Soapstone Prairie Natural Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Soapstone Prairie Natural Area clear sky chart from 2005-11-06 to 2025-11-18.

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	6% 6% 2 5% 4 4 5% 4 6% 8% 51%	135777
	Night	5% 6% 2 5% 4 3 4 3 5% 7% 56%	132053
Transparency	Day	30% 5% 10% 23% 22% 9%	130700
	Night	28% 5% 12% 25% 23% 8%	128134
Seeing	Day	12% 13% 30% 28% 14% 3	17100
	Night	9% 15% 28% 34% 12% 2	27095

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% 3 10% 5% 4 3 3 5% 7% 52%	3638
	11th to 20th	Day	1 4 2 7% 5% 5% 5% 3 6% 8% 54%	3640
	21st to end	Day	1 4 2 6% 3 3 3 3 5% 7% 63%	4492
February	1st to 10th	Day	2 6% 2 9% 4 4 4 4 6% 8% 52%	1800
	11th to 20th	Day	1 6% 2 6% 4 4 4 4 6% 9% 54%	1893
	21st to end	Day	1 7% 2 7% 4 3 3 3 5% 6% 57%	1650
March	1st to 10th	Day	3 11% 3 6% 3 3 3 3 5% 7% 53%	4500
	11th to 20th	Day	3 8% 3 6% 5% 4 5% 4 6% 7% 48%	4924
	21st to end	Day	5% 9% 3 6% 4 4 4 4 7% 9% 44%	5828
April	1st to 10th	Day	5% 7% 2 6% 3 4 4 5% 6% 7% 51%	2400
	11th to 20th	Day	8% 12% 4 6% 4 4 5% 4 5% 7% 42%	2371
	21st to end	Day	10% 9% 2 6% 4 5% 5% 4 7% 8% 40%	2400
May	1st to 10th	Day	12% 8% 3 6% 5% 4 5% 4 5% 6% 42%	5945
	11th to 20th	Day	9% 6% 2 5% 4 6% 5% 5% 7% 8% 42%	6298
	21st to end	Day	11% 7% 2 5% 4 4 5% 5% 7% 8% 42%	6925
June	1st to 10th	Day	6% 5% 1 5% 4 5% 5% 6% 8% 8% 46%	2800
	11th to 20th	Day	7% 4 1 4 4 4 6% 6% 6% 8% 49%	2800
	21st to end	Day	4 3 1 5% 4 4 6% 6% 7% 8% 51%	2800
July	1st to 10th	Day	5% 3 1 4 4 4 5% 5% 8% 10% 51%	6339
	11th to 20th	Day	5% 3 1 5% 4 5% 7% 6% 9% 9% 45%	6340
	21st to end	Day	7% 4 2 6% 5% 5% 5% 5% 7% 9% 44%	6903
August	1st to 10th	Day	9% 3 2 5% 4 5% 6% 5% 8% 10% 44%	5789
	11th to 20th	Day	3 2 1 5% 4 5% 5% 5% 7% 8% 54%	5437
	21st to end	Day	10% 5% 2 6% 4 5% 5% 4 7% 7% 45%	5984
September	1st to 10th	Day	7% 4 1 4 3 4 4 3 6% 6% 58%	2400
	11th to 20th	Day	7% 4 1 3 3 4 4 4 6% 8% 56%	2380
	21st to end	Day	7% 4 1 3 2 3 3 3 4 6% 63%	2200
October	1st to 10th	Day	6% 5% 1 2 2 2 2 2 3 4 73%	3277
	11th to 20th	Day	5% 5% 2 5% 3 3 4 3 5% 6% 59%	3250
	21st to end	Day	5% 6% 2 4 2 2 3 2 5% 6% 62%	3369
November	1st to 10th	Day	3 4 1 5% 2 3 4 3 5% 8% 61%	1853
	11th to 20th	Day	2 6% 2 3 3 3 3 3 5% 8% 62%	1863
	21st to end	Day	2 6% 3 4 3 3 3 4 6% 8% 57%	1639
December	1st to 10th	Day	1 4 2 4 2 3 2 2 3 6% 71%	2620
	11th to 20th	Day	2 5% 2 5% 2 2 2 2 4 7% 65%	3026
	21st to end	Day	2 5% 3 7% 4 5% 5% 4 5% 7% 51%	4004
January	1st to 10th	Night	2 8% 3 7% 4 3 4 3 5% 7% 53%	6327
	11th to 20th	Night	1 3 2 8% 5% 4 4 3 5% 7% 57%	6340
	21st to end	Night	2 5% 3 7% 4 3 3 3 3 6% 62%	6514
February	1st to 10th	Night	2 6% 3 7% 3 4 4 4 5% 8% 54%	2600
	11th to 20th	Night	2 6% 2 7% 6% 4 4 3 4 7% 55%	2392
	21st to end	Night	2 10% 3 5% 4 3 3 3 4 6% 58%	1980
March	1st to 10th	Night	3 11% 4 7% 4 3 3 2 4 6% 54%	5374
