Devils Tower National Monument
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Devils Tower National Monument clear sky chart from 2005-11-06 to 2026-03-18.

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	8% 8% 3 6% 4 4 4 4 5% 7% 48%	140207
	Night	7% 8% 3 7% 4 4 4 4 5% 7% 46%	138796
Transparency	Day	34% 5% 12% 27% 18% 4	134962
	Night	37% 5% 13% 26% 16% 3	135051
Seeing	Day	13% 15% 34% 26% 10% 1	17723
	Night	12% 12% 35% 32% 9%	27890

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 11% 5% 12% 6% 4 4 4 6% 8% 36%	4720
	11th to 20th	Day	5% 15% 9% 10% 5% 5% 5% 4 5% 6% 33%	4740
	21st to end	Day	2 10% 5% 12% 6% 4 5% 4 5% 5% 43%	5340
February	1st to 10th	Day	6% 16% 7% 10% 7% 5% 4 4 5% 5% 32%	1890
	11th to 20th	Day	7% 13% 4 10% 5% 4 5% 3 5% 7% 38%	1926
	21st to end	Day	5% 12% 4 8% 6% 4 4 4 6% 8% 39%	1730
March	1st to 10th	Day	3 12% 4 7% 4 3 3 3 4 7% 50%	4600
	11th to 20th	Day	8% 8% 2 5% 3 3 3 3 6% 8% 51%	4886
	21st to end	Day	14% 13% 3 8% 5% 4 4 4 5% 7% 33%	5876
April	1st to 10th	Day	11% 11% 4 5% 4 3 4 4 6% 7% 39%	2400
	11th to 20th	Day	14% 14% 4 8% 4 4 5% 4 6% 6% 32%	2371
	21st to end	Day	18% 12% 2 6% 4 4 3 3 6% 7% 35%	2490
May	1st to 10th	Day	14% 10% 2 5% 3 3 3 3 5% 7% 43%	6286
	11th to 20th	Day	16% 8% 2 6% 4 4 4 4 5% 8% 40%	6298
	21st to end	Day	12% 6% 2 5% 3 4 4 4 6% 8% 45%	6925
June	1st to 10th	Day	9% 4 1 4 4 4 5% 5% 6% 9% 49%	2800
	11th to 20th	Day	10% 4 2 5% 3 4 4 4 7% 9% 47%	2800
	21st to end	Day	7% 3 1 4 2 3 4 3 5% 8% 61%	2800
July	1st to 10th	Day	4 5% 2 5% 3 4 5% 4 6% 8% 55%	6339
	11th to 20th	Day	4 2 1 3 3 3 4 4 6% 9% 63%	6340
	21st to end	Day	3 3 1 4 3 4 5% 4 6% 9% 57%	6903
August	1st to 10th	Day	5% 4 1 4 3 3 4 4 6% 9% 55%	6232
	11th to 20th	Day	4 3 1 4 3 3 4 4 6% 8% 58%	5608
	21st to end	Day	6% 4 2 5% 4 3 3 3 5% 7% 58%	5984
September	1st to 10th	Day	7% 4 1 3 2 2 3 3 4 7% 65%	2400
	11th to 20th	Day	8% 4 1 4 3 3 3 3 4 6% 59%	2372
	21st to end	Day	10% 5% 2 4 3 3 2 3 4 5% 60%	2200
October	1st to 10th	Day	8% 4 1 3 3 3 3 2 4 5% 64%	3276
	11th to 20th	Day	10% 6% 2 3 2 3 3 2 5% 5% 59%	3250
	21st to end	Day	11% 9% 2 5% 3 3 3 3 5% 8% 48%	3209
November	1st to 10th	Day	8% 8% 3 5% 5% 4 4 4 6% 8% 45%	1853
	11th to 20th	Day	6% 11% 3 7% 4 3 4 3 5% 7% 46%	1785
	21st to end	Day	5% 9% 3 7% 4 4 5% 4 6% 8% 46%	1680
December	1st to 10th	Day	4 12% 7% 7% 4 3 3 2 4 6% 47%	2700
	11th to 20th	Day	3 9% 3 6% 4 4 5% 5% 7% 8% 46%	3106
	21st to end	Day	5% 11% 4 10% 5% 5% 5% 3 5% 6% 42%	4092
January	1st to 10th	Night	4 14% 5% 11% 5% 5% 4 4 6% 7% 35%	8201
	11th to 20th	Night	5% 10% 6% 13% 6% 5% 5% 4 5% 6% 35%	8250
	21st to end	Night	3 9% 6% 11% 5% 4 3 3 4 6% 46%	8929
February	1st to 10th	Night	8% 15% 6% 10% 6% 4 4 4 5% 6% 33%	2730
	11th to 20th	Night	5% 12% 4 11% 5% 5% 4 4 6% 7% 37%	2579
	21st to end	Night	4 12% 3 8% 5% 4 4 3 6% 9% 41%	2076
