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 2026-04-02.

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% 5% 2 5% 3 3 4 3 5% 7% 58%	140316
	Night	6% 4 2 4 3 3 3 3 5% 7% 60%	138913
Transparency	Day	27% 3 8% 25% 27% 11%	135244
	Night	25% 3 8% 24% 27% 12%	134994
Seeing	Day	9% 9% 29% 32% 18% 3	17183
	Night	9% 9% 35% 35% 11% 1	27248

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	5% 6% 2 6% 4 4 4 3 4 5% 56%	5287
	11th to 20th	Day	3 5% 2 3 2 3 2 1 3 4 71%	5310
	21st to end	Day	10% 7% 2 5% 3 3 3 2 4 5% 57%	5974
February	1st to 10th	Day	6% 7% 2 7% 3 3 2 2 5% 7% 56%	2100
	11th to 20th	Day	6% 6% 2 5% 3 3 3 2 4 6% 59%	2049
	21st to end	Day	4 5% 2 4 2 3 2 3 4 6% 63%	1730
March	1st to 10th	Day	8% 5% 2 4 2 2 3 3 4 5% 61%	4640
	11th to 20th	Day	5% 4 2 4 3 3 3 3 5% 7% 60%	5090
	21st to end	Day	6% 6% 2 6% 3 4 4 3 5% 6% 56%	5585
April	1st to 10th	Day	9% 4 1 4 3 2 3 3 4 6% 61%	2331
	11th to 20th	Day	11% 5% 2 5% 3 4 4 2 4 6% 53%	2371
	21st to end	Day	12% 4 2 4 3 3 3 3 5% 6% 54%	2565
May	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 4 6% 49%	5900
	11th to 20th	Day	7% 5% 2 4 3 3 3 3 4 6% 62%	5862
	21st to end	Day	11% 7% 2 6% 4 4 3 3 4 6% 51%	6446
June	1st to 10th	Day	6% 3 2 4 4 4 5% 5% 7% 9% 51%	2600
	11th to 20th	Day	4 4 2 4 3 4 3 3 5% 9% 59%	2600
	21st to end	Day	5% 4 1 3 4 4 4 4 6% 8% 58%	2600
July	1st to 10th	Day	7% 6% 2 6% 5% 5% 5% 5% 7% 8% 43%	5899
	11th to 20th	Day	4 3 1 4 4 4 4 4 6% 9% 57%	5900
	21st to end	Day	2 2 1 3 2 3 4 4 6% 10% 63%	6424
August	1st to 10th	Day	6% 4 2 5% 4 4 4 3 6% 7% 54%	5801
	11th to 20th	Day	3 3 1 5% 4 4 5% 4 7% 9% 54%	5485
	21st to end	Day	10% 4 1 4 3 3 4 3 6% 8% 54%	5984
September	1st to 10th	Day	9% 4 1 4 4 4 4 3 4 6% 57%	2276
	11th to 20th	Day	7% 5% 2 5% 3 4 5% 4 6% 7% 53%	2200
	21st to end	Day	6% 3 1 4 3 3 4 3 5% 6% 63%	2200
October	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 5% 72%	3590
	11th to 20th	Day	5% 3 1 3 2 3 3 2 4 6% 68%	3388
	21st to end	Day	5% 3 1 3 2 2 2 2 4 6% 69%	3398
November	1st to 10th	Day	6% 3 1 3 2 2 2 2 4 6% 68%	1853
	11th to 20th	Day	4 3 2 4 3 2 2 3 4 4 69%	1890
	21st to end	Day	7% 6% 2 3 3 2 3 2 4 6% 62%	1890
December	1st to 10th	Day	4 3 2 4 2 2 2 3 4 6% 68%	3030
	11th to 20th	Day	4 4 1 3 3 2 3 3 4 6% 66%	3481
	21st to end	Day	8% 10% 3 7% 4 4 4 3 4 5% 48%	4587
January	1st to 10th	Night	6% 6% 2 6% 4 4 4 4 6% 6% 52%	7634
	11th to 20th	Night	2 3 1 3 2 3 3 3 4 5% 72%	7680
	21st to end	Night	11% 9% 2 5% 3 3 3 3 4 5% 53%	8282
February	1st to 10th	Night	7% 7% 2 6% 3 3 3 3 3 5% 56%	2520
	11th to 20th	Night	8% 6% 2 5% 3 4 3 3 4 6% 54%	2458
	21st to end	Night	5% 5% 2 4 4 3 3 4 4 6% 60%	2076
March	1st to 10th	Night	4 6% 2 4 3 3 3 2 4 6% 63%	5451
	11th to 20th	Night	5% 3 1 4 3 3 3 3 4 6% 66%	5090
