Missouri Gulch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Missouri Gulch Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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	4 6% 3 6% 4 4 5% 4 6% 8% 49%	135673
	Night	2 5% 2 5% 3 3 4 3 6% 8% 59%	132139
Transparency	Day	28% 8% 12% 21% 21% 9%	130614
	Night	22% 6% 13% 24% 25% 9%	128203
Seeing	Day	11% 19% 35% 22% 10% 2	16996
	Night	9% 17% 37% 25% 11% 2	27009

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	4 4 9% 4 4 2 3 4 7% 58%	3638
	11th to 20th	Day	3 2 6% 6% 4 4 2 6% 8% 60%	3806
	21st to end	Day	5% 3 8% 3 3 3 3 5% 7% 59%	4510
February	1st to 10th	Day	4 3 10% 4 4 3 3 6% 9% 54%	1800
	11th to 20th	Day	4 2 6% 4 4 5% 4 6% 8% 58%	1895
	21st to end	Day	5% 4 8% 5% 4 3 3 5% 7% 57%	1650
March	1st to 10th	Day	1 7% 4 9% 4 4 4 3 5% 5% 54%	4517
	11th to 20th	Day	1 11% 6% 8% 4 5% 5% 3 5% 8% 43%	5000
	21st to end	Day	2 9% 4 7% 5% 5% 5% 4 6% 9% 45%	5780
April	1st to 10th	Day	3 7% 4 6% 4 4 4 4 7% 8% 49%	2400
	11th to 20th	Day	6% 13% 4 7% 5% 4 5% 4 5% 7% 41%	2371
	21st to end	Day	6% 11% 3 6% 5% 5% 6% 5% 8% 7% 39%	2400
May	1st to 10th	Day	8% 12% 3 7% 4 4 5% 4 7% 9% 36%	5746
	11th to 20th	Day	7% 8% 3 5% 4 5% 5% 5% 7% 9% 41%	6298
	21st to end	Day	6% 6% 2 5% 4 5% 6% 4 8% 10% 46%	6925
June	1st to 10th	Day	5% 5% 2 6% 5% 5% 6% 6% 8% 8% 45%	2800
	11th to 20th	Day	6% 5% 2 5% 4 4 6% 4 7% 8% 48%	2800
	21st to end	Day	4 5% 2 6% 6% 6% 6% 5% 8% 8% 45%	2800
July	1st to 10th	Day	4 3 2 5% 4 4 5% 5% 7% 10% 51%	6339
	11th to 20th	Day	4 4 2 7% 5% 6% 8% 7% 10% 10% 39%	6340
	21st to end	Day	7% 6% 3 7% 6% 6% 7% 5% 7% 7% 38%	6690
August	1st to 10th	Day	6% 5% 2 6% 5% 5% 7% 6% 9% 11% 37%	5779
	11th to 20th	Day	4 5% 2 6% 5% 5% 6% 5% 7% 8% 47%	5418
	21st to end	Day	8% 7% 3 8% 5% 6% 6% 4 7% 8% 38%	5984
September	1st to 10th	Day	5% 6% 2 5% 4 4 5% 4 6% 7% 53%	2400
	11th to 20th	Day	7% 4 2 5% 4 4 3 4 5% 8% 54%	2399
	21st to end	Day	7% 5% 2 5% 2 3 3 2 4 7% 59%	2180
October	1st to 10th	Day	3 4 1 4 2 2 2 2 3 5% 71%	3270
	11th to 20th	Day	4 5% 2 6% 4 4 5% 3 6% 7% 54%	3250
	21st to end	Day	3 6% 2 4 2 3 3 3 5% 7% 63%	3462
November	1st to 10th	Day	1 4 2 5% 3 3 3 3 5% 7% 66%	1853
	11th to 20th	Day	1 3 2 4 4 2 3 2 5% 9% 65%	1863
	21st to end	Day	4 3 8% 3 3 3 3 6% 8% 59%	1660
December	1st to 10th	Day	2 2 4 3 2 3 2 3 7% 71%	2620
	11th to 20th	Day	1 3 1 4 3 2 3 3 6% 9% 65%	3026
	21st to end	Day	1 5% 3 7% 4 3 4 4 6% 9% 55%	4004
January	1st to 10th	Night	3 3 9% 4 4 4 3 4 7% 60%	6327
	11th to 20th	Night	1 1 4 5% 4 4 3 5% 7% 65%	6202
	21st to end	Night	4 2 5% 4 3 3 2 4 7% 64%	6468
February	1st to 10th	Night	3 3 6% 3 3 4 3 5% 8% 62%	2600
	11th to 20th	Night	4 2 6% 4 3 3 4 6% 8% 62%	2392
	21st to end	Night	4 3 7% 3 3 3 3 4 7% 61%	1980
March	1st to 10th	Night	7% 4 7% 4 3 3 3 5% 7% 57%	5343