	11th to 20th	Night	4 8% 2 5% 3 4 4 3 5% 8% 53%	5071
	21st to end	Night	8% 9% 2 6% 4 4 5% 3 5% 8% 46%	5130
April	1st to 10th	Night	5% 7% 2 5% 3 4 4 4 6% 7% 53%	2000
	11th to 20th	Night	9% 8% 2 5% 4 3 3 3 5% 6% 51%	1977
	21st to end	Night	13% 9% 3 4 3 4 3 4 4 7% 46%	2000
May	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 5% 6% 45%	4032
	11th to 20th	Night	8% 6% 2 5% 4 4 5% 5% 6% 9% 45%	3617
	21st to end	Night	14% 7% 2 5% 3 3 3 3 4 6% 49%	3972
June	1st to 10th	Night	7% 5% 2 3 3 4 3 3 6% 10% 54%	1600
	11th to 20th	Night	7% 3 1 3 3 3 4 3 7% 6% 60%	1600
	21st to end	Night	6% 3 1 4 2 3 4 3 5% 8% 61%	1600
July	1st to 10th	Night	5% 4 2 4 3 4 5% 4 6% 8% 56%	3640
	11th to 20th	Night	5% 3 1 4 3 4 4 5% 8% 11% 52%	3640
	21st to end	Night	6% 3 2 5% 4 5% 5% 5% 7% 7% 52%	3970
August	1st to 10th	Night	11% 5% 1 4 3 4 4 4 7% 8% 49%	4019
	11th to 20th	Night	4 4 2 5% 4 4 5% 4 7% 8% 53%	4399
	21st to end	Night	11% 5% 2 5% 4 4 4 4 6% 8% 48%	4993
September	1st to 10th	Night	7% 4 1 4 3 3 3 3 5% 7% 59%	2000
	11th to 20th	Night	8% 4 1 3 2 3 3 3 5% 6% 62%	2020
	21st to end	Night	7% 5% 1 4 2 2 3 3 4 6% 63%	2200
October	1st to 10th	Night	7% 4 1 3 2 2 2 2 3 4 71%	3910
	11th to 20th	Night	7% 6% 2 5% 3 3 3 3 5% 6% 58%	3898
	21st to end	Night	5% 6% 2 4 2 3 3 3 4 7% 62%	4397
November	1st to 10th	Night	3 4 2 4 3 4 3 3 5% 7% 63%	2665
	11th to 20th	Night	3 5% 1 4 4 3 3 3 5% 7% 62%	2692
	21st to end	Night	2 7% 3 4 4 3 3 3 6% 7% 59%	2759
December	1st to 10th	Night	1 4 2 4 3 2 2 2 4 5% 72%	4570
	11th to 20th	Night	2 5% 2 4 3 3 3 3 5% 8% 63%	5181
	21st to end	Night	3 7% 3 6% 4 4 4 3 5% 7% 52%	6974

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	33% 3 10% 28% 19% 6%	3639
	11th to 20th	Day	28% 6% 12% 19% 29% 7%	3640
	21st to end	Day	21% 4 11% 26% 28% 9%	4492
February	1st to 10th	Day	30% 6% 16% 25% 18% 6%	1800
	11th to 20th	Day	27% 5% 12% 29% 21% 6%	1903
	21st to end	Day	29% 4 11% 26% 22% 8%	1650
March	1st to 10th	Day	30% 3 8% 20% 30% 8%	4500
	11th to 20th	Day	34% 5% 10% 25% 21% 4	4924
	21st to end	Day	35% 6% 13% 33% 12% 1	5828
April	1st to 10th	Day	30% 6% 13% 24% 18% 8%	2400
	11th to 20th	Day	40% 6% 12% 20% 16% 6%	2374
	21st to end	Day	39% 7% 11% 26% 15% 1	2400
May	1st to 10th	Day	40% 6% 10% 26% 14% 4	5945
	11th to 20th	Day	35% 7% 10% 18% 23% 6%	6302
	21st to end	Day	36% 7% 11% 23% 19% 4	6926
June	1st to 10th	Day	30% 11% 16% 22% 16% 5%	2800
	11th to 20th	Day	27% 9% 12% 20% 20% 13%	2800
	21st to end	Day	26% 8% 10% 23% 20% 14%	2800
July	1st to 10th	Day	26% 5% 7% 18% 25% 18%	6271
	11th to 20th	Day	31% 4 12% 22% 18% 13%	6265
	21st to end	Day	34% 5% 9% 15% 21% 16%	6705
August	1st to 10th	Day	36% 7% 13% 20% 16% 8%	4217
	11th to 20th	Day	28% 5% 12% 17% 22% 16%	3929
	21st to end	Day	27% 5% 10% 18% 24% 15%	4311
September	1st to 10th	Day	24% 5% 7% 20% 28% 15%	2400