	21st to end	Night	5% 4 2 5% 4 3 4 3 5% 7% 57%	5588
April	1st to 10th	Night	6% 4 2 4 2 4 3 3 5% 6% 60%	2086
	11th to 20th	Night	9% 5% 2 4 3 3 4 3 5% 6% 55%	1977
	21st to end	Night	12% 5% 2 3 3 2 3 3 6% 8% 54%	1835
May	1st to 10th	Night	15% 7% 2 5% 3 3 3 3 5% 5% 50%	4080
	11th to 20th	Night	6% 4 2 4 4 4 4 3 4 8% 59%	4053
	21st to end	Night	11% 5% 2 4 3 3 4 3 5% 7% 54%	4451
June	1st to 10th	Night	5% 3 1 4 4 4 4 5% 8% 10% 54%	1800
	11th to 20th	Night	4 3 1 3 3 3 5% 4 7% 11% 56%	1800
	21st to end	Night	4 3 1 4 2 4 4 4 7% 8% 59%	1800
July	1st to 10th	Night	7% 5% 2 5% 4 4 5% 4 6% 9% 49%	4080
	11th to 20th	Night	3 2 1 4 3 4 4 4 8% 12% 55%	4080
	21st to end	Night	2 2 1 4 3 4 4 3 6% 9% 62%	4449
August	1st to 10th	Night	3 3 1 4 3 4 5% 3 6% 12% 57%	4011
	11th to 20th	Night	3 3 1 4 4 4 6% 5% 9% 13% 49%	4347
	21st to end	Night	12% 4 1 4 3 3 4 4 5% 7% 53%	4993
September	1st to 10th	Night	6% 3 1 4 3 3 3 3 6% 7% 61%	2122
	11th to 20th	Night	9% 5% 1 5% 3 3 4 3 5% 8% 53%	2200
	21st to end	Night	5% 4 2 4 3 3 2 3 4 7% 63%	2200
October	1st to 10th	Night	4 2 1 2 2 2 2 3 4 5% 73%	3590
	11th to 20th	Night	5% 2 1 3 2 2 2 2 4 6% 71%	3715
	21st to end	Night	5% 2 1 2 2 2 2 2 4 7% 72%	4381
November	1st to 10th	Night	6% 3 1 3 2 2 3 2 5% 5% 68%	2665
	11th to 20th	Night	4 3 1 3 2 3 3 2 3 5% 70%	2730
	21st to end	Night	7% 4 2 4 3 3 3 2 4 5% 63%	2730
December	1st to 10th	Night	4 3 1 3 2 2 3 2 3 6% 70%	4380
	11th to 20th	Night	4 4 1 4 3 3 3 2 4 6% 67%	4946
	21st to end	Night	10% 8% 2 5% 3 3 3 3 4 6% 53%	6633

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	32% 2 5% 26% 25% 10%	5290
	11th to 20th	Day	21% 1 7% 18% 41% 13%	5310
	21st to end	Day	32% 2 4 21% 32% 9%	5974
February	1st to 10th	Day	30% 2 7% 25% 25% 10%	2100
	11th to 20th	Day	29% 2 7% 26% 25% 10%	2059
	21st to end	Day	24% 1 4 23% 32% 17%	1730
March	1st to 10th	Day	27% 1 5% 15% 22% 30%	4640
	11th to 20th	Day	25% 2 5% 19% 30% 19%	5090
	21st to end	Day	31% 1 8% 31% 24% 5%	5585
April	1st to 10th	Day	26% 2 8% 23% 26% 16%	2331
	11th to 20th	Day	33% 3 6% 23% 22% 13%	2374
	21st to end	Day	31% 3 9% 26% 24% 7%	2565
May	1st to 10th	Day	37% 3 11% 21% 18% 10%	5900
	11th to 20th	Day	26% 2 8% 23% 26% 15%	5866
	21st to end	Day	36% 3 9% 22% 17% 14%	6447
June	1st to 10th	Day	28% 4 16% 29% 15% 7%	2600
	11th to 20th	Day	24% 3 11% 27% 26% 9%	2600
	21st to end	Day	24% 5% 12% 27% 22% 11%	2600
July	1st to 10th	Day	36% 7% 9% 23% 20% 6%	5836
	11th to 20th	Day	23% 4 11% 31% 27% 4	5831
	21st to end	Day	16% 5% 16% 36% 24% 3	6240
August	1st to 10th	Day	25% 4 9% 28% 27% 6%	4220
	11th to 20th	Day	21% 5% 9% 27% 29% 8%	3964
	21st to end	Day	21% 4 11% 32% 27% 6%	4311
September	1st to 10th	Day	29% 3 10% 22% 23% 13%	2276
	11th to 20th	Day	30% 4 9% 23% 28% 5%	2200
	21st to end	Day	23% 4 7% 23% 33% 11%	2200
