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 2024-11-28.

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 8% 6% 7% 7% 6% 8% 10% 33%	100871
	Night	7% 5% 2 7% 5% 5% 5% 5% 7% 10% 41%	98613
Transparency	Day	41% 10% 18% 19% 10% 2	104568
	Night	36% 10% 20% 21% 11% 3	103042
Seeing	Day	8% 4 16% 27% 25% 20%	16050
	Night	8% 4 14% 32% 31% 12%	26161

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	10% 7% 3 8% 5% 5% 5% 4 6% 8% 39%	2836
	11th to 20th	Day	16% 8% 3 9% 7% 6% 6% 4 7% 9% 27%	2840
	21st to end	Day	8% 7% 3 10% 7% 6% 5% 4 6% 7% 38%	3131
February	1st to 10th	Day	10% 6% 2 7% 6% 5% 5% 4 8% 8% 39%	1900
	11th to 20th	Day	8% 4 1 5% 5% 4 4 4 6% 8% 50%	1949
	21st to end	Day	6% 5% 2 6% 6% 5% 5% 4 6% 8% 45%	1727
March	1st to 10th	Day	7% 5% 2 9% 7% 8% 7% 6% 9% 9% 28%	3435
	11th to 20th	Day	4 3 1 4 5% 4 5% 5% 7% 10% 51%	3480
	21st to end	Day	9% 4 2 6% 5% 4 5% 4 7% 9% 45%	3815
April	1st to 10th	Day	5% 4 1 5% 5% 6% 6% 6% 8% 10% 44%	2090
	11th to 20th	Day	7% 5% 3 7% 5% 5% 6% 5% 8% 10% 39%	2165
	21st to end	Day	7% 4 1 6% 6% 6% 6% 5% 7% 9% 42%	2280
May	1st to 10th	Day	3 2 1 3 4 4 5% 5% 7% 9% 57%	3765
	11th to 20th	Day	7% 5% 3 7% 6% 6% 8% 5% 7% 11% 34%	3856
	21st to end	Day	5% 5% 2 6% 5% 6% 6% 5% 7% 9% 43%	4476
June	1st to 10th	Day	14% 9% 4 11% 7% 8% 8% 6% 7% 9% 17%	2470
	11th to 20th	Day	8% 7% 4 11% 9% 9% 9% 5% 9% 10% 20%	2470
	21st to end	Day	9% 7% 3 11% 8% 8% 9% 7% 9% 9% 21%	2470
July	1st to 10th	Day	6% 7% 3 9% 7% 7% 9% 7% 9% 10% 27%	4120
	11th to 20th	Day	7% 6% 3 8% 8% 8% 8% 6% 9% 12% 26%	4120
	21st to end	Day	5% 6% 3 8% 7% 8% 8% 6% 10% 14% 25%	4466
August	1st to 10th	Day	5% 6% 3 10% 8% 9% 9% 8% 11% 12% 19%	4052
	11th to 20th	Day	5% 4 2 8% 7% 8% 8% 7% 11% 13% 26%	3730
	21st to end	Day	6% 4 2 8% 7% 7% 9% 7% 12% 16% 20%	3932
September	1st to 10th	Day	8% 7% 4 11% 8% 8% 9% 7% 9% 11% 18%	2090
	11th to 20th	Day	8% 8% 4 11% 8% 10% 9% 6% 8% 10% 19%	2090
	21st to end	Day	9% 8% 4 12% 9% 9% 8% 5% 7% 10% 19%	2090
October	1st to 10th	Day	8% 7% 4 10% 6% 7% 8% 6% 10% 9% 24%	1993
	11th to 20th	Day	8% 7% 3 9% 7% 8% 8% 5% 9% 9% 29%	1900
	21st to end	Day	11% 5% 3 8% 5% 7% 7% 5% 7% 9% 34%	2090
November	1st to 10th	Day	7% 5% 3 8% 5% 6% 6% 6% 6% 9% 39%	1957
	11th to 20th	Day	11% 7% 3 7% 6% 7% 5% 5% 7% 8% 35%	2000
	21st to end	Day	6% 6% 2 7% 5% 6% 6% 5% 8% 9% 41%	1970
December	1st to 10th	Day	9% 7% 3 7% 5% 5% 5% 4 6% 9% 40%	1839
	11th to 20th	Day	10% 6% 2 6% 6% 5% 5% 4 6% 9% 41%	2153
	21st to end	Day	12% 7% 3 8% 6% 6% 6% 5% 8% 9% 30%	3124
January	1st to 10th	Night	7% 8% 3 7% 5% 5% 6% 5% 6% 10% 39%	4109
	11th to 20th	Night	15% 10% 3 9% 6% 5% 5% 4 6% 8% 28%	4120
	21st to end	Night	8% 7% 3 8% 5% 6% 5% 5% 7% 8% 39%	4520
