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 2025-05-26.

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 6% 3 7% 5% 5% 5% 4 6% 8% 49%	118261
	Night	3 6% 3 8% 5% 5% 5% 4 6% 7% 49%	119960
Transparency	Day	30% 7% 12% 21% 19% 11%	118023
	Night	30% 7% 13% 23% 19% 8%	119787
Seeing	Day	6% 13% 29% 30% 17% 5%	16179
	Night	5% 8% 26% 39% 20% 2	26458

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 6% 4 16% 11% 8% 7% 6% 7% 9% 25%	4029
	11th to 20th	Day	5% 4 14% 8% 6% 7% 6% 8% 9% 33%	4100
	21st to end	Day	1 7% 5% 13% 7% 7% 6% 4 7% 9% 35%	4510
February	1st to 10th	Day	2 11% 4 13% 7% 6% 4 5% 7% 9% 31%	1800
	11th to 20th	Day	2 9% 5% 11% 7% 6% 6% 5% 7% 9% 34%	1755
	21st to end	Day	1 8% 4 12% 8% 7% 6% 5% 6% 7% 35%	1625
March	1st to 10th	Day	2 8% 4 11% 6% 6% 6% 4 7% 9% 37%	4912
	11th to 20th	Day	1 4 2 8% 7% 6% 6% 4 8% 10% 45%	5000
	21st to end	Day	3 10% 4 10% 6% 7% 6% 5% 7% 9% 32%	5486
April	1st to 10th	Day	4 8% 2 7% 5% 5% 7% 5% 7% 8% 42%	2285
	11th to 20th	Day	4 9% 3 8% 6% 5% 5% 5% 7% 7% 40%	2473
	21st to end	Day	4 8% 3 8% 5% 6% 6% 5% 6% 7% 42%	2600
May	1st to 10th	Day	7% 11% 4 8% 5% 5% 4 5% 7% 8% 36%	4240
	11th to 20th	Day	5% 6% 1 4 3 4 5% 5% 7% 8% 52%	4201
	21st to end	Day	5% 6% 2 7% 4 5% 5% 4 6% 8% 47%	4850
June	1st to 10th	Day	4 4 2 5% 4 4 5% 5% 7% 9% 51%	2660
	11th to 20th	Day	5% 4 2 5% 3 3 4 3 6% 7% 58%	2660
	21st to end	Day	2 2 1 3 2 4 2 3 5% 7% 69%	2660
July	1st to 10th	Day	2 2 1 2 2 2 2 2 3 5% 76%	4348
	11th to 20th	Day	3 2 1 3 3 3 4 4 6% 8% 63%	4110
	21st to end	Day	4 2 1 3 3 3 4 3 6% 7% 63%	4454
August	1st to 10th	Day	3 2 1 4 3 3 4 4 5% 6% 64%	4092
	11th to 20th	Day	2 2 1 4 4 3 4 4 5% 7% 64%	4028
	21st to end	Day	2 2 1 3 3 3 3 3 4 6% 70%	4433
September	1st to 10th	Day	4 3 1 3 3 3 4 3 5% 6% 68%	2244
	11th to 20th	Day	4 3 2 4 4 3 4 3 4 6% 64%	2090
	21st to end	Day	4 4 1 3 3 3 3 3 4 5% 67%	2090
October	1st to 10th	Day	4 4 1 3 3 2 3 3 4 6% 67%	3239
	11th to 20th	Day	6% 6% 2 4 3 4 3 3 5% 7% 57%	3150
	21st to end	Day	3 7% 3 6% 4 4 4 3 5% 7% 53%	3438
November	1st to 10th	Day	4 6% 3 9% 4 4 5% 5% 6% 8% 45%	1789
	11th to 20th	Day	3 11% 3 8% 4 5% 4 4 6% 9% 45%	1660
	21st to end	Day	2 7% 4 9% 6% 4 5% 5% 6% 10% 44%	1600
December	1st to 10th	Day	1 5% 3 7% 5% 3 4 3 5% 7% 59%	2620
	11th to 20th	Day	1 7% 4 10% 7% 7% 8% 6% 8% 9% 34%	3026
	21st to end	Day	2 8% 4 12% 8% 9% 8% 5% 7% 11% 27%	4004
January	1st to 10th	Night	1 7% 4 14% 9% 5% 5% 4 7% 10% 34%	5977
	11th to 20th	Night	1 5% 3 15% 10% 7% 7% 4 7% 10% 31%	5880
	21st to end	Night	1 8% 5% 12% 7% 6% 6% 4 5% 7% 38%	6468
February	1st to 10th	Night	2 9% 4 11% 6% 7% 7% 5% 8% 8% 33%	2600
	11th to 20th	Night	2 8% 4 10% 6% 5% 5% 5% 7% 9% 40%	2532
	21st to end	Night	1 9% 5% 9% 8% 6% 6% 5% 7% 8% 37%	2002
March	1st to 10th	Night	2 10% 3 8% 5% 5% 6% 4 7% 8% 42%	4982
