Sioux Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sioux Falls clear sky chart from 2005-11-06 to 2025-07-06.

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	12% 7% 3 7% 5% 4 4 4 5% 7% 41%	119898
	Night	10% 7% 3 7% 4 4 4 4 5% 7% 44%	119124
Transparency	Day	26% 41% 8% 16% 9% 1	123504
	Night	24% 39% 8% 17% 10% 1	123640
Seeing	Day	15% 11% 32% 28% 12% 2	16849
	Night	13% 9% 35% 33% 10% 1	26765

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	10% 13% 4 15% 10% 8% 7% 4 5% 5% 20%	3472
	11th to 20th	Day	5% 11% 5% 10% 7% 6% 8% 4 9% 9% 26%	3834
	21st to end	Day	5% 10% 6% 12% 7% 6% 6% 5% 4 6% 34%	4488
February	1st to 10th	Day	8% 13% 4 12% 7% 8% 6% 4 5% 6% 26%	1800
	11th to 20th	Day	8% 11% 5% 9% 7% 6% 6% 4 6% 5% 34%	1769
	21st to end	Day	10% 10% 4 8% 4 5% 5% 4 5% 7% 38%	1650
March	1st to 10th	Day	11% 7% 3 8% 4 3 3 3 4 7% 47%	4760
	11th to 20th	Day	8% 7% 3 6% 3 3 4 3 5% 8% 50%	4980
	21st to end	Day	22% 11% 4 10% 4 5% 4 4 5% 6% 25%	5462
April	1st to 10th	Day	16% 8% 3 6% 5% 4 5% 4 6% 7% 37%	2265
	11th to 20th	Day	18% 9% 3 6% 4 4 4 3 5% 6% 37%	2572
	21st to end	Day	22% 8% 2 6% 4 3 4 3 5% 7% 37%	2600
May	1st to 10th	Day	12% 5% 2 5% 3 4 4 4 6% 8% 48%	5862
	11th to 20th	Day	17% 7% 2 5% 3 3 3 2 4 5% 48%	5862
	21st to end	Day	18% 8% 3 6% 5% 4 5% 3 5% 7% 36%	6931
June	1st to 10th	Day	12% 5% 2 5% 3 4 4 3 6% 8% 48%	2898
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 4 5% 7% 44%	3000
	21st to end	Day	9% 5% 2 5% 4 4 4 4 7% 9% 48%	3000
July	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 5% 7% 9% 42%	4826
	11th to 20th	Day	7% 3 1 4 3 3 4 4 5% 7% 59%	4363
	21st to end	Day	4 3 2 4 4 4 5% 5% 7% 10% 52%	4465
August	1st to 10th	Day	8% 5% 3 6% 4 5% 5% 5% 7% 9% 45%	4104
	11th to 20th	Day	16% 7% 2 7% 4 4 5% 4 7% 8% 36%	4041
	21st to end	Day	9% 4 2 6% 4 4 4 3 5% 8% 52%	4532
September	1st to 10th	Day	14% 5% 1 4 3 3 3 3 4 6% 53%	2215
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 4 7% 55%	2090
	21st to end	Day	10% 4 2 4 5% 3 3 3 6% 7% 53%	2090
October	1st to 10th	Day	16% 7% 1 5% 3 3 3 3 5% 6% 48%	1955
	11th to 20th	Day	13% 7% 2 5% 3 3 4 2 4 5% 53%	1900
	21st to end	Day	15% 8% 3 6% 3 3 3 3 4 6% 46%	2012
November	1st to 10th	Day	11% 7% 3 5% 4 4 3 3 7% 8% 44%	1763
	11th to 20th	Day	9% 8% 2 11% 6% 5% 4 3 4 6% 41%	1648
	21st to end	Day	11% 9% 3 8% 4 4 5% 4 5% 7% 40%	1600
December	1st to 10th	Day	4 8% 4 11% 7% 5% 5% 4 6% 8% 39%	2610
	11th to 20th	Day	8% 13% 5% 11% 6% 6% 7% 4 6% 6% 27%	2981
	21st to end	Day	17% 9% 4 17% 6% 3 4 3 6% 7% 25%	3498
January	1st to 10th	Night	8% 11% 4 14% 10% 7% 6% 4 5% 7% 25%	6488
	11th to 20th	Night	4 8% 3 10% 7% 6% 7% 5% 8% 8% 34%	6141
	21st to end	Night	4 9% 5% 10% 5% 5% 5% 4 6% 7% 40%	6490
February	1st to 10th	Night	9% 11% 3 10% 6% 5% 4 4 5% 6% 37%	2600
	11th to 20th	Night	7% 10% 4 9% 5% 4 5% 3 5% 7% 40%	2533
