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 2026-08-15.

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 5% 4 4 5% 4 7% 8% 55%	152250
	Night	2 4 2 5% 4 4 4 4 6% 8% 58%	147186
Transparency	Day	23% 8% 12% 24% 24% 9%	147235
	Night	22% 8% 12% 26% 25% 7%	143210
Seeing	Day	15% 23% 31% 22% 9% 1	17841
	Night	8% 17% 34% 28% 12% 1	27828

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%	4720
	11th to 20th	Day	3 1 5% 4 3 3 2 4 6% 70%	5280
	21st to end	Day	5% 3 7% 4 3 4 3 6% 7% 58%	5844
February	1st to 10th	Day	5% 3 7% 3 4 3 3 6% 7% 59%	1893
	11th to 20th	Day	1 3 2 6% 5% 4 4 3 6% 9% 58%	2049
	21st to end	Day	6% 3 6% 4 3 3 4 5% 7% 58%	1730
March	1st to 10th	Day	5% 2 6% 4 3 4 3 5% 7% 59%	4661
	11th to 20th	Day	1 6% 3 10% 6% 6% 5% 4 7% 8% 43%	5110
	21st to end	Day	1 6% 2 7% 5% 4 4 4 6% 8% 54%	5876
April	1st to 10th	Day	2 6% 2 7% 4 4 4 3 6% 8% 53%	2520
	11th to 20th	Day	2 7% 3 6% 5% 4 5% 4 5% 8% 50%	2491
	21st to end	Day	3 8% 2 6% 5% 5% 4 4 7% 8% 47%	2520
May	1st to 10th	Day	4 8% 3 7% 5% 5% 6% 5% 7% 7% 43%	7109
	11th to 20th	Day	2 4 2 6% 4 5% 5% 4 6% 8% 53%	7999
	21st to end	Day	3 3 1 4 3 4 5% 4 7% 9% 57%	9026
June	1st to 10th	Day	3 4 1 4 5% 4 6% 5% 8% 9% 51%	2940
	11th to 20th	Day	2 3 1 4 3 3 5% 4 6% 8% 61%	2940
	21st to end	Day	2 3 2 5% 4 5% 6% 5% 7% 9% 52%	2940
July	1st to 10th	Day	2 2 1 4 3 4 5% 4 7% 8% 61%	8249
	11th to 20th	Day	2 2 1 5% 4 5% 7% 6% 10% 10% 49%	8250
	21st to end	Day	3 3 1 6% 5% 7% 8% 6% 10% 10% 41%	8312
August	1st to 10th	Day	3 4 2 6% 5% 7% 7% 7% 10% 10% 39%	5827
	11th to 20th	Day	2 2 1 4 4 5% 6% 5% 10% 12% 50%	5415
	21st to end	Day	4 5% 2 6% 6% 6% 7% 6% 9% 11% 38%	5984
September	1st to 10th	Day	4 4 2 6% 4 4 5% 4 6% 8% 52%	2400
	11th to 20th	Day	4 3 1 4 4 3 4 4 6% 6% 60%	2395
	21st to end	Day	3 3 1 4 3 4 4 3 5% 6% 64%	2195
October	1st to 10th	Day	2 4 1 3 3 2 2 2 4 5% 73%	3270
	11th to 20th	Day	2 2 1 3 3 3 4 4 7% 8% 63%	3250
	21st to end	Day	2 4 1 4 3 2 3 2 4 6% 69%	3548
November	1st to 10th	Day	3 2 4 3 4 2 2 5% 8% 67%	1863
	11th to 20th	Day	1 3 2 3 2 3 2 3 5% 9% 67%	1890
	21st to end	Day	1 5% 2 5% 4 3 3 3 4 7% 63%	1856
December	1st to 10th	Day	3 2 3 2 2 3 2 4 7% 71%	2700
	11th to 20th	Day	3 1 3 3 3 3 4 6% 10% 64%	3106
	21st to end	Day	3 2 5% 4 4 3 4 6% 8% 60%	4092
January	1st to 10th	Night	3 3 10% 5% 4 4 3 5% 6% 58%	8201
	11th to 20th	Night	2 1 4 3 3 3 3 4 6% 71%	7752
	21st to end	Night	5% 3 6% 4 4 3 3 4 6% 63%	8370
February	1st to 10th	Night	1 6% 3 6% 3 2 3 2 4 7% 63%	2725
	11th to 20th	Night	1 6% 3 6% 4 3 4 4 6% 7% 58%	2458
	21st to end	Night	1 5% 2 6% 4 4 4 4 5% 7% 60%	2076
March	1st to 10th	Night	1 6% 2 6% 3 3 3 3 4 6% 61%	5432
	11th to 20th	Night	1 7% 3 7% 5% 4 3 4 5% 6% 56%	5110
	21st to end	Night	1 6% 3 7% 4 3 4 3 5% 7% 56%	5314
