Black Kettle National Grasslands
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Kettle National Grasslands clear sky chart from 2005-11-06 to 2024-01-16.

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	7% 4 2 4 4 3 4 4 5% 7% 57%	74914
	Night	7% 4 2 3 3 2 4 4 5% 7% 59%	74925
Transparency	Day	28% 3 9% 25% 25% 10%	74642
	Night	26% 3 9% 24% 27% 11%	74720
Seeing	Day	9% 9% 29% 31% 18% 4	14233
	Night	9% 9% 35% 35% 11% 1	24287

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	4 5% 2 4 3 2 2 3 3 6% 65%	1707
	11th to 20th	Day	6% 6% 3 4 3 2 4 3 3 6% 60%	1670
	21st to end	Day	6% 4 2 4 3 2 4 3 5% 6% 61%	1832
February	1st to 10th	Day	6% 6% 3 5% 4 2 3 3 4 7% 57%	1800
	11th to 20th	Day	6% 5% 3 5% 3 2 3 3 4 6% 59%	1749
	21st to end	Day	5% 6% 3 4 3 2 3 4 4 6% 60%	1480
March	1st to 10th	Day	7% 6% 3 5% 3 2 4 4 5% 7% 53%	1813
	11th to 20th	Day	11% 5% 2 4 3 2 3 3 4 6% 56%	1980
	21st to end	Day	9% 5% 3 5% 4 2 4 4 5% 6% 55%	2178
April	1st to 10th	Day	8% 3 2 3 3 2 3 4 4 7% 62%	2088
	11th to 20th	Day	11% 5% 2 4 4 4 4 3 4 6% 52%	2131
	21st to end	Day	11% 4 2 3 4 3 4 4 4 6% 55%	2308
May	1st to 10th	Day	10% 4 3 4 4 4 5% 4 4 7% 52%	2340
	11th to 20th	Day	10% 5% 2 4 4 2 3 5% 5% 8% 53%	2302
	21st to end	Day	9% 5% 2 5% 5% 4 4 5% 6% 8% 48%	2531
June	1st to 10th	Day	6% 3 2 4 4 2 5% 6% 7% 9% 53%	2340
	11th to 20th	Day	4 4 2 4 3 3 4 4 4 9% 59%	2340
	21st to end	Day	5% 4 1 3 4 3 4 4 6% 7% 61%	2340
July	1st to 10th	Day	6% 4 2 4 5% 4 6% 6% 7% 9% 49%	2340
	11th to 20th	Day	4 3 1 3 4 3 4 5% 5% 9% 58%	2340
	21st to end	Day	3 3 1 4 4 2 5% 5% 6% 9% 58%	2546
August	1st to 10th	Day	3 2 2 4 4 3 5% 5% 8% 10% 54%	2328
	11th to 20th	Day	6% 4 2 5% 5% 4 4 5% 6% 8% 52%	2174
	21st to end	Day	5% 3 1 3 4 3 4 4 7% 10% 57%	2376
September	1st to 10th	Day	9% 4 2 3 4 2 3 4 4 6% 59%	2049
	11th to 20th	Day	8% 5% 2 4 4 3 5% 5% 6% 6% 53%	1980
	21st to end	Day	6% 3 1 3 4 2 3 4 5% 6% 63%	1980
October	1st to 10th	Day	11% 4 2 4 4 2 3 3 3 6% 58%	1980
	11th to 20th	Day	8% 3 1 3 3 2 2 2 3 4 70%	1887
	21st to end	Day	9% 4 2 4 3 2 2 2 3 4 65%	1906
November	1st to 10th	Day	5% 4 1 3 3 2 2 2 4 6% 68%	1673
	11th to 20th	Day	4 3 2 4 3 1 2 3 3 5% 70%	1710
	21st to end	Day	8% 5% 3 3 3 1 3 2 4 6% 61%	1710
December	1st to 10th	Day	6% 4 2 5% 3 2 3 4 5% 6% 61%	1710
	11th to 20th	Day	7% 6% 2 4 5% 2 4 4 4 5% 58%	2161
	21st to end	Day	7% 8% 3 6% 6% 4 5% 4 5% 6% 47%	3135
January	1st to 10th	Night	5% 3 2 3 4 3 4 4 5% 6% 61%	2458
	11th to 20th	Night	5% 5% 2 3 3 2 3 4 4 6% 63%	2418
	21st to end	Night	6% 4 2 2 3 2 2 3 4 7% 65%	2538
February	1st to 10th	Night	8% 7% 3 5% 4 2 3 3 3 5% 56%	2160
	11th to 20th	Night	8% 6% 2 4 4 3 4 3 4 6% 55%	2098
	21st to end	Night	7% 6% 2 4 4 2 3 5% 5% 6% 57%	1776
March	1st to 10th	Night	5% 4 3 4 5% 3 3 4 6% 8% 55%	2146
