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 2024-11-02.

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	3 6% 3 7% 5% 5% 5% 4 6% 8% 49%	101257
	Night	3 6% 3 8% 5% 5% 5% 4 6% 7% 49%	97970
Transparency	Day	30% 7% 13% 20% 19% 11%	101019
	Night	31% 7% 14% 22% 18% 9%	97797
Seeing	Day	6% 13% 28% 30% 17% 5%	15467
	Night	5% 8% 25% 39% 20% 2	25640

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% 4 16% 10% 8% 7% 6% 6% 7% 28%	2803
	11th to 20th	Day	1 7% 5% 19% 11% 7% 6% 4 7% 6% 28%	2860
	21st to end	Day	2 9% 6% 16% 9% 8% 7% 4 7% 9% 23%	3146
February	1st to 10th	Day	2 11% 4 13% 7% 6% 4 5% 6% 8% 32%	1710
	11th to 20th	Day	2 9% 5% 10% 7% 6% 6% 5% 6% 9% 36%	1665
	21st to end	Day	1 9% 4 12% 8% 7% 6% 5% 6% 7% 33%	1546
March	1st to 10th	Day	1 6% 4 11% 7% 7% 7% 5% 7% 10% 34%	3415
	11th to 20th	Day	1 5% 2 8% 6% 5% 5% 4 6% 9% 48%	3490
	21st to end	Day	3 12% 5% 12% 6% 6% 7% 5% 7% 9% 28%	3825
April	1st to 10th	Day	4 8% 2 7% 5% 5% 7% 5% 7% 7% 41%	2171
	11th to 20th	Day	4 9% 3 8% 6% 6% 5% 5% 7% 7% 40%	2348
	21st to end	Day	4 8% 3 8% 5% 6% 6% 5% 6% 7% 42%	2470
May	1st to 10th	Day	7% 11% 4 8% 6% 5% 4 5% 7% 8% 35%	4110
	11th to 20th	Day	5% 5% 1 4 3 4 5% 4 7% 8% 53%	4071
	21st to end	Day	5% 7% 2 6% 4 5% 5% 4 6% 7% 47%	4780
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	7% 6% 2 5% 4 3 4 4 5% 7% 54%	1943
	11th to 20th	Day	5% 5% 2 5% 3 4 3 3 5% 8% 57%	1900
	21st to end	Day	2 6% 3 7% 5% 4 4 3 5% 8% 53%	2090
November	1st to 10th	Day	4 7% 3 9% 5% 4 5% 4 6% 8% 45%	1708
	11th to 20th	Day	3 11% 3 8% 4 4 4 4 6% 9% 44%	1577
	21st to end	Day	2 7% 3 9% 6% 4 5% 5% 6% 9% 43%	1520
December	1st to 10th	Day	2 8% 5% 11% 7% 4 6% 4 5% 8% 38%	1520
	11th to 20th	Day	2 10% 4 11% 7% 6% 6% 5% 8% 8% 31%	1926
	21st to end	Day	2 8% 4 10% 7% 8% 7% 5% 7% 11% 30%	2794
January	1st to 10th	Night	1 8% 4 16% 10% 5% 5% 3 5% 7% 34%	4179
	11th to 20th	Night	1 7% 5% 18% 11% 7% 6% 4 6% 7% 29%	4110
	21st to end	Night	2 11% 7% 14% 8% 7% 7% 5% 5% 7% 26%	4521
February	1st to 10th	Night	2 9% 5% 11% 6% 7% 7% 5% 8% 8% 33%	2470
	11th to 20th	Night	2 8% 4 9% 6% 5% 5% 5% 6% 9% 41%	2402
	21st to end	Night	1 9% 5% 10% 8% 6% 6% 5% 7% 8% 36%	1905
March	1st to 10th	Night	1 8% 3 7% 5% 5% 7% 5% 7% 10% 43%	3459
	11th to 20th	Night	1 5% 2 6% 4 4 6% 4 6% 8% 53%	3490
	21st to end	Night	3 13% 4 11% 6% 6% 5% 4 6% 7% 35%	3828
April	1st to 10th	Night	4 10% 3 7% 4 5% 5% 4 5% 7% 45%	2009
	11th to 20th	Night	3 9% 2 7% 4 5% 5% 5% 7% 8% 46%	1777
	21st to end	Night	4 7% 3 7% 4 4 4 4 7% 8% 48%	1710
May	1st to 10th	Night	6% 11% 4 7% 4 5% 4 4 6% 7% 42%	2860
	11th to 20th	Night	6% 4 1 5% 3 3 3 3 5% 6% 59%	2834
	21st to end	Night	5% 5% 2 5% 5% 4 4 3 6% 7% 54%	2806
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	6% 5% 1 5% 3 3 3 3 5% 6% 58%	2237
	11th to 20th	Night	5% 6% 2 5% 3 3 3 3 4 6% 59%	2280
	21st to end	Night	4 6% 2 6% 3 4 4 3 6% 7% 54%	2508
November	1st to 10th	Night	3 8% 2 5% 4 4 4 4 6% 8% 50%	2401
	11th to 20th	Night	3 6% 3 6% 5% 6% 5% 4 7% 8% 48%	2583
	21st to end	Night	2 7% 3 7% 5% 5% 5% 5% 7% 7% 46%	2660
December	1st to 10th	Night	3 8% 4 10% 6% 6% 6% 4 6% 8% 39%	2660
	11th to 20th	Night	3 9% 4 13% 6% 6% 5% 4 6% 9% 36%	3271
	21st to end	Night	2 8% 4 12% 7% 7% 6% 5% 8% 9% 32%	4873

