"Flying F" Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the "Flying F" Observatory clear sky chart from 2005-11-06 to 2025-07-21.

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 6% 3 7% 5% 5% 5% 4 6% 7% 49%	124073
	Night	1 4 2 6% 4 4 4 4 6% 8% 58%	123952
Transparency	Day	32% 5% 9% 22% 24% 9%	123831
	Night	23% 5% 12% 26% 26% 8%	123782
Seeing	Day	18% 20% 25% 21% 13% 3	16291
	Night	8% 11% 30% 33% 17% 2	26390

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	2 2 12% 5% 4 4 3 6% 7% 55%	3867
	11th to 20th	Day	3 4 5% 4 5% 4 3 5% 8% 59%	4100
	21st to end	Day	4 3 7% 5% 4 4 3 6% 7% 56%	4510
February	1st to 10th	Day	5% 3 11% 4 4 3 3 5% 8% 54%	1800
	11th to 20th	Day	1 6% 2 7% 5% 4 5% 4 6% 9% 51%	1854
	21st to end	Day	4 4 11% 5% 5% 3 4 6% 8% 50%	1650
March	1st to 10th	Day	5% 5% 9% 5% 5% 5% 4 5% 6% 51%	4821
	11th to 20th	Day	1 9% 6% 8% 5% 5% 6% 5% 7% 9% 39%	5000
	21st to end	Day	1 10% 4 10% 6% 5% 5% 4 6% 8% 41%	5590
April	1st to 10th	Day	1 8% 3 7% 6% 5% 5% 4 5% 8% 50%	2400
	11th to 20th	Day	2 11% 4 8% 5% 5% 4 4 6% 6% 45%	2371
	21st to end	Day	2 9% 3 8% 6% 4 5% 4 6% 6% 46%	2400
May	1st to 10th	Day	3 11% 4 9% 6% 6% 5% 4 6% 7% 38%	5588
	11th to 20th	Day	3 8% 2 7% 6% 6% 6% 4 6% 8% 44%	6041
	21st to end	Day	3 5% 2 6% 4 5% 6% 5% 6% 7% 52%	6925
June	1st to 10th	Day	4 6% 2 5% 5% 4 6% 4 6% 8% 50%	2800
	11th to 20th	Day	4 4 2 5% 4 4 5% 4 5% 6% 58%	2800
	21st to end	Day	4 5% 2 6% 6% 6% 6% 5% 6% 7% 48%	2800
July	1st to 10th	Day	5% 5% 2 6% 5% 5% 6% 4 5% 6% 52%	4570
	11th to 20th	Day	4 5% 2 8% 7% 8% 8% 8% 9% 9% 32%	4319
	21st to end	Day	7% 6% 2 9% 7% 7% 7% 6% 7% 8% 34%	4455
August	1st to 10th	Day	9% 8% 3 10% 8% 8% 7% 6% 7% 9% 25%	4092
	11th to 20th	Day	6% 6% 3 8% 6% 7% 7% 7% 8% 8% 35%	3818
	21st to end	Day	6% 7% 3 9% 7% 8% 7% 6% 8% 8% 31%	4180
September	1st to 10th	Day	8% 7% 3 9% 6% 5% 5% 4 6% 6% 41%	2280
	11th to 20th	Day	7% 6% 3 8% 5% 4 5% 4 5% 6% 47%	2280
	21st to end	Day	6% 7% 2 6% 4 4 4 3 4 5% 55%	2025
October	1st to 10th	Day	5% 6% 1 5% 3 3 3 3 3 4 63%	3170
	11th to 20th	Day	3 8% 3 7% 5% 4 5% 4 5% 6% 50%	3150
	21st to end	Day	2 4 2 4 2 2 3 2 4 4 70%	3438
November	1st to 10th	Day	1 4 2 5% 3 2 3 3 4 6% 68%	1879
	11th to 20th	Day	3 1 3 2 2 3 3 4 5% 73%	1800
	21st to end	Day	1 4 2 5% 4 3 3 3 4 7% 63%	1650
December	1st to 10th	Day	3 2 4 3 2 3 2 4 7% 70%	2620
	11th to 20th	Day	3 2 4 3 3 3 3 5% 8% 66%	3026
	21st to end	Day	4 2 5% 3 3 4 3 5% 8% 61%	4004
January	1st to 10th	Night	1 2 9% 7% 6% 5% 4 5% 8% 53%	6128
	11th to 20th	Night	2 2 7% 4 4 4 3 5% 7% 63%	5880
	21st to end	Night	4 3 6% 3 3 4 4 6% 9% 57%	6468
February	1st to 10th	Night	4 3 7% 4 3 4 4 5% 6% 60%	2600
	11th to 20th	Night	4 2 5% 4 4 4 4 6% 6% 61%	2432
	21st to end	Night	3 3 7% 4 4 4 2 5% 7% 60%	1980
March	1st to 10th	Night	4 3 7% 4 4 4 4 6% 7% 57%	5053
