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 2024-10-20.

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	11% 7% 3 7% 4 4 4 4 5% 7% 44%	101100
	Night	9% 7% 3 7% 4 4 4 4 5% 7% 45%	97764
Transparency	Day	39% 6% 14% 26% 14% 2	100849
	Night	38% 6% 14% 25% 15% 2	97605
Seeing	Day	14% 8% 30% 31% 14% 2	15900
	Night	13% 8% 34% 35% 10% 1	25747

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	7% 12% 4 13% 9% 7% 7% 5% 5% 5% 27%	2538
	11th to 20th	Day	5% 12% 6% 13% 6% 6% 7% 4 6% 8% 27%	2540
	21st to end	Day	6% 11% 5% 13% 7% 6% 6% 5% 5% 6% 31%	3012
February	1st to 10th	Day	10% 12% 3 9% 7% 7% 6% 4 5% 6% 32%	1710
	11th to 20th	Day	8% 9% 5% 9% 6% 5% 6% 3 6% 7% 36%	1749
	21st to end	Day	8% 9% 4 10% 5% 5% 6% 3 6% 6% 36%	1570
March	1st to 10th	Day	9% 10% 3 8% 4 4 3 2 4 7% 45%	3216
	11th to 20th	Day	8% 8% 3 7% 4 4 4 4 5% 7% 47%	3480
	21st to end	Day	23% 11% 4 11% 5% 4 4 3 5% 6% 25%	3814
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	14% 6% 2 5% 4 2 3 3 4 6% 52%	2011
	11th to 20th	Day	13% 7% 1 4 3 3 3 2 5% 5% 52%	1890
	21st to end	Day	14% 7% 2 6% 3 3 3 3 4 6% 48%	1828
November	1st to 10th	Day	9% 7% 3 5% 4 3 4 3 6% 8% 48%	1673
	11th to 20th	Day	6% 7% 3 9% 5% 4 4 4 5% 7% 46%	1667
	21st to end	Day	9% 9% 3 7% 4 4 4 4 4 7% 45%	1520
December	1st to 10th	Day	7% 10% 2 8% 6% 6% 5% 4 6% 7% 38%	1520
	11th to 20th	Day	8% 10% 5% 8% 5% 5% 6% 4 5% 8% 37%	1698
	21st to end	Day	19% 11% 4 11% 7% 3 4 3 5% 5% 29%	2483
January	1st to 10th	Night	7% 11% 5% 13% 10% 7% 7% 5% 5% 6% 25%	4417
	11th to 20th	Night	4 9% 5% 10% 6% 6% 8% 5% 9% 8% 30%	4430
	21st to end	Night	5% 9% 6% 13% 6% 5% 6% 4 6% 6% 35%	4652
February	1st to 10th	Night	9% 11% 4 9% 5% 4 6% 4 5% 6% 36%	2470
	11th to 20th	Night	7% 10% 3 8% 5% 5% 5% 5% 6% 6% 41%	2333
	21st to end	Night	8% 8% 4 7% 5% 5% 4 5% 6% 6% 42%	1884
March	1st to 10th	Night	8% 9% 3 7% 5% 4 4 4 5% 6% 47%	3644
	11th to 20th	Night	9% 6% 2 6% 4 4 3 3 5% 9% 49%	3480
	21st to end	Night	18% 13% 3 9% 5% 4 4 3 5% 6% 30%	3817
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	15% 5% 2 5% 4 3 3 3 5% 5% 51%	2149
	11th to 20th	Night	12% 6% 1 4 3 3 3 3 4 6% 53%	2275
	21st to end	Night	13% 6% 2 6% 3 3 3 3 5% 6% 51%	2525
November	1st to 10th	Night	7% 5% 2 5% 3 4 4 4 5% 7% 53%	2405
	11th to 20th	Night	7% 7% 3 9% 5% 4 4 3 6% 6% 47%	2512
	21st to end	Night	7% 8% 3 5% 4 3 4 4 6% 7% 49%	2660
December	1st to 10th	Night	8% 9% 3 9% 6% 4 4 3 5% 6% 42%	2660
	11th to 20th	Night	6% 11% 3 8% 4 4 5% 3 5% 8% 44%	3495
	21st to end	Night	18% 11% 4 11% 5% 3 3 3 5% 5% 31%	5179

