Stargate Colorado Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stargate Colorado Observatory clear sky chart from 2005-11-06 to 2024-07-16.

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 4 3 4 4 4 6% 8% 56%	89769
	Night	3 5% 2 5% 3 3 3 3 5% 7% 60%	89880
Transparency	Day	12% 55% 4 10% 13% 7%	89482
	Night	12% 53% 4 11% 13% 6%	89690
Seeing	Day	8% 16% 30% 28% 15% 3	14971
	Night	6% 12% 34% 34% 12% 1	25010

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 4 2 8% 3 2 3 3 6% 8% 60%	2538
	11th to 20th	Day	1 4 1 3 2 2 4 4 5% 6% 69%	2767
	21st to end	Day	1 9% 2 4 3 3 4 3 6% 7% 57%	3146
February	1st to 10th	Day	1 4 3 6% 3 2 3 3 5% 8% 62%	1805
	11th to 20th	Day	1 4 2 4 3 4 4 3 5% 8% 60%	1849
	21st to end	Day	2 5% 2 5% 4 3 3 4 6% 6% 61%	1570
March	1st to 10th	Day	1 7% 3 4 3 3 2 3 4 5% 65%	3130
	11th to 20th	Day	6% 14% 4 5% 3 3 3 2 5% 6% 49%	3416
	21st to end	Day	3 8% 2 4 3 3 3 3 6% 7% 58%	4093
April	1st to 10th	Day	3 5% 1 4 3 3 3 4 6% 8% 59%	2280
	11th to 20th	Day	6% 6% 2 6% 3 4 4 3 5% 7% 55%	2251
	21st to end	Day	4 6% 2 5% 3 3 5% 4 6% 9% 53%	2280
May	1st to 10th	Day	6% 5% 2 4 3 3 3 4 5% 7% 60%	3896
	11th to 20th	Day	6% 6% 2 6% 4 4 5% 4 6% 8% 48%	4082
	21st to end	Day	3 3 1 3 4 4 4 5% 7% 8% 59%	4825
June	1st to 10th	Day	3 4 2 4 3 5% 6% 7% 8% 10% 48%	2660
	11th to 20th	Day	3 3 1 3 3 4 5% 5% 8% 9% 56%	2660
	21st to end	Day	5% 4 2 6% 4 5% 6% 6% 8% 9% 46%	2660
July	1st to 10th	Day	4 4 2 4 5% 6% 6% 7% 9% 9% 45%	2660
	11th to 20th	Day	3 3 1 4 5% 5% 8% 5% 8% 10% 47%	2593
	21st to end	Day	6% 4 2 5% 7% 7% 7% 8% 10% 10% 34%	2598
August	1st to 10th	Day	6% 3 2 6% 5% 6% 9% 7% 9% 9% 39%	2213
	11th to 20th	Day	6% 4 1 6% 5% 6% 6% 6% 7% 10% 43%	2123
	21st to end	Day	4 4 2 5% 5% 4 6% 6% 7% 10% 48%	2376
September	1st to 10th	Day	4 5% 2 5% 4 5% 4 4 6% 8% 52%	2160
	11th to 20th	Day	5% 3 1 5% 3 3 4 4 6% 7% 59%	2111
	21st to end	Day	4 3 1 4 3 3 3 3 5% 5% 65%	1980
October	1st to 10th	Day	6% 4 1 4 3 4 4 3 5% 8% 58%	1879
	11th to 20th	Day	2 2 1 2 2 2 3 3 3 6% 74%	1800
	21st to end	Day	5% 5% 1 4 2 2 2 2 3 4 69%	1949
November	1st to 10th	Day	1 3 1 3 2 2 3 3 4 5% 74%	1673
	11th to 20th	Day	1 3 1 5% 3 3 3 2 4 6% 68%	1710
	21st to end	Day	3 5% 2 5% 3 3 3 3 4 6% 64%	1710
December	1st to 10th	Day	1 4 3 4 2 2 3 2 5% 8% 65%	1606
	11th to 20th	Day	2 5% 2 6% 3 3 4 4 5% 7% 60%	1926
	21st to end	Day	1 4 2 6% 4 3 3 3 6% 7% 60%	2794
January	1st to 10th	Night	1 6% 3 8% 3 3 3 3 5% 7% 57%	4417
	11th to 20th	Night	1 4 2 5% 3 3 3 3 4 5% 67%	4234
	21st to end	Night	2 6% 3 5% 3 3 4 4 5% 6% 60%	4521
February	1st to 10th	Night	1 7% 2 5% 3 3 3 2 4 6% 63%	2374
	11th to 20th	Night	2 5% 3 4 4 3 3 4 6% 6% 60%	2218
	21st to end	Night	2 5% 1 5% 3 3 3 2 4 6% 68%	1884
March	1st to 10th	Night	2 6% 3 4 3 2 2 2 4 5% 67%	3734
