	11th to 20th	Day	18% 9% 3 6% 4 4 3 3 6% 6% 37%	2439
	21st to end	Day	18% 9% 3 5% 4 4 3 3 5% 7% 39%	2470
May	1st to 10th	Day	14% 7% 3 6% 5% 5% 4 4 6% 7% 40%	4120
	11th to 20th	Day	11% 5% 2 5% 4 3 4 3 5% 6% 51%	4082
	21st to end	Day	16% 6% 2 6% 4 4 4 3 6% 8% 41%	4722
June	1st to 10th	Day	12% 4 2 5% 4 3 4 3 6% 9% 48%	2850
	11th to 20th	Day	12% 6% 2 5% 4 3 5% 4 6% 7% 46%	2850
	21st to end	Day	8% 4 2 5% 4 4 4 4 6% 9% 50%	2850
July	1st to 10th	Day	12% 4 2 5% 4 4 4 4 7% 9% 46%	4539
	11th to 20th	Day	5% 3 2 4 3 4 3 3 5% 8% 59%	4430
	21st to end	Day	4 3 1 4 4 4 5% 4 6% 9% 54%	4602
August	1st to 10th	Day	8% 5% 2 6% 5% 4 4 3 6% 8% 48%	4103
	11th to 20th	Day	16% 7% 2 7% 4 4 4 4 6% 8% 37%	4041
	21st to end	Day	6% 4 2 6% 3 4 4 3 5% 7% 56%	4532
September	1st to 10th	Day	10% 6% 2 4 3 3 3 3 5% 5% 55%	2186
	11th to 20th	Day	8% 5% 1 4 3 3 3 3 5% 7% 58%	2090
	21st to end	Day	12% 4 2 4 3 3 2 2 4 6% 57%	2090
October	1st to 10th	Day	8% 4 1 3 3 2 3 3 4 5% 64%	3336
	11th to 20th	Day	8% 5% 1 5% 3 4 4 3 5% 6% 56%	3140
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 5% 7% 44%	3162
November	1st to 10th	Day	9% 7% 3 6% 4 3 4 4 6% 8% 47%	1763
	11th to 20th	Day	6% 7% 3 9% 5% 4 4 4 5% 7% 47%	1754
	21st to end	Day	8% 9% 3 7% 4 4 4 4 4 7% 45%	1600
December	1st to 10th	Day	4 9% 4 10% 7% 7% 6% 4 5% 6% 38%	2610
	11th to 20th	Day	8% 11% 5% 10% 5% 5% 5% 4 6% 8% 34%	2658
	21st to end	Day	15% 9% 4 13% 7% 4 4 3 5% 6% 30%	3567
January	1st to 10th	Night	6% 11% 6% 13% 10% 7% 7% 5% 5% 5% 25%	6327
	11th to 20th	Night	3 8% 5% 11% 6% 6% 7% 4 8% 8% 35%	6340
	21st to end	Night	4 8% 5% 11% 5% 4 5% 4 5% 5% 44%	6649
February	1st to 10th	Night	9% 10% 4 9% 5% 5% 6% 4 5% 6% 36%	2600
	11th to 20th	Night	7% 10% 3 8% 5% 5% 5% 5% 6% 6% 40%	2459
	21st to end	Night	8% 8% 3 7% 5% 4 4 4 6% 7% 43%	1980
March	1st to 10th	Night	9% 9% 3 7% 5% 4 4 3 5% 6% 47%	3761
	11th to 20th	Night	9% 6% 2 6% 4 4 3 3 5% 8% 50%	3590
	21st to end	Night	18% 12% 3 8% 5% 4 4 3 5% 7% 30%	3889
April	1st to 10th	Night	14% 7% 2 6% 4 4 5% 5% 4 8% 41%	1993
	11th to 20th	Night	16% 7% 3 6% 4 3 3 3 5% 6% 42%	1689
	21st to end	Night	14% 9% 2 6% 3 4 4 4 6% 6% 41%	1710
May	1st to 10th	Night	15% 5% 2 5% 4 3 4 3 6% 6% 47%	2850
	11th to 20th	Night	10% 5% 2 4 3 3 4 3 5% 8% 54%	2823
	21st to end	Night	14% 5% 3 6% 4 4 5% 4 6% 9% 41%	2856
June	1st to 10th	Night	8% 4 2 5% 3 3 3 3 5% 9% 55%	1330
	11th to 20th	Night	9% 5% 2 5% 4 3 4 3 6% 10% 49%	1330
	21st to end	Night	7% 3 1 4 3 3 4 3 5% 9% 59%	1330
July	1st to 10th	Night	10% 4 2 4 4 3 3 4 6% 9% 50%	2426
	11th to 20th	Night	3 3 1 3 3 3 3 4 5% 7% 64%	2540