	11th to 20th	Night	1 9% 4 6% 4 4 3 3 5% 7% 54%	5000
	21st to end	Night	2 6% 3 6% 3 3 4 4 6% 9% 55%	5179
April	1st to 10th	Night	2 6% 2 4 4 3 4 4 6% 7% 59%	2000
	11th to 20th	Night	4 9% 3 7% 3 3 4 3 6% 7% 52%	1977
	21st to end	Night	6% 11% 2 5% 4 3 4 3 5% 9% 49%	2000
May	1st to 10th	Night	7% 11% 3 6% 4 3 3 3 6% 8% 47%	4227
	11th to 20th	Night	7% 7% 2 5% 4 4 4 3 6% 8% 49%	3617
	21st to end	Night	4 7% 2 5% 3 3 3 2 4 6% 61%	3972
June	1st to 10th	Night	4 4 1 3 3 3 4 4 5% 10% 60%	1600
	11th to 20th	Night	4 3 1 4 2 3 3 3 7% 8% 63%	1600
	21st to end	Night	3 2 2 4 3 3 4 4 7% 8% 60%	1600
July	1st to 10th	Night	3 4 1 4 3 3 4 3 6% 7% 62%	3640
	11th to 20th	Night	2 4 1 4 3 4 5% 5% 9% 12% 52%	3640
	21st to end	Night	3 3 2 4 4 4 5% 5% 8% 10% 53%	4166
August	1st to 10th	Night	4 4 2 4 4 4 5% 5% 9% 10% 49%	4033
	11th to 20th	Night	3 3 1 3 3 3 5% 4 7% 9% 59%	4428
	21st to end	Night	5% 6% 2 6% 4 4 5% 5% 6% 8% 48%	4993
September	1st to 10th	Night	6% 3 2 4 3 3 4 3 5% 7% 60%	2000
	11th to 20th	Night	5% 4 1 4 2 3 3 3 5% 7% 63%	2000
	21st to end	Night	6% 4 1 4 3 3 3 3 5% 5% 63%	2216
October	1st to 10th	Night	2 4 1 2 2 2 2 2 3 4 75%	3920
	11th to 20th	Night	2 5% 2 4 3 3 3 2 5% 6% 66%	3898
	21st to end	Night	2 5% 3 4 2 2 3 2 4 6% 66%	4304
November	1st to 10th	Night	1 3 1 4 3 3 2 2 5% 6% 69%	2665
	11th to 20th	Night	1 4 1 4 3 3 2 3 5% 8% 65%	2692
	21st to end	Night	1 4 2 6% 4 2 4 3 6% 7% 62%	2735
December	1st to 10th	Night	2 1 3 2 2 2 2 3 6% 77%	4570
	11th to 20th	Night	3 2 5% 3 3 3 3 5% 8% 66%	5181
	21st to end	Night	6% 2 6% 3 3 4 4 7% 8% 54%	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	22% 6% 14% 26% 23% 8%	3639
	11th to 20th	Day	23% 6% 18% 20% 24% 9%	3806
	21st to end	Day	23% 6% 12% 22% 26% 10%	4510
February	1st to 10th	Day	28% 6% 19% 21% 18% 8%	1800
	11th to 20th	Day	24% 7% 16% 24% 24% 6%	1905
	21st to end	Day	28% 4 14% 21% 22% 11%	1650
March	1st to 10th	Day	27% 5% 10% 16% 30% 12%	4517
	11th to 20th	Day	33% 8% 12% 23% 20% 4	5000
	21st to end	Day	30% 8% 16% 31% 13% 2	5780
April	1st to 10th	Day	30% 7% 12% 24% 19% 8%	2400
	11th to 20th	Day	39% 7% 13% 18% 16% 6%	2374
	21st to end	Day	39% 10% 12% 23% 15% 1	2400
May	1st to 10th	Day	39% 8% 13% 21% 15% 3	5746
	11th to 20th	Day	32% 11% 13% 21% 19% 6%	6302
	21st to end	Day	29% 10% 13% 22% 22% 4	6926
June	1st to 10th	Day	29% 12% 15% 20% 18% 6%	2800
	11th to 20th	Day	29% 10% 11% 15% 23% 12%	2800
	21st to end	Day	30% 10% 12% 18% 21% 10%	2800
July	1st to 10th	Day	24% 8% 9% 17% 20% 22%	6271
	11th to 20th	Day	29% 12% 14% 21% 14% 9%	6265
	21st to end	Day	38% 9% 12% 16% 14% 12%	6497
August	1st to 10th	Day	38% 12% 14% 17% 14% 5%	4208
	11th to 20th	Day	32% 9% 14% 15% 20% 11%	3922
	21st to end	Day	36% 8% 10% 16% 22% 8%	4311
September	1st to 10th	Day	27% 7% 11% 19% 23% 14%	2400
	11th to 20th	Day	26% 7% 11% 20% 26% 10%	2399