March	1st to 10th	Night	6% 10% 3 6% 4 3 3 3 6% 8% 48%	5494
	11th to 20th	Night	6% 7% 2 6% 4 4 4 3 5% 9% 51%	5257
	21st to end	Night	10% 13% 4 9% 6% 5% 5% 5% 6% 8% 28%	5080
April	1st to 10th	Night	14% 10% 3 4 4 5% 3 4 6% 7% 39%	2000
	11th to 20th	Night	13% 11% 3 8% 5% 4 4 3 5% 6% 38%	1977
	21st to end	Night	12% 11% 3 6% 5% 5% 4 4 5% 7% 39%	1909
May	1st to 10th	Night	14% 9% 2 4 3 3 3 3 5% 6% 48%	3691
	11th to 20th	Night	13% 9% 2 6% 4 3 4 4 6% 9% 40%	3617
	21st to end	Night	14% 8% 2 5% 4 3 4 4 5% 7% 44%	3972
June	1st to 10th	Night	9% 5% 2 6% 3 4 3 3 7% 9% 49%	1600
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 3 6% 8% 45%	1600
	21st to end	Night	6% 3 1 4 4 3 5% 4 6% 8% 57%	1600
July	1st to 10th	Night	5% 4 2 4 4 3 4 4 6% 9% 55%	3640
	11th to 20th	Night	4 3 1 4 3 4 5% 4 7% 9% 55%	3640
	21st to end	Night	6% 4 2 4 3 3 4 4 6% 8% 56%	3970
August	1st to 10th	Night	4 3 1 5% 4 5% 5% 4 7% 9% 52%	3580
	11th to 20th	Night	5% 3 1 3 3 4 4 4 7% 11% 54%	4234
	21st to end	Night	6% 5% 2 5% 4 4 5% 3 6% 6% 54%	4993
September	1st to 10th	Night	6% 4 1 3 3 2 4 3 4 7% 63%	2000
	11th to 20th	Night	7% 4 2 4 3 4 4 4 6% 7% 55%	2027
	21st to end	Night	10% 4 1 4 3 3 3 3 4 7% 60%	2200
October	1st to 10th	Night	9% 5% 1 3 2 2 2 2 3 5% 67%	3910
	11th to 20th	Night	10% 5% 1 4 4 3 4 3 5% 6% 55%	3898
	21st to end	Night	10% 7% 2 5% 3 4 4 3 5% 7% 51%	4546
November	1st to 10th	Night	9% 7% 3 5% 4 3 4 4 6% 9% 45%	2665
	11th to 20th	Night	7% 10% 3 6% 5% 4 4 3 5% 8% 44%	2832
	21st to end	Night	6% 9% 4 6% 4 4 4 3 5% 8% 47%	2940
December	1st to 10th	Night	4 9% 5% 9% 5% 5% 4 3 5% 7% 44%	4710
	11th to 20th	Night	3 11% 4 8% 4 5% 4 4 6% 7% 43%	5321
	21st to end	Night	6% 11% 4 10% 5% 4 4 3 5% 6% 41%	7128

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	45% 5% 15% 27% 8% 1	4723
	11th to 20th	Day	51% 4 11% 21% 10% 2	4740
	21st to end	Day	42% 5% 13% 26% 13% 1	5340
February	1st to 10th	Day	54% 5% 11% 19% 10% 1	1890
	11th to 20th	Day	45% 5% 13% 22% 12% 2	1935
	21st to end	Day	42% 5% 13% 24% 13% 3	1730
March	1st to 10th	Day	34% 4 9% 30% 20% 3	4600
	11th to 20th	Day	30% 5% 16% 35% 14%	4886
	21st to end	Day	49% 6% 15% 24% 5%	5876
April	1st to 10th	Day	42% 6% 15% 25% 10% 2	2400
	11th to 20th	Day	51% 5% 12% 20% 11% 1	2374
	21st to end	Day	48% 5% 14% 24% 9%	2490
May	1st to 10th	Day	40% 5% 11% 25% 18% 1	6286
	11th to 20th	Day	40% 7% 12% 25% 14% 2	6302
	21st to end	Day	34% 7% 13% 31% 14% 1	6926
June	1st to 10th	Day	30% 8% 21% 26% 13% 2	2800
	11th to 20th	Day	31% 6% 17% 26% 17% 2	2800
	21st to end	Day	21% 6% 15% 29% 22% 6%	2800
July	1st to 10th	Day	24% 6% 9% 32% 23% 5%	6271
	11th to 20th	Day	18% 5% 9% 34% 25% 9%	6265
	21st to end	Day	21% 6% 9% 26% 27% 11%	6705
August	1st to 10th	Day	27% 7% 12% 24% 20% 11%	4536
	11th to 20th	Day	26% 5% 11% 29% 24% 5%	4055
	21st to end	Day	17% 4 10% 25% 35% 10%	4311