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	42% 12% 23% 15% 7% 1	2804
	11th to 20th	Day	45% 12% 22% 13% 7% 1	2860
	21st to end	Day	50% 12% 19% 12% 5% 2	3146
February	1st to 10th	Day	47% 9% 18% 15% 10% 1	1710
	11th to 20th	Day	42% 8% 20% 20% 7% 3	1674
	21st to end	Day	43% 9% 19% 19% 9% 2	1546
March	1st to 10th	Day	36% 10% 22% 22% 10% 1	3415
	11th to 20th	Day	29% 10% 21% 28% 10% 1	3490
	21st to end	Day	48% 9% 20% 18% 5% 1	3825
April	1st to 10th	Day	37% 9% 18% 21% 12% 3	2171
	11th to 20th	Day	39% 8% 14% 26% 13%	2351
	21st to end	Day	38% 6% 14% 27% 14% 1	2470
May	1st to 10th	Day	40% 8% 13% 20% 13% 5%	4110
	11th to 20th	Day	25% 6% 9% 36% 18% 6%	4074
	21st to end	Day	31% 7% 10% 30% 20% 2	4780
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	30% 4 12% 25% 22% 7%	1943
	11th to 20th	Day	26% 4 14% 31% 20% 5%	1900
	21st to end	Day	29% 5% 17% 26% 20% 2	2090
November	1st to 10th	Day	35% 7% 15% 25% 15% 3	1708
	11th to 20th	Day	34% 6% 21% 22% 15% 1	1577
	21st to end	Day	36% 7% 17% 24% 15% 2	1520
December	1st to 10th	Day	40% 10% 23% 15% 9% 3	1520
	11th to 20th	Day	45% 9% 19% 17% 10% 1	1924
	21st to end	Day	43% 14% 13% 14% 11% 6%	2794
January	1st to 10th	Night	40% 10% 17% 21% 11% 1	4179
	11th to 20th	Night	44% 12% 21% 14% 7% 1	4110
	21st to end	Night	49% 12% 18% 14% 5% 2	4521
February	1st to 10th	Night	43% 11% 19% 19% 8% 1	2470
	11th to 20th	Night	36% 8% 18% 22% 13% 3	2403
	21st to end	Night	38% 9% 18% 22% 11% 2	1905
March	1st to 10th	Night	30% 7% 20% 24% 18% 1	3459
	11th to 20th	Night	25% 9% 23% 31% 11% 1	3490
	21st to end	Night	43% 7% 19% 25% 5% 1	3828
April	1st to 10th	Night	36% 6% 17% 22% 13% 6%	2009
	11th to 20th	Night	31% 7% 18% 27% 17%	1777
	21st to end	Night	32% 5% 16% 31% 16%	1710
May	1st to 10th	Night	34% 9% 12% 23% 19% 3	2860
	11th to 20th	Night	24% 7% 11% 35% 19% 5%	2835
	21st to end	Night	26% 6% 12% 33% 21% 2	2806
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	25% 5% 11% 26% 26% 7%	2237
	11th to 20th	Night	26% 3 11% 32% 23% 5%	2280
	21st to end	Night	27% 5% 15% 31% 18% 3	2508
November	1st to 10th	Night	29% 7% 17% 25% 19% 3	2401
	11th to 20th	Night	31% 5% 21% 27% 14% 2	2583
	21st to end	Night	33% 6% 16% 27% 15% 3	2660
December	1st to 10th	Night	40% 8% 21% 18% 9% 3	2660
	11th to 20th	Night	43% 7% 18% 21% 11% 1	3272
	21st to end	Night	43% 10% 17% 16% 10% 5%	4873

