Great Sand Dunes National Park and Preserve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Sand Dunes National Park and Preserve clear sky chart from 2005-11-06 to 2025-04-11.

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	2 4 2 6% 4 4 5% 4 7% 8% 54%	117413
	Night	2 4 2 5% 4 4 4 4 6% 7% 58%	119768
Transparency	Day	24% 8% 12% 24% 24% 8%	117165
	Night	22% 8% 12% 25% 25% 7%	119606
Seeing	Day	14% 23% 31% 22% 9% 1	15903
	Night	8% 17% 33% 28% 12% 1	26109

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	3 3 8% 4 4 3 3 5% 7% 60%	3638
	11th to 20th	Day	3 2 6% 5% 3 3 3 5% 7% 62%	4054
	21st to end	Day	5% 3 7% 4 3 4 3 7% 7% 57%	4510
February	1st to 10th	Day	5% 4 7% 4 4 3 3 6% 7% 57%	1803
	11th to 20th	Day	1 3 2 6% 4 4 4 3 6% 9% 59%	1949
	21st to end	Day	6% 3 6% 4 4 4 4 5% 7% 57%	1650
March	1st to 10th	Day	6% 2 6% 4 3 4 3 5% 7% 59%	4560
	11th to 20th	Day	1 6% 3 11% 7% 6% 5% 4 7% 8% 42%	5000
	21st to end	Day	1 6% 2 7% 5% 4 4 4 6% 8% 54%	5749
April	1st to 10th	Day	3 6% 2 7% 4 4 4 3 6% 8% 53%	2400
	11th to 20th	Day	3 8% 3 6% 5% 5% 5% 4 5% 8% 49%	2252
	21st to end	Day	3 9% 2 6% 5% 5% 4 4 7% 8% 46%	2280
May	1st to 10th	Day	4 8% 3 7% 5% 4 5% 4 6% 7% 49%	3825
	11th to 20th	Day	3 6% 2 8% 6% 7% 6% 5% 7% 8% 43%	4285
	21st to end	Day	3 3 1 4 3 3 5% 4 7% 8% 59%	4825
June	1st to 10th	Day	3 4 1 4 5% 4 6% 5% 8% 10% 51%	2660
	11th to 20th	Day	2 3 1 4 3 3 5% 4 6% 8% 60%	2660
	21st to end	Day	2 3 2 5% 5% 5% 6% 5% 8% 9% 50%	2660
July	1st to 10th	Day	3 4 2 5% 4 5% 5% 5% 7% 7% 53%	4430
	11th to 20th	Day	3 3 2 6% 6% 6% 8% 7% 10% 10% 42%	4430
	21st to end	Day	4 4 2 6% 5% 6% 7% 6% 9% 9% 42%	4462
August	1st to 10th	Day	4 5% 2 7% 6% 7% 7% 8% 10% 10% 34%	4036
	11th to 20th	Day	3 3 1 4 4 5% 6% 5% 9% 11% 50%	3726
	21st to end	Day	3 5% 2 7% 6% 7% 8% 6% 10% 11% 37%	4180
September	1st to 10th	Day	4 4 2 6% 4 4 5% 4 6% 8% 51%	2280
	11th to 20th	Day	4 3 1 4 4 3 4 4 6% 6% 60%	2275
	21st to end	Day	4 3 1 4 3 4 4 3 5% 5% 65%	2085
October	1st to 10th	Day	2 4 1 3 2 2 2 2 4 5% 73%	3170
	11th to 20th	Day	2 2 1 3 3 3 4 4 6% 8% 63%	3150
	21st to end	Day	2 4 1 4 3 2 3 2 4 6% 69%	3438
November	1st to 10th	Day	3 2 4 3 4 2 3 5% 8% 66%	1773
	11th to 20th	Day	1 3 2 3 2 3 2 3 5% 9% 67%	1800
	21st to end	Day	1 6% 2 5% 4 3 3 3 4 7% 63%	1768
December	1st to 10th	Day	3 2 4 2 2 3 2 4 7% 71%	2620
	11th to 20th	Day	3 1 3 3 3 3 4 6% 10% 63%	3026
	21st to end	Day	3 2 5% 4 4 3 4 6% 8% 60%	4004
January	1st to 10th	Night	2 3 10% 5% 4 4 3 5% 6% 58%	6327
	11th to 20th	Night	2 1 5% 4 4 4 4 5% 7% 64%	5954
	21st to end	Night	4 3 6% 4 4 3 3 5% 6% 61%	6468
February	1st to 10th	Night	1 6% 3 7% 3 2 3 3 4 8% 61%	2595
	11th to 20th	Night	1 6% 3 6% 4 3 4 4 5% 6% 59%	2338
	21st to end	Night	1 5% 3 6% 4 4 4 3 6% 7% 59%	1980
March	1st to 10th	Night	1 7% 2 6% 4 3 3 3 4 6% 61%	5313