	21st to end	Night	2 2 1 4 3 3 4 4 6% 10% 61%	2961
August	1st to 10th	Night	8% 5% 1 6% 4 4 5% 4 6% 9% 49%	2836
	11th to 20th	Night	10% 5% 3 5% 4 4 4 3 5% 7% 50%	2798
	21st to end	Night	7% 4 1 4 3 4 4 4 5% 8% 57%	3135
September	1st to 10th	Night	9% 3 2 3 3 3 3 3 4 6% 61%	1990
	11th to 20th	Night	7% 4 2 3 3 3 4 3 6% 7% 59%	2090
	21st to end	Night	8% 5% 2 3 3 3 3 3 4 6% 60%	2090
October	1st to 10th	Night	9% 3 1 3 2 2 2 2 3 5% 68%	3591
	11th to 20th	Night	8% 5% 1 3 2 2 2 3 5% 8% 59%	3779
	21st to end	Night	10% 6% 2 6% 4 4 4 3 6% 8% 47%	4392
November	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 5% 7% 53%	2535
	11th to 20th	Night	7% 7% 3 8% 5% 3 4 3 6% 6% 48%	2645
	21st to end	Night	7% 8% 3 6% 4 3 4 4 6% 7% 49%	2800
December	1st to 10th	Night	5% 7% 4 8% 6% 6% 5% 3 5% 6% 47%	4580
	11th to 20th	Night	7% 11% 4 9% 6% 6% 5% 4 5% 7% 38%	5532
	21st to end	Night	15% 10% 4 11% 5% 4 4 3 5% 5% 33%	7406

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	62% 6% 13% 14% 5%	3639
	11th to 20th	Day	51% 4 14% 16% 15%	3640
	21st to end	Day	44% 6% 17% 21% 11%	4326
February	1st to 10th	Day	53% 6% 13% 18% 10%	1800
	11th to 20th	Day	47% 6% 14% 21% 10% 2	1853
	21st to end	Day	45% 7% 14% 20% 11% 2	1650
March	1st to 10th	Day	40% 5% 11% 28% 15% 2	3319
	11th to 20th	Day	35% 6% 11% 30% 16% 3	3590
	21st to end	Day	60% 7% 15% 14% 2 1	3880
April	1st to 10th	Day	42% 5% 13% 26% 12% 1	2185
	11th to 20th	Day	46% 6% 11% 21% 13% 3	2442
	21st to end	Day	45% 6% 12% 26% 11%	2470
May	1st to 10th	Day	41% 7% 10% 23% 17% 1	4120
	11th to 20th	Day	33% 6% 12% 27% 18% 3	4086
	21st to end	Day	40% 7% 12% 25% 14% 1	4722
June	1st to 10th	Day	32% 7% 15% 32% 12% 2	2850
	11th to 20th	Day	35% 7% 15% 25% 15% 3	2850
	21st to end	Day	29% 7% 16% 30% 15% 3	2850
July	1st to 10th	Day	33% 8% 19% 27% 12% 2	4470
	11th to 20th	Day	23% 6% 14% 34% 20% 4	4355
	21st to end	Day	24% 8% 16% 29% 21% 3	4456
August	1st to 10th	Day	32% 6% 15% 29% 15% 3	4090
	11th to 20th	Day	44% 7% 15% 24% 10% 1	4080
	21st to end	Day	27% 7% 19% 27% 18% 3	4531
September	1st to 10th	Day	31% 4 10% 31% 20% 3	2186
	11th to 20th	Day	27% 5% 15% 34% 18% 1	2090
	21st to end	Day	30% 4 10% 32% 21% 3	2090
October	1st to 10th	Day	23% 4 9% 25% 35% 5%	3336
	11th to 20th	Day	30% 4 12% 31% 20% 3	3140
	21st to end	Day	39% 5% 13% 22% 20% 2	3162
November	1st to 10th	Day	35% 6% 18% 25% 14% 3	1763
	11th to 20th	Day	37% 5% 15% 28% 14% 2	1754
	21st to end	Day	39% 5% 16% 27% 12% 1	1600
December	1st to 10th	Day	45% 7% 16% 23% 8% 1	2610
	11th to 20th	Day	48% 6% 19% 20% 7%	2655
