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 2026-10-29.

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% 5% 4 5% 4 6% 7% 42%	149759
	Night	10% 7% 3 7% 4 4 4 4 5% 7% 45%	142676
Transparency	Day	28% 34% 9% 18% 10% 1	153323
	Night	26% 34% 10% 18% 11% 1	147170
Seeing	Day	15% 11% 32% 28% 12% 2	18704
	Night	13% 9% 35% 33% 10% 1	28498

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% 14% 4 15% 9% 7% 6% 4 4 5% 22%	4502
	11th to 20th	Day	4 10% 4 11% 7% 7% 8% 4 8% 9% 27%	4999
	21st to end	Day	4 9% 5% 11% 7% 7% 6% 5% 5% 7% 34%	5812
February	1st to 10th	Day	8% 13% 4 12% 7% 8% 5% 4 5% 7% 26%	1890
	11th to 20th	Day	7% 10% 5% 10% 7% 6% 6% 4 6% 5% 35%	1860
	21st to end	Day	10% 10% 4 8% 4 5% 5% 4 5% 7% 38%	1730
March	1st to 10th	Day	11% 7% 3 8% 4 3 3 3 4 7% 47%	4866
	11th to 20th	Day	8% 7% 3 6% 3 3 4 3 5% 8% 50%	5090
	21st to end	Day	22% 11% 4 10% 4 5% 4 4 5% 6% 25%	5583
April	1st to 10th	Day	17% 8% 3 6% 5% 4 4 4 5% 7% 37%	2378
	11th to 20th	Day	18% 8% 3 6% 4 4 4 3 5% 6% 38%	2702
	21st to end	Day	22% 8% 2 6% 4 3 3 3 5% 7% 37%	2730
May	1st to 10th	Day	9% 4 2 5% 4 4 4 4 6% 8% 50%	7617
	11th to 20th	Day	16% 7% 2 5% 3 3 4 3 5% 6% 47%	7627
	21st to end	Day	19% 8% 3 6% 5% 4 5% 3 5% 7% 36%	9043
June	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 6% 8% 47%	3043
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 7% 44%	3150
	21st to end	Day	9% 5% 2 5% 4 4 4 4 7% 9% 47%	3150
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 41%	8850
	11th to 20th	Day	7% 3 1 4 3 3 3 3 4 7% 61%	8131
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 7% 10% 45%	8337
August	1st to 10th	Day	9% 5% 2 6% 4 4 4 4 6% 8% 47%	6014
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 7% 8% 32%	5948
	21st to end	Day	8% 4 2 5% 4 4 4 3 5% 8% 52%	6593
September	1st to 10th	Day	13% 5% 2 5% 3 3 3 3 4 7% 52%	2448
	11th to 20th	Day	12% 5% 2 5% 3 3 3 3 4 7% 52%	2310
	21st to end	Day	13% 5% 2 4 4 3 3 3 5% 6% 51%	2310
October	1st to 10th	Day	14% 6% 1 4 3 3 3 3 4 6% 50%	2161
	11th to 20th	Day	14% 6% 2 5% 3 3 3 2 4 6% 52%	2100
	21st to end	Day	16% 8% 3 6% 3 3 3 2 4 6% 45%	2197
November	1st to 10th	Day	11% 7% 3 5% 4 4 3 3 6% 8% 44%	1853
	11th to 20th	Day	9% 9% 2 11% 6% 5% 4 3 4 6% 41%	1730
	21st to end	Day	11% 10% 3 8% 5% 4 4 4 5% 7% 39%	1680
December	1st to 10th	Day	4 8% 4 12% 6% 5% 5% 4 6% 8% 38%	2690
	11th to 20th	Day	8% 13% 5% 11% 6% 6% 7% 4 6% 6% 27%	3060
	21st to end	Day	16% 9% 4 17% 6% 3 4 3 6% 7% 25%	3575
January	1st to 10th	Night	7% 10% 4 13% 8% 6% 6% 4 5% 7% 28%	8402
	11th to 20th	Night	3 8% 3 10% 7% 7% 7% 5% 8% 8% 35%	7986
	21st to end	Night	3 8% 4 10% 5% 5% 5% 4 6% 7% 42%	8402
February	1st to 10th	Night	8% 11% 3 10% 6% 5% 5% 4 5% 6% 36%	2730
	11th to 20th	Night	7% 10% 4 8% 5% 4 5% 3 5% 7% 41%	2663
	21st to end	Night	7% 8% 3 7% 5% 5% 4 5% 6% 7% 43%	2079
