Yankton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yankton 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	11% 7% 3 7% 4 4 4 4 5% 7% 44%	137844
	Night	9% 7% 3 7% 4 4 4 3 5% 7% 46%	135448
Transparency	Day	27% 35% 9% 17% 11% 2	141428
	Night	25% 35% 9% 18% 12% 1	139937
Seeing	Day	14% 9% 31% 29% 13% 3	18321
	Night	13% 9% 34% 35% 10% 1	28159

By Month

Percentage Cloud Cover SE (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% 12% 5% 15% 7% 6% 5% 3 4 5% 28%	4722
	11th to 20th	Day	4 10% 4 11% 8% 6% 6% 4 7% 7% 33%	4908
	21st to end	Day	4 9% 4 11% 6% 5% 6% 5% 5% 6% 38%	5812
February	1st to 10th	Day	9% 11% 4 10% 8% 5% 6% 4 5% 6% 30%	1890
	11th to 20th	Day	9% 11% 4 9% 5% 4 4 3 4 7% 39%	1919
	21st to end	Day	10% 9% 4 8% 7% 4 5% 3 5% 8% 37%	1730
March	1st to 10th	Day	12% 7% 3 7% 4 3 3 3 3 6% 48%	4814
	11th to 20th	Day	8% 7% 2 6% 3 3 4 3 4 7% 52%	5090
	21st to end	Day	22% 10% 4 10% 5% 5% 4 4 5% 6% 26%	5583
April	1st to 10th	Day	16% 8% 2 7% 4 4 4 4 5% 6% 40%	2374
	11th to 20th	Day	17% 9% 2 6% 4 4 3 4 5% 6% 40%	2702
	21st to end	Day	22% 6% 2 6% 4 4 4 2 5% 6% 39%	2730
May	1st to 10th	Day	9% 4 2 5% 4 4 5% 4 7% 8% 49%	7617
	11th to 20th	Day	14% 6% 2 6% 3 4 4 3 5% 6% 48%	7627
	21st to end	Day	19% 7% 2 6% 4 4 4 3 6% 7% 37%	8666
June	1st to 10th	Day	10% 4 2 5% 4 3 5% 4 6% 7% 49%	3061
	11th to 20th	Day	11% 6% 2 5% 4 4 4 4 6% 8% 47%	3150
	21st to end	Day	8% 4 2 5% 3 4 4 4 7% 8% 50%	3150
July	1st to 10th	Day	8% 4 2 6% 4 4 5% 5% 7% 9% 47%	6623
	11th to 20th	Day	9% 5% 2 6% 3 3 4 3 5% 7% 53%	6422
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 7% 8% 50%	6553
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 6% 8% 48%	4234
	11th to 20th	Day	16% 7% 3 6% 4 4 4 4 6% 6% 39%	4171
	21st to end	Day	8% 5% 2 5% 4 4 3 3 5% 7% 55%	4675
September	1st to 10th	Day	13% 5% 2 4 3 3 4 3 4 5% 53%	2292
	11th to 20th	Day	8% 5% 2 4 3 4 4 3 5% 8% 55%	2200
	21st to end	Day	10% 4 1 4 3 3 3 3 5% 7% 57%	2200
October	1st to 10th	Day	14% 5% 2 5% 3 3 3 3 4 5% 54%	2095
	11th to 20th	Day	12% 7% 2 5% 3 2 3 3 5% 6% 53%	2000
	21st to end	Day	15% 7% 2 5% 3 3 4 3 4 5% 48%	2090
November	1st to 10th	Day	9% 7% 2 5% 4 3 5% 4 5% 8% 48%	1853
	11th to 20th	Day	9% 7% 2 7% 5% 4 4 4 5% 7% 46%	1834
	21st to end	Day	10% 9% 3 8% 4 4 4 4 5% 7% 43%	1680
December	1st to 10th	Day	5% 7% 3 8% 7% 6% 5% 3 5% 8% 43%	2690
	11th to 20th	Day	8% 10% 4 9% 5% 5% 5% 4 5% 7% 37%	3018
	21st to end	Day	13% 9% 4 15% 5% 4 4 3 5% 7% 31%	3669
January	1st to 10th	Night	8% 10% 5% 12% 8% 7% 6% 4 6% 7% 28%	8201
	11th to 20th	Night	3 8% 4 10% 6% 6% 6% 4 8% 7% 38%	8065
	21st to end	Night	3 8% 5% 10% 5% 4 5% 4 6% 6% 44%	8402
February	1st to 10th	Night	9% 11% 4 9% 6% 5% 5% 4 5% 6% 38%	2730
	11th to 20th	Night	8% 11% 4 8% 4 3 4 3 5% 7% 42%	2605
	21st to end	Night	8% 8% 3 6% 4 4 5% 4 5% 6% 47%	2076