	21st to end	Day	25% 5% 8% 21% 33% 9%	2180
October	1st to 10th	Day	17% 5% 6% 15% 39% 19%	3270
	11th to 20th	Day	28% 6% 10% 26% 24% 6%	3250
	21st to end	Day	21% 5% 9% 28% 31% 7%	3462
November	1st to 10th	Day	18% 6% 12% 22% 32% 10%	1853
	11th to 20th	Day	18% 6% 13% 27% 28% 9%	1863
	21st to end	Day	23% 4 13% 24% 24% 11%	1660
December	1st to 10th	Day	15% 6% 10% 33% 27% 9%	2620
	11th to 20th	Day	14% 6% 14% 35% 25% 7%	3024
	21st to end	Day	23% 7% 12% 24% 26% 8%	4004
January	1st to 10th	Night	24% 5% 12% 25% 27% 8%	6327
	11th to 20th	Night	18% 7% 16% 21% 24% 13%	6202
	21st to end	Night	20% 6% 13% 24% 24% 13%	6468
February	1st to 10th	Night	21% 7% 18% 26% 21% 7%	2600
	11th to 20th	Night	21% 7% 15% 27% 24% 6%	2392
	21st to end	Night	22% 4 13% 24% 24% 12%	1980
March	1st to 10th	Night	25% 5% 10% 16% 32% 12%	5343
	11th to 20th	Night	27% 6% 10% 19% 28% 9%	5000
	21st to end	Night	23% 8% 15% 35% 16% 2	5179
April	1st to 10th	Night	23% 9% 12% 26% 23% 7%	2000
	11th to 20th	Night	31% 7% 13% 23% 21% 5%	1977
	21st to end	Night	31% 8% 13% 26% 19% 3	2000
May	1st to 10th	Night	32% 8% 15% 26% 13% 5%	4224
	11th to 20th	Night	28% 10% 15% 23% 21% 3	3618
	21st to end	Night	23% 7% 15% 26% 25% 4	3972
June	1st to 10th	Night	20% 8% 19% 30% 16% 7%	1600
	11th to 20th	Night	18% 7% 13% 18% 26% 18%	1600
	21st to end	Night	18% 7% 13% 22% 28% 13%	1600
July	1st to 10th	Night	21% 5% 9% 17% 28% 20%	3600
	11th to 20th	Night	20% 8% 19% 27% 19% 7%	3592
	21st to end	Night	23% 8% 18% 24% 15% 13%	4048
August	1st to 10th	Night	29% 9% 18% 21% 19% 4	2928
	11th to 20th	Night	22% 7% 22% 19% 20% 10%	3200
	21st to end	Night	27% 7% 14% 20% 27% 5%	3597
September	1st to 10th	Night	23% 6% 9% 23% 25% 13%	2000
	11th to 20th	Night	20% 6% 11% 24% 25% 14%	2000
	21st to end	Night	23% 5% 9% 23% 31% 10%	2216
October	1st to 10th	Night	15% 4 7% 21% 35% 18%	3920
	11th to 20th	Night	19% 5% 11% 30% 27% 8%	3898
	21st to end	Night	19% 4 8% 25% 32% 11%	4304
November	1st to 10th	Night	16% 6% 12% 24% 32% 11%	2665
	11th to 20th	Night	17% 5% 13% 27% 29% 9%	2692
	21st to end	Night	22% 6% 11% 24% 28% 10%	2735
December	1st to 10th	Night	12% 5% 10% 32% 33% 8%	4570
	11th to 20th	Night	15% 5% 13% 29% 33% 5%	5182
	21st to end	Night	24% 8% 14% 21% 27% 7%	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	12% 24% 41% 14% 7% 2	300
	11th to 20th	Day	11% 37% 37% 13% 2 1	300
	21st to end	Day	7% 36% 36% 16% 4 1	330
February	1st to 10th	Day	15% 41% 34% 8% 1 1	300
	11th to 20th	Day	14% 35% 40% 10% 2	300
	21st to end	Day	14% 36% 42% 7% 1	249
March	1st to 10th	Day	9% 34% 39% 14% 4	304
	11th to 20th	Day	16% 28% 33% 19% 3	500
	21st to end	Day	16% 32% 37% 13% 2	550
April	1st to 10th	Day	15% 32% 36% 13% 3	500
	11th to 20th	Day	17% 35% 35% 11% 2	492
	21st to end	Day	19% 24% 38% 16% 3 1	500
May	1st to 10th	Day	17% 23% 36% 17% 5% 1	600
