Fort Supply Reservoir
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Supply Reservoir clear sky chart from 2005-11-06 to 2026-02-01.

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	7% 5% 2 5% 3 3 4 3 5% 7% 57%	136194
	Night	7% 4 2 4 3 3 4 3 5% 7% 59%	133191
Transparency	Day	27% 4 10% 24% 26% 10%	131082
	Night	25% 4 9% 24% 26% 11%	129310
Seeing	Day	10% 8% 30% 32% 17% 4	17078
	Night	9% 10% 38% 34% 9%	27106

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	7% 7% 2 7% 4 4 4 4 4 5% 51%	4167
	11th to 20th	Day	4 5% 3 5% 3 2 3 3 4 6% 62%	4170
	21st to end	Day	8% 7% 3 7% 3 3 3 2 3 4 56%	4605
February	1st to 10th	Day	8% 9% 3 5% 3 3 2 3 4 6% 54%	2000
	11th to 20th	Day	6% 6% 2 6% 3 4 4 3 3 6% 58%	1949
	21st to end	Day	6% 6% 2 5% 3 3 3 3 4 5% 60%	1650
March	1st to 10th	Day	7% 7% 2 4 3 3 3 2 3 5% 61%	4560
	11th to 20th	Day	5% 4 2 5% 3 3 4 3 5% 6% 59%	4980
	21st to end	Day	7% 6% 2 5% 4 4 4 3 5% 7% 53%	5464
April	1st to 10th	Day	8% 4 2 5% 4 2 3 3 4 6% 59%	2310
	11th to 20th	Day	11% 7% 2 5% 3 4 3 4 5% 6% 52%	2371
	21st to end	Day	13% 5% 2 4 3 3 3 3 4 6% 52%	2597
May	1st to 10th	Day	13% 5% 2 5% 4 4 4 3 5% 6% 50%	5900
	11th to 20th	Day	7% 4 1 4 3 3 4 3 5% 6% 61%	5862
	21st to end	Day	13% 6% 2 5% 3 3 4 3 5% 6% 51%	6446
June	1st to 10th	Day	6% 4 2 5% 3 4 5% 4 7% 8% 54%	2600
	11th to 20th	Day	5% 3 1 4 3 4 5% 4 6% 7% 58%	2600
	21st to end	Day	6% 3 2 4 4 3 4 3 6% 8% 58%	2600
July	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 4 6% 8% 48%	5899
	11th to 20th	Day	5% 4 1 5% 3 3 4 3 5% 7% 58%	5900
	21st to end	Day	4 2 1 3 3 3 4 4 6% 10% 60%	6424
August	1st to 10th	Day	10% 4 2 5% 3 4 4 3 5% 7% 54%	5801
	11th to 20th	Day	3 3 2 4 4 4 4 4 6% 10% 56%	5619
	21st to end	Day	12% 4 2 4 2 3 4 4 6% 8% 52%	5984
September	1st to 10th	Day	10% 4 2 4 2 4 3 3 4 6% 58%	2272
	11th to 20th	Day	7% 3 1 5% 3 3 4 4 5% 7% 57%	2200
	21st to end	Day	6% 3 1 5% 3 3 3 3 4 6% 62%	2200
October	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 4 73%	3590
	11th to 20th	Day	5% 2 1 3 2 2 2 2 5% 7% 70%	3349
	21st to end	Day	6% 3 1 4 2 2 2 2 5% 5% 68%	3394
November	1st to 10th	Day	6% 3 1 3 3 2 3 2 4 4 68%	1853
	11th to 20th	Day	5% 4 1 3 2 2 3 2 4 7% 66%	1890
	21st to end	Day	9% 5% 2 4 3 3 3 2 3 5% 62%	1890
December	1st to 10th	Day	3 3 1 3 2 2 2 3 4 6% 70%	3030
	11th to 20th	Day	5% 4 1 3 2 2 3 3 5% 7% 66%	3481
	21st to end	Day	10% 12% 4 6% 4 4 3 2 3 5% 47%	4587
January	1st to 10th	Night	8% 7% 3 6% 4 4 4 4 4 5% 51%	6018
	11th to 20th	Night	3 3 2 5% 4 3 4 3 4 6% 63%	6030
	21st to end	Night	10% 7% 3 6% 3 3 3 2 4 4 56%	6633
February	1st to 10th	Night	8% 8% 3 6% 4 3 3 3 4 6% 54%	2410
	11th to 20th	Night	9% 6% 2 6% 4 4 3 3 5% 6% 52%	2338
	21st to end	Night	7% 4 2 4 3 3 3 3 5% 6% 60%	1980
March	1st to 10th	Night	4 6% 1 4 3 2 3 3 4 6% 64%	5310