	11th to 20th	Night	12% 5% 2 4 4 2 3 3 4 5% 57%	1980
	21st to end	Night	8% 5% 2 4 4 2 4 3 5% 7% 56%	2178
April	1st to 10th	Night	5% 4 2 4 3 3 3 4 5% 7% 61%	1868
	11th to 20th	Night	9% 5% 2 4 4 3 4 4 6% 7% 54%	1777
	21st to end	Night	11% 4 2 3 3 2 3 3 5% 8% 56%	1652
May	1st to 10th	Night	10% 5% 2 4 4 2 3 3 5% 6% 55%	1620
	11th to 20th	Night	8% 4 2 3 4 3 4 5% 5% 8% 54%	1593
	21st to end	Night	8% 3 2 4 4 2 5% 6% 6% 9% 51%	1745
June	1st to 10th	Night	5% 2 1 3 4 3 4 5% 8% 10% 56%	1620
	11th to 20th	Night	5% 2 1 3 3 3 4 5% 7% 11% 56%	1620
	21st to end	Night	5% 2 1 3 2 2 5% 4 6% 8% 61%	1620
July	1st to 10th	Night	6% 3 2 4 4 3 4 5% 5% 10% 55%	1620
	11th to 20th	Night	3 2 1 3 3 3 4 5% 6% 8% 62%	1620
	21st to end	Night	3 2 1 3 4 2 3 4 6% 11% 61%	1772
August	1st to 10th	Night	2 3 1 3 4 3 6% 6% 6% 10% 56%	1611
	11th to 20th	Night	7% 4 2 4 4 3 6% 5% 6% 10% 52%	1723
	21st to end	Night	3 3 1 4 4 3 4 6% 7% 10% 56%	1980
September	1st to 10th	Night	7% 3 1 3 3 2 3 3 6% 7% 62%	1909
	11th to 20th	Night	10% 6% 1 4 4 3 3 4 5% 8% 53%	1980
	21st to end	Night	5% 4 2 3 4 3 3 4 4 7% 63%	1980
October	1st to 10th	Night	7% 4 1 3 4 2 4 5% 5% 6% 59%	1980
	11th to 20th	Night	8% 3 1 3 2 1 2 2 3 4 72%	2052
	21st to end	Night	8% 3 1 2 3 1 3 3 3 5% 68%	2448
November	1st to 10th	Night	5% 3 1 2 2 1 3 3 4 7% 69%	2405
	11th to 20th	Night	4 3 1 2 3 2 3 3 3 5% 70%	2470
	21st to end	Night	8% 4 2 3 3 2 3 3 4 5% 62%	2470
December	1st to 10th	Night	7% 4 1 4 3 2 3 4 3 6% 62%	2470
	11th to 20th	Night	7% 5% 2 5% 4 2 3 3 5% 7% 57%	3036
	21st to end	Night	8% 7% 2 4 4 3 4 5% 5% 6% 52%	4532

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	24% 2 7% 28% 30% 10%	1708
	11th to 20th	Day	29% 1 8% 22% 32% 8%	1670
	21st to end	Day	25% 2 6% 28% 32% 8%	1832
February	1st to 10th	Day	30% 2 8% 26% 25% 8%	1800
	11th to 20th	Day	29% 2 6% 27% 24% 12%	1759
	21st to end	Day	27% 1 4 24% 29% 14%	1480
March	1st to 10th	Day	32% 2 8% 22% 21% 15%	1813
	11th to 20th	Day	31% 2 8% 24% 24% 11%	1980
	21st to end	Day	32% 2 8% 26% 23% 9%	2178
April	1st to 10th	Day	24% 2 8% 23% 27% 15%	2088
	11th to 20th	Day	34% 3 6% 23% 22% 11%	2134
	21st to end	Day	31% 3 9% 25% 25% 7%	2308
May	1st to 10th	Day	34% 3 10% 18% 22% 13%	2340
	11th to 20th	Day	31% 3 12% 28% 22% 4	2306
	21st to end	Day	35% 4 13% 27% 15% 7%	2531
June	1st to 10th	Day	27% 4 16% 29% 15% 8%	2340
	11th to 20th	Day	24% 3 11% 27% 26% 10%	2340
	21st to end	Day	23% 4 11% 27% 24% 12%	2340
July	1st to 10th	Day	31% 5% 10% 28% 21% 4	2276
	11th to 20th	Day	22% 3 11% 25% 30% 8%	2271
	21st to end	Day	23% 5% 12% 33% 24% 2	2405
August	1st to 10th	Day	24% 4 11% 33% 21% 6%	2314
	11th to 20th	Day	30% 5% 12% 27% 20% 5%	2174
	21st to end	Day	24% 5% 11% 29% 23% 9%	2376
September	1st to 10th	Day	28% 3 10% 23% 22% 14%	2049