April	1st to 10th	Night	2 6% 2 6% 4 4 3 3 5% 7% 58%	2100
	11th to 20th	Night	2 8% 2 5% 4 4 4 3 6% 8% 53%	2077
	21st to end	Night	3 7% 2 6% 3 5% 5% 4 5% 7% 53%	2100
May	1st to 10th	Night	4 6% 2 6% 4 4 5% 5% 6% 7% 50%	5836
	11th to 20th	Night	4 5% 2 5% 3 3 4 4 5% 7% 58%	4877
	21st to end	Night	3 4 1 5% 4 4 5% 5% 7% 7% 54%	5181
June	1st to 10th	Night	2 3 1 5% 4 5% 5% 5% 6% 8% 56%	1680
	11th to 20th	Night	1 3 1 3 3 4 4 3 6% 8% 65%	1680
	21st to end	Night	3 3 1 5% 4 5% 6% 6% 8% 7% 52%	1680
July	1st to 10th	Night	1 2 1 4 4 5% 4 4 9% 8% 57%	4740
	11th to 20th	Night	1 2 1 4 5% 5% 6% 6% 10% 11% 50%	4740
	21st to end	Night	3 4 2 5% 5% 7% 8% 8% 12% 12% 35%	5779
August	1st to 10th	Night	4 4 2 6% 5% 6% 7% 5% 9% 10% 42%	4203
	11th to 20th	Night	2 3 1 5% 4 5% 6% 6% 11% 14% 43%	4523
	21st to end	Night	4 4 2 8% 5% 7% 8% 7% 11% 10% 32%	4993
September	1st to 10th	Night	4 5% 1 5% 5% 5% 5% 5% 6% 8% 50%	2000
	11th to 20th	Night	4 3 1 4 3 4 4 3 7% 8% 58%	2005
	21st to end	Night	3 3 1 4 3 3 3 3 6% 7% 63%	2200
October	1st to 10th	Night	2 3 1 3 3 2 2 3 4 6% 71%	3920
	11th to 20th	Night	1 2 1 2 2 3 4 4 7% 8% 66%	3898
	21st to end	Night	2 3 1 3 2 2 2 2 4 5% 73%	4252
November	1st to 10th	Night	1 3 1 2 2 3 3 3 5% 6% 72%	2633
	11th to 20th	Night	1 2 1 2 2 3 3 3 5% 7% 70%	2730
	21st to end	Night	2 4 2 5% 4 2 4 2 6% 8% 62%	2762
December	1st to 10th	Night	1 3 2 5% 2 2 2 2 4 6% 72%	4710
	11th to 20th	Night	3 1 3 2 2 3 3 5% 8% 69%	5321
	21st to end	Night	4 2 6% 5% 4 5% 3 5% 7% 58%	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	22% 6% 12% 35% 20% 5%	4723
	11th to 20th	Day	15% 5% 13% 26% 32% 9%	5280
	21st to end	Day	24% 5% 9% 26% 26% 11%	5844
February	1st to 10th	Day	24% 6% 16% 26% 20% 7%	1893
	11th to 20th	Day	21% 9% 12% 29% 24% 6%	2059
	21st to end	Day	25% 6% 9% 21% 29% 10%	1730
March	1st to 10th	Day	19% 8% 7% 17% 34% 15%	4661
	11th to 20th	Day	29% 9% 10% 27% 20% 4	5110
	21st to end	Day	26% 8% 10% 38% 15% 2	5876
April	1st to 10th	Day	29% 7% 10% 24% 22% 8%	2520
	11th to 20th	Day	30% 8% 10% 22% 22% 8%	2494
	21st to end	Day	30% 8% 12% 22% 24% 4	2520
May	1st to 10th	Day	30% 9% 13% 25% 17% 6%	7109
	11th to 20th	Day	23% 8% 10% 22% 31% 6%	8003
	21st to end	Day	19% 8% 11% 23% 29% 10%	9027
June	1st to 10th	Day	24% 9% 15% 22% 20% 10%	2940
	11th to 20th	Day	19% 7% 8% 19% 25% 22%	2940
	21st to end	Day	24% 8% 12% 21% 21% 14%	2940
July	1st to 10th	Day	18% 6% 9% 13% 22% 32%	8181
	11th to 20th	Day	21% 11% 20% 27% 14% 7%	8175
	21st to end	Day	29% 13% 24% 18% 11% 4	8127
August	1st to 10th	Day	35% 13% 21% 17% 10% 4	4278
	11th to 20th	Day	25% 10% 18% 20% 19% 9%	3931
	21st to end	Day	34% 11% 15% 20% 18% 2	4311
September	1st to 10th	Day	27% 8% 11% 24% 21% 9%	2400
	11th to 20th	Day	22% 8% 10% 19% 30% 11%	2395
	21st to end	Day	21% 6% 8% 25% 34% 7%	2195