	11th to 20th	Night	6% 3 2 4 2 3 3 3 4 7% 63%	4980
	21st to end	Night	6% 5% 2 4 4 3 4 3 5% 6% 57%	5467
April	1st to 10th	Night	7% 4 1 3 3 4 3 3 4 7% 59%	2085
	11th to 20th	Night	9% 4 2 5% 3 3 4 3 6% 7% 53%	1977
	21st to end	Night	13% 4 2 4 3 3 4 4 4 6% 53%	1800
May	1st to 10th	Night	14% 6% 2 6% 4 3 3 4 5% 6% 48%	4080
	11th to 20th	Night	7% 3 1 3 2 3 4 3 6% 6% 62%	4053
	21st to end	Night	11% 6% 2 4 3 3 4 3 5% 7% 53%	4451
June	1st to 10th	Night	5% 4 1 4 3 4 3 4 7% 11% 54%	1800
	11th to 20th	Night	5% 2 1 4 3 3 4 4 7% 11% 56%	1800
	21st to end	Night	5% 3 2 3 3 3 4 3 5% 10% 58%	1800
July	1st to 10th	Night	5% 4 2 5% 3 4 5% 5% 6% 9% 52%	4080
	11th to 20th	Night	4 3 1 4 3 4 5% 5% 7% 11% 54%	4080
	21st to end	Night	3 3 1 4 3 3 4 4 7% 9% 59%	4449
August	1st to 10th	Night	6% 3 1 4 3 4 5% 4 7% 11% 51%	4011
	11th to 20th	Night	4 3 1 5% 4 4 6% 5% 7% 12% 50%	4212
	21st to end	Night	12% 5% 1 5% 3 3 4 3 6% 9% 50%	4993
September	1st to 10th	Night	8% 3 1 3 3 2 3 3 4 6% 62%	2126
	11th to 20th	Night	8% 4 2 5% 3 3 3 3 5% 5% 58%	2200
	21st to end	Night	6% 3 1 4 3 3 3 3 5% 6% 63%	2200
October	1st to 10th	Night	5% 2 1 3 2 2 2 2 3 4 74%	3590
	11th to 20th	Night	4 2 1 2 2 2 3 3 4 6% 72%	3756
	21st to end	Night	5% 2 1 2 1 2 2 2 3 7% 72%	4398
November	1st to 10th	Night	6% 4 1 3 2 2 2 3 5% 6% 67%	2665
	11th to 20th	Night	4 3 1 3 2 2 2 3 4 6% 68%	2730
	21st to end	Night	8% 5% 1 4 3 3 3 3 4 5% 62%	2730
December	1st to 10th	Night	4 3 1 3 2 2 2 2 4 5% 71%	4380
	11th to 20th	Night	5% 3 1 4 2 3 3 2 4 5% 67%	4946
	21st to end	Night	10% 8% 2 5% 3 3 3 3 4 6% 52%	6633

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	35% 4 8% 25% 23% 4	4168
	11th to 20th	Day	25% 3 10% 17% 33% 12%	4170
	21st to end	Day	33% 3 4 20% 34% 6%	4605
February	1st to 10th	Day	32% 3 10% 25% 22% 8%	2000
	11th to 20th	Day	31% 3 9% 26% 22% 9%	1959
	21st to end	Day	26% 3 5% 24% 26% 15%	1650
March	1st to 10th	Day	27% 2 6% 15% 22% 28%	4560
	11th to 20th	Day	25% 5% 7% 16% 29% 19%	4980
	21st to end	Day	29% 6% 10% 31% 21% 3	5464
April	1st to 10th	Day	26% 4 8% 23% 26% 13%	2310
	11th to 20th	Day	32% 5% 9% 23% 20% 11%	2374
	21st to end	Day	32% 5% 10% 25% 22% 5%	2597
May	1st to 10th	Day	35% 5% 14% 19% 18% 9%	5900
	11th to 20th	Day	23% 5% 10% 23% 24% 15%	5866
	21st to end	Day	34% 5% 9% 20% 19% 12%	6447
June	1st to 10th	Day	25% 8% 19% 26% 16% 7%	2600
	11th to 20th	Day	23% 6% 13% 25% 26% 8%	2600
	21st to end	Day	24% 5% 13% 25% 24% 10%	2600
July	1st to 10th	Day	33% 5% 13% 20% 23% 7%	5836
	11th to 20th	Day	25% 4 11% 28% 28% 5%	5831
	21st to end	Day	20% 4 14% 36% 23% 3	6240
August	1st to 10th	Day	29% 4 12% 29% 21% 4	4220
	11th to 20th	Day	23% 5% 12% 26% 29% 5%	4060
	21st to end	Day	21% 5% 12% 29% 27% 6%	4311
September	1st to 10th	Day	28% 5% 9% 22% 23% 13%	2272