	11th to 20th	Day	31% 4 10% 21% 28% 5%	1980
	21st to end	Day	23% 4 7% 23% 33% 10%	1980
October	1st to 10th	Day	29% 2 10% 21% 27% 10%	1980
	11th to 20th	Day	21% 2 6% 19% 31% 20%	1887
	21st to end	Day	26% 2 6% 23% 28% 15%	1906
November	1st to 10th	Day	20% 1 6% 25% 30% 18%	1673
	11th to 20th	Day	19% 2 5% 28% 33% 13%	1710
	21st to end	Day	27% 2 3 22% 32% 14%	1710
December	1st to 10th	Day	26% 2 10% 27% 28% 8%	1710
	11th to 20th	Day	30% 2 8% 20% 30% 11%	2159
	21st to end	Day	38% 1 6% 20% 26% 9%	3135
January	1st to 10th	Night	25% 3 8% 26% 30% 9%	2458
	11th to 20th	Night	24% 2 8% 23% 32% 11%	2418
	21st to end	Night	22% 2 5% 26% 34% 12%	2538
February	1st to 10th	Night	32% 2 6% 22% 28% 10%	2160
	11th to 20th	Night	32% 3 7% 21% 25% 12%	2098
	21st to end	Night	29% 3 4 23% 25% 17%	1776
March	1st to 10th	Night	28% 4 6% 22% 26% 14%	2146
	11th to 20th	Night	31% 2 6% 25% 23% 12%	1980
	21st to end	Night	29% 3 12% 26% 21% 9%	2178
April	1st to 10th	Night	24% 4 8% 22% 26% 16%	1868
	11th to 20th	Night	31% 4 9% 24% 23% 10%	1777
	21st to end	Night	28% 3 9% 28% 24% 7%	1652
May	1st to 10th	Night	32% 4 9% 17% 25% 12%	1620
	11th to 20th	Night	30% 4 14% 24% 19% 8%	1594
	21st to end	Night	29% 5% 16% 25% 18% 7%	1746
June	1st to 10th	Night	23% 5% 17% 32% 16% 6%	1620
	11th to 20th	Night	22% 5% 13% 28% 24% 8%	1620
	21st to end	Night	21% 4 11% 28% 25% 11%	1620
July	1st to 10th	Night	27% 3 15% 30% 20% 5%	1575
	11th to 20th	Night	19% 4 10% 25% 31% 11%	1566
	21st to end	Night	19% 3 14% 30% 29% 5%	1673
August	1st to 10th	Night	21% 5% 13% 30% 23% 8%	1601
	11th to 20th	Night	29% 5% 13% 25% 24% 5%	1723
	21st to end	Night	24% 5% 13% 26% 23% 9%	1980
September	1st to 10th	Night	23% 3 12% 25% 24% 12%	1909
	11th to 20th	Night	31% 4 9% 19% 29% 8%	1980
	21st to end	Night	23% 3 8% 24% 31% 12%	1980
October	1st to 10th	Night	27% 4 9% 20% 30% 11%	1980
	11th to 20th	Night	20% 2 5% 18% 35% 19%	2052
	21st to end	Night	21% 2 5% 25% 30% 17%	2448
November	1st to 10th	Night	19% 2 6% 26% 29% 18%	2405
	11th to 20th	Night	19% 2 5% 26% 33% 14%	2470
	21st to end	Night	26% 2 5% 21% 30% 16%	2470
December	1st to 10th	Night	25% 2 8% 25% 28% 11%	2470
	11th to 20th	Night	30% 2 4 23% 31% 9%	3037
	21st to end	Night	34% 1 8% 21% 26% 10%	4532

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	9% 13% 42% 25% 9% 1	270
	11th to 20th	Day	16% 17% 35% 23% 9% 1	257
	21st to end	Day	6% 14% 51% 23% 5%	264
February	1st to 10th	Day	9% 15% 48% 21% 7%	240
	11th to 20th	Day	10% 13% 52% 16% 8% 1	240
	21st to end	Day	7% 24% 44% 20% 5%	198
March	1st to 10th	Day	10% 14% 51% 20% 6%	240
	11th to 20th	Day	17% 18% 40% 17% 6% 2	240
	21st to end	Day	16% 14% 45% 20% 5%	264
April	1st to 10th	Day	14% 21% 35% 24% 5% 1	348
	11th to 20th	Day	14% 23% 42% 19% 2	412