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% 17% 22% 31% 16% 4	270
	11th to 20th	Day	6% 17% 27% 30% 19% 2	270
	21st to end	Day	3 11% 35% 32% 15% 3	297
February	1st to 10th	Day	6% 27% 35% 25% 6% 1	270
	11th to 20th	Day	4 20% 36% 26% 10% 4	270
	21st to end	Day	3 23% 36% 30% 7% 1	358
March	1st to 10th	Day	6% 17% 36% 29% 9% 2	460
	11th to 20th	Day	5% 14% 31% 33% 16% 1	460
	21st to end	Day	10% 21% 32% 30% 7% 1	506
April	1st to 10th	Day	11% 20% 28% 25% 14% 2	460
	11th to 20th	Day	10% 20% 35% 25% 9% 2	452
	21st to end	Day	10% 25% 26% 19% 15% 4	460
May	1st to 10th	Day	12% 21% 30% 23% 10% 3	463
	11th to 20th	Day	12% 14% 27% 31% 11% 4	488
	21st to end	Day	10% 13% 25% 25% 20% 7%	702
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% 31% 28% 14% 2	330
November	1st to 10th	Day	9% 16% 29% 26% 14% 6%	273
	11th to 20th	Day	10% 14% 26% 37% 10% 4	270
	21st to end	Day	4 13% 31% 31% 16% 4	270
December	1st to 10th	Day	6% 14% 29% 32% 17% 1	270
	11th to 20th	Day	4 18% 30% 34% 12% 1	270
	21st to end	Day	7% 16% 35% 24% 12% 6%	297
January	1st to 10th	Night	5% 11% 29% 34% 19% 2	803
	11th to 20th	Night	4 12% 31% 32% 18% 2	760
	21st to end	Night	5% 7% 32% 39% 14% 2	836
February	1st to 10th	Night	5% 14% 36% 33% 11% 2	760
	11th to 20th	Night	4 9% 33% 38% 14% 1	744
	21st to end	Night	4 10% 36% 39% 10% 1	628
March	1st to 10th	Night	6% 9% 31% 40% 13% 2	760
	11th to 20th	Night	3 7% 27% 46% 17% 1	760
	21st to end	Night	7% 8% 35% 36% 12% 1	836
April	1st to 10th	Night	8% 10% 32% 38% 12% 1	679
	11th to 20th	Night	7% 12% 34% 35% 11% 1	563
	21st to end	Night	8% 10% 27% 36% 16% 2	570
May	1st to 10th	Night	9% 10% 27% 36% 17% 1	570
	11th to 20th	Night	9% 7% 19% 38% 24% 3	561
	21st to end	Night	9% 7% 23% 32% 27% 3	617
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% 29% 37% 20% 3	748
	11th to 20th	Night	5% 12% 28% 38% 15% 2	873
	21st to end	Night	7% 10% 29% 35% 16% 3	950
December	1st to 10th	Night	6% 12% 31% 39% 12% 1	950
	11th to 20th	Night	5% 10% 32% 41% 11% 1	950
	21st to end	Night	5% 14% 34% 34% 11% 2	1045

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