	11th to 20th	Night	1 7% 3 7% 5% 4 4 4 5% 6% 55%	5000
	21st to end	Night	1 7% 3 7% 4 3 4 3 5% 7% 56%	5199
April	1st to 10th	Night	2 6% 2 6% 4 4 3 4 5% 7% 58%	2000
	11th to 20th	Night	2 9% 2 5% 4 4 4 3 6% 8% 52%	1882
	21st to end	Night	3 8% 2 6% 3 5% 5% 4 5% 7% 52%	1900
May	1st to 10th	Night	4 7% 2 5% 4 4 5% 3 4 6% 56%	3143
	11th to 20th	Night	6% 6% 2 7% 5% 4 4 5% 5% 7% 49%	2617
	21st to end	Night	3 4 1 4 3 4 4 4 5% 7% 61%	2762
June	1st to 10th	Night	1 3 2 5% 4 5% 5% 5% 6% 8% 56%	1520
	11th to 20th	Night	1 3 1 3 3 4 4 3 6% 8% 65%	1520
	21st to end	Night	3 3 1 5% 4 5% 6% 6% 9% 8% 50%	1520
July	1st to 10th	Night	2 4 1 6% 6% 6% 6% 5% 10% 7% 47%	2540
	11th to 20th	Night	2 3 2 4 5% 6% 7% 7% 11% 11% 41%	2540
	21st to end	Night	3 4 1 5% 4 6% 6% 7% 11% 10% 42%	3097
August	1st to 10th	Night	5% 5% 3 9% 7% 7% 8% 6% 9% 10% 31%	2901
	11th to 20th	Night	3 3 2 6% 5% 6% 7% 6% 10% 13% 40%	3113
	21st to end	Night	3 4 2 7% 5% 7% 9% 8% 12% 10% 33%	3487
September	1st to 10th	Night	5% 5% 1 5% 5% 5% 5% 5% 7% 8% 50%	1900
	11th to 20th	Night	4 3 1 5% 3 4 5% 3 6% 8% 58%	1905
	21st to end	Night	3 3 1 4 2 3 3 3 5% 6% 64%	2090
October	1st to 10th	Night	2 3 1 3 3 2 2 3 4 6% 71%	3800
	11th to 20th	Night	1 2 1 2 2 3 3 4 8% 8% 66%	3778
	21st to end	Night	2 3 1 3 2 2 3 2 4 5% 73%	4120
November	1st to 10th	Night	1 3 1 2 2 3 3 3 5% 7% 70%	2504
	11th to 20th	Night	1 2 1 2 2 3 3 3 4 7% 72%	2600
	21st to end	Night	2 4 2 5% 4 2 4 2 5% 8% 62%	2630
December	1st to 10th	Night	1 2 2 5% 2 2 2 2 4 6% 73%	4570
	11th to 20th	Night	1 3 1 3 2 2 3 3 5% 8% 68%	5181
	21st to end	Night	4 2 6% 5% 4 5% 4 5% 7% 57%	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	23% 6% 13% 30% 22% 6%	3639
	11th to 20th	Day	19% 6% 13% 23% 28% 10%	4054
	21st to end	Day	24% 6% 8% 27% 25% 10%	4510
February	1st to 10th	Day	25% 6% 17% 26% 18% 7%	1803
	11th to 20th	Day	22% 8% 12% 29% 24% 6%	1959
	21st to end	Day	26% 6% 9% 21% 27% 11%	1650
March	1st to 10th	Day	19% 8% 7% 17% 34% 15%	4560
	11th to 20th	Day	30% 10% 11% 26% 20% 4	5000
	21st to end	Day	26% 9% 10% 38% 15% 2	5749
April	1st to 10th	Day	29% 7% 10% 24% 22% 8%	2400
	11th to 20th	Day	32% 8% 10% 23% 21% 7%	2255
	21st to end	Day	31% 8% 12% 21% 23% 4	2280
May	1st to 10th	Day	30% 6% 10% 19% 24% 11%	3825
	11th to 20th	Day	33% 11% 11% 24% 17% 5%	4289
	21st to end	Day	20% 9% 8% 18% 34% 11%	4825
June	1st to 10th	Day	24% 9% 15% 21% 20% 10%	2660
	11th to 20th	Day	19% 7% 8% 19% 24% 22%	2660
	21st to end	Day	26% 8% 12% 22% 21% 12%	2660
July	1st to 10th	Day	26% 8% 11% 16% 17% 22%	4361
	11th to 20th	Day	28% 11% 18% 29% 10% 3	4355
	21st to end	Day	28% 13% 18% 21% 12% 8%	4321
August	1st to 10th	Day	36% 13% 22% 16% 9% 4	4022
	11th to 20th	Day	25% 10% 18% 19% 19% 9%	3762
	21st to end	Day	34% 11% 15% 19% 18% 2	4179
September	1st to 10th	Day	28% 8% 11% 22% 22% 9%	2280