	21st to end	Night	8% 8% 3 7% 5% 5% 4 5% 6% 7% 42%	1983
March	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 6% 53%	5101
	11th to 20th	Night	10% 6% 2 5% 3 3 4 4 6% 9% 49%	4980
	21st to end	Night	20% 11% 3 7% 5% 4 4 3 5% 6% 33%	5467
April	1st to 10th	Night	14% 8% 3 6% 4 4 4 5% 5% 6% 40%	2131
	11th to 20th	Night	17% 8% 2 6% 4 3 4 2 4 6% 45%	1779
	21st to end	Night	16% 8% 3 6% 4 3 5% 3 6% 6% 40%	1800
May	1st to 10th	Night	12% 5% 2 4 3 3 3 3 5% 6% 55%	4053
	11th to 20th	Night	12% 7% 2 4 3 4 4 3 5% 6% 51%	4053
	21st to end	Night	18% 6% 2 6% 4 4 3 3 5% 7% 42%	3943
June	1st to 10th	Night	8% 5% 2 5% 3 3 5% 3 6% 7% 54%	1496
	11th to 20th	Night	7% 4 1 5% 4 4 4 3 7% 8% 52%	1400
	21st to end	Night	8% 4 1 3 4 3 3 4 5% 9% 56%	1400
July	1st to 10th	Night	9% 5% 2 5% 3 3 4 4 5% 9% 51%	2255
	11th to 20th	Night	5% 2 1 3 3 3 3 3 5% 6% 66%	2589
	21st to end	Night	3 3 1 3 3 3 4 3 7% 10% 59%	3098
August	1st to 10th	Night	6% 6% 2 5% 4 5% 6% 5% 6% 8% 48%	2836
	11th to 20th	Night	12% 5% 2 4 4 4 3 3 5% 8% 50%	2798
	21st to end	Night	8% 3 1 5% 3 3 3 4 6% 8% 55%	3135
September	1st to 10th	Night	8% 3 1 4 3 2 3 3 5% 6% 59%	1960
	11th to 20th	Night	8% 5% 2 4 3 3 4 3 5% 7% 57%	2090
	21st to end	Night	9% 4 2 3 3 2 3 3 5% 6% 59%	2090
October	1st to 10th	Night	15% 5% 1 4 3 2 3 3 4 6% 54%	2205
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 6% 53%	2280
	21st to end	Night	13% 8% 2 6% 3 3 3 2 4 7% 49%	2584
November	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 7% 51%	2535
	11th to 20th	Night	9% 6% 2 8% 4 3 4 4 6% 7% 46%	2750
	21st to end	Night	9% 8% 3 7% 4 4 3 3 5% 7% 46%	2800
December	1st to 10th	Night	5% 7% 5% 10% 5% 5% 5% 4 5% 7% 43%	4580
	11th to 20th	Night	9% 9% 4 9% 7% 6% 5% 4 6% 7% 34%	5221
	21st to end	Night	15% 13% 4 14% 6% 4 4 3 4 6% 27%	7480

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	52% 27% 10% 8% 3	3473
	11th to 20th	Day	39% 27% 7% 14% 13%	3834
	21st to end	Day	33% 31% 12% 15% 9%	4488
February	1st to 10th	Day	24% 63% 4 5% 5%	1800
	11th to 20th	Day	20% 62% 4 9% 5% 1	1778
	21st to end	Day	16% 62% 4 9% 8%	1650
March	1st to 10th	Day	25% 29% 8% 27% 9% 2	4760
	11th to 20th	Day	20% 29% 6% 28% 15% 2	4980
	21st to end	Day	45% 30% 9% 12% 3 1	5464
April	1st to 10th	Day	19% 62% 5% 9% 4 1	2265
	11th to 20th	Day	18% 63% 4 10% 4 1	2572
	21st to end	Day	20% 62% 4 8% 6%	2600
May	1st to 10th	Day	19% 31% 8% 22% 20%	5900
	11th to 20th	Day	28% 29% 6% 16% 12% 9%	5866
	21st to end	Day	35% 31% 6% 17% 11%	6945
June	1st to 10th	Day	10% 63% 6% 13% 6% 1	2898
	11th to 20th	Day	17% 63% 6% 10% 4	3000
	21st to end	Day	15% 61% 6% 12% 5% 1	3000
July	1st to 10th	Day	28% 39% 13% 14% 7% 1	4752
	11th to 20th	Day	16% 38% 9% 26% 11%	4287
	21st to end	Day	17% 38% 13% 18% 14% 1	4325
August	1st to 10th	Day	24% 39% 8% 20% 9%	4090
	11th to 20th	Day	33% 39% 9% 15% 3	4080
