Astro Birdie Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro Birdie Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	101022
	Night	14% 7% 2 5% 4 3 4 3 5% 7% 46%	98003
Transparency	Day	41% 7% 12% 19% 16% 6%	100833
	Night	37% 6% 13% 20% 17% 8%	97863
Seeing	Day	13% 8% 21% 26% 23% 8%	14883
	Night	16% 8% 24% 33% 18% 2	24713

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	18% 9% 2 6% 2 3 3 3 4 5% 45%	2847
	11th to 20th	Day	19% 6% 2 4 3 3 2 2 4 4 51%	2850
	21st to end	Day	24% 9% 2 6% 3 2 3 3 5% 8% 36%	3135
February	1st to 10th	Day	22% 9% 3 7% 4 3 4 3 4 5% 37%	1794
	11th to 20th	Day	21% 9% 3 8% 4 3 3 2 3 6% 39%	1852
	21st to end	Day	20% 9% 2 6% 4 3 3 3 4 5% 40%	1727
March	1st to 10th	Day	19% 9% 3 9% 5% 5% 5% 4 5% 6% 30%	3436
	11th to 20th	Day	19% 9% 3 8% 6% 4 5% 4 6% 7% 29%	3480
	21st to end	Day	16% 8% 2 5% 5% 4 4 3 5% 6% 41%	3814
April	1st to 10th	Day	15% 10% 3 7% 5% 4 4 3 5% 5% 38%	2090
	11th to 20th	Day	17% 8% 3 7% 5% 4 4 3 6% 6% 38%	2211
	21st to end	Day	11% 8% 2 7% 5% 4 5% 4 6% 6% 41%	2280
May	1st to 10th	Day	19% 9% 3 7% 6% 6% 5% 4 6% 7% 29%	3890
	11th to 20th	Day	14% 6% 2 7% 4 4 5% 4 6% 7% 42%	4082
	21st to end	Day	9% 7% 2 7% 6% 6% 6% 5% 8% 11% 33%	4477
June	1st to 10th	Day	6% 6% 2 6% 6% 5% 6% 5% 8% 9% 41%	2470
	11th to 20th	Day	6% 4 1 5% 5% 6% 7% 5% 8% 11% 41%	2470
	21st to end	Day	6% 6% 2 9% 7% 8% 8% 6% 9% 10% 30%	2470
July	1st to 10th	Day	9% 4 2 6% 5% 6% 6% 5% 8% 12% 37%	4120
	11th to 20th	Day	7% 6% 3 8% 7% 6% 6% 6% 8% 11% 33%	4120
	21st to end	Day	15% 7% 3 8% 6% 5% 6% 5% 7% 10% 27%	4465
August	1st to 10th	Day	2 2 1 3 3 3 4 4 6% 9% 63%	4104
	11th to 20th	Day	3 2 1 4 4 5% 7% 6% 9% 12% 47%	3914
	21st to end	Day	7% 4 2 7% 5% 6% 6% 5% 7% 10% 40%	4098
September	1st to 10th	Day	7% 6% 2 6% 6% 6% 6% 6% 7% 9% 41%	2090
	11th to 20th	Day	12% 7% 3 7% 5% 6% 6% 3 6% 8% 37%	2090
	21st to end	Day	7% 4 2 6% 4 5% 5% 4 6% 8% 48%	2090
October	1st to 10th	Day	6% 3 2 5% 3 3 4 3 5% 6% 58%	1977
	11th to 20th	Day	9% 5% 3 5% 3 4 4 3 5% 5% 53%	1900
	21st to end	Day	13% 6% 2 4 3 3 3 3 4 5% 54%	2090
November	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 5% 7% 47%	1868
	11th to 20th	Day	11% 7% 3 6% 4 4 4 3 5% 6% 48%	1900
	21st to end	Day	17% 7% 3 6% 4 4 5% 3 4 5% 42%	1815
December	1st to 10th	Day	15% 8% 3 7% 5% 4 4 3 5% 5% 41%	1710
	11th to 20th	Day	15% 8% 3 7% 5% 3 3 3 5% 5% 42%	2161
	21st to end	Day	17% 8% 2 6% 4 3 3 3 4 5% 45%	3135
January	1st to 10th	Night	18% 7% 3 5% 3 3 3 2 4 6% 46%	4108
	11th to 20th	Night	18% 7% 2 5% 2 2 2 2 3 4 53%	4120