October	1st to 10th	Day	16% 4 5% 17% 41% 17%	3270
	11th to 20th	Day	16% 7% 12% 30% 29% 6%	3250
	21st to end	Day	16% 4 7% 24% 41% 7%	3548
November	1st to 10th	Day	17% 4 10% 26% 35% 8%	1863
	11th to 20th	Day	14% 5% 11% 35% 28% 6%	1890
	21st to end	Day	22% 5% 10% 29% 26% 9%	1856
December	1st to 10th	Day	14% 4 12% 32% 32% 6%	2700
	11th to 20th	Day	15% 7% 12% 34% 29% 3	3104
	21st to end	Day	21% 5% 13% 26% 28% 7%	4092
January	1st to 10th	Night	23% 7% 10% 37% 20% 4	8202
	11th to 20th	Night	14% 5% 11% 32% 26% 12%	7752
	21st to end	Night	22% 5% 10% 24% 27% 12%	8370
February	1st to 10th	Night	22% 5% 15% 26% 26% 6%	2725
	11th to 20th	Night	25% 7% 12% 30% 22% 4	2458
	21st to end	Night	24% 6% 9% 24% 31% 7%	2076
March	1st to 10th	Night	20% 8% 6% 17% 38% 10%	5432
	11th to 20th	Night	24% 8% 10% 25% 28% 5%	5110
	21st to end	Night	24% 9% 14% 37% 15% 2	5314
April	1st to 10th	Night	25% 7% 9% 28% 24% 7%	2100
	11th to 20th	Night	27% 7% 11% 23% 26% 5%	2077
	21st to end	Night	27% 8% 14% 26% 21% 4	2100
May	1st to 10th	Night	28% 8% 14% 28% 17% 6%	5834
	11th to 20th	Night	21% 8% 11% 29% 25% 6%	4878
	21st to end	Night	21% 9% 16% 17% 27% 9%	5182
June	1st to 10th	Night	23% 8% 15% 23% 18% 13%	1680
	11th to 20th	Night	16% 6% 10% 21% 26% 21%	1680
	21st to end	Night	25% 9% 12% 18% 22% 14%	1680
July	1st to 10th	Night	20% 7% 11% 15% 24% 22%	4700
	11th to 20th	Night	22% 10% 22% 26% 14% 6%	4692
	21st to end	Night	32% 15% 23% 16% 12% 2	5652
August	1st to 10th	Night	40% 13% 20% 14% 9% 4	3076
	11th to 20th	Night	31% 11% 23% 16% 16% 4	3283
	21st to end	Night	37% 12% 16% 21% 12% 2	3597
September	1st to 10th	Night	29% 9% 13% 22% 19% 7%	2000
	11th to 20th	Night	22% 8% 11% 19% 27% 12%	2005
	21st to end	Night	19% 7% 9% 24% 34% 7%	2200
October	1st to 10th	Night	15% 5% 7% 24% 35% 13%	3920
	11th to 20th	Night	13% 10% 12% 27% 31% 7%	3898
	21st to end	Night	14% 4 6% 30% 38% 7%	4252
November	1st to 10th	Night	14% 4 10% 31% 35% 7%	2633
	11th to 20th	Night	14% 4 8% 35% 32% 7%	2730
	21st to end	Night	22% 5% 9% 26% 30% 8%	2762
December	1st to 10th	Night	15% 4 10% 35% 30% 6%	4710
	11th to 20th	Night	14% 5% 11% 33% 33% 3	5322
	21st to end	Night	22% 8% 15% 22% 29% 4	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	21% 28% 30% 15% 6%	330
	11th to 20th	Day	17% 31% 34% 15% 2 1	330
	21st to end	Day	10% 30% 35% 19% 5% 1	363
February	1st to 10th	Day	24% 33% 28% 11% 2 1	330
	11th to 20th	Day	25% 37% 28% 8% 2	330
	21st to end	Day	32% 31% 25% 11% 1	273
March	1st to 10th	Day	26% 30% 26% 14% 4	352
	11th to 20th	Day	26% 31% 28% 12% 3 1	540
	21st to end	Day	29% 34% 30% 6% 2	594
April	1st to 10th	Day	25% 34% 29% 10% 1 1	540
	11th to 20th	Day	30% 38% 24% 7% 2	532
	21st to end	Day	25% 37% 27% 10% 1	540
May	1st to 10th	Day	20% 34% 31% 11% 3	557