March	1st to 10th	Night	13% 5% 2 5% 3 3 3 3 5% 6% 53%	5270
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 5% 8% 52%	5090
	21st to end	Night	17% 9% 3 8% 5% 4 4 4 5% 6% 36%	5588
April	1st to 10th	Night	14% 8% 2 6% 4 4 4 4 5% 7% 43%	2242
	11th to 20th	Night	14% 6% 2 6% 4 4 3 3 6% 6% 46%	1869
	21st to end	Night	17% 7% 2 6% 5% 3 4 3 5% 5% 43%	1890
May	1st to 10th	Night	10% 4 1 5% 3 3 4 3 6% 8% 53%	5266
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 6% 6% 52%	5265
	21st to end	Night	16% 7% 2 6% 4 4 3 4 5% 7% 40%	5504
June	1st to 10th	Night	7% 6% 2 3 3 4 3 3 6% 10% 54%	1554
	11th to 20th	Night	7% 5% 1 4 3 5% 3 4 6% 10% 52%	1470
	21st to end	Night	9% 3 1 4 3 3 4 3 6% 8% 55%	1470
July	1st to 10th	Night	7% 5% 2 6% 4 4 3 3 6% 9% 52%	3569
	11th to 20th	Night	8% 5% 2 5% 3 4 4 3 4 7% 57%	3762
	21st to end	Night	6% 3 1 4 3 4 4 4 6% 10% 55%	4539
August	1st to 10th	Night	5% 5% 2 6% 4 4 4 4 7% 9% 49%	2926
	11th to 20th	Night	10% 5% 2 5% 3 4 4 4 6% 9% 49%	2888
	21st to end	Night	7% 3 2 6% 3 3 4 3 6% 8% 55%	3234
September	1st to 10th	Night	8% 4 1 5% 2 3 4 3 5% 6% 60%	2101
	11th to 20th	Night	8% 3 2 4 3 2 3 3 5% 8% 58%	2200
	21st to end	Night	8% 4 1 4 3 3 4 3 4 7% 61%	2200
October	1st to 10th	Night	15% 4 2 5% 3 3 3 3 4 5% 54%	2285
	11th to 20th	Night	11% 5% 3 4 3 3 4 3 5% 5% 55%	2400
	21st to end	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	2745
November	1st to 10th	Night	8% 5% 2 5% 4 3 4 3 4 8% 54%	2665
	11th to 20th	Night	8% 6% 2 6% 4 4 4 3 6% 6% 49%	2783
	21st to end	Night	9% 7% 2 5% 4 4 4 4 7% 7% 48%	2940
December	1st to 10th	Night	5% 7% 4 8% 5% 5% 5% 3 5% 6% 47%	4720
	11th to 20th	Night	8% 9% 4 9% 6% 5% 5% 4 5% 8% 38%	5401
	21st to end	Night	15% 11% 4 11% 5% 4 3 3 5% 5% 32%	7533

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	49% 21% 11% 12% 5% 1	4723
	11th to 20th	Day	40% 20% 10% 16% 13%	4908
	21st to end	Day	34% 23% 15% 18% 9% 2	5812
February	1st to 10th	Day	24% 61% 6% 6% 3	1890
	11th to 20th	Day	20% 58% 4 11% 6% 1	1928
	21st to end	Day	17% 59% 5% 9% 9% 1	1730
March	1st to 10th	Day	27% 28% 6% 24% 13% 2	4814
	11th to 20th	Day	21% 27% 6% 23% 19% 2	5090
	21st to end	Day	45% 28% 9% 13% 3 1	5585
April	1st to 10th	Day	21% 59% 5% 10% 5%	2374
	11th to 20th	Day	18% 60% 5% 11% 5% 1	2702
	21st to end	Day	21% 59% 4 9% 7%	2730
May	1st to 10th	Day	23% 23% 7% 24% 22% 1	7655
	11th to 20th	Day	29% 23% 7% 18% 15% 8%	7631
	21st to end	Day	37% 23% 7% 20% 11% 1	8680
June	1st to 10th	Day	12% 59% 7% 14% 7% 1	3061
	11th to 20th	Day	15% 60% 7% 11% 6% 1	3150
	21st to end	Day	15% 59% 6% 13% 6% 1	3150
July	1st to 10th	Day	26% 28% 14% 22% 10% 1	6554
	11th to 20th	Day	26% 27% 10% 25% 12% 1	6347
	21st to end	Day	25% 28% 14% 19% 12% 2	6371
August	1st to 10th	Day	23% 37% 9% 20% 9% 1	4220
	11th to 20th	Day	33% 39% 8% 15% 5%	4210
	21st to end	Day	22% 38% 12% 17% 11% 1	4674