February	1st to 10th	Night	8% 6% 2 6% 4 4 4 5% 6% 8% 46%	2280
	11th to 20th	Night	7% 4 1 4 4 3 4 3 5% 8% 56%	2115
	21st to end	Night	5% 4 2 5% 3 4 4 4 6% 8% 55%	1727
March	1st to 10th	Night	8% 7% 3 10% 6% 7% 6% 5% 6% 8% 37%	3418
	11th to 20th	Night	4 3 1 4 3 4 4 4 7% 10% 55%	3480
	21st to end	Night	7% 4 1 5% 4 4 4 4 6% 9% 53%	3817
April	1st to 10th	Night	4 3 1 4 3 4 4 4 7% 10% 56%	2090
	11th to 20th	Night	5% 3 1 5% 4 5% 5% 5% 8% 9% 49%	1961
	21st to end	Night	5% 4 2 4 4 4 4 4 8% 9% 52%	1900
May	1st to 10th	Night	3 2 1 3 3 3 3 4 6% 8% 65%	3130
	11th to 20th	Night	5% 5% 2 5% 4 5% 5% 5% 7% 11% 47%	3050
	21st to end	Night	5% 4 2 6% 4 4 5% 4 7% 10% 50%	3079
June	1st to 10th	Night	10% 7% 2 8% 7% 6% 7% 6% 8% 11% 27%	1710
	11th to 20th	Night	7% 7% 3 7% 6% 6% 6% 7% 9% 12% 31%	1710
	21st to end	Night	5% 7% 2 6% 5% 6% 6% 6% 10% 13% 33%	1710
July	1st to 10th	Night	5% 6% 3 7% 5% 4 5% 5% 8% 12% 41%	2840
	11th to 20th	Night	4 4 2 6% 6% 6% 7% 8% 9% 13% 34%	2840
	21st to end	Night	4 4 2 6% 5% 6% 6% 5% 9% 13% 39%	3087
August	1st to 10th	Night	4 5% 2 8% 6% 6% 6% 5% 9% 11% 37%	2845
	11th to 20th	Night	3 4 2 6% 5% 5% 6% 5% 10% 15% 38%	3097
	21st to end	Night	5% 4 2 8% 6% 7% 8% 7% 11% 15% 27%	3718
September	1st to 10th	Night	7% 6% 2 9% 6% 6% 8% 7% 10% 14% 27%	2090
	11th to 20th	Night	7% 7% 3 8% 7% 6% 6% 6% 8% 10% 30%	2090
	21st to end	Night	8% 7% 2 10% 7% 7% 7% 6% 9% 10% 25%	2090
October	1st to 10th	Night	8% 7% 3 8% 5% 6% 6% 6% 8% 10% 33%	2185
	11th to 20th	Night	9% 6% 2 7% 5% 5% 5% 5% 7% 10% 41%	2280
	21st to end	Night	10% 6% 3 6% 4 5% 5% 4 7% 9% 41%	2508
November	1st to 10th	Night	7% 5% 2 6% 4 5% 5% 5% 7% 9% 45%	2341
	11th to 20th	Night	7% 5% 3 7% 6% 5% 5% 5% 7% 10% 41%	2400
	21st to end	Night	8% 6% 2 6% 5% 4 5% 3 6% 9% 44%	2365
December	1st to 10th	Night	6% 4 2 6% 5% 4 4 4 7% 9% 49%	2337
	11th to 20th	Night	13% 6% 2 5% 4 4 4 3 5% 8% 45%	3042
	21st to end	Night	10% 8% 3 9% 6% 6% 5% 5% 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	42% 6% 9% 20% 20% 4	2837
	11th to 20th	Day	53% 7% 12% 15% 9% 3	2840
	21st to end	Day	43% 8% 9% 20% 16% 6%	3131
February	1st to 10th	Day	39% 7% 10% 24% 14% 5%	1900
	11th to 20th	Day	28% 7% 9% 28% 19% 8%	1959
	21st to end	Day	33% 7% 11% 19% 22% 8%	1727
March	1st to 10th	Day	44% 12% 15% 16% 11% 3	3435
	11th to 20th	Day	24% 9% 18% 34% 12% 3	3480
	21st to end	Day	31% 8% 12% 28% 15% 6%	3815
April	1st to 10th	Day	28% 9% 16% 26% 16% 4	2090
	11th to 20th	Day	37% 9% 13% 22% 16% 3	2165
	21st to end	Day	33% 9% 13% 21% 20% 4	2280
May	1st to 10th	Day	18% 9% 13% 35% 21% 4	3800
	11th to 20th	Day	39% 11% 22% 21% 7%	3860
	21st to end	Day	31% 10% 15% 31% 13%	4489
June	1st to 10th	Day	58% 11% 16% 12% 3	2470