September	1st to 10th	Day	21% 4 8% 28% 30% 10%	2400
	11th to 20th	Day	25% 5% 9% 28% 26% 7%	2372
	21st to end	Day	28% 3 10% 32% 25% 3	2200
October	1st to 10th	Day	24% 2 7% 21% 32% 13%	3276
	11th to 20th	Day	28% 4 11% 29% 26% 2	3250
	21st to end	Day	35% 4 12% 29% 17% 2	3209
November	1st to 10th	Day	36% 6% 11% 24% 20% 2	1853
	11th to 20th	Day	37% 4 13% 27% 16% 3	1785
	21st to end	Day	35% 6% 17% 26% 14% 2	1680
December	1st to 10th	Day	38% 4 18% 26% 13% 1	2700
	11th to 20th	Day	33% 5% 22% 33% 6% 1	3104
	21st to end	Day	43% 4 8% 28% 14% 2	4092
January	1st to 10th	Night	47% 5% 12% 29% 6% 1	8202
	11th to 20th	Night	49% 5% 14% 18% 12% 2	8250
	21st to end	Night	40% 4 14% 26% 14% 2	8929
February	1st to 10th	Night	51% 5% 14% 18% 11% 1	2730
	11th to 20th	Night	45% 5% 12% 21% 14% 2	2580
	21st to end	Night	40% 5% 13% 24% 14% 3	2076
March	1st to 10th	Night	33% 5% 10% 31% 17% 4	5494
	11th to 20th	Night	30% 5% 18% 28% 18% 1	5257
	21st to end	Night	50% 8% 16% 19% 7%	5080
April	1st to 10th	Night	43% 7% 14% 24% 10% 2	2000
	11th to 20th	Night	47% 4 9% 26% 13% 1	1977
	21st to end	Night	45% 5% 14% 26% 9% 1	1909
May	1st to 10th	Night	37% 5% 10% 29% 18% 1	3691
	11th to 20th	Night	39% 6% 14% 27% 13% 1	3618
	21st to end	Night	38% 7% 11% 30% 13%	3972
June	1st to 10th	Night	32% 6% 23% 26% 13% 1	1600
	11th to 20th	Night	37% 6% 18% 23% 15% 3	1600
	21st to end	Night	24% 6% 15% 28% 23% 5%	1600
July	1st to 10th	Night	24% 5% 14% 30% 24% 4	3600
	11th to 20th	Night	23% 6% 10% 30% 26% 4	3592
	21st to end	Night	26% 6% 11% 25% 27% 6%	3856
August	1st to 10th	Night	28% 7% 12% 23% 20% 9%	2600
	11th to 20th	Night	24% 5% 15% 31% 20% 5%	3063
	21st to end	Night	23% 6% 10% 20% 31% 10%	3597
September	1st to 10th	Night	22% 4 6% 30% 26% 12%	2000
	11th to 20th	Night	27% 6% 9% 27% 24% 7%	2027
	21st to end	Night	26% 4 9% 29% 27% 6%	2200
October	1st to 10th	Night	23% 3 8% 24% 29% 14%	3910
	11th to 20th	Night	30% 4 9% 27% 28% 2	3898
	21st to end	Night	34% 4 12% 29% 16% 6%	4546
November	1st to 10th	Night	34% 6% 15% 24% 17% 4	2665
	11th to 20th	Night	39% 5% 12% 27% 16% 2	2832
	21st to end	Night	35% 5% 16% 27% 16% 2	2940
December	1st to 10th	Night	40% 5% 16% 26% 13% 1	4710
	11th to 20th	Night	39% 5% 17% 30% 8%	5322
	21st to end	Night	43% 4 8% 29% 13% 2	7128

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	11% 18% 35% 24% 8% 4	330
	11th to 20th	Day	17% 20% 36% 22% 5% 1	330
	21st to end	Day	14% 27% 37% 16% 5% 1	363
February	1st to 10th	Day	17% 18% 48% 15% 2	330
	11th to 20th	Day	13% 18% 50% 16% 4	330
	21st to end	Day	12% 24% 42% 16% 4 1	273
March	1st to 10th	Day	14% 24% 38% 17% 5% 2	330
	11th to 20th	Day	16% 21% 37% 21% 4 1	441
	21st to end	Day	22% 19% 33% 17% 8% 1	550
April	1st to 10th	Day	20% 21% 38% 18% 3	500
	11th to 20th	Day	24% 24% 34% 16% 2	492
	21st to end	Day	24% 15% 30% 22% 6% 2	590