	11th to 20th	Day	26% 6% 11% 23% 29% 6%	2200
	21st to end	Day	23% 5% 10% 22% 28% 11%	2200
October	1st to 10th	Day	17% 3 6% 16% 42% 17%	3590
	11th to 20th	Day	17% 2 9% 27% 27% 18%	3349
	21st to end	Day	20% 2 6% 24% 35% 13%	3394
November	1st to 10th	Day	20% 3 7% 22% 32% 15%	1853
	11th to 20th	Day	20% 3 7% 26% 32% 12%	1890
	21st to end	Day	27% 3 6% 24% 28% 11%	1890
December	1st to 10th	Day	17% 3 7% 37% 30% 6%	3030
	11th to 20th	Day	19% 3 5% 25% 38% 9%	3479
	21st to end	Day	41% 3 8% 20% 21% 7%	4587
January	1st to 10th	Night	35% 4 10% 29% 19% 4	6018
	11th to 20th	Night	21% 5% 11% 20% 33% 10%	6030
	21st to end	Night	33% 4 5% 17% 33% 8%	6633
February	1st to 10th	Night	33% 4 7% 24% 22% 10%	2410
	11th to 20th	Night	32% 5% 10% 21% 24% 9%	2338
	21st to end	Night	26% 3 6% 21% 27% 17%	1980
March	1st to 10th	Night	22% 3 5% 18% 25% 27%	5310
	11th to 20th	Night	21% 4 7% 18% 24% 27%	4980
	21st to end	Night	27% 5% 8% 30% 24% 5%	5467
April	1st to 10th	Night	25% 5% 9% 21% 25% 14%	2085
	11th to 20th	Night	29% 6% 11% 24% 20% 10%	1977
	21st to end	Night	30% 6% 12% 25% 22% 4	1800
May	1st to 10th	Night	37% 6% 12% 15% 19% 11%	4080
	11th to 20th	Night	21% 6% 10% 23% 21% 19%	4054
	21st to end	Night	31% 5% 12% 20% 17% 14%	4452
June	1st to 10th	Night	24% 7% 18% 30% 16% 6%	1800
	11th to 20th	Night	22% 8% 13% 27% 23% 8%	1800
	21st to end	Night	22% 5% 13% 27% 23% 11%	1800
July	1st to 10th	Night	29% 5% 17% 27% 19% 4	4035
	11th to 20th	Night	24% 4 11% 27% 29% 5%	4026
	21st to end	Night	21% 4 13% 32% 26% 3	4320
August	1st to 10th	Night	26% 6% 12% 26% 24% 6%	2916
	11th to 20th	Night	25% 5% 11% 30% 25% 5%	3047
	21st to end	Night	21% 5% 14% 32% 23% 6%	3597
September	1st to 10th	Night	23% 5% 10% 25% 26% 11%	2126
	11th to 20th	Night	28% 4 10% 21% 28% 8%	2200
	21st to end	Night	22% 4 9% 23% 30% 12%	2200
October	1st to 10th	Night	17% 3 5% 16% 39% 21%	3590
	11th to 20th	Night	15% 2 8% 23% 34% 18%	3756
	21st to end	Night	16% 2 5% 25% 36% 16%	4398
November	1st to 10th	Night	19% 4 8% 23% 28% 18%	2665
	11th to 20th	Night	19% 3 7% 26% 32% 13%	2730
	21st to end	Night	25% 3 6% 26% 27% 13%	2730
December	1st to 10th	Night	18% 2 5% 39% 31% 4	4380
	11th to 20th	Night	21% 3 5% 25% 36% 11%	4947
	21st to end	Night	33% 4 9% 25% 21% 7%	6633

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	10% 10% 41% 28% 10% 1	330
	11th to 20th	Day	14% 16% 35% 25% 10%	330
	21st to end	Day	8% 12% 44% 26% 9% 1	363
February	1st to 10th	Day	12% 13% 40% 29% 5% 1	300
	11th to 20th	Day	13% 13% 48% 19% 6% 2	300
	21st to end	Day	10% 12% 53% 20% 4	249
March	1st to 10th	Day	10% 13% 48% 23% 6%	300
	11th to 20th	Day	17% 13% 41% 21% 6% 2	300
	21st to end	Day	15% 16% 40% 24% 4 1	330
April	1st to 10th	Day	14% 16% 39% 23% 7%	410
	11th to 20th	Day	14% 19% 43% 22% 2	492
	21st to end	Day	15% 17% 37% 21% 9% 1	697