	11th to 20th	Night	8% 11% 3 6% 3 3 3 2 4 6% 52%	3559
	21st to end	Night	3 7% 2 4 4 2 3 3 5% 6% 61%	3551
April	1st to 10th	Night	3 4 2 3 3 3 3 3 5% 6% 66%	1900
	11th to 20th	Night	5% 7% 2 5% 4 2 3 3 5% 7% 58%	1877
	21st to end	Night	6% 7% 1 5% 3 3 3 3 5% 7% 56%	1900
May	1st to 10th	Night	7% 6% 2 3 2 2 2 2 4 5% 64%	3060
	11th to 20th	Night	9% 7% 2 5% 3 4 5% 3 5% 9% 47%	2806
	21st to end	Night	4 4 1 3 3 3 3 4 5% 6% 63%	2762
June	1st to 10th	Night	4 4 2 3 3 3 4 4 7% 10% 55%	1520
	11th to 20th	Night	2 3 1 4 4 3 4 4 7% 7% 60%	1520
	21st to end	Night	5% 4 2 5% 4 5% 6% 5% 9% 11% 46%	1520
July	1st to 10th	Night	5% 5% 2 5% 5% 5% 6% 5% 8% 10% 44%	1520
	11th to 20th	Night	5% 3 1 3 3 5% 6% 5% 9% 9% 49%	1488
	21st to end	Night	6% 6% 3 6% 5% 6% 5% 6% 9% 12% 37%	1716
August	1st to 10th	Night	5% 3 2 5% 5% 5% 7% 6% 8% 10% 44%	1726
	11th to 20th	Night	6% 5% 2 5% 4 5% 5% 6% 8% 9% 44%	1778
	21st to end	Night	4 4 2 4 3 4 5% 4 10% 11% 50%	1980
September	1st to 10th	Night	5% 4 2 4 3 3 4 4 7% 9% 54%	1800
	11th to 20th	Night	5% 4 1 4 3 3 2 3 5% 8% 62%	1849
	21st to end	Night	4 4 1 4 3 3 3 3 4 6% 64%	1980
October	1st to 10th	Night	5% 5% 2 3 3 3 3 2 5% 6% 64%	2078
	11th to 20th	Night	2 2 1 2 1 2 2 3 4 5% 75%	2160
	21st to end	Night	5% 5% 2 4 2 2 3 2 4 5% 66%	2389
November	1st to 10th	Night	1 3 1 3 2 2 2 3 4 6% 73%	2405
	11th to 20th	Night	1 4 1 3 2 2 2 3 4 6% 73%	2470
	21st to end	Night	2 5% 2 4 3 3 3 3 6% 7% 64%	2470
December	1st to 10th	Night	2 4 2 4 3 3 3 4 6% 9% 61%	2570
	11th to 20th	Night	1 4 2 4 4 3 4 3 5% 7% 62%	3271
	21st to end	Night	1 5% 2 6% 3 4 4 3 5% 7% 60%	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	17% 37% 6% 18% 16% 6%	2539
	11th to 20th	Day	10% 37% 4 21% 25% 3	2767
	21st to end	Day	18% 40% 5% 15% 18% 3	3146
February	1st to 10th	Day	7% 64% 4 9% 9% 6%	1805
	11th to 20th	Day	7% 64% 3 10% 12% 5%	1859
	21st to end	Day	7% 66% 3 6% 11% 8%	1570
March	1st to 10th	Day	11% 41% 3 5% 26% 14%	3130
	11th to 20th	Day	25% 41% 5% 10% 15% 4	3416
	21st to end	Day	14% 41% 4 19% 20% 2	4093
April	1st to 10th	Day	8% 65% 4 10% 9% 4	2280
	11th to 20th	Day	11% 66% 4 8% 6% 5%	2254
	21st to end	Day	12% 65% 4 9% 9% 1	2280
May	1st to 10th	Day	15% 41% 5% 12% 13% 15%	3896
	11th to 20th	Day	20% 42% 5% 11% 14% 8%	4086
	21st to end	Day	9% 43% 6% 11% 14% 18%	4825
June	1st to 10th	Day	8% 67% 6% 8% 7% 3	2660
	11th to 20th	Day	7% 66% 5% 6% 9% 8%	2660
	21st to end	Day	10% 65% 5% 9% 7% 4	2660
July	1st to 10th	Day	11% 62% 5% 7% 9% 6%	2591
	11th to 20th	Day	12% 63% 6% 8% 7% 4	2518
	21st to end	Day	14% 67% 7% 9% 3 1	2454
August	1st to 10th	Day	13% 67% 8% 6% 4 2	2198
	11th to 20th	Day	13% 67% 6% 7% 5% 2	2123
	21st to end	Day	10% 65% 5% 9% 8% 3	2376
September	1st to 10th	Day	10% 65% 4 9% 8% 4	2160