	11th to 20th	Night	1 6% 2 7% 5% 5% 6% 4 6% 8% 50%	5000
	21st to end	Night	2 10% 3 9% 5% 6% 5% 4 6% 8% 40%	5489
April	1st to 10th	Night	4 9% 3 7% 4 5% 5% 4 5% 7% 45%	2115
	11th to 20th	Night	3 8% 2 7% 5% 4 5% 5% 7% 8% 46%	1871
	21st to end	Night	4 6% 3 7% 4 4 4 4 7% 8% 47%	1800
May	1st to 10th	Night	6% 11% 4 7% 4 5% 4 4 6% 6% 43%	2950
	11th to 20th	Night	6% 4 1 5% 3 3 3 3 5% 6% 59%	2924
	21st to end	Night	5% 6% 2 5% 4 4 4 3 6% 7% 54%	2852
June	1st to 10th	Night	4 4 1 4 4 4 4 4 6% 9% 57%	1520
	11th to 20th	Night	4 4 1 3 3 4 4 3 5% 7% 63%	1520
	21st to end	Night	2 3 1 4 2 2 3 2 4 6% 71%	1520
July	1st to 10th	Night	2 2 1 2 2 3 2 2 4 5% 74%	2604
	11th to 20th	Night	2 2 1 3 3 4 5% 4 6% 9% 62%	2860
	21st to end	Night	2 2 1 4 3 4 4 4 6% 8% 62%	3109
August	1st to 10th	Night	3 2 1 4 3 3 3 4 6% 7% 62%	2847
	11th to 20th	Night	4 4 1 5% 4 4 4 3 4 5% 63%	2811
	21st to end	Night	1 1 1 3 2 2 3 2 4 5% 75%	3234
September	1st to 10th	Night	3 3 2 4 3 3 3 2 4 6% 69%	1932
	11th to 20th	Night	4 3 1 3 2 4 3 5% 6% 6% 65%	2090
	21st to end	Night	4 3 1 3 3 3 3 2 4 4 70%	2090
October	1st to 10th	Night	4 3 1 3 2 2 2 2 3 5% 72%	3733
	11th to 20th	Night	4 5% 2 6% 4 4 4 3 4 6% 57%	3778
	21st to end	Night	4 7% 2 6% 3 4 4 3 6% 8% 52%	4120
November	1st to 10th	Night	3 8% 2 6% 4 4 4 4 6% 8% 51%	2506
	11th to 20th	Night	3 6% 3 6% 5% 5% 5% 4 7% 8% 48%	2719
	21st to end	Night	2 7% 3 7% 5% 5% 5% 5% 6% 8% 47%	2800
December	1st to 10th	Night	1 4 3 6% 4 4 4 3 5% 7% 58%	4570
	11th to 20th	Night	2 8% 4 10% 6% 6% 5% 4 6% 8% 41%	5181
	21st to end	Night	2 8% 5% 12% 8% 8% 7% 5% 9% 9% 28%	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	43% 13% 21% 13% 9% 1	4030
	11th to 20th	Day	37% 14% 17% 17% 13% 3	4100
	21st to end	Day	41% 9% 15% 19% 13% 3	4510
February	1st to 10th	Day	46% 10% 18% 15% 11% 1	1800
	11th to 20th	Day	43% 8% 19% 19% 7% 3	1764
	21st to end	Day	41% 9% 18% 19% 10% 2	1625
March	1st to 10th	Day	38% 8% 15% 26% 9% 5%	4912
	11th to 20th	Day	29% 10% 17% 29% 14% 1	5000
	21st to end	Day	44% 8% 22% 21% 5%	5486
April	1st to 10th	Day	36% 9% 17% 23% 13% 3	2285
	11th to 20th	Day	38% 8% 14% 27% 14%	2476
	21st to end	Day	38% 7% 14% 27% 14% 1	2600
May	1st to 10th	Day	40% 8% 13% 21% 13% 5%	4240
	11th to 20th	Day	25% 6% 9% 35% 18% 6%	4204
	21st to end	Day	31% 7% 10% 30% 20% 2	4850
June	1st to 10th	Day	27% 6% 15% 26% 23% 4	2660
	11th to 20th	Day	24% 5% 9% 20% 29% 13%	2660
	21st to end	Day	16% 4 5% 18% 34% 23%	2660
July	1st to 10th	Day	12% 3 4 10% 17% 52%	4281
	11th to 20th	Day	17% 4 4 11% 28% 36%	4041
	21st to end	Day	20% 5% 5% 11% 30% 30%	4314
August	1st to 10th	Day	20% 4 5% 17% 30% 24%	4078
	11th to 20th	Day	18% 5% 5% 20% 31% 21%	4067
	21st to end	Day	15% 4 6% 13% 39% 24%	4432
September	1st to 10th	Day	17% 4 7% 18% 32% 21%	2244
