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 2024-01-14.

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	8% 5% 2 4 4 2 4 4 5% 7% 57%	74894
	Night	7% 4 2 4 4 2 4 4 5% 7% 58%	74893
Transparency	Day	27% 5% 11% 24% 24% 9%	74622
	Night	25% 5% 10% 25% 25% 10%	74688
Seeing	Day	10% 7% 30% 32% 17% 4	14292
	Night	9% 9% 37% 35% 10%	24342

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 6% 2 3 4 2 2 4 5% 5% 64%	1707
	11th to 20th	Day	8% 5% 2 5% 4 1 3 3 4 7% 58%	1647
	21st to end	Day	5% 4 3 4 4 2 4 5% 5% 6% 58%	1786
February	1st to 10th	Day	8% 9% 3 4 3 2 2 3 3 7% 55%	1800
	11th to 20th	Day	6% 5% 2 5% 4 3 4 4 3 6% 58%	1749
	21st to end	Day	6% 6% 2 4 4 2 4 4 4 6% 58%	1480
March	1st to 10th	Day	8% 6% 3 4 4 3 4 4 5% 6% 53%	1821
	11th to 20th	Day	12% 6% 2 3 3 2 3 3 4 6% 56%	1980
	21st to end	Day	10% 7% 3 4 3 2 4 4 4 6% 53%	2178
April	1st to 10th	Day	8% 4 2 4 4 2 3 3 4 6% 60%	2078
	11th to 20th	Day	11% 6% 2 4 4 3 4 4 5% 6% 51%	2131
	21st to end	Day	12% 4 2 4 4 2 3 4 4 7% 53%	2337
May	1st to 10th	Day	12% 5% 2 4 4 2 4 3 5% 7% 53%	2340
	11th to 20th	Day	10% 4 2 4 4 3 4 5% 5% 7% 54%	2302
	21st to end	Day	8% 4 2 4 5% 2 6% 4 7% 8% 49%	2531
June	1st to 10th	Day	6% 3 2 4 3 2 4 5% 6% 8% 55%	2340
	11th to 20th	Day	5% 3 1 3 4 3 5% 5% 6% 8% 58%	2340
	21st to end	Day	6% 3 2 3 4 2 4 3 6% 8% 59%	2340
July	1st to 10th	Day	7% 4 2 4 4 3 4 5% 6% 9% 51%	2340
	11th to 20th	Day	5% 3 1 3 3 3 4 5% 6% 8% 59%	2340
	21st to end	Day	5% 3 2 3 4 3 5% 5% 6% 10% 54%	2546
August	1st to 10th	Day	5% 3 2 4 4 3 4 4 6% 9% 55%	2328
	11th to 20th	Day	6% 5% 3 4 4 3 4 5% 6% 8% 52%	2225
	21st to end	Day	5% 3 2 3 3 3 4 4 6% 8% 59%	2376
September	1st to 10th	Day	10% 4 2 4 3 2 3 4 4 5% 58%	2046
	11th to 20th	Day	8% 3 1 4 4 2 4 5% 5% 7% 56%	1980
	21st to end	Day	6% 3 1 4 4 3 3 4 4 6% 63%	1980
October	1st to 10th	Day	11% 4 1 4 3 2 3 3 4 4 61%	1980
	11th to 20th	Day	8% 3 1 3 3 1 1 2 3 5% 70%	1864
	21st to end	Day	9% 5% 1 4 3 2 2 2 3 4 64%	1903
November	1st to 10th	Day	5% 3 2 3 3 2 3 3 4 4 69%	1673
	11th to 20th	Day	5% 4 2 3 2 2 2 3 4 7% 67%	1710
	21st to end	Day	10% 5% 2 3 3 2 3 3 3 4 62%	1710
December	1st to 10th	Day	6% 5% 1 4 4 2 3 4 5% 7% 59%	1710
	11th to 20th	Day	8% 6% 2 4 3 2 4 4 4 5% 59%	2161
	21st to end	Day	7% 12% 4 6% 6% 3 3 3 3 6% 47%	3135
January	1st to 10th	Night	5% 5% 2 4 3 2 4 4 4 6% 61%	2458
	11th to 20th	Night	6% 4 2 3 3 2 4 4 4 5% 62%	2392
	21st to end	Night	6% 4 2 4 3 2 3 3 4 5% 63%	2574
February	1st to 10th	Night	9% 7% 3 5% 4 2 3 3 4 5% 55%	2169
	11th to 20th	Night	9% 5% 2 5% 5% 3 4 3 5% 6% 53%	2098
	21st to end	Night	8% 4 2 4 3 3 4 4 5% 6% 59%	1776
March	1st to 10th	Night	6% 4 2 4 4 2 4 5% 5% 8% 57%	2138
	11th to 20th	Night	12% 5% 2 3 3 2 4 4 3 6% 56%	1980
	21st to end	Night	10% 6% 2 4 5% 3 4 4 5% 6% 51%	2178
