Flying Cow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Flying Cow Observatory 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% 6% 3 7% 8% 5% 7% 7% 8% 9% 32%	74903
	Night	7% 5% 2 5% 6% 4 5% 6% 7% 10% 42%	74861
Transparency	Day	43% 11% 15% 17% 11% 3	74626
	Night	34% 10% 19% 21% 12% 3	74657
Seeing	Day	8% 4 15% 27% 26% 21%	14807
	Night	7% 3 14% 32% 32% 12%	24972

By Month

Percentage Cloud Cover SE (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	8% 5% 3 6% 5% 5% 6% 5% 7% 9% 42%	1706
	11th to 20th	Day	8% 6% 3 6% 6% 3 6% 6% 7% 10% 39%	1647
	21st to end	Day	10% 5% 2 6% 7% 4 5% 6% 7% 8% 40%	1789
February	1st to 10th	Day	11% 6% 3 5% 7% 3 6% 5% 7% 8% 39%	1800
	11th to 20th	Day	8% 3 2 5% 5% 3 4 5% 6% 8% 51%	1844
	21st to end	Day	7% 5% 3 5% 7% 4 6% 5% 6% 9% 43%	1628
March	1st to 10th	Day	4 3 2 6% 6% 5% 6% 7% 8% 10% 43%	1980
	11th to 20th	Day	6% 4 2 5% 6% 4 6% 5% 6% 10% 45%	1980
	21st to end	Day	5% 4 2 6% 6% 4 5% 6% 7% 8% 47%	2178
April	1st to 10th	Day	5% 4 2 4 5% 4 6% 7% 8% 10% 44%	1980
	11th to 20th	Day	8% 5% 3 6% 7% 3 7% 6% 8% 10% 37%	2049
	21st to end	Day	7% 4 2 5% 6% 5% 6% 6% 7% 9% 42%	2160
May	1st to 10th	Day	4 3 2 4 5% 3 7% 6% 7% 9% 49%	2160
	11th to 20th	Day	9% 6% 4 7% 8% 5% 8% 8% 7% 9% 28%	2174
	21st to end	Day	9% 7% 4 7% 9% 6% 8% 7% 7% 8% 27%	2531
June	1st to 10th	Day	15% 8% 4 10% 9% 5% 8% 7% 7% 9% 16%	2340
	11th to 20th	Day	7% 6% 4 9% 10% 7% 10% 7% 9% 10% 20%	2340
	21st to end	Day	9% 6% 3 9% 9% 6% 10% 9% 9% 9% 21%	2340
July	1st to 10th	Day	7% 7% 4 8% 9% 5% 11% 10% 10% 10% 19%	2340
	11th to 20th	Day	8% 7% 4 7% 10% 6% 9% 8% 10% 10% 21%	2340
	21st to end	Day	6% 7% 4 9% 10% 7% 9% 8% 8% 10% 21%	2547
August	1st to 10th	Day	7% 6% 4 8% 10% 6% 8% 10% 10% 11% 21%	2302
	11th to 20th	Day	5% 5% 3 8% 9% 6% 10% 8% 11% 11% 24%	2126
	21st to end	Day	10% 6% 3 9% 10% 6% 8% 8% 9% 10% 20%	2240
September	1st to 10th	Day	8% 7% 4 9% 10% 5% 9% 10% 9% 10% 19%	1980
	11th to 20th	Day	9% 7% 5% 9% 9% 7% 9% 8% 8% 10% 20%	1980
	21st to end	Day	10% 8% 5% 10% 11% 7% 8% 7% 7% 9% 19%	1980
October	1st to 10th	Day	7% 7% 4 8% 8% 5% 8% 9% 10% 10% 25%	1889
	11th to 20th	Day	8% 6% 3 7% 8% 6% 8% 6% 9% 9% 30%	1800
	21st to end	Day	11% 5% 3 6% 7% 5% 7% 7% 7% 10% 33%	1980
November	1st to 10th	Day	7% 5% 3 7% 6% 5% 6% 7% 6% 9% 39%	1857
	11th to 20th	Day	12% 7% 3 6% 6% 5% 6% 6% 6% 8% 34%	1900
	21st to end	Day	7% 5% 2 6% 6% 5% 6% 7% 8% 9% 39%	1900
December	1st to 10th	Day	9% 6% 3 6% 6% 3 6% 5% 6% 10% 40%	1839
	11th to 20th	Day	10% 5% 2 5% 7% 4 6% 6% 6% 8% 41%	2153
	21st to end	Day	12% 7% 3 7% 7% 4 6% 7% 8% 10% 30%	3124
January	1st to 10th	Night	6% 5% 2 5% 4 3 5% 5% 6% 10% 49%	2459
	11th to 20th	Night	8% 5% 3 5% 6% 3 5% 5% 7% 8% 44%	2391
	21st to end	Night	7% 5% 2 6% 5% 4 5% 6% 7% 10% 44%	2562
February	1st to 10th	Night	8% 5% 3 6% 5% 3 4 6% 6% 8% 46%	2160
