Fossil Butte National Monument
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fossil Butte National Monument clear sky chart from 2005-11-06 to 2026-09-29.

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	3 5% 2 7% 5% 5% 5% 4 6% 8% 51%	158083
	Night	2 6% 2 7% 5% 5% 5% 4 6% 8% 51%	150980
Transparency	Day	28% 6% 11% 22% 20% 12%	152840
	Night	29% 7% 13% 23% 20% 9%	147231
Seeing	Day	7% 13% 29% 29% 16% 5%	18091
	Night	5% 8% 26% 39% 20% 2	28208

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	1 7% 5% 16% 10% 8% 8% 6% 7% 8% 25%	5236
	11th to 20th	Day	4 3 11% 6% 5% 5% 5% 7% 9% 44%	5340
	21st to end	Day	1 5% 4 11% 7% 6% 6% 4 7% 9% 39%	5844
February	1st to 10th	Day	2 10% 4 12% 7% 6% 5% 5% 7% 9% 32%	1890
	11th to 20th	Day	2 9% 5% 11% 7% 6% 7% 5% 7% 9% 33%	1845
	21st to end	Day	1 8% 4 12% 8% 7% 6% 5% 6% 7% 36%	1704
March	1st to 10th	Day	2 8% 4 11% 6% 6% 6% 4 7% 9% 37%	5021
	11th to 20th	Day	1 4 2 8% 7% 5% 6% 4 7% 10% 46%	5110
	21st to end	Day	3 10% 4 10% 6% 7% 6% 5% 7% 9% 33%	5607
April	1st to 10th	Day	4 8% 2 7% 5% 5% 7% 5% 7% 8% 42%	2399
	11th to 20th	Day	4 9% 3 7% 6% 6% 6% 5% 7% 7% 40%	2598
	21st to end	Day	3 8% 3 8% 5% 6% 6% 5% 6% 8% 42%	2730
May	1st to 10th	Day	5% 7% 3 6% 4 4 4 4 6% 8% 51%	7626
	11th to 20th	Day	5% 6% 2 5% 4 4 5% 5% 7% 8% 49%	7596
	21st to end	Day	5% 5% 2 6% 4 4 5% 4 7% 9% 50%	8925
June	1st to 10th	Day	4 4 2 5% 4 4 5% 5% 7% 8% 53%	2940
	11th to 20th	Day	4 4 2 4 3 3 3 3 6% 8% 60%	2940
	21st to end	Day	2 2 1 4 2 3 2 3 5% 7% 69%	2940
July	1st to 10th	Day	3 3 1 4 3 3 3 3 4 6% 68%	8097
	11th to 20th	Day	2 2 1 4 3 3 4 4 6% 8% 63%	7650
	21st to end	Day	3 2 1 4 4 4 5% 3 6% 7% 61%	8304
August	1st to 10th	Day	2 2 1 3 3 2 3 3 4 6% 72%	7549
	11th to 20th	Day	2 2 1 4 4 4 5% 4 6% 8% 59%	7565
	21st to end	Day	3 2 2 5% 4 5% 5% 4 6% 7% 56%	8208
September	1st to 10th	Day	3 3 1 3 3 2 3 3 5% 6% 68%	2480
	11th to 20th	Day	3 3 2 4 4 4 4 3 5% 6% 63%	2310
	21st to end	Day	4 4 1 3 3 3 3 3 4 5% 66%	2289
October	1st to 10th	Day	4 4 2 3 3 2 3 3 4 6% 67%	3341
	11th to 20th	Day	6% 6% 2 4 3 4 3 3 5% 7% 56%	3250
	21st to end	Day	3 7% 3 6% 4 4 4 3 5% 7% 54%	3548
November	1st to 10th	Day	4 6% 3 9% 5% 4 5% 5% 6% 8% 46%	1880
	11th to 20th	Day	3 11% 3 8% 5% 5% 4 4 5% 9% 44%	1743
	21st to end	Day	2 7% 3 9% 6% 4 5% 5% 6% 10% 45%	1680
December	1st to 10th	Day	1 5% 3 7% 4 3 4 3 5% 7% 58%	2700
	11th to 20th	Day	2 7% 3 9% 7% 7% 8% 6% 8% 9% 34%	3106
	21st to end	Day	2 8% 4 12% 8% 9% 8% 5% 7% 11% 27%	4092
January	1st to 10th	Night	1 8% 3 13% 8% 6% 6% 5% 7% 10% 32%	7740
	11th to 20th	Night	1 4 3 11% 7% 6% 5% 4 6% 9% 45%	7650
	21st to end	Night	1 7% 4 10% 6% 5% 6% 4 6% 9% 42%	8370
February	1st to 10th	Night	2 8% 4 11% 6% 6% 7% 5% 8% 8% 34%	2730
	11th to 20th	Night	2 8% 4 10% 6% 5% 6% 5% 7% 9% 39%	2662
	21st to end	Night	1 8% 4 9% 8% 6% 6% 5% 7% 8% 38%	2099