	21st to end	Day	23% 40% 14% 16% 7%	4531
September	1st to 10th	Day	15% 60% 5% 15% 5%	2215
	11th to 20th	Day	11% 60% 8% 15% 6%	2090
	21st to end	Day	15% 61% 4 11% 8% 1	2090
October	1st to 10th	Day	14% 37% 4 20% 23% 3	3241
	11th to 20th	Day	18% 37% 9% 16% 16% 3	3140
	21st to end	Day	27% 37% 8% 15% 13% 1	3293
November	1st to 10th	Day	21% 56% 6% 10% 6%	1763
	11th to 20th	Day	19% 57% 5% 13% 6% 1	1648
	21st to end	Day	23% 57% 5% 9% 6%	1600
December	1st to 10th	Day	27% 36% 10% 20% 6% 1	2610
	11th to 20th	Day	39% 33% 12% 12% 4	2978
	21st to end	Day	44% 27% 10% 13% 5%	3498
January	1st to 10th	Night	47% 27% 8% 12% 6%	6488
	11th to 20th	Night	32% 27% 12% 12% 16% 1	6141
	21st to end	Night	29% 31% 10% 18% 12%	6490
February	1st to 10th	Night	20% 62% 6% 6% 6%	2600
	11th to 20th	Night	20% 60% 4 9% 6% 1	2534
	21st to end	Night	13% 62% 5% 9% 9% 2	1983
March	1st to 10th	Night	21% 29% 6% 27% 15% 1	5101
	11th to 20th	Night	20% 29% 8% 26% 15% 2	4980
	21st to end	Night	39% 30% 9% 17% 4 1	5467
April	1st to 10th	Night	18% 63% 5% 9% 4	2131
	11th to 20th	Night	15% 63% 5% 9% 7% 1	1779
	21st to end	Night	18% 62% 3 9% 7% 1	1800
May	1st to 10th	Night	20% 30% 7% 23% 19% 2	4080
	11th to 20th	Night	24% 30% 7% 15% 15% 8%	4054
	21st to end	Night	30% 30% 6% 23% 10%	3951
June	1st to 10th	Night	9% 62% 6% 12% 9% 2	1496
	11th to 20th	Night	13% 63% 6% 12% 6% 1	1400
	21st to end	Night	12% 61% 8% 12% 7% 1	1400
July	1st to 10th	Night	23% 37% 15% 16% 7% 2	2220
	11th to 20th	Night	13% 36% 9% 28% 12% 1	2542
	21st to end	Night	12% 39% 13% 21% 13% 2	2999
August	1st to 10th	Night	24% 39% 9% 17% 10% 1	2826
	11th to 20th	Night	25% 40% 12% 17% 5%	2825
	21st to end	Night	20% 40% 12% 16% 11%	3135
September	1st to 10th	Night	11% 60% 7% 13% 9% 1	1960
	11th to 20th	Night	9% 60% 7% 15% 7% 1	2090
	21st to end	Night	13% 60% 6% 11% 9% 1	2090
October	1st to 10th	Night	10% 36% 3 16% 32% 3	3686
	11th to 20th	Night	12% 36% 9% 21% 19% 2	3779
	21st to end	Night	25% 37% 7% 21% 9%	4245
November	1st to 10th	Night	18% 56% 6% 12% 8%	2535
	11th to 20th	Night	14% 57% 6% 14% 7% 1	2750
	21st to end	Night	19% 57% 6% 13% 6%	2800
December	1st to 10th	Night	26% 36% 11% 21% 6%	4580
	11th to 20th	Night	33% 34% 13% 16% 4	5223
	21st to end	Night	46% 27% 7% 14% 5%	7480

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% 38% 24% 10% 3	300
	11th to 20th	Day	17% 12% 36% 27% 6% 1	300
	21st to end	Day	15% 12% 39% 23% 10% 1	330
February	1st to 10th	Day	14% 19% 40% 25% 2	300
	11th to 20th	Day	12% 17% 41% 22% 8%	300
	21st to end	Day	17% 14% 44% 22% 2	249
March	1st to 10th	Day	19% 14% 41% 20% 5% 1	300
	11th to 20th	Day	20% 14% 36% 20% 8% 1	300
	21st to end	Day	28% 14% 31% 20% 5% 1	330
April	1st to 10th	Day	24% 17% 38% 18% 3	365
	11th to 20th	Day	24% 17% 32% 21% 5% 1	690
	21st to end	Day	26% 15% 28% 21% 9% 2	700