October	1st to 10th	Day	17% 2 6% 15% 41% 20%	3590
	11th to 20th	Day	19% 3 9% 24% 26% 19%	3388
	21st to end	Day	18% 2 6% 25% 36% 13%	3398
November	1st to 10th	Day	20% 1 6% 25% 30% 18%	1853
	11th to 20th	Day	20% 2 5% 27% 33% 14%	1890
	21st to end	Day	26% 2 4 23% 31% 13%	1890
December	1st to 10th	Day	19% 2 7% 36% 29% 7%	3030
	11th to 20th	Day	21% 1 5% 21% 40% 12%	3479
	21st to end	Day	40% 1 5% 22% 22% 9%	4587
January	1st to 10th	Night	31% 2 6% 30% 25% 4	7635
	11th to 20th	Night	17% 2 9% 20% 36% 16%	7680
	21st to end	Night	36% 1 5% 17% 30% 10%	8282
February	1st to 10th	Night	32% 2 6% 22% 27% 12%	2520
	11th to 20th	Night	32% 3 7% 22% 24% 12%	2458
	21st to end	Night	26% 2 3 22% 27% 19%	2076
March	1st to 10th	Night	24% 2 3 17% 23% 30%	5451
	11th to 20th	Night	22% 1 5% 20% 24% 28%	5090
	21st to end	Night	27% 2 9% 27% 25% 9%	5588
April	1st to 10th	Night	26% 3 8% 21% 26% 16%	2086
	11th to 20th	Night	30% 3 8% 24% 24% 12%	1977
	21st to end	Night	29% 3 9% 28% 23% 7%	1835
May	1st to 10th	Night	38% 4 11% 16% 20% 11%	4080
	11th to 20th	Night	27% 2 10% 20% 22% 19%	4054
	21st to end	Night	31% 4 11% 18% 16% 19%	4452
June	1st to 10th	Night	24% 5% 18% 32% 16% 6%	1800
	11th to 20th	Night	22% 5% 13% 29% 24% 7%	1800
	21st to end	Night	22% 4 12% 28% 23% 11%	1800
July	1st to 10th	Night	30% 7% 13% 30% 17% 3	4035
	11th to 20th	Night	21% 4 12% 30% 27% 6%	4026
	21st to end	Night	19% 4 13% 32% 28% 4	4320
August	1st to 10th	Night	20% 4 12% 27% 28% 8%	2916
	11th to 20th	Night	24% 5% 10% 27% 28% 6%	3143
	21st to end	Night	21% 4 13% 32% 25% 5%	3597
September	1st to 10th	Night	24% 3 13% 24% 25% 12%	2122
	11th to 20th	Night	30% 5% 9% 21% 28% 8%	2200
	21st to end	Night	23% 3 8% 24% 31% 12%	2200
October	1st to 10th	Night	16% 2 5% 16% 39% 21%	3590
	11th to 20th	Night	17% 3 7% 21% 36% 16%	3715
	21st to end	Night	15% 2 5% 26% 38% 16%	4381
November	1st to 10th	Night	19% 2 6% 25% 29% 18%	2665
	11th to 20th	Night	19% 2 5% 26% 34% 14%	2730
	21st to end	Night	25% 2 5% 24% 29% 15%	2730
December	1st to 10th	Night	18% 2 6% 37% 31% 6%	4380
	11th to 20th	Night	22% 1 3 23% 38% 12%	4947
	21st to end	Night	35% 1 7% 25% 24% 9%	6633

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	10% 12% 43% 25% 9% 1	330
	11th to 20th	Day	12% 18% 36% 22% 12% 1	330
	21st to end	Day	9% 13% 46% 25% 6% 1	363
February	1st to 10th	Day	8% 15% 46% 23% 8%	330
	11th to 20th	Day	11% 16% 46% 18% 8% 1	330
	21st to end	Day	7% 22% 42% 21% 8%	273
March	1st to 10th	Day	10% 16% 47% 22% 5%	330
	11th to 20th	Day	17% 16% 42% 17% 6% 2	330
	21st to end	Day	14% 14% 45% 23% 4 1	363
April	1st to 10th	Day	17% 20% 34% 24% 5%	423
	11th to 20th	Day	13% 23% 43% 18% 2	492
	21st to end	Day	15% 19% 37% 22% 6% 1	665
May	1st to 10th	Day	13% 13% 38% 30% 6% 1	703