	11th to 20th	Day	53% 14% 18% 13% 1	2470
	21st to end	Day	51% 16% 22% 10% 1	2470
July	1st to 10th	Day	44% 13% 26% 16% 2	4055
	11th to 20th	Day	46% 10% 32% 12%	4051
	21st to end	Day	42% 12% 31% 14%	4324
August	1st to 10th	Day	50% 14% 26% 9% 1	4039
	11th to 20th	Day	41% 12% 31% 16% 1	3766
	21st to end	Day	44% 13% 36% 6% 1	3932
September	1st to 10th	Day	51% 18% 20% 10% 1	2090
	11th to 20th	Day	55% 14% 19% 10% 2	2090
	21st to end	Day	56% 13% 15% 10% 5% 1	2090
October	1st to 10th	Day	52% 11% 17% 14% 5% 1	3305
	11th to 20th	Day	44% 7% 16% 18% 14% 1	3140
	21st to end	Day	37% 6% 9% 26% 17% 4	3428
November	1st to 10th	Day	36% 9% 11% 19% 16% 8%	1957
	11th to 20th	Day	45% 7% 10% 18% 14% 6%	2000
	21st to end	Day	37% 7% 13% 20% 18% 6%	1970
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	39% 7% 14% 22% 15% 3	4109
	11th to 20th	Night	52% 7% 12% 18% 8% 3	4120
	21st to end	Night	40% 7% 12% 21% 13% 7%	4520
February	1st to 10th	Night	34% 6% 14% 25% 17% 4	2280
	11th to 20th	Night	26% 6% 11% 28% 22% 7%	2116
	21st to end	Night	25% 7% 14% 24% 25% 6%	1727
March	1st to 10th	Night	42% 10% 13% 19% 12% 4	3418
	11th to 20th	Night	21% 9% 25% 30% 12% 3	3480
	21st to end	Night	25% 8% 14% 26% 23% 4	3817
April	1st to 10th	Night	22% 6% 20% 31% 16% 4	2090
	11th to 20th	Night	26% 9% 18% 25% 19% 3	1961
	21st to end	Night	25% 8% 17% 26% 20% 4	1900
May	1st to 10th	Night	16% 7% 19% 40% 15% 3	3160
	11th to 20th	Night	27% 11% 24% 29% 9%	3051
	21st to end	Night	26% 10% 20% 34% 10%	3087
June	1st to 10th	Night	46% 14% 22% 15% 3	1710
	11th to 20th	Night	40% 15% 25% 18% 2	1710
	21st to end	Night	39% 14% 32% 13% 2	1710
July	1st to 10th	Night	34% 11% 35% 19%	2795
	11th to 20th	Night	37% 12% 42% 9%	2786
	21st to end	Night	32% 14% 36% 16% 1	2988
August	1st to 10th	Night	37% 13% 32% 15% 2	2834
	11th to 20th	Night	30% 12% 36% 20% 1	3127
	21st to end	Night	41% 15% 37% 7% 1	3718
September	1st to 10th	Night	42% 19% 27% 12% 1	2090
	11th to 20th	Night	44% 17% 26% 12% 2	2090
	21st to end	Night	48% 16% 19% 12% 5%	2090
October	1st to 10th	Night	51% 11% 19% 13% 6% 1	3640
	11th to 20th	Night	41% 6% 15% 22% 15% 1	3779
	21st to end	Night	36% 5% 12% 28% 15% 4	4120
November	1st to 10th	Night	32% 7% 15% 20% 18% 7%	2341
	11th to 20th	Night	36% 8% 13% 23% 15% 5%	2400
	21st to end	Night	36% 7% 12% 20% 19% 6%	2365
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	9% 10% 36% 28% 14% 3	270
	21st to end	Day	12% 12% 36% 31% 8% 1	297
February	1st to 10th	Day	7% 8% 31% 34% 16% 3	270
	11th to 20th	Day	8% 7% 25% 38% 18% 5%	371
	21st to end	Day	5% 6% 22% 40% 23% 4	382
March	1st to 10th	Day	3 9% 32% 37% 16% 3	460
	11th to 20th	Day	6% 6% 27% 35% 23% 3	460
	21st to end	Day	4 5% 28% 36% 22% 6%	506