March	1st to 10th	Night	2 10% 3 8% 5% 5% 6% 4 7% 8% 42%	5093
	11th to 20th	Night	1 6% 2 7% 5% 5% 6% 4 6% 8% 51%	5110
	21st to end	Night	2 10% 3 9% 5% 6% 5% 4 6% 8% 41%	5610
April	1st to 10th	Night	4 9% 3 7% 4 4 5% 4 5% 7% 46%	2221
	11th to 20th	Night	3 8% 2 7% 5% 5% 5% 5% 7% 8% 46%	1966
	21st to end	Night	4 6% 3 7% 4 4 4 4 7% 8% 48%	1890
May	1st to 10th	Night	4 7% 3 5% 3 4 4 4 6% 8% 51%	5321
	11th to 20th	Night	5% 5% 2 5% 3 3 3 3 5% 5% 61%	5296
	21st to end	Night	4 5% 2 5% 4 4 5% 4 7% 8% 53%	5281
June	1st to 10th	Night	4 4 1 4 4 4 4 3 6% 9% 58%	1680
	11th to 20th	Night	3 3 1 3 3 4 4 3 5% 7% 64%	1680
	21st to end	Night	2 3 1 4 2 2 3 2 4 6% 71%	1680
July	1st to 10th	Night	2 2 1 3 3 4 4 3 5% 6% 66%	4860
	11th to 20th	Night	2 2 1 4 4 4 5% 4 6% 8% 59%	5340
	21st to end	Night	2 2 1 4 3 4 4 4 6% 8% 61%	5805
August	1st to 10th	Night	2 1 1 3 2 3 3 3 5% 6% 71%	5273
	11th to 20th	Night	3 4 2 6% 4 4 4 3 5% 6% 59%	5291
	21st to end	Night	3 3 2 6% 4 5% 5% 4 6% 7% 56%	6008
September	1st to 10th	Night	3 3 2 4 3 2 3 2 4 7% 68%	2136
	11th to 20th	Night	4 3 1 3 3 4 3 5% 6% 6% 63%	2310
	21st to end	Night	4 3 1 3 3 3 4 2 4 4 68%	2288
October	1st to 10th	Night	4 3 1 3 2 2 2 2 3 5% 72%	3851
	11th to 20th	Night	4 6% 3 7% 4 4 4 3 4 6% 57%	3898
	21st to end	Night	4 7% 2 6% 3 4 4 3 6% 8% 53%	4252
November	1st to 10th	Night	3 8% 2 6% 4 4 4 4 6% 8% 51%	2635
	11th to 20th	Night	3 6% 3 6% 5% 5% 5% 4 7% 8% 47%	2855
	21st to end	Night	2 7% 3 7% 5% 5% 5% 5% 7% 8% 47%	2940
December	1st to 10th	Night	1 5% 3 6% 4 4 4 3 5% 7% 57%	4710
	11th to 20th	Night	2 8% 4 10% 6% 6% 5% 4 6% 8% 42%	5321
	21st to end	Night	2 8% 5% 12% 8% 8% 7% 5% 9% 9% 28%	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	44% 14% 21% 14% 7% 1	5239
	11th to 20th	Day	29% 11% 17% 25% 13% 5%	5340
	21st to end	Day	38% 9% 15% 22% 14% 3	5844
February	1st to 10th	Day	45% 9% 18% 16% 11% 1	1890
	11th to 20th	Day	44% 8% 18% 19% 8% 3	1854
	21st to end	Day	40% 9% 18% 21% 10% 2	1704
March	1st to 10th	Day	38% 8% 15% 26% 9% 5%	5021
	11th to 20th	Day	29% 10% 17% 29% 14% 1	5110
	21st to end	Day	43% 8% 22% 21% 5%	5607
April	1st to 10th	Day	35% 9% 17% 24% 13% 3	2399
	11th to 20th	Day	37% 8% 13% 26% 15%	2601
	21st to end	Day	38% 7% 13% 27% 14% 1	2730
May	1st to 10th	Day	29% 6% 10% 28% 21% 6%	7626
	11th to 20th	Day	29% 6% 7% 27% 25% 6%	7599
	21st to end	Day	28% 6% 8% 30% 25% 3	8926
June	1st to 10th	Day	26% 6% 13% 25% 26% 4	2940
	11th to 20th	Day	23% 4 8% 19% 31% 14%	2940
	21st to end	Day	16% 4 5% 18% 35% 22%	2940
July	1st to 10th	Day	18% 3 3 11% 22% 44%	8031
	11th to 20th	Day	18% 4 6% 14% 26% 32%	7581
	21st to end	Day	20% 4 5% 15% 28% 28%	8120
August	1st to 10th	Day	16% 4 4 14% 26% 37%	5978
	11th to 20th	Day	24% 6% 9% 24% 23% 15%	5964
	21st to end	Day	20% 4 10% 22% 28% 16%	6439
September	1st to 10th	Day	16% 4 8% 19% 33% 21%	2480