May	1st to 10th	Day	19% 17% 27% 23% 12% 2	703
	11th to 20th	Day	21% 12% 29% 24% 13% 1	725
	21st to end	Day	18% 13% 33% 25% 10% 1	789
June	1st to 10th	Day	10% 11% 27% 34% 16% 2	730
	11th to 20th	Day	12% 17% 37% 25% 8%	730
	21st to end	Day	9% 9% 33% 31% 15% 2	730
July	1st to 10th	Day	6% 4 30% 40% 18% 1	721
	11th to 20th	Day	3 8% 36% 40% 13% 1	718
	21st to end	Day	4 8% 31% 39% 15% 3	794
August	1st to 10th	Day	6% 7% 30% 39% 17% 1	726
	11th to 20th	Day	8% 6% 34% 33% 17% 2	517
	21st to end	Day	4 11% 32% 35% 14% 4	583
September	1st to 10th	Day	6% 9% 36% 33% 14% 2	530
	11th to 20th	Day	9% 10% 30% 33% 16% 2	502
	21st to end	Day	16% 11% 32% 25% 12% 5%	330
October	1st to 10th	Day	18% 13% 28% 24% 12% 5%	330
	11th to 20th	Day	18% 21% 32% 19% 8% 2	330
	21st to end	Day	14% 22% 33% 21% 8% 1	363
November	1st to 10th	Day	16% 19% 43% 16% 6%	330
	11th to 20th	Day	14% 16% 44% 19% 5% 1	330
	21st to end	Day	10% 17% 43% 22% 6% 1	330
December	1st to 10th	Day	18% 22% 36% 18% 5%	330
	11th to 20th	Day	17% 22% 46% 13% 2	330
	21st to end	Day	16% 21% 39% 20% 3 1	363
January	1st to 10th	Night	11% 15% 36% 29% 8% 1	1050
	11th to 20th	Night	16% 17% 38% 23% 7%	1050
	21st to end	Night	12% 18% 40% 26% 5%	1123
February	1st to 10th	Night	14% 16% 42% 22% 6%	840
	11th to 20th	Night	11% 14% 42% 28% 5%	824
	21st to end	Night	11% 14% 38% 29% 7% 1	692
March	1st to 10th	Night	11% 16% 38% 29% 6% 1	840
	11th to 20th	Night	12% 11% 39% 29% 7%	828
	21st to end	Night	16% 13% 33% 31% 7% 1	704
April	1st to 10th	Night	20% 12% 34% 29% 7%	600
	11th to 20th	Night	22% 13% 31% 29% 5%	593
	21st to end	Night	20% 11% 28% 32% 9% 1	600
May	1st to 10th	Night	16% 9% 28% 33% 13% 2	600
	11th to 20th	Night	17% 11% 27% 33% 12%	591
	21st to end	Night	16% 11% 35% 28% 9%	650
June	1st to 10th	Night	10% 12% 29% 36% 13% 1	600
	11th to 20th	Night	12% 13% 38% 31% 7%	600
	21st to end	Night	6% 7% 33% 42% 12%	600
July	1st to 10th	Night	5% 5% 34% 38% 16% 1	585
	11th to 20th	Night	6% 5% 36% 43% 10%	582
	21st to end	Night	4 4 35% 46% 11%	657
August	1st to 10th	Night	6% 5% 34% 42% 14%	597
	11th to 20th	Night	8% 5% 24% 47% 15% 1	594
	21st to end	Night	6% 6% 29% 46% 13% 1	660
September	1st to 10th	Night	8% 4 28% 42% 17% 1	600
	11th to 20th	Night	11% 9% 25% 39% 14% 1	600
	21st to end	Night	11% 8% 31% 36% 13% 1	600
October	1st to 10th	Night	18% 9% 27% 31% 13% 1	790
	11th to 20th	Night	15% 12% 29% 34% 10%	800
	21st to end	Night	16% 11% 36% 29% 8% 1	1060
November	1st to 10th	Night	14% 12% 40% 27% 7%	1025
	11th to 20th	Night	14% 15% 38% 28% 6%	1050
	21st to end	Night	12% 13% 39% 32% 4	1050
December	1st to 10th	Night	11% 17% 41% 25% 5%	1050
	11th to 20th	Night	10% 14% 43% 28% 5%	1050
	21st to end	Night	16% 15% 38% 25% 5%	1155

Page generated at 2026-03-15 00:23:55. Version ac07

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