	11th to 20th	Day	22% 8% 11% 18% 30% 11%	2275
	21st to end	Day	20% 6% 7% 24% 35% 7%	2085
October	1st to 10th	Day	16% 4 5% 17% 41% 17%	3170
	11th to 20th	Day	16% 7% 11% 30% 29% 6%	3150
	21st to end	Day	16% 4 7% 25% 41% 7%	3438
November	1st to 10th	Day	17% 4 11% 24% 35% 8%	1773
	11th to 20th	Day	14% 5% 12% 34% 29% 7%	1800
	21st to end	Day	22% 5% 9% 28% 27% 9%	1768
December	1st to 10th	Day	14% 4 11% 32% 32% 6%	2620
	11th to 20th	Day	15% 7% 12% 34% 29% 2	3024
	21st to end	Day	21% 5% 13% 26% 27% 7%	4004
January	1st to 10th	Night	24% 7% 10% 32% 22% 5%	6327
	11th to 20th	Night	18% 7% 12% 27% 23% 13%	5954
	21st to end	Night	22% 6% 10% 27% 24% 12%	6468
February	1st to 10th	Night	23% 5% 16% 26% 24% 7%	2595
	11th to 20th	Night	25% 6% 12% 30% 23% 4	2338
	21st to end	Night	24% 6% 8% 23% 31% 7%	1980
March	1st to 10th	Night	21% 8% 6% 17% 39% 10%	5313
	11th to 20th	Night	24% 8% 11% 24% 28% 5%	5000
	21st to end	Night	24% 9% 14% 36% 15% 2	5199
April	1st to 10th	Night	25% 7% 9% 28% 24% 7%	2000
	11th to 20th	Night	29% 8% 11% 23% 25% 5%	1882
	21st to end	Night	28% 8% 14% 27% 20% 3	1900
May	1st to 10th	Night	27% 7% 8% 20% 27% 10%	3143
	11th to 20th	Night	30% 10% 12% 26% 15% 7%	2618
	21st to end	Night	19% 9% 11% 21% 32% 9%	2762
June	1st to 10th	Night	23% 8% 15% 23% 19% 13%	1520
	11th to 20th	Night	16% 6% 10% 22% 24% 21%	1520
	21st to end	Night	25% 10% 13% 19% 22% 11%	1520
July	1st to 10th	Night	28% 9% 13% 15% 17% 18%	2500
	11th to 20th	Night	26% 11% 24% 29% 7% 3	2492
	21st to end	Night	25% 15% 22% 22% 14% 3	3000
August	1st to 10th	Night	42% 14% 20% 12% 9% 3	2892
	11th to 20th	Night	31% 11% 23% 15% 16% 4	3143
	21st to end	Night	37% 12% 16% 21% 12% 2	3487
September	1st to 10th	Night	29% 9% 13% 21% 20% 8%	1900
	11th to 20th	Night	22% 8% 11% 19% 27% 13%	1905
	21st to end	Night	19% 7% 9% 24% 35% 6%	2090
October	1st to 10th	Night	15% 5% 7% 24% 35% 13%	3800
	11th to 20th	Night	13% 10% 12% 28% 31% 7%	3778
	21st to end	Night	14% 4 6% 30% 38% 7%	4120
November	1st to 10th	Night	14% 4 11% 29% 34% 7%	2504
	11th to 20th	Night	13% 4 8% 34% 33% 7%	2600
	21st to end	Night	21% 5% 9% 25% 32% 9%	2630
December	1st to 10th	Night	15% 4 10% 35% 30% 6%	4570
	11th to 20th	Night	15% 6% 11% 33% 33% 3	5182
	21st to end	Night	22% 8% 15% 22% 29% 4	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	20% 27% 30% 16% 7%	300
	11th to 20th	Day	17% 32% 34% 15% 2 1	300
	21st to end	Day	9% 28% 36% 20% 5% 1	330
February	1st to 10th	Day	25% 34% 28% 10% 2	300
	11th to 20th	Day	22% 38% 29% 8% 3	300
	21st to end	Day	30% 31% 25% 12% 1	249
March	1st to 10th	Day	25% 30% 26% 15% 4	321
	11th to 20th	Day	24% 30% 29% 13% 4 1	500
	21st to end	Day	29% 33% 29% 6% 2	550
April	1st to 10th	Day	26% 34% 28% 11% 1 1	500
	11th to 20th	Day	25% 39% 27% 8% 2	453
	21st to end	Day	21% 38% 29% 10% 1	460
