Gunnison Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gunnison Valley Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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% 5% 3 6% 6% 7% 9% 50%	78807
	Night	2 5% 2 6% 5% 4 5% 6% 7% 9% 50%	81035
Transparency	Day	27% 9% 15% 23% 20% 7%	78522
	Night	26% 9% 15% 25% 20% 5%	80842
Seeing	Day	5% 12% 25% 32% 19% 7%	14447
	Night	4 5% 24% 45% 21% 2	24728

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 2 7% 8% 4 9% 8% 9% 11% 38%	2616
	11th to 20th	Day	3 2 6% 6% 6% 9% 10% 10% 11% 37%	2860
	21st to end	Day	5% 5% 8% 7% 5% 6% 8% 9% 12% 35%	3146
February	1st to 10th	Day	4 3 5% 4 4 6% 7% 8% 12% 46%	1710
	11th to 20th	Day	1 3 2 4 6% 4 6% 6% 9% 13% 46%	1745
	21st to end	Day	1 4 3 6% 8% 4 6% 4 8% 9% 47%	1570
March	1st to 10th	Day	1 5% 2 5% 4 3 6% 5% 7% 11% 50%	2022
	11th to 20th	Day	1 4 2 5% 6% 3 5% 6% 8% 8% 52%	2058
	21st to end	Day	1 5% 3 5% 6% 3 6% 6% 6% 11% 48%	2222
April	1st to 10th	Day	1 5% 2 4 5% 3 5% 5% 8% 9% 53%	2160
	11th to 20th	Day	2 5% 2 5% 5% 3 5% 6% 8% 11% 49%	2131
	21st to end	Day	2 4 2 5% 5% 3 6% 5% 8% 10% 50%	2160
May	1st to 10th	Day	3 5% 2 4 5% 3 5% 7% 8% 9% 48%	2243
	11th to 20th	Day	3 4 2 5% 5% 4 6% 7% 7% 10% 47%	2410
	21st to end	Day	3 4 2 4 6% 3 5% 6% 7% 8% 53%	2724
June	1st to 10th	Day	2 3 2 3 4 3 4 5% 7% 8% 59%	2520
	11th to 20th	Day	3 3 1 3 4 3 4 4 4 8% 63%	2520
	21st to end	Day	1 2 1 4 4 3 5% 6% 6% 9% 58%	2520
July	1st to 10th	Day	4 4 2 5% 6% 3 6% 6% 8% 8% 48%	2520
	11th to 20th	Day	3 3 2 4 5% 4 7% 6% 8% 10% 47%	2439
	21st to end	Day	4 5% 3 7% 7% 4 8% 7% 8% 10% 36%	2545
August	1st to 10th	Day	6% 6% 3 5% 6% 5% 5% 7% 7% 9% 41%	2328
	11th to 20th	Day	4 3 2 5% 5% 4 6% 6% 7% 8% 49%	2197
	21st to end	Day	3 4 2 6% 6% 4 6% 7% 8% 9% 46%	2376
September	1st to 10th	Day	5% 4 2 5% 6% 3 5% 5% 6% 7% 52%	2160
	11th to 20th	Day	4 4 2 4 4 3 5% 4 6% 7% 57%	2160
	21st to end	Day	4 4 1 4 3 3 4 3 3 6% 64%	1919
October	1st to 10th	Day	4 4 2 3 4 3 4 6% 6% 7% 58%	1800
	11th to 20th	Day	2 2 1 4 3 2 3 4 4 7% 67%	1800
	21st to end	Day	2 5% 2 4 4 2 4 5% 4 5% 63%	1980
November	1st to 10th	Day	1 2 1 2 3 2 3 4 5% 8% 68%	1758
	11th to 20th	Day	1 4 2 3 4 2 4 5% 6% 7% 64%	1710
	21st to end	Day	1 3 2 4 4 3 4 6% 7% 9% 57%	1538
December	1st to 10th	Day	1 4 2 4 6% 3 5% 5% 8% 10% 51%	1520
	11th to 20th	Day	1 6% 2 6% 7% 5% 7% 8% 10% 11% 37%	1926
	21st to end	Day	1 4 3 6% 7% 3 6% 8% 10% 13% 41%	2794
January	1st to 10th	Night	1 4 3 10% 9% 6% 8% 9% 8% 9% 33%	4353
	11th to 20th	Night	3 3 7% 7% 6% 8% 8% 8% 10% 40%	4110
	21st to end	Night	1 11% 5% 10% 9% 6% 8% 7% 6% 7% 30%	4521
February	1st to 10th	Night	4 2 8% 6% 3 6% 5% 8% 11% 45%	2470
	11th to 20th	Night	1 5% 3 5% 5% 3 5% 6% 7% 11% 48%	2322
	21st to end	Night	1 7% 4 6% 5% 4 4 7% 7% 10% 47%	1884
March	1st to 10th	Night	1 5% 2 5% 4 3 5% 6% 6% 11% 51%	2156