April	1st to 10th	Day	3 8% 30% 33% 18% 7%	460
	11th to 20th	Day	6% 6% 26% 33% 21% 8%	452
	21st to end	Day	8% 4 20% 34% 25% 9%	460
May	1st to 10th	Day	3 19% 34% 28% 15%	463
	11th to 20th	Day	11% 4 16% 30% 24% 15%	487
	21st to end	Day	9% 2 8% 25% 30% 26%	529
June	1st to 10th	Day	12% 3 7% 23% 28% 26%	490
	11th to 20th	Day	9% 2 6% 20% 27% 35%	490
	21st to end	Day	6% 2 3 12% 29% 48%	490
July	1st to 10th	Day	4 2 2 14% 26% 52%	485
	11th to 20th	Day	6% 2 2 12% 33% 46%	484
	21st to end	Day	6% 2 4 14% 29% 46%	532
August	1st to 10th	Day	6% 2 4 17% 28% 42%	486
	11th to 20th	Day	4 1 3 12% 30% 49%	479
	21st to end	Day	10% 2 4 20% 29% 35%	539
September	1st to 10th	Day	7% 3 4 15% 32% 40%	490
	11th to 20th	Day	7% 3 5% 15% 30% 40%	490
	21st to end	Day	10% 3 6% 20% 31% 30%	490
October	1st to 10th	Day	11% 4 9% 31% 31% 14%	490
	11th to 20th	Day	10% 4 16% 28% 30% 12%	490
	21st to end	Day	10% 4 18% 34% 26% 8%	539
November	1st to 10th	Day	9% 5% 19% 35% 22% 9%	495
	11th to 20th	Day	11% 5% 23% 34% 21% 6%	500
	21st to end	Day	5% 5% 25% 37% 25% 4	488
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	11% 6% 25% 39% 19% 1	760
	21st to end	Night	7% 8% 28% 43% 14%	836
February	1st to 10th	Night	8% 8% 22% 41% 20% 1	760
	11th to 20th	Night	8% 5% 23% 40% 22% 1	743
	21st to end	Night	6% 4 24% 45% 20% 1	628
March	1st to 10th	Night	5% 4 30% 43% 17% 1	760
	11th to 20th	Night	7% 4 22% 47% 19% 2	760
	21st to end	Night	5% 4 24% 45% 21% 1	836
April	1st to 10th	Night	4 4 22% 46% 23% 2	760
	11th to 20th	Night	4 5% 19% 47% 23% 1	751
	21st to end	Night	5% 3 20% 45% 25% 2	760
May	1st to 10th	Night	4 2 15% 44% 33% 2	760
	11th to 20th	Night	8% 3 14% 41% 31% 4	708
	21st to end	Night	6% 4 5% 26% 49% 10%	617
June	1st to 10th	Night	11% 2 3 25% 45% 14%	570
	11th to 20th	Night	8% 1 3 16% 45% 26%	570
	21st to end	Night	5% 4 3 11% 43% 35%	570
July	1st to 10th	Night	5% 2 4 6% 46% 37%	555
	11th to 20th	Night	5% 2 1 9% 42% 41%	552
	21st to end	Night	4 1 2 7% 44% 41%	624
August	1st to 10th	Night	6% 1 2 9% 49% 33%	574
	11th to 20th	Night	5% 1 2 9% 46% 37%	750
	21st to end	Night	9% 2 5% 16% 41% 28%	836
September	1st to 10th	Night	8% 3 5% 11% 41% 33%	760
	11th to 20th	Night	9% 2 4 14% 43% 28%	760
	21st to end	Night	11% 2 5% 18% 40% 24%	760
October	1st to 10th	Night	11% 3 7% 31% 38% 10%	760
	11th to 20th	Night	9% 4 8% 32% 39% 8%	760
	21st to end	Night	12% 3 14% 36% 29% 7%	836
November	1st to 10th	Night	10% 4 18% 34% 31% 3	780
	11th to 20th	Night	9% 4 18% 36% 30% 4	800
	21st to end	Night	8% 4 18% 42% 26% 1	789
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

Page generated at 2024-11-25 00:22:21. Version ac07

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