	11th to 20th	Day	22% 4 7% 23% 31% 14%	2310
	21st to end	Day	21% 4 7% 24% 35% 8%	2289
October	1st to 10th	Day	20% 3 7% 20% 31% 19%	3341
	11th to 20th	Day	27% 4 9% 28% 25% 7%	3250
	21st to end	Day	30% 4 12% 32% 19% 2	3548
November	1st to 10th	Day	34% 7% 15% 26% 16% 3	1880
	11th to 20th	Day	35% 6% 21% 22% 14% 1	1743
	21st to end	Day	34% 7% 17% 26% 15% 2	1680
December	1st to 10th	Day	24% 8% 20% 32% 14% 2	2700
	11th to 20th	Day	40% 9% 21% 21% 8% 1	3104
	21st to end	Day	45% 12% 12% 16% 10% 4	4092
January	1st to 10th	Night	38% 11% 17% 21% 12% 1	7741
	11th to 20th	Night	30% 10% 18% 29% 12% 1	7650
	21st to end	Night	35% 9% 13% 22% 19% 2	8370
February	1st to 10th	Night	42% 10% 19% 19% 9% 1	2730
	11th to 20th	Night	37% 8% 17% 22% 13% 3	2663
	21st to end	Night	36% 9% 17% 24% 12% 3	2099
March	1st to 10th	Night	34% 6% 15% 24% 14% 7%	5093
	11th to 20th	Night	27% 8% 18% 33% 13% 1	5110
	21st to end	Night	37% 8% 23% 24% 8% 1	5610
April	1st to 10th	Night	35% 7% 16% 24% 13% 5%	2221
	11th to 20th	Night	30% 7% 17% 27% 19% 1	1966
	21st to end	Night	33% 5% 16% 30% 17%	1890
May	1st to 10th	Night	27% 7% 10% 24% 29% 4	5319
	11th to 20th	Night	23% 5% 7% 29% 31% 5%	5297
	21st to end	Night	25% 6% 11% 32% 25% 2	5282
June	1st to 10th	Night	22% 6% 17% 22% 28% 5%	1680
	11th to 20th	Night	19% 5% 9% 23% 30% 15%	1680
	21st to end	Night	15% 4 6% 15% 34% 26%	1680
July	1st to 10th	Night	18% 4 3 11% 21% 43%	4818
	11th to 20th	Night	21% 4 6% 12% 24% 33%	5286
	21st to end	Night	20% 5% 5% 17% 29% 24%	5677
August	1st to 10th	Night	14% 3 4 14% 26% 39%	4168
	11th to 20th	Night	28% 4 8% 23% 22% 16%	4168
	21st to end	Night	23% 4 8% 19% 25% 22%	4708
September	1st to 10th	Night	17% 3 7% 19% 28% 25%	2136
	11th to 20th	Night	19% 4 10% 22% 30% 15%	2310
	21st to end	Night	20% 4 7% 26% 34% 10%	2288
October	1st to 10th	Night	16% 3 7% 20% 41% 13%	3851
	11th to 20th	Night	29% 3 8% 28% 24% 8%	3898
	21st to end	Night	29% 4 10% 34% 20% 3	4252
November	1st to 10th	Night	29% 7% 16% 25% 20% 3	2635
	11th to 20th	Night	32% 6% 21% 27% 13% 2	2855
	21st to end	Night	32% 6% 16% 28% 14% 3	2940
December	1st to 10th	Night	25% 7% 16% 33% 16% 2	4710
	11th to 20th	Night	37% 8% 22% 24% 8% 1	5322
	21st to end	Night	44% 11% 15% 18% 9% 3	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	8% 17% 28% 29% 15% 4	330
	11th to 20th	Day	5% 16% 33% 27% 17% 2	330
	21st to end	Day	3 10% 38% 32% 14% 3	363
February	1st to 10th	Day	7% 25% 35% 25% 6% 2	330
	11th to 20th	Day	5% 21% 37% 24% 9% 3	330
	21st to end	Day	5% 22% 35% 28% 8% 1	420
March	1st to 10th	Day	7% 17% 36% 27% 10% 4	540
	11th to 20th	Day	7% 17% 30% 32% 14% 1	540
	21st to end	Day	10% 21% 32% 28% 8% 1	594
April	1st to 10th	Day	10% 19% 30% 24% 15% 3	540
	11th to 20th	Day	11% 20% 35% 23% 9% 2	532
	21st to end	Day	12% 25% 26% 20% 14% 4	540