	11th to 20th	Night	1 6% 2 5% 4 3 5% 5% 7% 9% 54%	2068
	21st to end	Night	2 6% 2 5% 5% 3 6% 6% 7% 8% 50%	2134
April	1st to 10th	Night	2 6% 2 4 4 3 5% 6% 6% 8% 55%	1800
	11th to 20th	Night	2 7% 2 6% 4 2 4 5% 6% 8% 51%	1777
	21st to end	Night	2 5% 2 5% 4 3 5% 5% 6% 9% 55%	1800
May	1st to 10th	Night	3 6% 2 4 4 3 5% 4 6% 9% 55%	1714
	11th to 20th	Night	5% 5% 2 5% 4 2 4 4 5% 9% 53%	1482
	21st to end	Night	4 4 1 3 4 2 5% 5% 6% 9% 59%	1552
June	1st to 10th	Night	1 1 1 3 4 3 3 4 6% 7% 66%	1440
	11th to 20th	Night	1 2 1 3 3 2 3 4 4 7% 69%	1440
	21st to end	Night	1 1 1 2 3 3 5% 5% 5% 10% 65%	1440
July	1st to 10th	Night	3 3 2 5% 5% 3 5% 6% 7% 10% 51%	1440
	11th to 20th	Night	2 3 2 4 5% 3 5% 5% 6% 11% 55%	1517
	21st to end	Night	4 4 3 5% 6% 4 6% 5% 8% 15% 41%	1773
August	1st to 10th	Night	5% 4 2 6% 4 3 4 5% 7% 11% 48%	1611
	11th to 20th	Night	3 4 2 4 4 3 5% 5% 6% 9% 54%	1704
	21st to end	Night	4 5% 2 5% 5% 4 5% 5% 6% 9% 51%	1980
September	1st to 10th	Night	5% 3 1 4 5% 3 5% 5% 7% 8% 54%	1800
	11th to 20th	Night	4 3 1 4 3 3 3 5% 6% 8% 60%	1800
	21st to end	Night	3 3 2 3 3 2 3 4 4 5% 68%	2036
October	1st to 10th	Night	4 5% 2 4 4 3 4 3 4 8% 59%	2160
	11th to 20th	Night	2 3 1 3 3 2 3 3 4 6% 70%	2160
	21st to end	Night	3 4 2 4 4 2 3 4 4 8% 62%	2376
November	1st to 10th	Night	1 3 1 3 2 1 3 4 4 8% 69%	2300
	11th to 20th	Night	1 3 2 4 3 3 4 4 6% 7% 63%	2470
	21st to end	Night	2 4 2 5% 5% 3 4 5% 5% 8% 56%	2641
December	1st to 10th	Night	1 5% 3 5% 4 4 5% 5% 6% 10% 52%	2660
	11th to 20th	Night	1 6% 3 6% 6% 5% 7% 10% 11% 10% 35%	3271
	21st to end	Night	1 6% 4 9% 8% 5% 6% 7% 9% 11% 33%	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	28% 10% 25% 22% 14% 1	2617
	11th to 20th	Day	35% 11% 21% 22% 10% 1	2860
	21st to end	Day	29% 11% 19% 29% 10% 2	3146
February	1st to 10th	Day	26% 13% 21% 22% 14% 3	1710
	11th to 20th	Day	28% 9% 13% 26% 20% 3	1754
	21st to end	Day	31% 9% 12% 23% 22% 3	1570
March	1st to 10th	Day	28% 7% 17% 27% 20% 2	2022
	11th to 20th	Day	27% 6% 17% 31% 16% 3	2058
	21st to end	Day	32% 8% 15% 26% 15% 3	2222
April	1st to 10th	Day	27% 8% 15% 23% 19% 7%	2160
	11th to 20th	Day	28% 8% 16% 24% 21% 3	2134
	21st to end	Day	26% 8% 17% 28% 19% 2	2160
May	1st to 10th	Day	29% 10% 14% 24% 20% 4	2243
	11th to 20th	Day	30% 10% 15% 25% 17% 3	2414
	21st to end	Day	25% 8% 14% 21% 23% 7%	2724
June	1st to 10th	Day	20% 8% 12% 22% 27% 11%	2520
	11th to 20th	Day	20% 6% 9% 18% 24% 23%	2520
	21st to end	Day	20% 7% 11% 17% 25% 21%	2520
July	1st to 10th	Day	31% 8% 12% 14% 19% 16%	2451
	11th to 20th	Day	27% 11% 18% 20% 13% 10%	2364
	21st to end	Day	37% 13% 20% 16% 10% 4	2404
August	1st to 10th	Day	36% 12% 14% 15% 15% 8%	2313
	11th to 20th	Day	29% 9% 12% 16% 24% 9%	2197
	21st to end	Day	30% 11% 14% 19% 20% 7%	2376