	11th to 20th	Day	24% 6% 9% 22% 26% 13%	2380
	21st to end	Day	23% 5% 7% 21% 35% 10%	2200
October	1st to 10th	Day	19% 3 4 17% 33% 24%	3277
	11th to 20th	Day	24% 3 10% 27% 26% 9%	3250
	21st to end	Day	24% 3 6% 29% 32% 6%	3369
November	1st to 10th	Day	22% 4 12% 26% 27% 8%	1853
	11th to 20th	Day	21% 4 10% 29% 29% 7%	1863
	21st to end	Day	25% 4 11% 25% 27% 8%	1639
December	1st to 10th	Day	17% 3 8% 33% 31% 7%	2620
	11th to 20th	Day	21% 2 10% 37% 26% 3	3024
	21st to end	Day	32% 4 11% 25% 18% 9%	4004
January	1st to 10th	Night	31% 5% 11% 26% 20% 7%	6327
	11th to 20th	Night	27% 7% 12% 19% 25% 10%	6340
	21st to end	Night	26% 5% 12% 23% 26% 9%	6514
February	1st to 10th	Night	29% 4 16% 28% 19% 5%	2600
	11th to 20th	Night	31% 4 13% 28% 20% 4	2392
	21st to end	Night	28% 4 10% 23% 25% 10%	1980
March	1st to 10th	Night	33% 2 8% 18% 30% 9%	5374
	11th to 20th	Night	29% 4 11% 17% 31% 8%	5071
	21st to end	Night	36% 5% 16% 27% 14% 2	5130
April	1st to 10th	Night	29% 6% 12% 27% 19% 7%	2000
	11th to 20th	Night	34% 5% 13% 24% 19% 4	1977
	21st to end	Night	39% 5% 10% 27% 19% 1	2000
May	1st to 10th	Night	39% 5% 11% 29% 11% 4	4030
	11th to 20th	Night	34% 8% 14% 24% 15% 5%	3618
	21st to end	Night	35% 7% 16% 24% 16% 3	3972
June	1st to 10th	Night	24% 9% 21% 26% 15% 5%	1600
	11th to 20th	Night	23% 6% 14% 22% 20% 15%	1600
	21st to end	Night	22% 5% 11% 26% 25% 11%	1600
July	1st to 10th	Night	26% 4 9% 23% 27% 11%	3600
	11th to 20th	Night	26% 4 19% 24% 20% 8%	3592
	21st to end	Night	29% 5% 13% 23% 20% 10%	3856
August	1st to 10th	Night	34% 5% 16% 21% 19% 4	2915
	11th to 20th	Night	33% 6% 12% 23% 16% 11%	3182
	21st to end	Night	26% 4 14% 23% 22% 11%	3597
September	1st to 10th	Night	25% 5% 9% 20% 24% 16%	2000
	11th to 20th	Night	23% 5% 11% 24% 24% 13%	2020
	21st to end	Night	24% 4 6% 23% 31% 11%	2200
October	1st to 10th	Night	19% 3 6% 20% 29% 23%	3910
	11th to 20th	Night	29% 2 9% 28% 25% 7%	3898
	21st to end	Night	24% 3 7% 28% 28% 10%	4397
November	1st to 10th	Night	22% 4 13% 25% 27% 9%	2665
	11th to 20th	Night	22% 4 10% 29% 26% 8%	2692
	21st to end	Night	24% 4 11% 26% 27% 7%	2759
December	1st to 10th	Night	18% 3 10% 34% 29% 6%	4570
	11th to 20th	Night	21% 4 9% 39% 26% 2	5182
	21st to end	Night	31% 5% 11% 25% 23% 6%	6974

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	13% 18% 30% 24% 12% 2	300
	11th to 20th	Day	13% 29% 32% 19% 7%	300
	21st to end	Day	8% 32% 36% 19% 5% 1	330
February	1st to 10th	Day	12% 30% 40% 15% 2	300
	11th to 20th	Day	12% 23% 40% 21% 4	300
	21st to end	Day	22% 19% 37% 20% 2	249
March	1st to 10th	Day	9% 23% 34% 28% 5%	300
	11th to 20th	Day	17% 18% 36% 21% 7%	463
	21st to end	Day	18% 20% 38% 18% 5%	550
April	1st to 10th	Day	15% 25% 33% 22% 5% 1	500
	11th to 20th	Day	22% 21% 38% 14% 4 1	492
	21st to end	Day	21% 16% 33% 21% 8% 2	500