	11th to 20th	Day	19% 12% 35% 24% 9% 2	725
	21st to end	Day	13% 14% 32% 28% 11% 2	789
June	1st to 10th	Day	8% 11% 30% 32% 15% 5%	730
	11th to 20th	Day	8% 13% 38% 27% 10% 3	730
	21st to end	Day	6% 11% 37% 27% 13% 5%	730
July	1st to 10th	Day	7% 6% 27% 34% 22% 5%	721
	11th to 20th	Day	6% 5% 28% 34% 20% 7%	718
	21st to end	Day	8% 6% 26% 33% 22% 5%	708
August	1st to 10th	Day	11% 9% 33% 29% 14% 4	527
	11th to 20th	Day	8% 7% 34% 31% 16% 3	517
	21st to end	Day	10% 8% 33% 30% 17% 3	583
September	1st to 10th	Day	9% 8% 34% 31% 14% 3	530
	11th to 20th	Day	9% 12% 36% 31% 11% 1	529
	21st to end	Day	10% 15% 35% 22% 14% 3	330
October	1st to 10th	Day	10% 17% 33% 23% 13% 4	330
	11th to 20th	Day	10% 25% 37% 20% 6% 2	330
	21st to end	Day	11% 27% 40% 17% 4 1	363
November	1st to 10th	Day	11% 25% 42% 14% 8% 1	330
	11th to 20th	Day	15% 25% 41% 15% 3 1	321
	21st to end	Day	9% 30% 41% 17% 2	300
December	1st to 10th	Day	13% 30% 38% 15% 3 1	300
	11th to 20th	Day	14% 32% 42% 9% 2	300
	21st to end	Day	14% 35% 37% 12% 3	330
January	1st to 10th	Night	11% 24% 40% 16% 7% 2	1000
	11th to 20th	Night	12% 31% 35% 15% 5% 1	940
	21st to end	Night	9% 25% 45% 15% 5% 1	880
February	1st to 10th	Night	10% 28% 46% 13% 4	800
	11th to 20th	Night	9% 27% 44% 15% 4	784
	21st to end	Night	7% 29% 47% 15% 2	660
March	1st to 10th	Night	6% 24% 46% 18% 6%	800
	11th to 20th	Night	9% 20% 39% 25% 6% 1	800
	21st to end	Night	9% 24% 41% 22% 3 1	751
April	1st to 10th	Night	10% 18% 48% 21% 3	600
	11th to 20th	Night	11% 20% 41% 21% 7% 1	593
	21st to end	Night	12% 17% 41% 22% 8% 1	600
May	1st to 10th	Night	12% 10% 41% 27% 9% 1	600
	11th to 20th	Night	18% 6% 28% 36% 10% 2	591
	21st to end	Night	10% 9% 31% 33% 16% 2	650
June	1st to 10th	Night	6% 3 26% 41% 21% 3	600
	11th to 20th	Night	7% 4 36% 40% 12% 1	600
	21st to end	Night	5% 4 23% 42% 24% 2	600
July	1st to 10th	Night	7% 3 16% 38% 33% 3	585
	11th to 20th	Night	3 1 17% 42% 33% 5%	582
	21st to end	Night	6% 2 14% 38% 34% 6%	657
August	1st to 10th	Night	6% 4 18% 39% 31% 3	597
	11th to 20th	Night	6% 2 17% 46% 24% 5%	594
	21st to end	Night	6% 3 16% 42% 26% 7%	660
September	1st to 10th	Night	5% 3 21% 44% 22% 6%	600
	11th to 20th	Night	9% 5% 29% 36% 18% 4	600
	21st to end	Night	9% 8% 30% 34% 14% 5%	616
October	1st to 10th	Night	7% 12% 37% 30% 11% 3	800
	11th to 20th	Night	7% 16% 41% 26% 9% 2	800
	21st to end	Night	11% 18% 42% 20% 8% 1	908
November	1st to 10th	Night	7% 19% 47% 19% 7% 1	1025
	11th to 20th	Night	10% 25% 44% 16% 4 1	1036
	21st to end	Night	6% 20% 47% 23% 4	1000
December	1st to 10th	Night	11% 22% 46% 18% 3	1000
	11th to 20th	Night	10% 26% 47% 13% 5% 1	1000
	21st to end	Night	9% 28% 42% 16% 4 1	1100

Page generated at 2025-11-14 22:55:55. Version ac07

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