April	1st to 10th	Night	6% 3 2 3 3 4 3 4 4 7% 61%	1877
	11th to 20th	Night	10% 4 2 4 4 3 4 4 6% 7% 51%	1777
	21st to end	Night	12% 3 2 3 4 2 4 5% 4 7% 54%	1620
May	1st to 10th	Night	11% 4 1 4 4 3 3 6% 5% 7% 52%	1620
	11th to 20th	Night	10% 3 2 4 3 3 4 5% 6% 6% 54%	1593
	21st to end	Night	7% 3 2 3 4 2 5% 5% 8% 11% 50%	1745
June	1st to 10th	Night	5% 4 1 3 3 3 4 4 6% 11% 56%	1620
	11th to 20th	Night	5% 1 1 4 4 3 4 5% 6% 11% 57%	1620
	21st to end	Night	6% 3 2 3 3 2 3 4 5% 10% 60%	1620
July	1st to 10th	Night	5% 3 1 3 4 2 4 5% 6% 9% 56%	1620
	11th to 20th	Night	4 2 1 2 3 2 4 5% 6% 11% 59%	1620
	21st to end	Night	5% 3 1 3 4 3 3 4 6% 11% 57%	1772
August	1st to 10th	Night	4 3 2 4 4 3 6% 6% 8% 10% 51%	1611
	11th to 20th	Night	7% 3 2 4 4 3 4 4 5% 8% 55%	1672
	21st to end	Night	4 2 1 3 5% 2 4 5% 6% 11% 57%	1980
September	1st to 10th	Night	9% 3 2 3 3 2 3 3 4 7% 63%	1912
	11th to 20th	Night	8% 4 2 5% 4 3 4 4 5% 6% 56%	1980
	21st to end	Night	5% 3 1 3 3 2 4 4 5% 7% 64%	1980
October	1st to 10th	Night	9% 3 1 3 4 2 3 3 4 5% 62%	1980
	11th to 20th	Night	7% 3 1 3 3 1 2 2 3 4 71%	2077
	21st to end	Night	8% 3 1 3 3 2 2 3 3 5% 67%	2451
November	1st to 10th	Night	6% 3 1 2 2 1 2 3 4 7% 68%	2405
	11th to 20th	Night	4 3 1 3 3 2 3 3 4 5% 68%	2470
	21st to end	Night	8% 4 2 3 3 2 3 4 4 5% 62%	2470
December	1st to 10th	Night	6% 5% 2 4 4 2 3 3 5% 7% 60%	2470
	11th to 20th	Night	8% 5% 1 4 4 2 3 3 4 6% 59%	3036
	21st to end	Night	7% 7% 3 5% 5% 3 4 4 5% 6% 50%	4532

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	23% 3 9% 30% 28% 6%	1708
	11th to 20th	Day	29% 3 10% 23% 28% 8%	1647
	21st to end	Day	27% 4 8% 30% 25% 6%	1786
February	1st to 10th	Day	32% 3 11% 26% 21% 7%	1800
	11th to 20th	Day	30% 4 9% 26% 21% 10%	1759
	21st to end	Day	28% 4 6% 25% 24% 13%	1480
March	1st to 10th	Day	32% 4 9% 22% 21% 12%	1821
	11th to 20th	Day	31% 5% 11% 19% 25% 9%	1980
	21st to end	Day	33% 6% 11% 23% 21% 7%	2178
April	1st to 10th	Day	25% 5% 8% 24% 26% 12%	2078
	11th to 20th	Day	33% 5% 9% 23% 20% 9%	2134
	21st to end	Day	31% 5% 11% 26% 23% 4	2337
May	1st to 10th	Day	32% 6% 12% 18% 21% 10%	2340
	11th to 20th	Day	28% 7% 15% 30% 19% 2	2306
	21st to end	Day	31% 9% 13% 27% 15% 5%	2531
June	1st to 10th	Day	25% 8% 18% 25% 16% 7%	2340
	11th to 20th	Day	23% 6% 12% 24% 25% 9%	2340
	21st to end	Day	23% 5% 12% 25% 25% 11%	2340
July	1st to 10th	Day	28% 9% 13% 25% 20% 5%	2276
	11th to 20th	Day	20% 7% 12% 24% 28% 8%	2271
	21st to end	Day	24% 8% 13% 29% 24% 2	2405
August	1st to 10th	Day	25% 7% 15% 31% 16% 6%	2314
	11th to 20th	Day	30% 7% 13% 24% 20% 5%	2225
	21st to end	Day	23% 8% 12% 25% 22% 10%	2376
September	1st to 10th	Day	28% 6% 9% 22% 22% 14%	2046
	11th to 20th	Day	26% 7% 12% 21% 29% 6%	1980