September	1st to 10th	Day	29% 7% 12% 15% 23% 14%	2160
	11th to 20th	Day	24% 7% 12% 20% 25% 12%	2160
	21st to end	Day	23% 5% 7% 22% 33% 10%	1919
October	1st to 10th	Day	24% 7% 11% 25% 24% 9%	1800
	11th to 20th	Day	18% 5% 8% 27% 33% 10%	1800
	21st to end	Day	22% 6% 12% 29% 24% 7%	1980
November	1st to 10th	Day	15% 6% 12% 27% 35% 5%	1758
	11th to 20th	Day	18% 5% 13% 37% 23% 4	1710
	21st to end	Day	23% 6% 14% 30% 22% 5%	1538
December	1st to 10th	Day	25% 10% 20% 28% 15% 3	1520
	11th to 20th	Day	31% 10% 14% 29% 15% 1	1924
	21st to end	Day	26% 11% 16% 21% 21% 5%	2794
January	1st to 10th	Night	35% 12% 17% 23% 12% 1	4353
	11th to 20th	Night	34% 11% 20% 24% 10% 1	4110
	21st to end	Night	36% 11% 19% 24% 8% 2	4521
February	1st to 10th	Night	28% 9% 19% 25% 16% 2	2470
	11th to 20th	Night	27% 9% 16% 28% 18% 3	2323
	21st to end	Night	29% 7% 11% 27% 22% 4	1884
March	1st to 10th	Night	24% 7% 16% 29% 22% 2	2156
	11th to 20th	Night	23% 8% 16% 33% 17% 3	2068
	21st to end	Night	28% 9% 14% 31% 15% 2	2134
April	1st to 10th	Night	25% 8% 15% 25% 22% 5%	1800
	11th to 20th	Night	28% 8% 14% 25% 21% 4	1777
	21st to end	Night	23% 10% 14% 30% 21% 2	1800
May	1st to 10th	Night	25% 8% 13% 28% 22% 4	1714
	11th to 20th	Night	27% 9% 17% 26% 19% 2	1483
	21st to end	Night	21% 8% 15% 24% 25% 8%	1552
June	1st to 10th	Night	14% 7% 13% 24% 28% 14%	1440
	11th to 20th	Night	15% 5% 11% 18% 25% 26%	1440
	21st to end	Night	14% 6% 12% 21% 25% 22%	1440
July	1st to 10th	Night	26% 11% 15% 12% 20% 16%	1400
	11th to 20th	Night	21% 12% 20% 21% 14% 12%	1469
	21st to end	Night	29% 16% 26% 17% 9% 3	1674
August	1st to 10th	Night	26% 13% 20% 17% 16% 9%	1602
	11th to 20th	Night	23% 10% 18% 17% 21% 11%	1704
	21st to end	Night	28% 9% 16% 20% 19% 8%	1980
September	1st to 10th	Night	26% 7% 14% 18% 21% 14%	1800
	11th to 20th	Night	21% 7% 15% 16% 27% 14%	1800
	21st to end	Night	17% 6% 8% 26% 35% 8%	2036
October	1st to 10th	Night	24% 6% 12% 24% 24% 10%	2160
	11th to 20th	Night	15% 5% 10% 26% 36% 9%	2160
	21st to end	Night	21% 5% 10% 32% 27% 5%	2376
November	1st to 10th	Night	15% 5% 13% 33% 29% 5%	2300
	11th to 20th	Night	18% 5% 13% 36% 25% 3	2470
	21st to end	Night	25% 7% 10% 29% 26% 3	2641
December	1st to 10th	Night	25% 8% 20% 26% 18% 2	2660
	11th to 20th	Night	30% 9% 16% 25% 19% 1	3272
	21st to end	Night	32% 10% 14% 20% 21% 2	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	3 12% 21% 39% 20% 5%	270
	11th to 20th	Day	6% 11% 26% 41% 15% 1	270
	21st to end	Day	1 6% 22% 45% 20% 6%	297
February	1st to 10th	Day	4 14% 33% 36% 11% 2	270
	11th to 20th	Day	3 16% 33% 36% 10% 3	270
	21st to end	Day	3 19% 32% 38% 7%	225
March	1st to 10th	Day	6% 16% 33% 28% 16% 1	392
	11th to 20th	Day	6% 15% 29% 33% 14% 2	449
	21st to end	Day	6% 24% 35% 28% 6%	462
April	1st to 10th	Day	6% 26% 28% 27% 10% 3	420