	11th to 20th	Day	21% 5% 7% 22% 31% 15%	2090
	21st to end	Day	21% 4 7% 24% 36% 8%	2090
October	1st to 10th	Day	20% 3 7% 20% 30% 20%	3239
	11th to 20th	Day	27% 3 9% 28% 25% 7%	3150
	21st to end	Day	30% 4 12% 31% 19% 2	3438
November	1st to 10th	Day	35% 7% 15% 25% 16% 3	1789
	11th to 20th	Day	33% 7% 21% 22% 15% 1	1660
	21st to end	Day	35% 7% 16% 25% 15% 2	1600
December	1st to 10th	Day	24% 7% 20% 33% 14% 2	2620
	11th to 20th	Day	40% 9% 21% 20% 8%	3024
	21st to end	Day	46% 12% 12% 16% 11% 4	4004
January	1st to 10th	Night	37% 10% 15% 23% 14% 1	5977
	11th to 20th	Night	39% 13% 16% 22% 10% 1	5880
	21st to end	Night	40% 9% 14% 18% 16% 2	6468
February	1st to 10th	Night	43% 10% 18% 19% 9% 1	2600
	11th to 20th	Night	37% 8% 17% 22% 13% 3	2533
	21st to end	Night	37% 9% 18% 22% 12% 3	2002
March	1st to 10th	Night	33% 6% 15% 24% 14% 7%	4982
	11th to 20th	Night	28% 8% 17% 33% 13% 1	5000
	21st to end	Night	37% 8% 23% 24% 8% 1	5489
April	1st to 10th	Night	35% 7% 17% 22% 13% 5%	2115
	11th to 20th	Night	31% 7% 17% 27% 18% 1	1871
	21st to end	Night	33% 5% 16% 30% 16%	1800
May	1st to 10th	Night	34% 9% 12% 23% 20% 3	2950
	11th to 20th	Night	24% 7% 11% 35% 19% 5%	2925
	21st to end	Night	26% 6% 12% 33% 21% 2	2852
June	1st to 10th	Night	23% 6% 19% 23% 26% 4	1520
	11th to 20th	Night	20% 5% 9% 24% 29% 13%	1520
	21st to end	Night	15% 4 6% 15% 33% 28%	1520
July	1st to 10th	Night	13% 4 4 10% 19% 52%	2562
	11th to 20th	Night	18% 4 4 13% 29% 33%	2806
	21st to end	Night	18% 4 6% 13% 33% 26%	3011
August	1st to 10th	Night	19% 4 5% 17% 29% 26%	2838
	11th to 20th	Night	24% 3 5% 16% 29% 22%	2838
	21st to end	Night	13% 3 6% 14% 34% 31%	3234
September	1st to 10th	Night	17% 3 8% 19% 28% 26%	1932
	11th to 20th	Night	18% 5% 11% 21% 30% 16%	2090
	21st to end	Night	19% 4 7% 26% 35% 10%	2090
October	1st to 10th	Night	16% 3 7% 20% 41% 14%	3733
	11th to 20th	Night	29% 3 8% 27% 24% 8%	3778
	21st to end	Night	29% 4 10% 34% 20% 3	4120
November	1st to 10th	Night	30% 7% 16% 25% 20% 3	2506
	11th to 20th	Night	31% 6% 21% 27% 14% 2	2719
	21st to end	Night	32% 6% 16% 28% 15% 3	2800
December	1st to 10th	Night	25% 6% 16% 34% 16% 2	4570
	11th to 20th	Night	37% 8% 22% 24% 8%	5182
	21st to end	Night	44% 11% 14% 18% 8% 3	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	8% 17% 24% 31% 16% 4	300
	11th to 20th	Day	5% 17% 30% 28% 17% 2	300
	21st to end	Day	4 10% 35% 32% 15% 3	330
February	1st to 10th	Day	7% 27% 34% 25% 6% 1	300
	11th to 20th	Day	5% 21% 37% 24% 9% 3	300
	21st to end	Day	3 22% 37% 28% 8% 1	389
March	1st to 10th	Day	7% 16% 36% 29% 10% 4	500
	11th to 20th	Day	5% 15% 31% 33% 15% 1	500
	21st to end	Day	10% 20% 32% 29% 8% 1	550
April	1st to 10th	Day	10% 19% 29% 25% 14% 3	500
	11th to 20th	Day	10% 20% 35% 24% 9% 1	492
	21st to end	Day	11% 25% 27% 20% 15% 4	500