September	1st to 10th	Day	15% 58% 6% 15% 6%	2292
	11th to 20th	Day	11% 58% 7% 17% 7% 1	2200
	21st to end	Day	15% 58% 4 13% 10% 2	2200
October	1st to 10th	Day	12% 35% 4 16% 30% 4	3407
	11th to 20th	Day	14% 36% 11% 19% 15% 5%	3240
	21st to end	Day	23% 36% 8% 19% 13% 2	3359
November	1st to 10th	Day	20% 54% 8% 12% 7%	1853
	11th to 20th	Day	16% 55% 7% 14% 7% 2	1834
	21st to end	Day	23% 55% 5% 10% 6% 1	1680
December	1st to 10th	Day	26% 35% 11% 20% 7% 1	2690
	11th to 20th	Day	33% 32% 13% 16% 7%	3015
	21st to end	Day	41% 26% 9% 19% 4	3669
January	1st to 10th	Night	47% 21% 12% 14% 6% 1	8202
	11th to 20th	Night	34% 21% 12% 17% 14% 1	8065
	21st to end	Night	29% 22% 13% 22% 14%	8402
February	1st to 10th	Night	20% 60% 7% 8% 5% 1	2730
	11th to 20th	Night	20% 58% 6% 9% 5% 2	2606
	21st to end	Night	14% 59% 5% 11% 9% 3	2076
March	1st to 10th	Night	21% 29% 6% 23% 20% 1	5270
	11th to 20th	Night	21% 28% 6% 22% 20% 3	5090
	21st to end	Night	36% 29% 11% 18% 5% 1	5588
April	1st to 10th	Night	18% 60% 6% 10% 5% 1	2242
	11th to 20th	Night	15% 61% 4 12% 8% 1	1869
	21st to end	Night	18% 59% 6% 9% 7% 1	1890
May	1st to 10th	Night	22% 23% 7% 23% 23% 2	5293
	11th to 20th	Night	26% 23% 8% 15% 21% 8%	5266
	21st to end	Night	34% 23% 9% 22% 11% 1	5515
June	1st to 10th	Night	9% 60% 7% 13% 9% 2	1554
	11th to 20th	Night	13% 60% 6% 10% 9% 1	1470
	21st to end	Night	13% 58% 8% 13% 6% 1	1470
July	1st to 10th	Night	24% 27% 14% 25% 9% 2	3531
	11th to 20th	Night	24% 26% 9% 28% 11% 1	3717
	21st to end	Night	19% 28% 17% 22% 11% 2	4410
August	1st to 10th	Night	21% 38% 10% 21% 10% 1	2916
	11th to 20th	Night	25% 39% 11% 18% 7% 1	2915
	21st to end	Night	20% 39% 12% 15% 13% 1	3234
September	1st to 10th	Night	12% 58% 7% 13% 10% 1	2101
	11th to 20th	Night	11% 57% 7% 16% 9% 1	2200
	21st to end	Night	13% 58% 4 12% 12% 1	2200
October	1st to 10th	Night	9% 35% 3 12% 37% 4	3740
	11th to 20th	Night	11% 35% 7% 22% 20% 4	3899
	21st to end	Night	24% 36% 7% 21% 12%	4432
November	1st to 10th	Night	16% 54% 8% 13% 8% 1	2665
	11th to 20th	Night	14% 54% 7% 14% 9% 2	2783
	21st to end	Night	18% 54% 8% 14% 6%	2940
December	1st to 10th	Night	24% 35% 9% 24% 8%	4720
	11th to 20th	Night	32% 32% 9% 20% 6%	5403
	21st to end	Night	43% 26% 9% 16% 5%	7533

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% 12% 30% 28% 10% 3	330
	11th to 20th	Day	15% 15% 34% 29% 6% 1	330
	21st to end	Day	12% 10% 42% 26% 9% 1	363
February	1st to 10th	Day	10% 18% 42% 26% 4	330
	11th to 20th	Day	15% 12% 38% 25% 9% 1	330
	21st to end	Day	16% 14% 38% 25% 6%	273
March	1st to 10th	Day	16% 11% 44% 25% 3 2	330
	11th to 20th	Day	18% 13% 37% 21% 10% 1	330
	21st to end	Day	27% 13% 37% 18% 4 1	363
April	1st to 10th	Day	22% 19% 37% 18% 4	394
	11th to 20th	Day	24% 15% 31% 24% 5%	740
	21st to end	Day	26% 11% 32% 21% 8% 2	750