May	1st to 10th	Day	11% 20% 29% 23% 12% 4	543
	11th to 20th	Day	13% 16% 27% 29% 11% 4	568
	21st to end	Day	10% 13% 25% 26% 19% 7%	808
June	1st to 10th	Day	5% 9% 27% 29% 23% 6%	780
	11th to 20th	Day	5% 13% 33% 31% 16% 2	780
	21st to end	Day	4 9% 29% 34% 19% 4	780
July	1st to 10th	Day	4 5% 22% 40% 23% 6%	725
	11th to 20th	Day	3 5% 28% 36% 21% 7%	564
	21st to end	Day	5% 5% 21% 38% 22% 9%	619
August	1st to 10th	Day	4 5% 28% 35% 20% 7%	567
	11th to 20th	Day	2 5% 29% 32% 24% 8%	557
	21st to end	Day	3 7% 28% 32% 21% 10%	627
September	1st to 10th	Day	4 9% 25% 29% 22% 11%	570
	11th to 20th	Day	6% 11% 34% 24% 15% 10%	570
	21st to end	Day	5% 11% 25% 31% 20% 9%	563
October	1st to 10th	Day	7% 11% 25% 25% 22% 11%	375
	11th to 20th	Day	7% 18% 23% 26% 18% 8%	330
	21st to end	Day	8% 18% 29% 28% 14% 3	363
November	1st to 10th	Day	8% 16% 28% 29% 13% 6%	330
	11th to 20th	Day	9% 13% 28% 36% 11% 3	330
	21st to end	Day	4 14% 32% 32% 15% 4	330
December	1st to 10th	Day	5% 17% 29% 29% 17% 2	330
	11th to 20th	Day	5% 18% 32% 32% 12% 2	330
	21st to end	Day	9% 16% 36% 24% 11% 5%	363
January	1st to 10th	Night	6% 11% 30% 34% 17% 2	887
	11th to 20th	Night	4 12% 32% 33% 18% 2	840
	21st to end	Night	5% 6% 34% 39% 14% 2	924
February	1st to 10th	Night	5% 14% 37% 33% 11% 2	840
	11th to 20th	Night	4 10% 33% 38% 13% 1	824
	21st to end	Night	4 10% 37% 38% 10% 1	692
March	1st to 10th	Night	6% 10% 31% 39% 13% 2	840
	11th to 20th	Night	3 8% 28% 44% 16% 1	840
	21st to end	Night	6% 8% 36% 36% 13% 1	924
April	1st to 10th	Night	7% 10% 30% 39% 13% 1	751
	11th to 20th	Night	7% 13% 34% 35% 10% 1	623
	21st to end	Night	8% 10% 28% 37% 16% 2	630
May	1st to 10th	Night	9% 10% 27% 36% 18% 1	630
	11th to 20th	Night	9% 8% 20% 37% 23% 3	621
	21st to end	Night	8% 7% 23% 34% 26% 2	683
June	1st to 10th	Night	4 7% 22% 40% 25% 3	630
	11th to 20th	Night	5% 9% 28% 41% 17% 1	630
	21st to end	Night	3 3 21% 46% 25% 2	630
July	1st to 10th	Night	3 2 13% 43% 36% 2	615
	11th to 20th	Night	3 2 13% 49% 31% 2	612
	21st to end	Night	2 1 9% 48% 37% 2	690
August	1st to 10th	Night	4 2 12% 50% 30% 3	627
	11th to 20th	Night	3 2 11% 47% 34% 2	624
	21st to end	Night	3 1 12% 45% 34% 4	693
September	1st to 10th	Night	4 2 17% 44% 31% 3	666
	11th to 20th	Night	4 4 16% 40% 31% 5%	840
	21st to end	Night	6% 3 16% 38% 29% 8%	832
October	1st to 10th	Night	7% 5% 20% 39% 26% 4	800
	11th to 20th	Night	7% 9% 22% 36% 23% 3	800
	21st to end	Night	7% 7% 23% 41% 19% 3	880
November	1st to 10th	Night	5% 7% 28% 39% 19% 2	820
	11th to 20th	Night	5% 11% 28% 38% 14% 2	965
	21st to end	Night	6% 10% 30% 36% 15% 3	1050
December	1st to 10th	Night	6% 12% 31% 37% 13% 1	1050
	11th to 20th	Night	6% 10% 33% 39% 11% 1	1050
	21st to end	Night	5% 15% 35% 33% 11% 1	1155

Page generated at 2026-09-26 02:18:37. Version ac07

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