	11th to 20th	Day	8% 64% 3 7% 11% 7%	2111
	21st to end	Day	9% 63% 3 7% 11% 6%	1980
October	1st to 10th	Day	10% 64% 4 6% 12% 4	1879
	11th to 20th	Day	4 63% 4 6% 12% 11%	1800
	21st to end	Day	9% 62% 3 9% 10% 7%	1949
November	1st to 10th	Day	6% 58% 3 8% 15% 11%	1673
	11th to 20th	Day	9% 60% 2 8% 14% 7%	1710
	21st to end	Day	11% 60% 3 6% 12% 8%	1710
December	1st to 10th	Day	7% 60% 3 12% 12% 7%	1606
	11th to 20th	Day	12% 48% 3 9% 19% 10%	1924
	21st to end	Day	14% 36% 4 12% 20% 14%	2794
January	1st to 10th	Night	21% 37% 3 16% 19% 4	4417
	11th to 20th	Night	13% 37% 5% 22% 19% 4	4234
	21st to end	Night	16% 42% 5% 17% 17% 3	4521
February	1st to 10th	Night	8% 65% 3 10% 8% 6%	2374
	11th to 20th	Night	8% 64% 3 10% 10% 4	2218
	21st to end	Night	7% 65% 2 6% 13% 8%	1884
March	1st to 10th	Night	12% 40% 2 5% 28% 13%	3734
	11th to 20th	Night	25% 41% 5% 11% 13% 4	3559
	21st to end	Night	15% 41% 2 23% 17% 2	3551
April	1st to 10th	Night	8% 65% 4 11% 9% 4	1900
	11th to 20th	Night	10% 66% 5% 7% 8% 3	1877
	21st to end	Night	12% 66% 6% 7% 8% 1	1900
May	1st to 10th	Night	14% 42% 4 10% 13% 17%	3060
	11th to 20th	Night	21% 41% 5% 17% 8% 7%	2807
	21st to end	Night	11% 42% 7% 11% 13% 17%	2762
June	1st to 10th	Night	8% 66% 7% 8% 6% 3	1520
	11th to 20th	Night	7% 66% 4 6% 8% 8%	1520
	21st to end	Night	12% 65% 5% 8% 8% 3	1520
July	1st to 10th	Night	14% 61% 5% 7% 8% 6%	1480
	11th to 20th	Night	12% 62% 6% 10% 6% 3	1440
	21st to end	Night	16% 66% 9% 8% 1	1621
August	1st to 10th	Night	14% 67% 9% 5% 4 2	1717
	11th to 20th	Night	11% 67% 8% 8% 4 2	1778
	21st to end	Night	10% 65% 8% 9% 7% 1	1980
September	1st to 10th	Night	9% 64% 5% 11% 7% 4	1800
	11th to 20th	Night	8% 64% 5% 8% 9% 6%	1849
	21st to end	Night	8% 64% 4 7% 12% 6%	1980
October	1st to 10th	Night	11% 64% 3 5% 11% 5%	2078
	11th to 20th	Night	5% 63% 4 6% 13% 10%	2160
	21st to end	Night	11% 61% 3 8% 11% 6%	2389
November	1st to 10th	Night	7% 58% 2 8% 17% 8%	2405
	11th to 20th	Night	7% 59% 2 11% 15% 7%	2470
	21st to end	Night	12% 60% 3 8% 11% 7%	2470
December	1st to 10th	Night	8% 59% 3 14% 12% 4	2570
	11th to 20th	Night	11% 50% 3 8% 21% 7%	3272
	21st to end	Night	14% 38% 5% 12% 20% 11%	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	7% 16% 38% 27% 12% 1	270
	11th to 20th	Day	10% 19% 36% 25% 7% 3	270
	21st to end	Day	4 21% 34% 25% 13% 3	297
February	1st to 10th	Day	4 25% 40% 23% 7% 1	270
	11th to 20th	Day	6% 29% 37% 22% 5% 1	270
	21st to end	Day	19% 26% 32% 20% 4	225
March	1st to 10th	Day	8% 27% 37% 20% 9%	270
	11th to 20th	Day	12% 25% 33% 20% 8% 1	412
	21st to end	Day	17% 36% 30% 13% 4 1	506
April	1st to 10th	Day	12% 29% 38% 15% 4 1	460
	11th to 20th	Day	14% 33% 36% 13% 3 1	452
	21st to end	Day	12% 32% 36% 17% 3	460