May	1st to 10th	Day	20% 12% 30% 25% 10% 2	703
	11th to 20th	Day	22% 11% 28% 25% 11% 2	725
	21st to end	Day	20% 9% 28% 30% 11% 1	789
June	1st to 10th	Day	9% 9% 26% 33% 20% 3	730
	11th to 20th	Day	14% 8% 35% 29% 11% 3	730
	21st to end	Day	11% 7% 36% 31% 14% 1	730
July	1st to 10th	Day	8% 3 22% 40% 22% 5%	697
	11th to 20th	Day	6% 6% 30% 36% 18% 3	668
	21st to end	Day	5% 3 26% 41% 21% 4	739
August	1st to 10th	Day	10% 4 24% 38% 21% 4	676
	11th to 20th	Day	12% 4 26% 33% 22% 3	665
	21st to end	Day	8% 6% 28% 36% 18% 4	748
September	1st to 10th	Day	15% 8% 27% 30% 17% 3	425
	11th to 20th	Day	10% 7% 34% 34% 13% 3	300
	21st to end	Day	12% 17% 31% 26% 10% 4	300
October	1st to 10th	Day	19% 11% 30% 25% 10% 5%	300
	11th to 20th	Day	13% 19% 35% 25% 8%	300
	21st to end	Day	22% 17% 35% 19% 6% 1	330
November	1st to 10th	Day	21% 12% 35% 23% 8% 2	300
	11th to 20th	Day	16% 19% 41% 18% 7%	300
	21st to end	Day	18% 18% 34% 23% 8%	300
December	1st to 10th	Day	10% 13% 43% 23% 10% 1	300
	11th to 20th	Day	16% 16% 39% 26% 4	300
	21st to end	Day	21% 14% 39% 22% 4	330
January	1st to 10th	Night	11% 11% 38% 30% 9% 1	1000
	11th to 20th	Night	11% 12% 38% 31% 6% 1	1000
	21st to end	Night	14% 10% 41% 28% 7%	1100
February	1st to 10th	Night	13% 13% 40% 29% 6% 1	1000
	11th to 20th	Night	12% 11% 40% 31% 5% 1	979
	21st to end	Night	12% 8% 40% 30% 8% 1	663
March	1st to 10th	Night	14% 10% 41% 28% 6% 1	683
	11th to 20th	Night	16% 13% 38% 30% 4	600
	21st to end	Night	19% 11% 35% 26% 8% 1	660
April	1st to 10th	Night	18% 14% 38% 27% 4	600
	11th to 20th	Night	21% 15% 32% 26% 5% 1	593
	21st to end	Night	20% 14% 33% 25% 8% 1	600
May	1st to 10th	Night	18% 9% 35% 30% 9%	600
	11th to 20th	Night	16% 9% 33% 31% 9% 1	591
	21st to end	Night	17% 6% 32% 32% 13%	650
June	1st to 10th	Night	9% 7% 28% 39% 17% 1	600
	11th to 20th	Night	8% 5% 37% 40% 10% 1	600
	21st to end	Night	10% 5% 26% 47% 13%	600
July	1st to 10th	Night	7% 2 22% 43% 25% 1	570
	11th to 20th	Night	4 2 27% 49% 18%	552
	21st to end	Night	4 2 24% 51% 18% 1	624
August	1st to 10th	Night	7% 3 25% 45% 20% 1	567
	11th to 20th	Night	9% 3 23% 40% 24% 1	564
	21st to end	Night	6% 4 29% 41% 19% 1	627
September	1st to 10th	Night	9% 4 28% 42% 15% 2	570
	11th to 20th	Night	9% 6% 33% 35% 14% 2	570
	21st to end	Night	12% 7% 34% 34% 12% 1	570
October	1st to 10th	Night	16% 9% 35% 28% 12% 1	685
	11th to 20th	Night	16% 12% 36% 29% 7%	760
	21st to end	Night	18% 12% 34% 28% 9%	912
November	1st to 10th	Night	13% 9% 37% 32% 8% 1	975
	11th to 20th	Night	14% 12% 39% 28% 7% 1	1000
	21st to end	Night	13% 11% 38% 31% 7%	1000
December	1st to 10th	Night	13% 11% 38% 32% 6%	1000
	11th to 20th	Night	16% 9% 39% 29% 7%	1000
	21st to end	Night	20% 11% 36% 26% 6% 1	1100

Page generated at 2025-07-03 00:30:13. Version ac07

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