	21st to end	Day	22% 5% 11% 23% 28% 11%	1980
October	1st to 10th	Day	27% 4 10% 20% 28% 10%	1980
	11th to 20th	Day	19% 3 7% 21% 32% 18%	1864
	21st to end	Day	27% 3 8% 21% 29% 13%	1903
November	1st to 10th	Day	20% 4 8% 22% 31% 16%	1673
	11th to 20th	Day	19% 3 7% 27% 32% 11%	1710
	21st to end	Day	27% 3 5% 23% 30% 12%	1710
December	1st to 10th	Day	26% 5% 10% 28% 25% 6%	1710
	11th to 20th	Day	27% 5% 8% 23% 28% 9%	2159
	21st to end	Day	39% 5% 8% 19% 23% 6%	3135
January	1st to 10th	Night	25% 4 9% 29% 27% 7%	2458
	11th to 20th	Night	24% 4 8% 25% 30% 9%	2392
	21st to end	Night	25% 3 6% 29% 28% 9%	2574
February	1st to 10th	Night	33% 4 8% 24% 22% 9%	2169
	11th to 20th	Night	32% 5% 9% 22% 23% 9%	2098
	21st to end	Night	27% 3 6% 23% 25% 16%	1776
March	1st to 10th	Night	25% 4 8% 23% 27% 12%	2138
	11th to 20th	Night	31% 4 9% 22% 23% 11%	1980
	21st to end	Night	32% 6% 11% 24% 20% 7%	2178
April	1st to 10th	Night	24% 5% 10% 22% 25% 14%	1877
	11th to 20th	Night	31% 6% 12% 23% 19% 9%	1777
	21st to end	Night	30% 6% 11% 25% 23% 5%	1620
May	1st to 10th	Night	31% 7% 11% 20% 23% 9%	1620
	11th to 20th	Night	28% 7% 15% 24% 20% 6%	1594
	21st to end	Night	26% 9% 17% 29% 16% 4	1746
June	1st to 10th	Night	23% 7% 17% 31% 16% 6%	1620
	11th to 20th	Night	22% 8% 12% 26% 24% 8%	1620
	21st to end	Night	21% 5% 12% 27% 24% 11%	1620
July	1st to 10th	Night	24% 7% 15% 29% 20% 5%	1575
	11th to 20th	Night	16% 6% 12% 27% 29% 9%	1566
	21st to end	Night	21% 7% 13% 27% 29% 4	1673
August	1st to 10th	Night	24% 8% 14% 29% 18% 7%	1601
	11th to 20th	Night	27% 7% 14% 25% 21% 7%	1672
	21st to end	Night	21% 8% 13% 24% 24% 9%	1980
September	1st to 10th	Night	23% 5% 11% 25% 26% 11%	1912
	11th to 20th	Night	29% 5% 10% 18% 29% 9%	1980
	21st to end	Night	21% 5% 9% 23% 30% 12%	1980
October	1st to 10th	Night	25% 5% 9% 20% 30% 12%	1980
	11th to 20th	Night	20% 2 6% 19% 34% 18%	2077
	21st to end	Night	22% 3 6% 24% 28% 17%	2451
November	1st to 10th	Night	18% 4 9% 23% 27% 19%	2405
	11th to 20th	Night	19% 3 7% 27% 31% 12%	2470
	21st to end	Night	25% 3 5% 23% 28% 14%	2470
December	1st to 10th	Night	25% 3 9% 28% 28% 7%	2470
	11th to 20th	Night	27% 4 7% 25% 29% 8%	3037
	21st to end	Night	32% 5% 11% 21% 23% 8%	4532

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	8% 10% 42% 30% 9% 1	270
	11th to 20th	Day	16% 14% 35% 26% 10%	249
	21st to end	Day	6% 13% 47% 26% 8% 1	264
February	1st to 10th	Day	12% 12% 40% 29% 6% 1	240
	11th to 20th	Day	11% 12% 51% 19% 6% 1	240
	21st to end	Day	11% 12% 57% 18% 3 1	198
March	1st to 10th	Day	9% 12% 52% 22% 6%	240
	11th to 20th	Day	17% 15% 39% 20% 6% 3	240
	21st to end	Day	17% 16% 38% 24% 5%	264
April	1st to 10th	Day	13% 16% 40% 23% 8%	338
	11th to 20th	Day	15% 18% 42% 23% 2	412