May	1st to 10th	Day	19% 35% 32% 11% 3	475
	11th to 20th	Day	10% 23% 34% 25% 8% 1	675
	21st to end	Day	12% 25% 32% 21% 9% 1	734
June	1st to 10th	Day	6% 15% 34% 28% 16% 1	680
	11th to 20th	Day	9% 19% 35% 24% 11% 2	680
	21st to end	Day	7% 16% 34% 25% 15% 3	680
July	1st to 10th	Day	7% 10% 29% 35% 17% 3	671
	11th to 20th	Day	6% 4 22% 41% 23% 4	668
	21st to end	Day	8% 5% 27% 39% 19% 1	539
August	1st to 10th	Day	8% 7% 31% 37% 15% 2	487
	11th to 20th	Day	7% 9% 36% 35% 12% 2	477
	21st to end	Day	6% 10% 35% 35% 13% 2	539
September	1st to 10th	Day	9% 11% 33% 32% 13% 2	490
	11th to 20th	Day	7% 19% 38% 26% 8% 1	485
	21st to end	Day	8% 17% 28% 30% 12% 4	300
October	1st to 10th	Day	11% 24% 28% 23% 10% 4	300
	11th to 20th	Day	13% 23% 35% 16% 9% 3	300
	21st to end	Day	16% 29% 27% 19% 8% 2	330
November	1st to 10th	Day	18% 28% 32% 15% 7% 1	300
	11th to 20th	Day	15% 26% 32% 18% 8%	300
	21st to end	Day	13% 30% 31% 19% 6%	300
December	1st to 10th	Day	16% 28% 30% 19% 7% 1	300
	11th to 20th	Day	13% 33% 36% 13% 4 1	300
	21st to end	Day	22% 30% 31% 14% 2	330
January	1st to 10th	Night	7% 19% 40% 25% 8% 1	1000
	11th to 20th	Night	8% 18% 40% 24% 8% 2	835
	21st to end	Night	4 16% 42% 30% 7%	880
February	1st to 10th	Night	7% 23% 46% 20% 4	800
	11th to 20th	Night	9% 27% 43% 15% 6%	784
	21st to end	Night	11% 22% 49% 17% 1	660
March	1st to 10th	Night	12% 27% 34% 23% 4 1	800
	11th to 20th	Night	8% 21% 37% 26% 8% 1	800
	21st to end	Night	13% 24% 39% 20% 4	758
April	1st to 10th	Night	13% 24% 38% 22% 3	600
	11th to 20th	Night	12% 25% 32% 25% 5%	565
	21st to end	Night	10% 24% 35% 24% 6%	570
May	1st to 10th	Night	12% 19% 35% 25% 8% 1	570
	11th to 20th	Night	9% 19% 32% 29% 9% 2	561
	21st to end	Night	11% 21% 30% 26% 12% 1	617
June	1st to 10th	Night	5% 11% 30% 36% 17% 2	570
	11th to 20th	Night	2 16% 33% 34% 13% 1	570
	21st to end	Night	5% 8% 25% 38% 23% 2	570
July	1st to 10th	Night	6% 4 21% 37% 28% 4	555
	11th to 20th	Night	4 2 14% 38% 37% 5%	552
	21st to end	Night	7% 2 15% 29% 42% 6%	624
August	1st to 10th	Night	6% 4 13% 38% 34% 4	567
	11th to 20th	Night	6% 2 17% 47% 24% 4	564
	21st to end	Night	7% 3 17% 43% 27% 4	627
September	1st to 10th	Night	6% 6% 21% 39% 23% 4	570
	11th to 20th	Night	5% 10% 25% 36% 21% 2	570
	21st to end	Night	6% 12% 24% 38% 17% 2	570
October	1st to 10th	Night	6% 18% 29% 32% 13% 2	760
	11th to 20th	Night	5% 15% 36% 29% 13% 2	760
	21st to end	Night	8% 18% 30% 30% 13% 1	836
November	1st to 10th	Night	8% 19% 32% 30% 11%	944
	11th to 20th	Night	7% 17% 39% 26% 9% 1	1000
	21st to end	Night	9% 20% 32% 28% 10% 1	1000
December	1st to 10th	Night	8% 20% 36% 28% 7%	1000
	11th to 20th	Night	7% 22% 40% 23% 8%	1000
	21st to end	Night	10% 24% 39% 22% 4 1	1100

Page generated at 2025-04-08 07:17:24. Version ac07

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