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 2024-02-15.

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 6% 5% 3 4 5% 5% 7% 44%	78159
	Night	9% 7% 3 6% 5% 3 5% 5% 5% 7% 45%	80957
Transparency	Day	39% 6% 14% 26% 13% 2	77869
	Night	39% 6% 14% 25% 14% 2	80770
Seeing	Day	15% 8% 30% 31% 14% 2	14861
	Night	13% 8% 34% 35% 10% 1	24965

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% 11% 5% 11% 11% 5% 7% 7% 5% 4 27%	2538
	11th to 20th	Day	5% 11% 6% 11% 8% 4 8% 6% 6% 8% 27%	2540
	21st to end	Day	6% 11% 5% 12% 8% 5% 5% 6% 5% 6% 31%	3012
February	1st to 10th	Day	10% 11% 4 8% 8% 5% 6% 5% 5% 6% 33%	1710
	11th to 20th	Day	8% 8% 5% 8% 7% 4 6% 4 6% 7% 36%	1691
	21st to end	Day	9% 9% 4 9% 7% 4 7% 4 6% 7% 35%	1480
March	1st to 10th	Day	11% 10% 4 9% 6% 3 3 3 4 7% 40%	1847
	11th to 20th	Day	11% 9% 4 7% 6% 3 4 5% 5% 8% 38%	1980
	21st to end	Day	15% 11% 5% 8% 6% 3 5% 5% 6% 7% 30%	2178
April	1st to 10th	Day	16% 6% 3 6% 6% 3 4 5% 6% 8% 39%	2070
	11th to 20th	Day	19% 9% 4 6% 5% 3 4 4 6% 6% 36%	2309
	21st to end	Day	18% 8% 3 5% 4 3 3 4 4 8% 39%	2340
May	1st to 10th	Day	15% 6% 3 5% 6% 3 5% 5% 6% 7% 40%	2340
	11th to 20th	Day	14% 6% 2 6% 5% 3 4 5% 6% 6% 43%	2302
	21st to end	Day	15% 6% 3 5% 6% 3 4 5% 6% 8% 40%	2655
June	1st to 10th	Day	12% 3 2 5% 4 2 4 4 6% 9% 48%	2700
	11th to 20th	Day	11% 5% 2 4 5% 2 4 5% 6% 8% 47%	2700
	21st to end	Day	7% 4 2 4 5% 3 4 5% 6% 8% 51%	2700
July	1st to 10th	Day	7% 3 1 3 4 3 4 5% 7% 10% 54%	2587
	11th to 20th	Day	5% 3 2 2 3 2 4 4 5% 8% 61%	2520
	21st to end	Day	6% 2 1 3 4 3 5% 6% 6% 9% 56%	2630
August	1st to 10th	Day	8% 5% 2 6% 6% 4 5% 5% 6% 8% 45%	2328
	11th to 20th	Day	8% 3 2 4 4 3 4 5% 6% 10% 51%	2301
	21st to end	Day	7% 3 2 4 4 2 4 4 5% 7% 59%	2574
September	1st to 10th	Day	11% 6% 2 4 3 2 3 3 5% 5% 54%	2072
	11th to 20th	Day	8% 5% 1 4 4 3 3 3 5% 7% 57%	1980
	21st to end	Day	13% 5% 2 4 4 2 3 3 4 6% 55%	1980
October	1st to 10th	Day	14% 6% 2 4 5% 2 3 4 4 5% 51%	1906
	11th to 20th	Day	14% 7% 1 4 3 2 4 3 5% 5% 52%	1800
	21st to end	Day	14% 6% 3 5% 4 2 3 4 4 6% 48%	1828
November	1st to 10th	Day	9% 7% 3 4 4 2 4 4 6% 8% 48%	1673
	11th to 20th	Day	6% 7% 3 9% 5% 3 4 5% 5% 7% 46%	1667
	21st to end	Day	9% 8% 4 6% 4 3 5% 5% 4 8% 45%	1520
December	1st to 10th	Day	8% 9% 3 8% 7% 4 6% 5% 6% 7% 38%	1520
	11th to 20th	Day	8% 9% 5% 7% 6% 4 6% 5% 4 8% 37%	1698
	21st to end	Day	19% 10% 5% 9% 8% 2 4 3 5% 5% 29%	2483
January	1st to 10th	Night	7% 10% 5% 10% 12% 6% 7% 6% 5% 6% 25%	4417
	11th to 20th	Night	4 9% 5% 8% 7% 4 9% 6% 9% 9% 30%	4430
	21st to end	Night	5% 9% 6% 12% 7% 3 6% 5% 5% 6% 35%	4652
February	1st to 10th	Night	9% 9% 5% 9% 6% 3 6% 5% 5% 6% 36%	2470
	11th to 20th	Night	8% 10% 3 7% 6% 3 6% 6% 6% 6% 41%	2265
	21st to end	Night	9% 9% 4 6% 6% 4 4 5% 6% 6% 41%	1776
March	1st to 10th	Night	9% 8% 4 6% 6% 4 4 5% 5% 6% 43%	2112
	11th to 20th	Night	13% 8% 3 6% 5% 3 4 4 4 8% 42%	1980
	21st to end	Night	13% 9% 3 6% 6% 3 5% 4 4 8% 39%	2178
April	1st to 10th	Night	15% 7% 2 6% 4 4 4 5% 4 8% 41%	1889
	11th to 20th	Night	16% 7% 3 5% 5% 3 3 4 5% 7% 42%	1599