March	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 7% 52%	5215
	11th to 20th	Night	10% 6% 2 5% 3 3 4 4 6% 8% 49%	5090
	21st to end	Night	19% 10% 3 6% 5% 4 4 3 5% 6% 34%	5588
April	1st to 10th	Night	14% 8% 3 7% 4 4 4 5% 5% 6% 40%	2238
	11th to 20th	Night	17% 7% 2 6% 4 4 4 2 4 6% 45%	1869
	21st to end	Night	16% 8% 4 6% 4 3 4 3 6% 6% 41%	1890
May	1st to 10th	Night	10% 4 2 4 3 3 3 4 6% 7% 54%	5266
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 5% 7% 51%	5265
	21st to end	Night	17% 7% 2 6% 4 4 4 3 5% 7% 40%	5140
June	1st to 10th	Night	8% 4 2 5% 3 3 5% 3 6% 7% 54%	1571
	11th to 20th	Night	7% 4 1 5% 4 4 4 3 6% 8% 53%	1470
	21st to end	Night	8% 4 1 3 4 4 3 4 5% 8% 55%	1470
July	1st to 10th	Night	7% 5% 2 5% 3 4 5% 4 7% 11% 46%	4138
	11th to 20th	Night	7% 3 1 4 2 2 3 3 4 6% 65%	4824
	21st to end	Night	7% 4 2 5% 3 3 4 3 6% 9% 53%	5770
August	1st to 10th	Night	6% 5% 2 5% 3 4 5% 4 6% 8% 52%	4156
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 6% 9% 46%	4118
	21st to end	Night	7% 3 1 5% 3 4 4 4 7% 9% 55%	4555
September	1st to 10th	Night	8% 3 1 4 4 3 3 3 5% 6% 59%	2166
	11th to 20th	Night	9% 5% 2 4 3 3 4 3 5% 7% 55%	2310
	21st to end	Night	11% 5% 2 4 3 2 3 3 4 6% 57%	2310
October	1st to 10th	Night	14% 5% 1 4 3 2 3 3 4 6% 55%	2437
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 4 6% 52%	2520
	21st to end	Night	14% 8% 2 6% 3 3 4 2 4 6% 48%	2818
November	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 7% 51%	2665
	11th to 20th	Night	9% 6% 2 8% 4 3 4 4 6% 7% 45%	2888
	21st to end	Night	9% 8% 3 7% 4 4 3 3 5% 7% 46%	2940
December	1st to 10th	Night	5% 8% 5% 11% 5% 5% 5% 4 5% 7% 42%	4720
	11th to 20th	Night	9% 9% 4 9% 7% 6% 5% 4 6% 7% 34%	5362
	21st to end	Night	15% 13% 4 14% 6% 4 4 3 4 6% 27%	7645

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	54% 21% 9% 9% 4 2	4503
	11th to 20th	Day	41% 21% 8% 16% 14%	4999
	21st to end	Day	35% 25% 12% 19% 10%	5812
February	1st to 10th	Day	25% 60% 5% 5% 5%	1890
	11th to 20th	Day	21% 59% 4 11% 5% 1	1869
	21st to end	Day	18% 59% 4 10% 8%	1730
March	1st to 10th	Day	26% 29% 8% 27% 9% 2	4866
	11th to 20th	Day	20% 28% 6% 28% 15% 2	5090
	21st to end	Day	45% 29% 9% 13% 4 1	5585
April	1st to 10th	Day	21% 60% 5% 10% 4 1	2378
	11th to 20th	Day	20% 60% 5% 11% 4 1	2702
	21st to end	Day	21% 59% 4 9% 7%	2730
May	1st to 10th	Day	20% 25% 7% 23% 24%	7655
	11th to 20th	Day	31% 23% 6% 18% 15% 8%	7631
	21st to end	Day	38% 24% 6% 21% 11% 1	9057
June	1st to 10th	Day	12% 60% 7% 14% 6% 1	3043
	11th to 20th	Day	17% 61% 6% 11% 5%	3150
	21st to end	Day	16% 59% 6% 13% 5% 1	3150
July	1st to 10th	Day	31% 24% 15% 22% 8% 1	8776
	11th to 20th	Day	20% 21% 10% 28% 19% 2	8055
	21st to end	Day	29% 23% 16% 21% 10%	8155
August	1st to 10th	Day	26% 28% 9% 27% 9% 1	6000
	11th to 20th	Day	41% 30% 13% 13% 3	5987