May	1st to 10th	Day	20% 15% 30% 22% 11% 2	668
	11th to 20th	Day	22% 8% 26% 27% 13% 3	725
	21st to end	Day	15% 12% 26% 27% 18% 4	789
June	1st to 10th	Day	10% 7% 23% 33% 21% 5%	730
	11th to 20th	Day	9% 7% 33% 32% 16% 3	730
	21st to end	Day	6% 7% 30% 33% 18% 6%	730
July	1st to 10th	Day	9% 2 18% 39% 26% 7%	721
	11th to 20th	Day	6% 3 20% 39% 25% 6%	718
	21st to end	Day	7% 4 18% 34% 29% 8%	794
August	1st to 10th	Day	9% 3 25% 38% 20% 5%	537
	11th to 20th	Day	5% 6% 25% 36% 22% 6%	517
	21st to end	Day	8% 5% 29% 35% 18% 5%	583
September	1st to 10th	Day	9% 4 29% 35% 18% 6%	530
	11th to 20th	Day	8% 6% 34% 29% 17% 5%	510
	21st to end	Day	13% 5% 30% 26% 16% 10%	330
October	1st to 10th	Day	13% 6% 28% 28% 17% 7%	330
	11th to 20th	Day	10% 18% 34% 24% 11% 4	330
	21st to end	Day	11% 19% 36% 25% 7% 2	363
November	1st to 10th	Day	12% 17% 35% 25% 7% 4	330
	11th to 20th	Day	13% 23% 35% 22% 7% 1	321
	21st to end	Day	12% 28% 32% 22% 5% 1	300
December	1st to 10th	Day	12% 26% 32% 22% 7%	300
	11th to 20th	Day	16% 29% 32% 20% 3	300
	21st to end	Day	15% 28% 33% 20% 4 1	330
January	1st to 10th	Night	8% 27% 31% 25% 6% 2	1000
	11th to 20th	Night	7% 34% 34% 18% 6% 1	1000
	21st to end	Night	7% 27% 35% 25% 5% 1	900
February	1st to 10th	Night	7% 29% 36% 22% 5%	800
	11th to 20th	Night	7% 23% 39% 27% 4	784
	21st to end	Night	10% 25% 38% 25% 2	660
March	1st to 10th	Night	7% 19% 36% 32% 5%	800
	11th to 20th	Night	10% 16% 31% 33% 10% 1	800
	21st to end	Night	13% 15% 33% 31% 6% 1	728
April	1st to 10th	Night	11% 16% 36% 33% 5%	600
	11th to 20th	Night	15% 14% 33% 31% 7% 1	593
	21st to end	Night	20% 12% 23% 35% 9% 1	600
May	1st to 10th	Night	18% 11% 25% 33% 13% 2	600
	11th to 20th	Night	20% 5% 19% 38% 16% 2	591
	21st to end	Night	13% 6% 25% 34% 20% 2	650
June	1st to 10th	Night	8% 6% 18% 43% 23% 2	600
	11th to 20th	Night	8% 5% 21% 52% 14% 1	600
	21st to end	Night	7% 4 20% 46% 21% 3	600
July	1st to 10th	Night	9% 2 12% 44% 30% 4	585
	11th to 20th	Night	4 2 9% 50% 32% 2	582
	21st to end	Night	6% 1 7% 47% 36% 3	657
August	1st to 10th	Night	8% 3 11% 47% 29% 2	597
	11th to 20th	Night	6% 1 11% 53% 26% 3	594
	21st to end	Night	6% 3 13% 45% 30% 3	660
September	1st to 10th	Night	8% 4 14% 45% 25% 5%	600
	11th to 20th	Night	9% 4 17% 45% 21% 5%	600
	21st to end	Night	9% 6% 23% 43% 17% 2	600
October	1st to 10th	Night	13% 9% 22% 38% 16% 3	790
	11th to 20th	Night	8% 12% 31% 36% 11% 2	800
	21st to end	Night	10% 17% 31% 33% 7% 2	963
November	1st to 10th	Night	7% 14% 35% 34% 8% 2	1025
	11th to 20th	Night	9% 20% 36% 31% 4 1	1036
	21st to end	Night	6% 22% 33% 32% 7%	1000
December	1st to 10th	Night	7% 27% 34% 27% 5%	1000
	11th to 20th	Night	11% 22% 37% 25% 5% 1	1000
	21st to end	Night	8% 25% 36% 24% 5% 1	1100

Page generated at 2025-11-14 22:55:59. Version ac07

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