	11th to 20th	Night	7% 4 1 4 4 2 3 5% 5% 8% 56%	2000
	21st to end	Night	5% 3 3 5% 4 3 5% 5% 6% 8% 54%	1628
March	1st to 10th	Night	3 3 2 4 5% 3 4 4 5% 9% 57%	1980
	11th to 20th	Night	6% 3 1 3 4 3 4 6% 6% 9% 56%	1980
	21st to end	Night	4 3 2 4 5% 2 4 5% 6% 10% 56%	2178
April	1st to 10th	Night	4 3 1 4 3 3 4 4 6% 10% 58%	1980
	11th to 20th	Night	5% 3 2 5% 5% 4 5% 6% 8% 10% 48%	1857
	21st to end	Night	6% 3 2 3 5% 3 5% 5% 7% 9% 52%	1800
May	1st to 10th	Night	4 3 2 3 4 3 4 4 7% 10% 58%	1800
	11th to 20th	Night	6% 6% 2 5% 6% 4 5% 7% 8% 10% 40%	1732
	21st to end	Night	8% 5% 3 6% 5% 3 6% 6% 7% 11% 40%	1744
June	1st to 10th	Night	11% 6% 3 7% 8% 4 7% 8% 9% 11% 26%	1620
	11th to 20th	Night	6% 6% 3 6% 6% 4 8% 8% 9% 12% 32%	1620
	21st to end	Night	5% 6% 3 6% 5% 5% 6% 7% 9% 14% 33%	1620
July	1st to 10th	Night	5% 7% 4 6% 6% 4 7% 7% 8% 13% 34%	1620
	11th to 20th	Night	5% 5% 2 6% 6% 5% 6% 10% 7% 12% 35%	1620
	21st to end	Night	4 5% 2 7% 7% 4 6% 7% 8% 11% 38%	1771
August	1st to 10th	Night	5% 4 2 5% 6% 4 5% 6% 8% 14% 39%	1617
	11th to 20th	Night	4 4 3 5% 6% 4 7% 6% 9% 14% 37%	1774
	21st to end	Night	7% 5% 3 8% 7% 5% 6% 8% 8% 12% 30%	2110
September	1st to 10th	Night	7% 5% 2 7% 7% 4 8% 9% 10% 14% 28%	1980
	11th to 20th	Night	7% 6% 4 7% 8% 5% 6% 7% 8% 10% 31%	1980
	21st to end	Night	9% 7% 3 9% 8% 5% 8% 8% 9% 10% 25%	1980
October	1st to 10th	Night	7% 6% 3 6% 7% 5% 6% 7% 8% 11% 34%	2070
	11th to 20th	Night	8% 5% 2 5% 6% 3 5% 6% 7% 10% 43%	2160
	21st to end	Night	10% 6% 2 4 5% 3 5% 5% 7% 10% 41%	2376
November	1st to 10th	Night	8% 4 2 5% 5% 3 5% 5% 7% 9% 46%	2221
	11th to 20th	Night	7% 5% 3 6% 6% 4 6% 6% 7% 10% 41%	2280
	21st to end	Night	8% 6% 3 6% 6% 4 4 5% 6% 9% 43%	2280
December	1st to 10th	Night	7% 3 3 5% 5% 3 5% 5% 6% 9% 50%	2337
	11th to 20th	Night	13% 5% 3 4 5% 3 4 4 5% 8% 45%	3042
	21st to end	Night	10% 8% 3 7% 7% 4 6% 6% 6% 8% 33%	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	37% 8% 10% 20% 19% 6%	1707
	11th to 20th	Day	39% 6% 13% 21% 15% 5%	1647
	21st to end	Day	41% 7% 10% 18% 17% 7%	1789
February	1st to 10th	Day	40% 7% 11% 24% 14% 5%	1800
	11th to 20th	Day	28% 7% 9% 28% 20% 8%	1854
	21st to end	Day	35% 7% 11% 18% 22% 7%	1628
March	1st to 10th	Day	32% 7% 14% 23% 19% 5%	1980
	11th to 20th	Day	32% 8% 12% 27% 17% 5%	1980
	21st to end	Day	32% 7% 14% 24% 18% 6%	2178
April	1st to 10th	Day	29% 10% 17% 25% 16% 3	1980
	11th to 20th	Day	39% 9% 13% 21% 16% 2	2049
	21st to end	Day	34% 9% 12% 21% 20% 4	2160
May	1st to 10th	Day	26% 8% 13% 25% 20% 7%	2160
	11th to 20th	Day	47% 10% 13% 20% 9%	2178
	21st to end	Day	50% 10% 13% 15% 11%	2531
June	1st to 10th	Day	60% 11% 16% 10% 3	2340
	11th to 20th	Day	52% 15% 19% 13% 1	2340
	21st to end	Day	50% 17% 22% 10% 1	2340
July	1st to 10th	Day	50% 21% 22% 7% 1	2275
	11th to 20th	Day	50% 17% 22% 11%	2271
	21st to end	Day	50% 16% 23% 11%	2405