	11th to 20th	Night	7% 5% 11% 5% 4 4 4 6% 8% 46%	5000
	21st to end	Night	7% 3 7% 5% 5% 4 3 6% 10% 50%	5366
April	1st to 10th	Night	5% 2 5% 3 4 3 4 5% 8% 61%	2000
	11th to 20th	Night	1 7% 2 5% 4 5% 5% 3 7% 8% 54%	1977
	21st to end	Night	1 6% 2 4 3 3 4 4 5% 7% 60%	2000
May	1st to 10th	Night	2 8% 3 6% 4 4 4 4 6% 8% 50%	4376
	11th to 20th	Night	2 5% 2 4 3 3 3 3 7% 11% 56%	3856
	21st to end	Night	2 3 1 3 2 2 3 3 5% 6% 70%	3972
June	1st to 10th	Night	2 3 1 3 2 4 4 3 6% 8% 65%	1600
	11th to 20th	Night	2 3 1 2 2 2 3 2 5% 6% 71%	1600
	21st to end	Night	2 4 2 3 3 3 5% 4 7% 8% 59%	1600
July	1st to 10th	Night	4 4 1 5% 4 4 5% 3 5% 8% 57%	2620
	11th to 20th	Night	2 4 1 3 3 3 5% 6% 9% 17% 45%	2866
	21st to end	Night	3 6% 3 7% 5% 4 5% 5% 8% 12% 42%	3109
August	1st to 10th	Night	4 4 2 8% 6% 6% 7% 6% 11% 13% 33%	2847
	11th to 20th	Night	3 4 1 4 4 4 5% 6% 11% 16% 42%	3018
	21st to end	Night	5% 8% 4 9% 6% 5% 6% 5% 6% 10% 38%	3487
September	1st to 10th	Night	5% 5% 2 5% 5% 4 5% 5% 7% 9% 48%	1900
	11th to 20th	Night	5% 4 1 5% 4 4 4 3 6% 8% 56%	1900
	21st to end	Night	4 3 1 5% 3 3 2 3 5% 5% 65%	2151
October	1st to 10th	Night	3 3 1 3 2 2 3 2 3 5% 72%	3800
	11th to 20th	Night	2 6% 3 6% 3 3 3 3 4 7% 59%	3778
	21st to end	Night	1 4 2 5% 2 2 2 2 3 6% 71%	4120
November	1st to 10th	Night	1 3 2 3 2 2 3 3 4 7% 69%	2397
	11th to 20th	Night	2 1 2 2 2 3 3 5% 6% 74%	2600
	21st to end	Night	1 6% 3 5% 3 3 2 3 5% 6% 64%	2746
December	1st to 10th	Night	2 1 3 3 2 2 2 3 6% 75%	4570
	11th to 20th	Night	3 1 4 2 2 3 3 5% 8% 69%	5181
	21st to end	Night	4 2 5% 4 4 4 3 5% 8% 61%	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	28% 3 10% 27% 25% 7%	3868
	11th to 20th	Day	25% 3 10% 19% 30% 13%	4100
	21st to end	Day	28% 2 5% 26% 30% 10%	4510
February	1st to 10th	Day	29% 3 12% 25% 19% 11%	1800
	11th to 20th	Day	29% 4 7% 25% 26% 9%	1863
	21st to end	Day	33% 3 6% 19% 25% 13%	1650
March	1st to 10th	Day	30% 4 6% 19% 28% 13%	4821
	11th to 20th	Day	38% 4 6% 29% 21% 3	5000
	21st to end	Day	37% 3 11% 30% 16% 3	5590
April	1st to 10th	Day	32% 4 9% 23% 24% 9%	2400
	11th to 20th	Day	35% 3 8% 23% 24% 7%	2374
	21st to end	Day	36% 3 7% 29% 22% 3	2400
May	1st to 10th	Day	38% 6% 9% 20% 19% 8%	5588
	11th to 20th	Day	36% 3 6% 23% 25% 6%	6045
	21st to end	Day	29% 4 5% 20% 35% 7%	6926
June	1st to 10th	Day	30% 4 10% 26% 22% 9%	2800
	11th to 20th	Day	24% 4 7% 18% 29% 19%	2800
	21st to end	Day	33% 4 7% 17% 24% 15%	2800
July	1st to 10th	Day	31% 5% 9% 10% 18% 26%	4501
	11th to 20th	Day	40% 10% 19% 18% 11% 3	4247
	21st to end	Day	42% 9% 16% 13% 12% 8%	4315
August	1st to 10th	Day	52% 10% 16% 11% 8% 4	4078
	11th to 20th	Day	41% 10% 14% 13% 17% 5%	3856
	21st to end	Day	42% 9% 13% 16% 17% 4	4179
September	1st to 10th	Day	43% 4 10% 15% 21% 8%	2280
	11th to 20th	Day	37% 3 7% 18% 25% 9%	2280