May	1st to 10th	Day	12% 20% 29% 23% 12% 4	503
	11th to 20th	Day	13% 16% 27% 30% 11% 4	528
	21st to end	Day	10% 13% 25% 25% 20% 7%	726
June	1st to 10th	Day	6% 8% 26% 30% 23% 7%	680
	11th to 20th	Day	6% 13% 32% 31% 16% 2	680
	21st to end	Day	3 8% 29% 35% 21% 5%	680
July	1st to 10th	Day	4 5% 21% 41% 23% 6%	630
	11th to 20th	Day	3 5% 29% 36% 21% 5%	484
	21st to end	Day	5% 4 20% 39% 23% 9%	531
August	1st to 10th	Day	5% 4 27% 36% 22% 6%	487
	11th to 20th	Day	2 6% 28% 32% 24% 8%	477
	21st to end	Day	3 7% 27% 32% 21% 10%	539
September	1st to 10th	Day	4 7% 24% 29% 23% 12%	490
	11th to 20th	Day	6% 10% 33% 24% 17% 10%	490
	21st to end	Day	5% 12% 23% 31% 20% 8%	490
October	1st to 10th	Day	7% 10% 25% 24% 22% 11%	343
	11th to 20th	Day	7% 17% 20% 28% 19% 9%	300
	21st to end	Day	8% 18% 30% 28% 14% 2	330
November	1st to 10th	Day	8% 16% 29% 27% 14% 6%	300
	11th to 20th	Day	9% 14% 27% 36% 9% 3	300
	21st to end	Day	4 14% 32% 32% 14% 4	300
December	1st to 10th	Day	5% 14% 29% 32% 19% 2	300
	11th to 20th	Day	4 18% 30% 34% 12% 1	300
	21st to end	Day	7% 16% 35% 25% 12% 5%	330
January	1st to 10th	Night	5% 12% 29% 34% 18% 2	845
	11th to 20th	Night	4 12% 32% 33% 18% 2	800
	21st to end	Night	5% 7% 33% 39% 14% 2	880
February	1st to 10th	Night	5% 14% 37% 33% 10% 2	800
	11th to 20th	Night	4 9% 34% 38% 14% 1	784
	21st to end	Night	4 10% 35% 39% 10% 1	660
March	1st to 10th	Night	6% 9% 30% 39% 14% 2	800
	11th to 20th	Night	3 7% 28% 45% 17% 1	800
	21st to end	Night	7% 9% 35% 35% 13% 1	880
April	1st to 10th	Night	8% 9% 31% 38% 13% 1	715
	11th to 20th	Night	7% 13% 33% 35% 11% 2	593
	21st to end	Night	8% 10% 28% 37% 16% 2	600
May	1st to 10th	Night	9% 10% 27% 36% 18% 1	600
	11th to 20th	Night	9% 8% 20% 37% 23% 3	591
	21st to end	Night	9% 7% 23% 33% 26% 3	634
June	1st to 10th	Night	4 7% 21% 39% 26% 3	570
	11th to 20th	Night	6% 9% 27% 41% 18% 1	570
	21st to end	Night	2 2 21% 47% 26% 2	570
July	1st to 10th	Night	3 2 13% 42% 37% 2	555
	11th to 20th	Night	3 2 13% 49% 31% 2	552
	21st to end	Night	2 1 8% 48% 39% 3	624
August	1st to 10th	Night	4 2 11% 48% 32% 3	567
	11th to 20th	Night	3 2 11% 48% 34% 2	564
	21st to end	Night	3 1 12% 44% 36% 4	627
September	1st to 10th	Night	3 2 17% 43% 32% 3	602
	11th to 20th	Night	4 3 15% 39% 33% 5%	760
	21st to end	Night	6% 3 17% 36% 29% 8%	760
October	1st to 10th	Night	7% 5% 21% 38% 26% 4	760
	11th to 20th	Night	7% 8% 21% 36% 24% 3	760
	21st to end	Night	7% 7% 24% 40% 19% 3	836
November	1st to 10th	Night	5% 7% 28% 38% 20% 2	780
	11th to 20th	Night	5% 12% 29% 38% 14% 2	919
	21st to end	Night	7% 10% 30% 36% 15% 3	1000
December	1st to 10th	Night	6% 11% 31% 38% 13% 1	1000
	11th to 20th	Night	6% 10% 33% 40% 11% 1	1000
	21st to end	Night	5% 15% 34% 33% 11% 2	1100

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