	21st to end	Day	55% 5% 14% 22% 5%	3567
January	1st to 10th	Night	59% 6% 10% 16% 8%	6327
	11th to 20th	Night	44% 5% 16% 18% 16% 1	6340
	21st to end	Night	40% 7% 15% 26% 12%	6649
February	1st to 10th	Night	47% 6% 15% 20% 12% 1	2600
	11th to 20th	Night	43% 5% 15% 21% 13% 3	2460
	21st to end	Night	39% 5% 15% 25% 13% 4	1980
March	1st to 10th	Night	36% 6% 12% 24% 20% 2	3761
	11th to 20th	Night	33% 5% 11% 31% 18% 2	3590
	21st to end	Night	54% 7% 14% 18% 6% 1	3889
April	1st to 10th	Night	41% 6% 13% 26% 13% 1	1993
	11th to 20th	Night	42% 6% 10% 23% 18% 2	1689
	21st to end	Night	41% 6% 13% 26% 13% 2	1710
May	1st to 10th	Night	36% 6% 14% 24% 16% 4	2850
	11th to 20th	Night	28% 5% 13% 27% 24% 3	2824
	21st to end	Night	38% 7% 13% 26% 15% 1	2857
June	1st to 10th	Night	27% 7% 16% 28% 19% 4	1330
	11th to 20th	Night	30% 6% 17% 22% 21% 4	1330
	21st to end	Night	23% 5% 16% 32% 21% 3	1330
July	1st to 10th	Night	31% 6% 22% 24% 13% 4	2386
	11th to 20th	Night	19% 6% 12% 38% 21% 4	2492
	21st to end	Night	17% 7% 18% 33% 22% 4	2868
August	1st to 10th	Night	30% 7% 16% 29% 15% 2	2826
	11th to 20th	Night	34% 7% 15% 29% 13% 2	2825
	21st to end	Night	26% 6% 17% 25% 21% 4	3135
September	1st to 10th	Night	24% 4 15% 29% 23% 5%	1990
	11th to 20th	Night	23% 6% 14% 34% 19% 2	2090
	21st to end	Night	27% 4 9% 30% 27% 3	2090
October	1st to 10th	Night	21% 3 6% 20% 45% 6%	3591
	11th to 20th	Night	24% 3 11% 33% 24% 5%	3779
	21st to end	Night	35% 4 14% 26% 19% 1	4392
November	1st to 10th	Night	31% 4 14% 26% 20% 5%	2535
	11th to 20th	Night	36% 5% 14% 24% 18% 2	2645
	21st to end	Night	35% 4 17% 28% 16% 1	2800
December	1st to 10th	Night	39% 5% 15% 31% 10% 1	4580
	11th to 20th	Night	46% 6% 18% 24% 7%	5534
	21st to end	Night	53% 4 13% 23% 6%	7406

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	16% 9% 29% 32% 14% 1	300
	11th to 20th	Day	13% 14% 35% 29% 8% 2	300
	21st to end	Day	16% 9% 37% 25% 11% 2	330
February	1st to 10th	Day	11% 19% 39% 28% 4	300
	11th to 20th	Day	13% 12% 42% 22% 8% 2	300
	21st to end	Day	14% 12% 37% 32% 5%	249
March	1st to 10th	Day	15% 13% 38% 29% 4 1	300
	11th to 20th	Day	16% 10% 35% 24% 13% 2	300
	21st to end	Day	27% 9% 33% 23% 7% 2	315
April	1st to 10th	Day	24% 17% 34% 21% 4 1	365
	11th to 20th	Day	25% 13% 31% 23% 7%	640
	21st to end	Day	25% 12% 26% 25% 10% 2	650
May	1st to 10th	Day	19% 11% 32% 27% 10% 1	653
	11th to 20th	Day	20% 9% 27% 25% 16% 3	675
	21st to end	Day	18% 6% 31% 30% 12% 3	734
June	1st to 10th	Day	10% 6% 24% 34% 19% 6%	680
	11th to 20th	Day	14% 7% 34% 29% 14% 3	680
	21st to end	Day	11% 5% 29% 37% 16% 2	680