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	58% 7% 11% 17% 7%	2539
	11th to 20th	Day	54% 5% 13% 21% 7%	2540
	21st to end	Day	52% 7% 16% 16% 8%	3012
February	1st to 10th	Day	52% 6% 14% 18% 10%	1710
	11th to 20th	Day	46% 6% 15% 21% 10% 2	1758
	21st to end	Day	47% 7% 14% 19% 11% 2	1570
March	1st to 10th	Day	40% 5% 11% 27% 15% 2	3216
	11th to 20th	Day	35% 6% 10% 30% 15% 3	3480
	21st to end	Day	60% 7% 15% 14% 2 1	3814
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	34% 5% 12% 27% 21% 1	2011
	11th to 20th	Day	35% 4 10% 31% 17% 4	1890
	21st to end	Day	38% 5% 13% 27% 16% 2	1828
November	1st to 10th	Day	33% 6% 19% 25% 14% 3	1673
	11th to 20th	Day	37% 5% 16% 27% 13% 1	1667
	21st to end	Day	38% 5% 16% 27% 13% 1	1520
December	1st to 10th	Day	43% 8% 16% 23% 10% 1	1520
	11th to 20th	Day	45% 6% 18% 23% 6%	1695
	21st to end	Day	58% 5% 11% 21% 5%	2483
January	1st to 10th	Night	58% 7% 10% 17% 7% 1	4417
	11th to 20th	Night	48% 6% 14% 22% 9% 1	4430
	21st to end	Night	48% 8% 17% 19% 8%	4652
February	1st to 10th	Night	47% 6% 15% 20% 11% 1	2470
	11th to 20th	Night	42% 5% 15% 22% 13% 3	2334
	21st to end	Night	41% 5% 14% 23% 13% 4	1884
March	1st to 10th	Night	36% 7% 12% 23% 20% 2	3644
	11th to 20th	Night	33% 5% 11% 31% 18% 2	3480
	21st to end	Night	54% 7% 14% 17% 6% 1	3817
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	35% 4 10% 25% 24% 2	2149
	11th to 20th	Night	31% 4 9% 31% 20% 5%	2275
	21st to end	Night	35% 4 13% 24% 21% 2	2525
November	1st to 10th	Night	31% 4 14% 26% 20% 5%	2405
	11th to 20th	Night	37% 5% 14% 24% 17% 2	2512
	21st to end	Night	34% 4 16% 28% 17% 1	2660
December	1st to 10th	Night	42% 5% 16% 26% 10% 1	2660
	11th to 20th	Night	39% 5% 21% 28% 7%	3497
	21st to end	Night	55% 5% 12% 22% 7%	5179

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	17% 9% 27% 33% 14%	270
	11th to 20th	Day	13% 14% 34% 29% 8% 1	270
	21st to end	Day	18% 8% 36% 25% 10% 2	297
February	1st to 10th	Day	11% 15% 39% 30% 4	270
	11th to 20th	Day	14% 13% 41% 23% 8% 2	270
	21st to end	Day	14% 12% 36% 32% 4	225
March	1st to 10th	Day	15% 14% 36% 30% 5% 1	270
	11th to 20th	Day	17% 7% 36% 25% 12% 2	270
	21st to end	Day	27% 7% 32% 24% 8% 2	297
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% 11% 35% 26% 9% 2	297
	21st to end	Day	18% 15% 34% 23% 9% 1	297
November	1st to 10th	Day	20% 10% 31% 26% 10% 2	270
	11th to 20th	Day	12% 14% 40% 24% 8% 1	270
	21st to end	Day	16% 17% 29% 28% 10%	270
December	1st to 10th	Day	12% 7% 40% 28% 11% 1	270
	11th to 20th	Day	12% 12% 41% 29% 5%	270
	21st to end	Day	23% 12% 35% 23% 7% 1	297
January	1st to 10th	Night	11% 9% 37% 34% 8% 1	950
	11th to 20th	Night	10% 12% 37% 33% 7% 1	950
	21st to end	Night	13% 9% 37% 32% 8% 1	1045
February	1st to 10th	Night	15% 10% 37% 31% 7%	950
	11th to 20th	Night	12% 11% 36% 32% 8%	859
	21st to end	Night	13% 9% 37% 31% 8% 2	628
March	1st to 10th	Night	15% 7% 40% 32% 6%	709
	11th to 20th	Night	15% 8% 38% 31% 7%	570
	21st to end	Night	20% 8% 35% 29% 8%	627
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	759
	21st to end	Night	16% 11% 33% 31% 8%	941
November	1st to 10th	Night	10% 9% 35% 35% 9% 1	925
	11th to 20th	Night	11% 9% 37% 32% 10% 1	950
	21st to end	Night	10% 9% 38% 35% 9%	950
December	1st to 10th	Night	13% 11% 37% 30% 8%	950
	11th to 20th	Night	14% 9% 32% 36% 8%	950
	21st to end	Night	20% 11% 33% 29% 8%	1045

Page generated at 2024-10-17 12:09:40. Version ac07

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