May	1st to 10th	Day	10% 26% 37% 20% 6% 1	520
	11th to 20th	Day	10% 16% 33% 26% 13% 2	675
	21st to end	Day	9% 19% 35% 25% 10% 2	734
June	1st to 10th	Day	5% 13% 27% 31% 20% 4	680
	11th to 20th	Day	5% 13% 35% 30% 15% 2	680
	21st to end	Day	6% 7% 34% 29% 20% 3	680
July	1st to 10th	Day	5% 7% 22% 32% 28% 6%	671
	11th to 20th	Day	3 1 16% 38% 33% 9%	645
	21st to end	Day	4 2 14% 36% 33% 11%	540
August	1st to 10th	Day	5% 4 21% 34% 26% 10%	447
	11th to 20th	Day	4 4 26% 41% 20% 5%	437
	21st to end	Day	5% 3 23% 44% 21% 5%	495
September	1st to 10th	Day	5% 5% 26% 40% 19% 6%	450
	11th to 20th	Day	4 10% 29% 31% 20% 4	401
	21st to end	Day	7% 11% 24% 31% 23% 4	270
October	1st to 10th	Day	8% 20% 24% 24% 17% 7%	270
	11th to 20th	Day	5% 16% 29% 27% 16% 6%	270
	21st to end	Day	12% 17% 26% 28% 14% 3	297
November	1st to 10th	Day	4 21% 31% 28% 14% 2	270
	11th to 20th	Day	5% 15% 34% 28% 14% 4	270
	21st to end	Day	9% 18% 33% 26% 11% 4	270
December	1st to 10th	Day	5% 21% 35% 27% 10% 1	270
	11th to 20th	Day	6% 17% 41% 28% 7% 1	270
	21st to end	Day	10% 22% 38% 25% 5%	297
January	1st to 10th	Night	5% 11% 34% 37% 11% 1	950
	11th to 20th	Night	7% 12% 36% 34% 9% 2	832
	21st to end	Night	5% 11% 35% 38% 11%	836
February	1st to 10th	Night	6% 15% 41% 30% 7%	760
	11th to 20th	Night	5% 19% 45% 24% 7%	744
	21st to end	Night	7% 18% 43% 29% 3	628
March	1st to 10th	Night	7% 18% 39% 31% 5%	760
	11th to 20th	Night	8% 15% 37% 32% 8% 1	760
	21st to end	Night	8% 22% 38% 25% 6%	675
April	1st to 10th	Night	7% 20% 46% 25% 3	570
	11th to 20th	Night	9% 22% 37% 28% 4	563
	21st to end	Night	12% 16% 38% 26% 7%	570
May	1st to 10th	Night	9% 15% 36% 32% 8% 1	570
	11th to 20th	Night	12% 10% 32% 34% 11% 1	561
	21st to end	Night	9% 14% 38% 30% 8% 1	617
June	1st to 10th	Night	6% 8% 37% 32% 15% 1	570
	11th to 20th	Night	5% 10% 43% 34% 9%	570
	21st to end	Night	6% 6% 29% 40% 17% 2	570
July	1st to 10th	Night	5% 6% 24% 41% 22% 2	555
	11th to 20th	Night	6% 2 22% 42% 25% 3	540
	21st to end	Night	7% 2 19% 37% 32% 4	591
August	1st to 10th	Night	4 1 16% 37% 35% 6%	537
	11th to 20th	Night	7% 2 25% 38% 26% 2	534
	21st to end	Night	3 2 26% 40% 26% 3	594
September	1st to 10th	Night	6% 5% 26% 42% 20% 2	540
	11th to 20th	Night	6% 6% 29% 39% 18% 2	540
	21st to end	Night	5% 11% 30% 35% 17% 2	540
October	1st to 10th	Night	9% 13% 33% 31% 13% 2	638
	11th to 20th	Night	3 7% 34% 39% 15% 2	720
	21st to end	Night	8% 8% 30% 38% 14% 3	805
November	1st to 10th	Night	4 12% 30% 39% 14% 1	925
	11th to 20th	Night	4 12% 36% 36% 11% 2	950
	21st to end	Night	6% 13% 30% 36% 13% 2	950
December	1st to 10th	Night	4 11% 38% 36% 9% 1	950
	11th to 20th	Night	5% 12% 38% 35% 10%	950
	21st to end	Night	8% 15% 35% 35% 6% 1	1045

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