	11th to 20th	Day	12% 9% 31% 29% 17% 2	725
	21st to end	Day	12% 8% 36% 28% 14% 2	789
June	1st to 10th	Day	7% 5% 25% 38% 20% 5%	730
	11th to 20th	Day	6% 4 30% 40% 18% 2	730
	21st to end	Day	5% 4 26% 42% 21% 4	730
July	1st to 10th	Day	8% 2 13% 37% 31% 10%	721
	11th to 20th	Day	3 3 11% 43% 33% 7%	718
	21st to end	Day	4 1 9% 40% 39% 8%	794
August	1st to 10th	Day	5% 2 13% 45% 30% 4	726
	11th to 20th	Day	6% 1 14% 41% 31% 6%	573
	21st to end	Day	7% 1 10% 42% 32% 9%	583
September	1st to 10th	Day	9% 1 13% 39% 31% 7%	406
	11th to 20th	Day	5% 3 15% 46% 25% 6%	330
	21st to end	Day	9% 5% 22% 32% 28% 6%	330
October	1st to 10th	Day	10% 5% 28% 34% 20% 4	330
	11th to 20th	Day	7% 10% 32% 35% 13% 3	330
	21st to end	Day	17% 9% 36% 22% 13% 3	363
November	1st to 10th	Day	8% 10% 38% 31% 11% 2	330
	11th to 20th	Day	7% 15% 35% 28% 12% 3	330
	21st to end	Day	13% 14% 38% 22% 11% 2	330
December	1st to 10th	Day	5% 13% 44% 27% 9% 1	330
	11th to 20th	Day	9% 11% 42% 26% 11% 1	330
	21st to end	Day	13% 20% 35% 22% 9%	363
January	1st to 10th	Night	7% 12% 39% 34% 7%	1050
	11th to 20th	Night	9% 14% 37% 33% 8%	1050
	21st to end	Night	9% 11% 42% 32% 6% 1	1113
February	1st to 10th	Night	11% 12% 39% 32% 5% 1	840
	11th to 20th	Night	12% 14% 45% 24% 6%	824
	21st to end	Night	11% 15% 44% 26% 4	692
March	1st to 10th	Night	7% 16% 43% 30% 4	823
	11th to 20th	Night	13% 15% 39% 28% 4	630
	21st to end	Night	11% 16% 45% 25% 3	693
April	1st to 10th	Night	9% 16% 44% 26% 5%	603
	11th to 20th	Night	13% 16% 49% 21% 2	593
	21st to end	Night	15% 13% 40% 27% 5%	600
May	1st to 10th	Night	15% 11% 41% 30% 4	600
	11th to 20th	Night	10% 9% 38% 30% 11% 1	591
	21st to end	Night	9% 8% 38% 34% 10% 1	650
June	1st to 10th	Night	6% 6% 36% 39% 13% 1	600
	11th to 20th	Night	4 4 45% 39% 8%	600
	21st to end	Night	6% 3 34% 45% 13% 1	600
July	1st to 10th	Night	8% 1 21% 45% 23% 2	585
	11th to 20th	Night	4 1 18% 54% 22% 2	582
	21st to end	Night	4 1 12% 55% 27% 2	657
August	1st to 10th	Night	4 1 17% 52% 24% 2	597
	11th to 20th	Night	6% 3 15% 51% 25%	594
	21st to end	Night	6% 2 16% 42% 32% 2	660
September	1st to 10th	Night	7% 2 19% 48% 24% 1	600
	11th to 20th	Night	13% 2 25% 41% 18% 1	600
	21st to end	Night	8% 4 30% 37% 20% 2	600
October	1st to 10th	Night	8% 6% 27% 43% 16% 1	600
	11th to 20th	Night	9% 9% 38% 36% 7%	681
	21st to end	Night	11% 9% 36% 29% 15%	960
November	1st to 10th	Night	8% 8% 37% 36% 10% 1	1025
	11th to 20th	Night	6% 11% 41% 33% 8%	1050
	21st to end	Night	10% 13% 34% 32% 11% 1	1050
December	1st to 10th	Night	9% 10% 39% 33% 8% 1	1050
	11th to 20th	Night	11% 11% 43% 30% 5%	1050
	21st to end	Night	12% 14% 38% 30% 6%	1155

Page generated at 2026-03-30 01:18:46. Version ac07

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