August	1st to 10th	Day	48% 17% 24% 10% 1	2289
	11th to 20th	Day	45% 17% 26% 11%	2126
	21st to end	Day	52% 18% 21% 8% 2	2240
September	1st to 10th	Day	51% 18% 20% 11% 1	1980
	11th to 20th	Day	55% 14% 19% 10% 2	1980
	21st to end	Day	58% 13% 14% 9% 5% 1	1980
October	1st to 10th	Day	46% 13% 15% 16% 8% 2	1889
	11th to 20th	Day	45% 10% 13% 19% 11% 2	1800
	21st to end	Day	43% 8% 10% 17% 14% 6%	1980
November	1st to 10th	Day	37% 10% 11% 18% 16% 9%	1857
	11th to 20th	Day	46% 7% 10% 18% 13% 5%	1900
	21st to end	Day	38% 7% 13% 20% 17% 4	1900
December	1st to 10th	Day	38% 7% 14% 21% 16% 3	1839
	11th to 20th	Day	38% 8% 10% 18% 18% 8%	2150
	21st to end	Day	45% 8% 14% 16% 14% 2	3124
January	1st to 10th	Night	30% 7% 16% 25% 17% 5%	2459
	11th to 20th	Night	36% 6% 13% 27% 14% 4	2391
	21st to end	Night	34% 7% 14% 23% 15% 7%	2562
February	1st to 10th	Night	34% 6% 14% 25% 17% 4	2160
	11th to 20th	Night	25% 6% 11% 28% 22% 7%	2001
	21st to end	Night	26% 7% 14% 24% 25% 5%	1628
March	1st to 10th	Night	24% 6% 14% 30% 21% 6%	1980
	11th to 20th	Night	24% 7% 17% 29% 17% 5%	1980
	21st to end	Night	23% 6% 14% 30% 22% 5%	2178
April	1st to 10th	Night	22% 6% 21% 31% 17% 4	1980
	11th to 20th	Night	27% 9% 18% 24% 19% 2	1857
	21st to end	Night	26% 8% 16% 26% 19% 4	1800
May	1st to 10th	Night	21% 7% 15% 34% 18% 6%	1800
	11th to 20th	Night	35% 11% 19% 24% 11%	1733
	21st to end	Night	35% 10% 20% 24% 11%	1745
June	1st to 10th	Night	47% 14% 21% 15% 3	1620
	11th to 20th	Night	39% 15% 25% 18% 2	1620
	21st to end	Night	38% 15% 32% 13% 2	1620
July	1st to 10th	Night	39% 16% 32% 13%	1575
	11th to 20th	Night	37% 16% 34% 12% 1	1566
	21st to end	Night	35% 18% 32% 14% 2	1672
August	1st to 10th	Night	32% 16% 34% 16% 1	1606
	11th to 20th	Night	33% 17% 37% 12%	1774
	21st to end	Night	42% 17% 29% 10% 2	2110
September	1st to 10th	Night	40% 19% 28% 12% 1	1980
	11th to 20th	Night	42% 17% 26% 12% 2	1980
	21st to end	Night	49% 16% 18% 11% 5%	1980
October	1st to 10th	Night	40% 12% 20% 16% 11% 1	2070
	11th to 20th	Night	36% 8% 17% 24% 15% 1	2160
	21st to end	Night	37% 7% 14% 21% 16% 6%	2376
November	1st to 10th	Night	33% 7% 15% 20% 18% 7%	2221
	11th to 20th	Night	36% 8% 13% 23% 15% 5%	2280
	21st to end	Night	37% 7% 12% 21% 18% 4	2280
December	1st to 10th	Night	31% 7% 15% 27% 18% 3	2337
	11th to 20th	Night	36% 7% 11% 20% 17% 9%	3044
	21st to end	Night	45% 9% 15% 16% 13% 3	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% 9% 35% 36% 11% 1	270
	11th to 20th	Day	7% 8% 35% 30% 16% 3	249
	21st to end	Day	13% 12% 34% 32% 8% 1	264
February	1st to 10th	Day	8% 7% 30% 34% 18% 4	240
	11th to 20th	Day	7% 6% 23% 40% 20% 5%	336
	21st to end	Day	6% 5% 21% 39% 24% 4	346
March	1st to 10th	Day	3 7% 31% 38% 17% 3	420
	11th to 20th	Day	6% 6% 25% 35% 25% 3	420
	21st to end	Day	3 4 27% 37% 23% 6%	462
April	1st to 10th	Day	4 8% 28% 33% 19% 8%	420