May	1st to 10th	Day	13% 10% 40% 30% 6% 1	703
	11th to 20th	Day	13% 7% 32% 31% 14% 2	725
	21st to end	Day	10% 11% 34% 31% 10% 3	789
June	1st to 10th	Day	6% 6% 27% 37% 18% 6%	730
	11th to 20th	Day	5% 6% 29% 38% 19% 2	730
	21st to end	Day	6% 2 30% 42% 17% 3	730
July	1st to 10th	Day	6% 2 17% 36% 31% 9%	721
	11th to 20th	Day	4 2 14% 42% 32% 7%	718
	21st to end	Day	6% 1 11% 40% 34% 8%	794
August	1st to 10th	Day	6% 2 17% 40% 30% 5%	726
	11th to 20th	Day	6% 1 14% 41% 33% 5%	630
	21st to end	Day	7% 2 15% 38% 29% 10%	583
September	1st to 10th	Day	11% 1 13% 37% 29% 8%	402
	11th to 20th	Day	5% 3 20% 46% 20% 5%	330
	21st to end	Day	9% 3 25% 31% 26% 6%	330
October	1st to 10th	Day	11% 4 30% 31% 20% 4	330
	11th to 20th	Day	8% 6% 37% 36% 13% 1	330
	21st to end	Day	18% 9% 34% 25% 11% 4	363
November	1st to 10th	Day	8% 8% 40% 29% 12% 2	330
	11th to 20th	Day	7% 12% 36% 28% 14% 2	330
	21st to end	Day	16% 11% 34% 25% 12% 3	330
December	1st to 10th	Day	5% 9% 46% 30% 8% 2	330
	11th to 20th	Day	9% 12% 38% 28% 11% 2	330
	21st to end	Day	15% 16% 38% 23% 7% 1	363
January	1st to 10th	Night	8% 10% 42% 33% 6%	1050
	11th to 20th	Night	8% 14% 39% 32% 7%	1050
	21st to end	Night	9% 11% 43% 31% 6%	1155
February	1st to 10th	Night	12% 11% 44% 29% 4	810
	11th to 20th	Night	11% 16% 43% 27% 3	784
	21st to end	Night	10% 15% 46% 25% 4	660
March	1st to 10th	Night	9% 13% 46% 29% 4	775
	11th to 20th	Night	15% 12% 42% 26% 6%	600
	21st to end	Night	11% 17% 45% 23% 3	660
April	1st to 10th	Night	9% 15% 47% 26% 4	600
	11th to 20th	Night	11% 18% 45% 22% 3	593
	21st to end	Night	15% 15% 42% 23% 5%	600
May	1st to 10th	Night	12% 12% 44% 27% 5%	600
	11th to 20th	Night	10% 10% 35% 34% 10% 1	591
	21st to end	Night	8% 8% 41% 32% 10% 1	650
June	1st to 10th	Night	7% 5% 41% 34% 12%	600
	11th to 20th	Night	4 6% 43% 39% 7%	600
	21st to end	Night	6% 2 41% 40% 10%	600
July	1st to 10th	Night	6% 1 23% 46% 22% 2	585
	11th to 20th	Night	4 1 22% 53% 19% 1	582
	21st to end	Night	5% 1 18% 53% 20% 2	657
August	1st to 10th	Night	5% 2 24% 48% 21% 1	597
	11th to 20th	Night	7% 3 18% 52% 19%	594
	21st to end	Night	5% 1 20% 45% 27% 2	660
September	1st to 10th	Night	9% 2 22% 48% 18% 1	600
	11th to 20th	Night	9% 4 32% 42% 13% 1	600
	21st to end	Night	7% 5% 33% 39% 16% 1	600
October	1st to 10th	Night	9% 7% 33% 39% 12%	600
	11th to 20th	Night	8% 9% 42% 35% 5%	709
	21st to end	Night	10% 11% 36% 30% 12% 1	964
November	1st to 10th	Night	8% 8% 39% 35% 9%	1025
	11th to 20th	Night	6% 12% 42% 33% 6%	1050
	21st to end	Night	9% 14% 34% 34% 9%	1050
December	1st to 10th	Night	9% 10% 39% 35% 8%	1050
	11th to 20th	Night	12% 11% 42% 31% 4	1050
	21st to end	Night	12% 13% 40% 31% 5%	1155

Page generated at 2026-01-29 00:21:45. Version ac07

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