	21st to end	Night	14% 8% 3 5% 4 3 4 5% 6% 7% 41%	1620
May	1st to 10th	Night	14% 5% 2 4 4 3 4 4 6% 7% 46%	1620
	11th to 20th	Night	14% 6% 3 4 4 2 3 4 4 8% 48%	1593
	21st to end	Night	14% 6% 3 6% 5% 3 5% 5% 7% 9% 40%	1612
June	1st to 10th	Night	8% 3 2 3 4 2 3 4 5% 9% 55%	1260
	11th to 20th	Night	8% 4 2 5% 5% 2 4 4 6% 11% 49%	1260
	21st to end	Night	6% 3 1 3 3 2 5% 4 5% 10% 59%	1260
July	1st to 10th	Night	5% 3 2 3 3 2 4 4 6% 10% 58%	1368
	11th to 20th	Night	4 2 1 3 3 3 4 5% 6% 7% 62%	1440
	21st to end	Night	3 2 2 4 3 3 4 4 6% 9% 61%	1688
August	1st to 10th	Night	6% 4 1 5% 4 4 5% 5% 6% 11% 49%	1611
	11th to 20th	Night	6% 3 1 3 4 2 4 4 6% 7% 60%	1600
	21st to end	Night	5% 2 1 3 2 3 4 3 5% 8% 63%	1782
September	1st to 10th	Night	10% 3 2 3 3 2 3 4 4 6% 60%	1884
	11th to 20th	Night	7% 4 2 3 3 2 4 3 6% 7% 59%	1980
	21st to end	Night	9% 5% 2 3 4 2 4 4 4 6% 59%	1980
October	1st to 10th	Night	15% 5% 2 4 5% 3 3 3 5% 6% 49%	2035
	11th to 20th	Night	13% 6% 2 3 3 3 4 4 4 6% 53%	2160
	21st to end	Night	13% 6% 2 5% 4 3 3 4 4 6% 51%	2525
November	1st to 10th	Night	8% 5% 2 4 4 3 5% 4 5% 7% 54%	2405
	11th to 20th	Night	7% 7% 3 7% 6% 3 4 4 6% 6% 47%	2512
	21st to end	Night	8% 7% 3 5% 4 2 4 5% 6% 7% 50%	2660
December	1st to 10th	Night	8% 8% 4 7% 6% 3 5% 4 5% 6% 43%	2660
	11th to 20th	Night	6% 10% 3 7% 5% 3 4 5% 5% 8% 44%	3495
	21st to end	Night	18% 11% 4 10% 6% 2 3 4 4 6% 32%	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	1700
	21st to end	Day	48% 8% 14% 18% 10% 2	1480
March	1st to 10th	Day	47% 5% 14% 24% 9% 1	1847
	11th to 20th	Day	45% 6% 12% 26% 10% 1	1980
	21st to end	Day	54% 7% 16% 18% 4 2	2178
April	1st to 10th	Day	42% 6% 14% 26% 11% 1	2070
	11th to 20th	Day	48% 6% 11% 21% 12% 3	2312
	21st to end	Day	44% 6% 12% 26% 11%	2340
May	1st to 10th	Day	43% 7% 13% 23% 14% 1	2340
	11th to 20th	Day	41% 6% 16% 23% 14% 1	2306
	21st to end	Day	42% 7% 14% 23% 12% 1	2655
June	1st to 10th	Day	32% 7% 16% 31% 12% 1	2700
	11th to 20th	Day	33% 7% 15% 26% 15% 3	2700
	21st to end	Day	28% 8% 17% 31% 14% 3	2700
July	1st to 10th	Day	25% 7% 16% 34% 15% 2	2518
	11th to 20th	Day	21% 5% 14% 30% 23% 6%	2445
	21st to end	Day	23% 8% 15% 29% 21% 3	2484
August	1st to 10th	Day	35% 7% 16% 28% 12% 3	2314
	11th to 20th	Day	28% 7% 16% 33% 14% 1	2301
	21st to end	Day	25% 6% 13% 33% 19% 4	2574
September	1st to 10th	Day	33% 4 10% 30% 20% 3	2072
	11th to 20th	Day	28% 5% 15% 33% 17% 1	1980
	21st to end	Day	32% 5% 10% 32% 20% 1	1980
October	1st to 10th	Day	35% 5% 13% 27% 19% 1	1906
	11th to 20th	Day	35% 4 11% 31% 16% 4	1800
	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	43% 5% 15% 21% 13% 3	2266
	21st to end	Night	43% 5% 14% 22% 12% 4	1776
March	1st to 10th	Night	41% 6% 17% 23% 11% 2	2112
	11th to 20th	Night	42% 5% 11% 26% 15% 2	1980
	21st to end	Night	45% 6% 15% 24% 9% 2	2178
April	1st to 10th	Night	42% 6% 13% 26% 13% 1	1889
	11th to 20th	Night	42% 6% 10% 23% 17% 2	1599
	21st to end	Night	41% 6% 13% 26% 12% 2	1620
May	1st to 10th	Night	36% 6% 16% 26% 15% 1	1620
	11th to 20th	Night	35% 5% 15% 26% 18% 1	1594
	21st to end	Night	41% 7% 16% 22% 13% 1	1613