	21st to end	Day	29% 3 6% 23% 33% 7%	2025
October	1st to 10th	Day	24% 3 5% 19% 32% 17%	3170
	11th to 20th	Day	28% 7% 7% 24% 26% 7%	3150
	21st to end	Day	18% 2 7% 25% 39% 8%	3438
November	1st to 10th	Day	18% 3 7% 27% 35% 11%	1879
	11th to 20th	Day	14% 2 8% 32% 34% 11%	1800
	21st to end	Day	22% 3 8% 26% 29% 13%	1650
December	1st to 10th	Day	16% 2 11% 34% 30% 7%	2620
	11th to 20th	Day	17% 4 11% 34% 29% 5%	3024
	21st to end	Day	22% 4 9% 26% 27% 13%	4004
January	1st to 10th	Night	29% 3 8% 30% 25% 5%	6128
	11th to 20th	Night	19% 2 9% 22% 33% 15%	5880
	21st to end	Night	25% 3 5% 28% 27% 12%	6468
February	1st to 10th	Night	24% 3 13% 26% 24% 11%	2600
	11th to 20th	Night	21% 4 10% 29% 28% 9%	2433
	21st to end	Night	25% 2 7% 25% 31% 11%	1980
March	1st to 10th	Night	24% 3 7% 21% 40% 5%	5053
	11th to 20th	Night	34% 4 8% 25% 25% 5%	5000
	21st to end	Night	29% 7% 14% 31% 17% 2	5366
April	1st to 10th	Night	20% 5% 13% 28% 27% 7%	2000
	11th to 20th	Night	27% 2 9% 28% 28% 6%	1977
	21st to end	Night	23% 3 11% 36% 23% 3	2000
May	1st to 10th	Night	31% 6% 12% 21% 25% 6%	4373
	11th to 20th	Night	25% 3 8% 33% 25% 5%	3857
	21st to end	Night	15% 3 10% 23% 39% 9%	3972
June	1st to 10th	Night	18% 3 14% 27% 28% 10%	1600
	11th to 20th	Night	15% 3 7% 22% 32% 22%	1600
	21st to end	Night	21% 5% 10% 21% 26% 18%	1600
July	1st to 10th	Night	25% 4 14% 10% 19% 28%	2580
	11th to 20th	Night	22% 12% 32% 22% 7% 5%	2815
	21st to end	Night	30% 13% 27% 16% 9% 5%	3011
August	1st to 10th	Night	39% 16% 19% 11% 10% 5%	2838
	11th to 20th	Night	27% 16% 24% 12% 17% 4	3046
	21st to end	Night	39% 10% 16% 18% 15% 2	3487
September	1st to 10th	Night	31% 5% 16% 19% 22% 7%	1900
	11th to 20th	Night	27% 4 12% 20% 28% 10%	1900
	21st to end	Night	21% 3 7% 30% 34% 6%	2151
October	1st to 10th	Night	18% 2 8% 29% 29% 14%	3800
	11th to 20th	Night	19% 8% 10% 32% 24% 7%	3778
	21st to end	Night	15% 3 14% 34% 29% 6%	4120
November	1st to 10th	Night	15% 3 11% 32% 31% 8%	2397
	11th to 20th	Night	12% 3 9% 33% 34% 8%	2600
	21st to end	Night	22% 3 8% 27% 31% 10%	2746
December	1st to 10th	Night	14% 2 18% 31% 28% 6%	4570
	11th to 20th	Night	14% 4 10% 32% 35% 5%	5182
	21st to end	Night	23% 4 13% 23% 28% 9%	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	17% 17% 34% 21% 9% 2	300
	11th to 20th	Day	20% 21% 26% 25% 6% 1	300
	21st to end	Day	9% 22% 35% 25% 9% 1	330
February	1st to 10th	Day	24% 26% 32% 16% 2 1	300
	11th to 20th	Day	23% 28% 29% 16% 3 1	300
	21st to end	Day	29% 24% 26% 18% 3	249
March	1st to 10th	Day	26% 28% 26% 15% 5% 1	440
	11th to 20th	Day	25% 29% 25% 14% 5% 1	500
	21st to end	Day	32% 30% 26% 8% 3	550
April	1st to 10th	Day	26% 30% 28% 12% 3 1	500
	11th to 20th	Day	33% 35% 20% 10% 4	492
	21st to end	Day	29% 32% 23% 12% 3	500
May	1st to 10th	Day	26% 32% 24% 11% 6% 1	503