	11th to 20th	Day	8% 26% 35% 22% 8% 1	412
	21st to end	Day	8% 22% 31% 27% 10% 1	420
May	1st to 10th	Day	9% 24% 33% 22% 9% 3	423
	11th to 20th	Day	5% 13% 28% 30% 20% 3	557
	21st to end	Day	7% 14% 25% 30% 18% 6%	679
June	1st to 10th	Day	4 10% 22% 30% 28% 6%	630
	11th to 20th	Day	4 8% 27% 35% 20% 5%	630
	21st to end	Day	3 9% 22% 34% 27% 6%	630
July	1st to 10th	Day	5% 4 15% 30% 37% 11%	621
	11th to 20th	Day	4 3 13% 34% 31% 14%	537
	21st to end	Day	8% 3 15% 34% 25% 15%	487
August	1st to 10th	Day	9% 5% 22% 32% 20% 12%	447
	11th to 20th	Day	4 5% 24% 32% 20% 14%	437
	21st to end	Day	5% 4 21% 35% 24% 11%	495
September	1st to 10th	Day	8% 4 22% 31% 22% 13%	450
	11th to 20th	Day	4 10% 27% 32% 19% 8%	450
	21st to end	Day	4 10% 24% 27% 23% 12%	333
October	1st to 10th	Day	10% 11% 15% 23% 24% 17%	270
	11th to 20th	Day	10% 10% 24% 27% 22% 8%	270
	21st to end	Day	9% 12% 23% 31% 21% 5%	297
November	1st to 10th	Day	4 15% 22% 36% 17% 6%	270
	11th to 20th	Day	5% 11% 17% 42% 20% 6%	270
	21st to end	Day	3 10% 22% 38% 23% 3	270
December	1st to 10th	Day	5% 9% 26% 40% 13% 7%	270
	11th to 20th	Day	4 11% 21% 43% 18% 3	270
	21st to end	Day	3 14% 26% 42% 11% 3	297
January	1st to 10th	Night	2 7% 27% 46% 17% 1	912
	11th to 20th	Night	2 6% 30% 46% 15% 2	760
	21st to end	Night	3 3 28% 50% 13% 3	836
February	1st to 10th	Night	2 7% 35% 46% 10% 1	760
	11th to 20th	Night	2 5% 37% 45% 10%	744
	21st to end	Night	4 6% 37% 49% 5%	628
March	1st to 10th	Night	3 5% 35% 46% 10% 1	760
	11th to 20th	Night	3 4 28% 50% 15% 1	752
	21st to end	Night	3 6% 32% 50% 9%	748
April	1st to 10th	Night	5% 6% 34% 46% 8%	540
	11th to 20th	Night	5% 9% 32% 42% 12%	533
	21st to end	Night	5% 6% 30% 44% 14% 1	540
May	1st to 10th	Night	5% 6% 28% 45% 15%	540
	11th to 20th	Night	9% 3 16% 47% 22% 2	531
	21st to end	Night	6% 5% 22% 43% 21% 3	584
June	1st to 10th	Night	1 2 18% 44% 33% 1	540
	11th to 20th	Night	2 3 19% 54% 20% 1	540
	21st to end	Night	1 2 14% 48% 34% 1	540
July	1st to 10th	Night	5% 1 7% 42% 43% 3	525
	11th to 20th	Night	3 1 5% 35% 50% 6%	522
	21st to end	Night	5% 2 4 31% 52% 7%	591
August	1st to 10th	Night	7% 2 7% 34% 45% 4	537
	11th to 20th	Night	4 2 6% 45% 38% 4	534
	21st to end	Night	7% 2 6% 39% 40% 6%	594
September	1st to 10th	Night	5% 2 8% 45% 37% 3	540
	11th to 20th	Night	5% 2 10% 49% 33% 2	540
	21st to end	Night	3 3 14% 43% 32% 6%	660
October	1st to 10th	Night	4 4 19% 46% 24% 3	720
	11th to 20th	Night	3 4 21% 47% 22% 3	720
	21st to end	Night	5% 4 24% 44% 20% 3	792
November	1st to 10th	Night	4 3 26% 46% 18% 2	820
	11th to 20th	Night	3 6% 26% 47% 16% 2	950
	21st to end	Night	4 7% 26% 43% 18% 1	950
December	1st to 10th	Night	4 6% 30% 48% 11% 2	950
	11th to 20th	Night	4 6% 33% 43% 14% 1	950
	21st to end	Night	3 8% 31% 47% 10% 1	1045

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