June	1st to 10th	Night	27% 6% 16% 28% 20% 3	1260
	11th to 20th	Night	30% 7% 17% 22% 21% 4	1260
	21st to end	Night	22% 5% 16% 32% 21% 3	1260
July	1st to 10th	Night	23% 5% 17% 33% 19% 4	1328
	11th to 20th	Night	21% 6% 10% 31% 25% 8%	1392
	21st to end	Night	20% 5% 14% 31% 23% 5%	1594
August	1st to 10th	Night	29% 7% 18% 28% 16% 2	1601
	11th to 20th	Night	23% 7% 13% 35% 18% 3	1600
	21st to end	Night	20% 5% 14% 33% 22% 7%	1782
September	1st to 10th	Night	25% 4 15% 28% 22% 5%	1884
	11th to 20th	Night	24% 6% 14% 34% 19% 2	1980
	21st to end	Night	28% 4 9% 31% 25% 3	1980
October	1st to 10th	Night	36% 4 10% 25% 22% 2	2035
	11th to 20th	Night	32% 4 9% 30% 20% 4	2160
	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% 12% 43% 22% 8% 1	252
	21st to end	Day	15% 13% 37% 31% 5%	198
March	1st to 10th	Day	16% 14% 35% 30% 5% 1	240
	11th to 20th	Day	18% 7% 36% 25% 13% 2	240
	21st to end	Day	26% 8% 31% 24% 9% 2	264
April	1st to 10th	Day	24% 15% 34% 22% 4 1	330
	11th to 20th	Day	26% 12% 30% 24% 7% 1	590
	21st to end	Day	24% 11% 27% 26% 10% 2	600
May	1st to 10th	Day	19% 11% 32% 27% 10% 1	603
	11th to 20th	Day	21% 8% 27% 25% 16% 3	625
	21st to end	Day	18% 6% 30% 30% 13% 3	679
June	1st to 10th	Day	9% 6% 24% 35% 20% 6%	630
	11th to 20th	Day	13% 7% 33% 29% 15% 3	630
	21st to end	Day	11% 5% 27% 38% 17% 2	630
July	1st to 10th	Day	7% 3 21% 41% 23% 5%	621
	11th to 20th	Day	7% 3 31% 39% 18% 2	618
	21st to end	Day	6% 2 24% 44% 22% 2	684
August	1st to 10th	Day	9% 3 21% 40% 23% 3	626
	11th to 20th	Day	9% 3 24% 39% 21% 5%	615
	21st to end	Day	8% 4 27% 38% 21% 3	693
September	1st to 10th	Day	14% 7% 30% 30% 16% 3	362
	11th to 20th	Day	11% 4 31% 33% 17% 4	270
	21st to end	Day	16% 11% 33% 25% 14% 1	270
October	1st to 10th	Day	20% 7% 26% 31% 13% 2	270
	11th to 20th	Day	19% 10% 34% 26% 9% 3	270
	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% 35% 33% 8%	835
	21st to end	Night	14% 9% 36% 31% 9% 2	592
March	1st to 10th	Night	15% 7% 39% 32% 6%	672
	11th to 20th	Night	16% 7% 38% 32% 7%	540
	21st to end	Night	19% 8% 35% 30% 9%	594
April	1st to 10th	Night	19% 11% 38% 28% 4	540
	11th to 20th	Night	21% 11% 32% 28% 8%	533
	21st to end	Night	17% 11% 35% 29% 8% 1	540
May	1st to 10th	Night	16% 8% 35% 29% 12%	540
	11th to 20th	Night	17% 7% 32% 31% 12%	531
	21st to end	Night	17% 5% 32% 36% 10% 1	584
June	1st to 10th	Night	9% 5% 31% 37% 18% 1	540
	11th to 20th	Night	10% 4 32% 41% 12%	540
	21st to end	Night	6% 4 29% 47% 14% 1	540
July	1st to 10th	Night	6% 2 22% 46% 23%	525
	11th to 20th	Night	5% 2 28% 50% 14%	522
	21st to end	Night	4 2 28% 52% 15% 1	591
August	1st to 10th	Night	7% 2 21% 50% 19%	537
	11th to 20th	Night	8% 2 26% 40% 23% 1	534
	21st to end	Night	6% 2 28% 45% 18% 1	594
September	1st to 10th	Night	10% 5% 28% 42% 14% 2	540
	11th to 20th	Night	8% 4 33% 39% 14% 2	540
	21st to end	Night	10% 7% 35% 34% 13% 1	540
October	1st to 10th	Night	17% 9% 33% 30% 10% 1	595
	11th to 20th	Night	17% 9% 34% 30% 9% 1	720
	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

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