	21st to end	Day	24% 29% 17% 20% 9%	6592
September	1st to 10th	Day	16% 55% 6% 16% 6%	2448
	11th to 20th	Day	15% 55% 8% 15% 6%	2310
	21st to end	Day	19% 55% 4 11% 9% 1	2310
October	1st to 10th	Day	14% 35% 4 22% 23% 3	3447
	11th to 20th	Day	19% 35% 9% 17% 17% 3	3340
	21st to end	Day	28% 35% 8% 15% 13% 1	3478
November	1st to 10th	Day	22% 54% 7% 11% 6%	1853
	11th to 20th	Day	20% 54% 5% 13% 6% 1	1730
	21st to end	Day	25% 54% 5% 10% 6%	1680
December	1st to 10th	Day	28% 35% 10% 20% 6% 1	2690
	11th to 20th	Day	40% 32% 12% 12% 4	3057
	21st to end	Day	43% 26% 11% 13% 5%	3575
January	1st to 10th	Night	46% 22% 12% 14% 6% 1	8403
	11th to 20th	Night	34% 22% 12% 16% 16% 1	7986
	21st to end	Night	29% 24% 12% 22% 13%	8402
February	1st to 10th	Night	21% 59% 7% 7% 6%	2730
	11th to 20th	Night	21% 58% 4 11% 6% 1	2664
	21st to end	Night	14% 59% 5% 11% 10% 2	2079
March	1st to 10th	Night	22% 29% 6% 27% 15% 1	5215
	11th to 20th	Night	20% 29% 8% 26% 15% 2	5090
	21st to end	Night	38% 30% 10% 17% 5% 1	5588
April	1st to 10th	Night	20% 60% 6% 10% 4	2238
	11th to 20th	Night	16% 60% 5% 10% 8% 1	1869
	21st to end	Night	19% 59% 3 9% 8% 1	1890
May	1st to 10th	Night	22% 24% 6% 27% 20% 1	5293
	11th to 20th	Night	26% 24% 6% 16% 20% 8%	5266
	21st to end	Night	34% 24% 7% 23% 11% 1	5150
June	1st to 10th	Night	10% 59% 7% 13% 9% 2	1571
	11th to 20th	Night	14% 60% 6% 12% 8% 1	1470
	21st to end	Night	14% 58% 8% 13% 7% 1	1470
July	1st to 10th	Night	27% 23% 17% 23% 10% 1	4105
	11th to 20th	Night	19% 21% 10% 28% 22% 1	4780
	21st to end	Night	24% 23% 19% 24% 9% 1	5641
August	1st to 10th	Night	23% 27% 11% 24% 13% 1	4146
	11th to 20th	Night	29% 30% 20% 16% 4	4145
	21st to end	Night	21% 29% 16% 21% 12%	4555
September	1st to 10th	Night	13% 55% 8% 14% 9% 1	2166
	11th to 20th	Night	14% 55% 8% 16% 6% 1	2310
	21st to end	Night	17% 55% 6% 11% 10% 1	2310
October	1st to 10th	Night	10% 34% 4 18% 32% 3	3918
	11th to 20th	Night	14% 34% 9% 21% 20% 2	4019
	21st to end	Night	27% 35% 8% 21% 9%	4479
November	1st to 10th	Night	19% 53% 7% 13% 8%	2665
	11th to 20th	Night	15% 54% 7% 15% 7% 1	2888
	21st to end	Night	20% 54% 6% 14% 5%	2940
December	1st to 10th	Night	27% 35% 11% 21% 6%	4720
	11th to 20th	Night	34% 33% 13% 16% 4	5364
	21st to end	Night	46% 27% 8% 14% 5%	7645

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% 10% 37% 25% 10% 3	330
	11th to 20th	Day	17% 12% 38% 26% 6% 1	330
	21st to end	Day	14% 12% 41% 22% 10% 1	363
February	1st to 10th	Day	13% 19% 41% 23% 3 1	330
	11th to 20th	Day	13% 15% 40% 24% 8%	330
	21st to end	Day	17% 16% 43% 21% 3	273
March	1st to 10th	Day	20% 14% 41% 19% 5% 1	330
	11th to 20th	Day	21% 14% 36% 20% 8% 1	330
	21st to end	Day	27% 16% 33% 18% 6% 1	363
April	1st to 10th	Day	25% 17% 37% 18% 3	398
	11th to 20th	Day	24% 17% 33% 21% 5% 1	740
	21st to end	Day	26% 15% 28% 21% 8% 1	750