	21st to end	Day	15% 17% 37% 20% 10% 1	597
May	1st to 10th	Day	13% 10% 41% 28% 6% 1	603
	11th to 20th	Day	14% 6% 30% 32% 15% 2	625
	21st to end	Day	10% 10% 34% 32% 11% 3	679
June	1st to 10th	Day	6% 6% 27% 37% 17% 7%	630
	11th to 20th	Day	6% 6% 29% 38% 19% 2	630
	21st to end	Day	6% 2 28% 42% 19% 3	630
July	1st to 10th	Day	6% 1 15% 35% 33% 10%	621
	11th to 20th	Day	3 2 13% 41% 33% 8%	618
	21st to end	Day	6% 1 9% 40% 36% 8%	684
August	1st to 10th	Day	6% 1 16% 41% 31% 5%	626
	11th to 20th	Day	7% 1 13% 40% 33% 5%	539
	21st to end	Day	6% 2 16% 37% 29% 10%	495
September	1st to 10th	Day	12% 1 14% 34% 30% 9%	336
	11th to 20th	Day	7% 1 19% 44% 22% 6%	270
	21st to end	Day	9% 3 27% 30% 26% 6%	270
October	1st to 10th	Day	13% 4 31% 27% 19% 5%	270
	11th to 20th	Day	7% 6% 37% 35% 14%	270
	21st to end	Day	17% 7% 37% 24% 12% 3	297
November	1st to 10th	Day	8% 6% 40% 30% 13% 3	270
	11th to 20th	Day	7% 10% 39% 28% 14% 3	270
	21st to end	Day	18% 10% 33% 26% 10% 3	270
December	1st to 10th	Day	7% 9% 43% 30% 10% 2	270
	11th to 20th	Day	11% 12% 36% 29% 11% 1	270
	21st to end	Day	14% 19% 42% 19% 5%	297
January	1st to 10th	Night	8% 10% 42% 34% 6%	950
	11th to 20th	Night	9% 13% 37% 33% 7%	920
	21st to end	Night	8% 9% 44% 32% 7% 1	990
February	1st to 10th	Night	12% 11% 43% 29% 4 1	729
	11th to 20th	Night	11% 15% 43% 27% 4	704
	21st to end	Night	10% 16% 43% 26% 5%	592
March	1st to 10th	Night	8% 12% 47% 28% 5%	698
	11th to 20th	Night	16% 10% 41% 26% 6%	540
	21st to end	Night	12% 17% 45% 23% 3	594
April	1st to 10th	Night	8% 14% 48% 27% 3	540
	11th to 20th	Night	11% 18% 44% 23% 4	533
	21st to end	Night	14% 15% 42% 24% 6%	540
May	1st to 10th	Night	12% 11% 46% 25% 5%	540
	11th to 20th	Night	11% 9% 34% 35% 10% 1	531
	21st to end	Night	7% 8% 41% 32% 11% 1	584
June	1st to 10th	Night	7% 5% 41% 33% 14%	540
	11th to 20th	Night	4 6% 44% 39% 7%	540
	21st to end	Night	7% 1 39% 42% 11%	540
July	1st to 10th	Night	6% 1 23% 45% 23% 2	525
	11th to 20th	Night	4 1 21% 54% 20% 1	522
	21st to end	Night	5% 1 17% 54% 21% 2	591
August	1st to 10th	Night	5% 1 22% 48% 23% 1	537
	11th to 20th	Night	8% 3 17% 53% 19%	534
	21st to end	Night	4 1 20% 46% 27% 3	594
September	1st to 10th	Night	9% 2 22% 48% 18% 1	540
	11th to 20th	Night	9% 3 30% 43% 14% 1	540
	21st to end	Night	6% 6% 34% 38% 16% 1	540
October	1st to 10th	Night	10% 7% 34% 38% 12%	540
	11th to 20th	Night	8% 9% 42% 35% 6%	637
	21st to end	Night	10% 10% 37% 29% 13% 1	867
November	1st to 10th	Night	7% 8% 39% 36% 10% 1	925
	11th to 20th	Night	6% 12% 42% 32% 7%	950
	21st to end	Night	9% 14% 34% 35% 9%	950
December	1st to 10th	Night	9% 9% 37% 35% 9%	950
	11th to 20th	Night	13% 11% 41% 31% 4	950
	21st to end	Night	12% 13% 40% 30% 5%	1045

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