July	1st to 10th	Day	7% 3 21% 40% 23% 6%	671
	11th to 20th	Day	7% 3 29% 40% 19% 2	668
	21st to end	Day	6% 2 24% 43% 21% 3	739
August	1st to 10th	Day	9% 4 23% 40% 22% 3	676
	11th to 20th	Day	10% 3 24% 38% 20% 4	665
	21st to end	Day	8% 5% 27% 37% 20% 3	748
September	1st to 10th	Day	12% 6% 29% 32% 17% 4	396
	11th to 20th	Day	10% 6% 33% 31% 16% 4	300
	21st to end	Day	15% 11% 32% 26% 14% 4	300
October	1st to 10th	Day	19% 7% 26% 31% 14% 3	300
	11th to 20th	Day	17% 10% 37% 25% 9% 2	300
	21st to end	Day	17% 15% 34% 23% 9% 1	330
November	1st to 10th	Day	21% 10% 31% 26% 10% 2	300
	11th to 20th	Day	13% 15% 40% 23% 8% 1	300
	21st to end	Day	14% 17% 31% 28% 10%	300
December	1st to 10th	Day	12% 7% 39% 28% 12% 1	300
	11th to 20th	Day	13% 15% 40% 27% 5%	300
	21st to end	Day	21% 11% 36% 24% 7% 1	330
January	1st to 10th	Night	11% 9% 37% 34% 8% 1	1000
	11th to 20th	Night	10% 12% 37% 33% 7% 1	1000
	21st to end	Night	13% 9% 39% 31% 8% 1	1100
February	1st to 10th	Night	15% 11% 38% 30% 6%	1000
	11th to 20th	Night	12% 11% 37% 32% 7%	905
	21st to end	Night	12% 9% 38% 31% 8% 2	660
March	1st to 10th	Night	15% 8% 40% 32% 5%	746
	11th to 20th	Night	16% 9% 38% 31% 7%	600
	21st to end	Night	19% 7% 36% 29% 8%	647
April	1st to 10th	Night	19% 12% 38% 28% 4	570
	11th to 20th	Night	21% 11% 32% 28% 8%	563
	21st to end	Night	18% 10% 35% 29% 7% 1	570
May	1st to 10th	Night	16% 8% 35% 29% 12%	570
	11th to 20th	Night	17% 7% 32% 32% 13%	561
	21st to end	Night	17% 5% 34% 35% 9%	617
June	1st to 10th	Night	8% 5% 31% 37% 17% 1	570
	11th to 20th	Night	11% 4 32% 41% 12%	570
	21st to end	Night	7% 4 29% 47% 13% 1	570
July	1st to 10th	Night	7% 2 22% 46% 23% 1	555
	11th to 20th	Night	5% 2 28% 50% 15% 1	552
	21st to end	Night	3 2 28% 51% 15% 1	624
August	1st to 10th	Night	8% 3 22% 49% 19%	567
	11th to 20th	Night	8% 2 27% 41% 21% 1	564
	21st to end	Night	7% 2 29% 44% 18% 1	627
September	1st to 10th	Night	9% 4 27% 42% 15% 2	570
	11th to 20th	Night	8% 4 35% 38% 13% 2	570
	21st to end	Night	9% 7% 35% 33% 14% 2	570
October	1st to 10th	Night	16% 9% 33% 30% 11% 1	629
	11th to 20th	Night	16% 9% 34% 31% 8% 1	760
	21st to end	Night	16% 11% 34% 31% 8%	994
November	1st to 10th	Night	10% 9% 36% 35% 9% 1	975
	11th to 20th	Night	11% 10% 38% 31% 9% 1	1000
	21st to end	Night	10% 9% 37% 35% 9%	1000
December	1st to 10th	Night	13% 12% 38% 30% 8%	1000
	11th to 20th	Night	14% 9% 34% 35% 7%	1000
	21st to end	Night	19% 11% 34% 28% 8%	1100

Page generated at 2025-03-24 08:04:28. Version ac07

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