	11th to 20th	Day	7% 6% 24% 33% 23% 8%	412
	21st to end	Day	9% 3 21% 32% 26% 9%	420
May	1st to 10th	Day	4 19% 34% 27% 15%	423
	11th to 20th	Day	12% 4 14% 29% 25% 17%	447
	21st to end	Day	10% 2 7% 24% 30% 27%	485
June	1st to 10th	Day	13% 4 8% 22% 28% 26%	450
	11th to 20th	Day	7% 2 5% 19% 28% 38%	450
	21st to end	Day	6% 2 3 12% 29% 49%	450
July	1st to 10th	Day	4 2 1 12% 27% 54%	445
	11th to 20th	Day	5% 2 2 11% 33% 47%	444
	21st to end	Day	6% 2 4 13% 28% 47%	488
August	1st to 10th	Day	5% 2 3 15% 30% 45%	446
	11th to 20th	Day	4 1 4 11% 31% 49%	439
	21st to end	Day	10% 2 4 19% 29% 36%	495
September	1st to 10th	Day	6% 3 5% 14% 32% 40%	450
	11th to 20th	Day	8% 2 5% 15% 32% 39%	450
	21st to end	Day	10% 4 5% 18% 32% 30%	450
October	1st to 10th	Day	9% 4 9% 33% 33% 13%	450
	11th to 20th	Day	10% 4 15% 27% 31% 13%	450
	21st to end	Day	10% 4 15% 34% 28% 8%	495
November	1st to 10th	Day	10% 5% 20% 33% 23% 9%	455
	11th to 20th	Day	12% 5% 23% 33% 21% 6%	460
	21st to end	Day	5% 5% 25% 37% 25% 4	460
December	1st to 10th	Day	9% 5% 23% 35% 24% 5%	399
	11th to 20th	Day	8% 7% 24% 41% 17% 4	270
	21st to end	Day	9% 8% 25% 36% 19% 4	297
January	1st to 10th	Night	9% 5% 19% 41% 23% 2	760
	11th to 20th	Night	10% 5% 25% 39% 19% 1	736
	21st to end	Night	8% 7% 27% 43% 14% 1	792
February	1st to 10th	Night	9% 7% 21% 42% 20% 1	720
	11th to 20th	Night	8% 5% 22% 41% 23% 1	703
	21st to end	Night	6% 4 22% 46% 21% 1	592
March	1st to 10th	Night	5% 3 30% 43% 17% 1	720
	11th to 20th	Night	7% 4 22% 46% 20% 2	720
	21st to end	Night	4 4 23% 46% 22% 1	792
April	1st to 10th	Night	4 3 21% 45% 24% 2	720
	11th to 20th	Night	4 5% 18% 47% 24% 2	711
	21st to end	Night	6% 3 20% 45% 25% 2	720
May	1st to 10th	Night	4 2 15% 44% 33% 2	720
	11th to 20th	Night	8% 3 13% 41% 32% 4	671
	21st to end	Night	7% 4 5% 26% 48% 10%	584
June	1st to 10th	Night	12% 2 4 23% 45% 14%	540
	11th to 20th	Night	7% 1 3 14% 47% 28%	540
	21st to end	Night	4 3 3 11% 44% 35%	540
July	1st to 10th	Night	5% 2 4 6% 45% 38%	525
	11th to 20th	Night	6% 2 1 8% 43% 40%	522
	21st to end	Night	4 1 3 7% 45% 41%	591
August	1st to 10th	Night	6% 1 2 8% 49% 34%	543
	11th to 20th	Night	5% 1 2 9% 46% 37%	710
	21st to end	Night	9% 2 5% 16% 40% 28%	792
September	1st to 10th	Night	8% 3 5% 10% 41% 34%	720
	11th to 20th	Night	8% 2 3 14% 43% 30%	720
	21st to end	Night	12% 2 4 17% 40% 25%	720
October	1st to 10th	Night	10% 2 7% 32% 38% 11%	720
	11th to 20th	Night	8% 3 8% 32% 40% 8%	720
	21st to end	Night	12% 2 13% 35% 30% 7%	792
November	1st to 10th	Night	10% 4 19% 33% 31% 3	740
	11th to 20th	Night	8% 4 19% 36% 29% 4	760
	21st to end	Night	9% 4 18% 42% 27% 1	760
December	1st to 10th	Night	7% 3 17% 38% 31% 4	760
	11th to 20th	Night	10% 5% 18% 37% 26% 4	760
	21st to end	Night	8% 4 20% 38% 27% 3	836

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