	11th to 20th	Day	13% 24% 32% 23% 7% 1	775
	21st to end	Day	12% 25% 33% 21% 8% 1	844
June	1st to 10th	Day	7% 17% 34% 26% 16% 1	780
	11th to 20th	Day	9% 19% 36% 23% 11% 1	780
	21st to end	Day	9% 18% 34% 24% 14% 2	780
July	1st to 10th	Day	6% 11% 29% 35% 15% 3	771
	11th to 20th	Day	5% 4 23% 42% 23% 4	768
	21st to end	Day	7% 6% 30% 38% 18% 1	627
August	1st to 10th	Day	7% 10% 33% 35% 13% 2	567
	11th to 20th	Day	6% 8% 35% 37% 12% 2	534
	21st to end	Day	7% 10% 36% 35% 12% 2	583
September	1st to 10th	Day	8% 11% 35% 31% 12% 2	530
	11th to 20th	Day	8% 20% 39% 25% 8% 1	525
	21st to end	Day	8% 19% 28% 30% 11% 4	330
October	1st to 10th	Day	12% 25% 28% 22% 9% 4	330
	11th to 20th	Day	19% 23% 32% 15% 8% 3	330
	21st to end	Day	16% 29% 28% 19% 7% 1	363
November	1st to 10th	Day	18% 27% 33% 15% 6% 1	330
	11th to 20th	Day	15% 27% 32% 18% 8%	330
	21st to end	Day	14% 29% 32% 19% 6%	330
December	1st to 10th	Day	17% 29% 30% 17% 7% 1	330
	11th to 20th	Day	14% 31% 37% 13% 4 1	330
	21st to end	Day	23% 31% 30% 13% 2	363
January	1st to 10th	Night	7% 19% 41% 24% 8% 1	1050
	11th to 20th	Night	8% 18% 41% 24% 8% 2	877
	21st to end	Night	4 16% 43% 29% 7%	924
February	1st to 10th	Night	6% 22% 47% 20% 4	840
	11th to 20th	Night	10% 27% 42% 15% 6%	824
	21st to end	Night	10% 22% 50% 17% 1	692
March	1st to 10th	Night	11% 28% 34% 22% 4	840
	11th to 20th	Night	8% 21% 38% 25% 7%	840
	21st to end	Night	12% 24% 40% 20% 4	796
April	1st to 10th	Night	14% 24% 38% 22% 3	630
	11th to 20th	Night	13% 25% 33% 24% 5%	623
	21st to end	Night	12% 23% 37% 23% 5%	630
May	1st to 10th	Night	11% 19% 36% 26% 8% 1	630
	11th to 20th	Night	10% 19% 33% 28% 9% 2	621
	21st to end	Night	10% 20% 32% 25% 12% 1	683
June	1st to 10th	Night	5% 10% 31% 36% 16% 1	630
	11th to 20th	Night	3 16% 34% 34% 12% 1	630
	21st to end	Night	6% 10% 26% 37% 20% 1	630
July	1st to 10th	Night	6% 4 23% 37% 27% 3	615
	11th to 20th	Night	4 2 16% 39% 35% 4	612
	21st to end	Night	6% 2 15% 31% 41% 5%	690
August	1st to 10th	Night	6% 5% 16% 39% 31% 4	627
	11th to 20th	Night	6% 3 18% 46% 23% 3	606
	21st to end	Night	7% 3 18% 42% 26% 4	660
September	1st to 10th	Night	6% 7% 22% 40% 22% 4	600
	11th to 20th	Night	5% 10% 27% 36% 21% 2	600
	21st to end	Night	6% 12% 26% 38% 17% 2	600
October	1st to 10th	Night	6% 18% 31% 31% 13% 2	800
	11th to 20th	Night	7% 15% 36% 28% 12% 2	800
	21st to end	Night	7% 18% 31% 30% 13% 1	880
November	1st to 10th	Night	7% 19% 34% 29% 11%	993
	11th to 20th	Night	7% 17% 41% 25% 9% 1	1050
	21st to end	Night	9% 19% 34% 27% 10% 1	1050
December	1st to 10th	Night	8% 20% 38% 27% 7%	1050
	11th to 20th	Night	7% 22% 40% 23% 8%	1050
	21st to end	Night	10% 23% 41% 21% 4 1	1155

Page generated at 2026-08-12 01:37:18. Version ac07

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