	21st to end	Day	14% 20% 37% 21% 6% 2	568
May	1st to 10th	Day	13% 12% 40% 29% 5% 1	603
	11th to 20th	Day	13% 8% 30% 30% 18% 2	625
	21st to end	Day	12% 8% 34% 29% 15% 2	679
June	1st to 10th	Day	6% 5% 25% 37% 21% 6%	630
	11th to 20th	Day	6% 4 30% 39% 19% 2	630
	21st to end	Day	5% 4 24% 42% 22% 4	630
July	1st to 10th	Day	7% 1 12% 36% 33% 11%	621
	11th to 20th	Day	4 2 10% 42% 34% 7%	618
	21st to end	Day	4 1 7% 39% 40% 8%	684
August	1st to 10th	Day	4 2 13% 45% 31% 4	626
	11th to 20th	Day	7% 1 15% 41% 31% 5%	488
	21st to end	Day	6% 1 11% 41% 32% 9%	495
September	1st to 10th	Day	9% 1 12% 38% 33% 7%	339
	11th to 20th	Day	6% 3 13% 44% 27% 7%	270
	21st to end	Day	9% 5% 23% 30% 28% 5%	270
October	1st to 10th	Day	11% 6% 31% 31% 18% 3	270
	11th to 20th	Day	7% 10% 34% 34% 13% 3	270
	21st to end	Day	18% 7% 38% 23% 11% 3	297
November	1st to 10th	Day	8% 9% 37% 33% 11% 2	270
	11th to 20th	Day	7% 15% 36% 26% 12% 3	270
	21st to end	Day	16% 13% 37% 19% 11% 3	270
December	1st to 10th	Day	6% 14% 42% 27% 10% 1	270
	11th to 20th	Day	11% 11% 42% 26% 10% 1	270
	21st to end	Day	15% 21% 35% 22% 6%	297
January	1st to 10th	Night	7% 12% 39% 35% 7%	950
	11th to 20th	Night	9% 13% 36% 33% 8%	930
	21st to end	Night	8% 10% 43% 33% 6% 1	954
February	1st to 10th	Night	12% 11% 40% 30% 6% 1	720
	11th to 20th	Night	11% 12% 46% 24% 6%	704
	21st to end	Night	11% 17% 42% 26% 4	592
March	1st to 10th	Night	7% 15% 43% 30% 4	706
	11th to 20th	Night	14% 14% 38% 29% 5%	540
	21st to end	Night	12% 16% 44% 24% 3	594
April	1st to 10th	Night	7% 15% 46% 26% 5%	540
	11th to 20th	Night	13% 15% 49% 21% 2	533
	21st to end	Night	14% 13% 40% 27% 6%	540
May	1st to 10th	Night	14% 10% 42% 30% 4	540
	11th to 20th	Night	11% 8% 38% 30% 11% 1	531
	21st to end	Night	8% 8% 38% 33% 11% 2	584
June	1st to 10th	Night	6% 5% 35% 39% 14% 1	540
	11th to 20th	Night	4 4 46% 38% 8%	540
	21st to end	Night	6% 3 31% 45% 14% 1	540
July	1st to 10th	Night	7% 1 20% 45% 25% 2	525
	11th to 20th	Night	4 1 17% 53% 23% 2	522
	21st to end	Night	4 1 11% 54% 28% 2	591
August	1st to 10th	Night	4 1 15% 52% 26% 2	537
	11th to 20th	Night	7% 3 16% 50% 25%	534
	21st to end	Night	5% 1 15% 44% 33% 2	594
September	1st to 10th	Night	8% 2 19% 47% 24% 1	540
	11th to 20th	Night	14% 2 24% 39% 19% 1	540
	21st to end	Night	8% 4 31% 37% 19% 2	540
October	1st to 10th	Night	8% 7% 27% 42% 15% 1	540
	11th to 20th	Night	10% 9% 38% 36% 7%	612
	21st to end	Night	11% 8% 36% 29% 15%	864
November	1st to 10th	Night	8% 8% 36% 37% 10% 1	925
	11th to 20th	Night	6% 11% 41% 33% 8%	950
	21st to end	Night	11% 12% 34% 32% 10% 1	950
December	1st to 10th	Night	10% 10% 39% 33% 8% 1	950
	11th to 20th	Night	12% 11% 43% 29% 6%	950
	21st to end	Night	12% 15% 37% 30% 6%	1045

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