	11th to 20th	Day	18% 28% 27% 16% 9% 2	611
	21st to end	Day	20% 24% 21% 21% 13% 2	789
June	1st to 10th	Day	9% 20% 25% 25% 18% 3	730
	11th to 20th	Day	11% 23% 25% 23% 14% 4	730
	21st to end	Day	8% 20% 22% 24% 22% 5%	730
July	1st to 10th	Day	9% 9% 19% 32% 25% 6%	721
	11th to 20th	Day	9% 7% 18% 31% 27% 8%	574
	21st to end	Day	13% 8% 16% 32% 23% 8%	532
August	1st to 10th	Day	19% 8% 20% 28% 20% 6%	487
	11th to 20th	Day	13% 9% 22% 32% 18% 5%	477
	21st to end	Day	12% 10% 25% 28% 20% 4	539
September	1st to 10th	Day	12% 12% 24% 24% 23% 5%	490
	11th to 20th	Day	13% 22% 29% 22% 12% 2	490
	21st to end	Day	17% 16% 23% 21% 20% 3	367
October	1st to 10th	Day	18% 15% 23% 20% 20% 5%	300
	11th to 20th	Day	16% 20% 26% 20% 16% 2	300
	21st to end	Day	18% 22% 23% 21% 12% 4	330
November	1st to 10th	Day	20% 20% 23% 27% 9% 1	300
	11th to 20th	Day	16% 19% 27% 27% 10% 2	300
	21st to end	Day	16% 17% 30% 21% 13% 3	300
December	1st to 10th	Day	16% 18% 32% 19% 12% 3	300
	11th to 20th	Day	16% 18% 32% 23% 10% 1	300
	21st to end	Day	21% 20% 33% 20% 6% 1	330
January	1st to 10th	Night	6% 14% 36% 33% 10% 2	918
	11th to 20th	Night	8% 12% 35% 33% 10% 1	800
	21st to end	Night	4 12% 40% 34% 8% 2	880
February	1st to 10th	Night	6% 16% 46% 27% 5% 1	800
	11th to 20th	Night	7% 14% 45% 27% 7%	784
	21st to end	Night	10% 14% 46% 27% 3	660
March	1st to 10th	Night	10% 20% 33% 30% 7%	800
	11th to 20th	Night	6% 14% 37% 31% 12% 1	800
	21st to end	Night	10% 15% 41% 29% 5%	834
April	1st to 10th	Night	11% 18% 38% 29% 5%	600
	11th to 20th	Night	13% 18% 36% 26% 7%	593
	21st to end	Night	8% 18% 36% 29% 9% 1	600
May	1st to 10th	Night	9% 12% 35% 32% 11% 1	600
	11th to 20th	Night	9% 12% 26% 36% 15% 2	591
	21st to end	Night	10% 15% 26% 31% 17% 2	650
June	1st to 10th	Night	5% 8% 23% 38% 25% 1	600
	11th to 20th	Night	5% 9% 28% 38% 19% 2	600
	21st to end	Night	4 8% 17% 40% 28% 2	600
July	1st to 10th	Night	5% 3 10% 39% 39% 3	585
	11th to 20th	Night	5% 2 5% 33% 48% 7%	582
	21st to end	Night	8% 2 4 28% 50% 8%	624
August	1st to 10th	Night	7% 3 6% 29% 49% 6%	567
	11th to 20th	Night	5% 2 8% 38% 41% 5%	564
	21st to end	Night	7% 3 11% 37% 37% 5%	627
September	1st to 10th	Night	6% 3 13% 38% 36% 4	570
	11th to 20th	Night	8% 4 19% 39% 27% 3	570
	21st to end	Night	6% 8% 17% 38% 27% 4	698
October	1st to 10th	Night	9% 9% 24% 37% 19% 2	760
	11th to 20th	Night	6% 9% 31% 36% 15% 3	760
	21st to end	Night	8% 11% 27% 35% 16% 3	836
November	1st to 10th	Night	6% 13% 30% 35% 14% 2	837
	11th to 20th	Night	8% 11% 37% 32% 11% 2	1000
	21st to end	Night	9% 12% 33% 33% 12% 1	1000
December	1st to 10th	Night	8% 14% 39% 29% 9% 1	1000
	11th to 20th	Night	8% 17% 38% 28% 9% 1	1000
	21st to end	Night	10% 13% 41% 29% 6% 1	1100

Page generated at 2025-07-17 23:10:04. Version ac07

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