May	1st to 10th	Day	19% 12% 31% 25% 10% 2	753
	11th to 20th	Day	22% 11% 28% 25% 11% 2	775
	21st to end	Day	20% 9% 28% 30% 11% 2	844
June	1st to 10th	Day	9% 9% 27% 32% 19% 3	780
	11th to 20th	Day	14% 9% 35% 28% 11% 3	780
	21st to end	Day	11% 7% 36% 30% 14% 2	780
July	1st to 10th	Day	7% 4 22% 39% 23% 5%	771
	11th to 20th	Day	6% 6% 30% 36% 18% 4	768
	21st to end	Day	6% 3 26% 42% 19% 3	849
August	1st to 10th	Day	10% 5% 24% 38% 20% 3	776
	11th to 20th	Day	12% 4 28% 32% 21% 3	765
	21st to end	Day	7% 5% 28% 38% 18% 4	858
September	1st to 10th	Day	13% 10% 28% 30% 16% 3	498
	11th to 20th	Day	14% 7% 36% 30% 11% 3	360
	21st to end	Day	16% 15% 28% 24% 12% 5%	360
October	1st to 10th	Day	16% 11% 31% 27% 11% 4	360
	11th to 20th	Day	16% 18% 35% 24% 8%	360
	21st to end	Day	23% 16% 34% 19% 6% 1	387
November	1st to 10th	Day	20% 11% 38% 22% 7% 2	330
	11th to 20th	Day	15% 18% 42% 18% 7%	330
	21st to end	Day	18% 18% 34% 22% 8% 1	330
December	1st to 10th	Day	10% 13% 42% 24% 9% 1	330
	11th to 20th	Day	16% 17% 38% 25% 4	330
	21st to end	Day	20% 13% 41% 23% 4	363
January	1st to 10th	Night	11% 10% 38% 31% 9% 1	1050
	11th to 20th	Night	11% 13% 38% 31% 6% 1	1050
	21st to end	Night	14% 11% 41% 28% 7%	1155
February	1st to 10th	Night	12% 12% 40% 29% 6% 1	1050
	11th to 20th	Night	12% 11% 40% 31% 5% 1	1029
	21st to end	Night	12% 9% 41% 30% 8% 1	695
March	1st to 10th	Night	14% 10% 42% 27% 6% 1	717
	11th to 20th	Night	17% 12% 38% 29% 3	630
	21st to end	Night	18% 11% 36% 26% 8% 1	693
April	1st to 10th	Night	18% 13% 39% 26% 4	630
	11th to 20th	Night	20% 15% 32% 26% 5% 1	623
	21st to end	Night	20% 14% 33% 25% 8% 1	630
May	1st to 10th	Night	17% 9% 35% 31% 8%	630
	11th to 20th	Night	16% 10% 33% 31% 8% 1	621
	21st to end	Night	18% 6% 32% 32% 12%	683
June	1st to 10th	Night	9% 7% 29% 38% 16% 1	630
	11th to 20th	Night	8% 5% 38% 39% 10%	630
	21st to end	Night	10% 5% 26% 46% 12%	630
July	1st to 10th	Night	7% 2 22% 44% 25% 1	615
	11th to 20th	Night	5% 2 26% 49% 18%	612
	21st to end	Night	6% 3 24% 50% 17% 1	690
August	1st to 10th	Night	6% 3 25% 47% 18% 1	627
	11th to 20th	Night	9% 4 23% 40% 23% 1	624
	21st to end	Night	6% 4 27% 44% 18% 1	693
September	1st to 10th	Night	9% 4 26% 43% 15% 2	630
	11th to 20th	Night	11% 6% 32% 36% 13% 2	630
	21st to end	Night	14% 8% 32% 33% 13% 1	630
October	1st to 10th	Night	15% 9% 35% 29% 11% 1	757
	11th to 20th	Night	16% 13% 35% 29% 7%	840
	21st to end	Night	19% 12% 34% 27% 8%	994
November	1st to 10th	Night	12% 10% 38% 31% 8% 1	1025
	11th to 20th	Night	13% 12% 40% 28% 7%	1050
	21st to end	Night	13% 11% 37% 31% 8%	1050
December	1st to 10th	Night	13% 11% 38% 32% 6%	1050
	11th to 20th	Night	16% 9% 39% 28% 7%	1050
	21st to end	Night	20% 11% 37% 26% 6% 1	1155

Page generated at 2026-10-26 03:37:48. Version ac07

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