May	1st to 10th	Day	16% 13% 33% 25% 11% 2	753
	11th to 20th	Day	20% 10% 29% 23% 15% 2	775
	21st to end	Day	20% 8% 29% 28% 12% 3	844
June	1st to 10th	Day	9% 8% 24% 33% 21% 5%	780
	11th to 20th	Day	12% 7% 36% 29% 14% 2	780
	21st to end	Day	11% 7% 29% 35% 15% 2	780
July	1st to 10th	Day	6% 3 21% 36% 27% 6%	771
	11th to 20th	Day	7% 4 23% 42% 19% 4	768
	21st to end	Day	6% 4 24% 44% 18% 4	845
August	1st to 10th	Day	9% 4 21% 41% 21% 3	726
	11th to 20th	Day	11% 4 24% 35% 21% 6%	715
	21st to end	Day	8% 4 26% 36% 23% 3	803
September	1st to 10th	Day	16% 5% 27% 30% 18% 4	422
	11th to 20th	Day	8% 5% 35% 32% 17% 3	330
	21st to end	Day	15% 10% 29% 27% 13% 6%	330
October	1st to 10th	Day	17% 9% 28% 27% 15% 4	330
	11th to 20th	Day	18% 15% 36% 22% 8% 1	330
	21st to end	Day	20% 15% 33% 23% 8% 1	363
November	1st to 10th	Day	19% 10% 34% 26% 8% 3	330
	11th to 20th	Day	13% 17% 39% 25% 6%	330
	21st to end	Day	19% 17% 31% 21% 11% 1	330
December	1st to 10th	Day	12% 11% 35% 30% 9% 2	330
	11th to 20th	Day	16% 13% 40% 23% 8%	330
	21st to end	Day	20% 9% 37% 26% 6%	363
January	1st to 10th	Night	12% 11% 36% 32% 9%	1050
	11th to 20th	Night	11% 15% 35% 30% 7% 1	1050
	21st to end	Night	12% 9% 41% 31% 8%	1155
February	1st to 10th	Night	15% 11% 39% 30% 5%	1050
	11th to 20th	Night	13% 11% 39% 32% 5%	971
	21st to end	Night	14% 10% 36% 32% 8% 1	692
March	1st to 10th	Night	13% 10% 42% 29% 6% 1	746
	11th to 20th	Night	17% 11% 38% 29% 6%	630
	21st to end	Night	17% 9% 41% 25% 6%	693
April	1st to 10th	Night	18% 13% 39% 27% 3	630
	11th to 20th	Night	17% 13% 36% 26% 6%	623
	21st to end	Night	19% 10% 37% 27% 6% 1	630
May	1st to 10th	Night	14% 9% 34% 33% 10%	630
	11th to 20th	Night	16% 9% 30% 35% 10%	621
	21st to end	Night	20% 5% 30% 35% 10%	683
June	1st to 10th	Night	9% 6% 26% 41% 17%	630
	11th to 20th	Night	9% 5% 33% 41% 11% 1	630
	21st to end	Night	9% 5% 26% 46% 14%	630
July	1st to 10th	Night	6% 4 18% 46% 25%	615
	11th to 20th	Night	5% 2 20% 55% 17%	612
	21st to end	Night	6% 1 21% 55% 16% 1	687
August	1st to 10th	Night	7% 4 23% 46% 19% 1	597
	11th to 20th	Night	8% 4 23% 43% 22% 1	594
	21st to end	Night	7% 3 25% 46% 18% 1	660
September	1st to 10th	Night	9% 5% 25% 43% 17% 1	600
	11th to 20th	Night	8% 5% 31% 40% 14% 2	600
	21st to end	Night	10% 6% 36% 33% 15% 1	600
October	1st to 10th	Night	17% 8% 31% 32% 11% 1	685
	11th to 20th	Night	15% 11% 37% 29% 7% 1	800
	21st to end	Night	16% 13% 33% 30% 8%	985
November	1st to 10th	Night	11% 10% 37% 33% 9% 1	1025
	11th to 20th	Night	12% 11% 38% 32% 6%	1050
	21st to end	Night	11% 11% 34% 34% 9%	1050
December	1st to 10th	Night	12% 10% 38% 32% 7%	1050
	11th to 20th	Night	14% 9% 35% 34% 8% 1	1050
	21st to end	Night	20% 10% 36% 28% 6%	1155

Page generated at 2026-07-28 02:25:19. Version ac07

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