	21st to end	Night	23% 10% 3 5% 3 3 3 3 4 6% 38%	4532
February	1st to 10th	Night	20% 10% 2 7% 4 3 3 3 4 5% 40%	2402
	11th to 20th	Night	22% 8% 2 6% 3 3 3 2 4 5% 43%	2214
	21st to end	Night	21% 8% 2 6% 4 3 4 3 4 6% 40%	1727
March	1st to 10th	Night	23% 11% 3 7% 4 4 3 3 5% 5% 31%	3419
	11th to 20th	Night	22% 10% 3 8% 4 4 4 3 5% 6% 30%	3480
	21st to end	Night	14% 8% 3 7% 5% 5% 4 3 4 5% 43%	3817
April	1st to 10th	Night	15% 7% 2 6% 5% 4 4 3 6% 6% 41%	2090
	11th to 20th	Night	15% 8% 3 5% 4 3 3 3 6% 7% 44%	1916
	21st to end	Night	15% 6% 2 6% 4 3 4 3 5% 6% 46%	1900
May	1st to 10th	Night	22% 10% 3 7% 5% 4 4 3 5% 7% 30%	2991
	11th to 20th	Night	14% 7% 3 6% 4 4 4 3 5% 7% 43%	2823
	21st to end	Night	12% 7% 2 6% 5% 4 4 5% 7% 10% 37%	3090
June	1st to 10th	Night	6% 3 1 4 3 4 5% 4 7% 10% 54%	1710
	11th to 20th	Night	4 3 1 3 3 4 3 5% 7% 12% 55%	1710
	21st to end	Night	4 5% 2 6% 4 4 4 6% 8% 11% 45%	1710
July	1st to 10th	Night	6% 4 2 5% 4 5% 5% 5% 8% 13% 44%	2850
	11th to 20th	Night	5% 4 1 6% 5% 4 5% 5% 7% 12% 47%	2850
	21st to end	Night	12% 7% 2 7% 5% 4 5% 4 6% 10% 38%	3098
August	1st to 10th	Night	2 1 1 2 2 2 3 2 5% 9% 71%	2836
	11th to 20th	Night	2 2 1 3 2 3 4 3 8% 13% 60%	2920
	21st to end	Night	6% 3 2 5% 3 4 6% 5% 8% 12% 47%	3539
September	1st to 10th	Night	5% 6% 2 6% 5% 4 4 4 7% 9% 48%	2090
	11th to 20th	Night	11% 6% 2 7% 5% 4 5% 4 6% 8% 43%	2090
	21st to end	Night	8% 4 2 4 3 3 3 3 6% 9% 55%	2090
October	1st to 10th	Night	5% 3 1 4 3 3 4 3 5% 9% 60%	2182
	11th to 20th	Night	10% 4 1 4 2 2 3 3 4 6% 60%	2280
	21st to end	Night	12% 6% 2 4 3 3 3 2 3 4 59%	2508
November	1st to 10th	Night	10% 6% 2 4 3 3 4 3 4 7% 53%	2233
	11th to 20th	Night	12% 6% 3 5% 4 3 4 3 5% 6% 50%	2280
	21st to end	Night	17% 6% 3 6% 3 4 4 3 5% 5% 43%	2360
December	1st to 10th	Night	18% 8% 2 6% 4 4 3 3 4 6% 42%	2470
	11th to 20th	Night	16% 10% 3 6% 4 4 3 3 4 5% 42%	3036
	21st to end	Night	17% 7% 2 6% 3 3 3 3 4 5% 47%	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% 4 6% 15% 23% 10%	2848
	11th to 20th	Day	37% 4 5% 19% 28% 7%	2850
	21st to end	Day	48% 3 4 17% 17% 11%	3135
February	1st to 10th	Day	50% 4 5% 13% 16% 11%	1794
	11th to 20th	Day	49% 4 6% 13% 17% 11%	1862
	21st to end	Day	47% 4 8% 15% 15% 11%	1727
March	1st to 10th	Day	52% 5% 11% 12% 15% 4	3436
	11th to 20th	Day	51% 7% 11% 12% 15% 5%	3480
	21st to end	Day	44% 5% 8% 17% 21% 4	3814
April	1st to 10th	Day	48% 5% 6% 16% 15% 9%	2090
	11th to 20th	Day	46% 5% 9% 14% 17% 9%	2211
	21st to end	Day	40% 7% 9% 19% 20% 6%	2280
May	1st to 10th	Day	52% 8% 11% 15% 10% 4	3925
	11th to 20th	Day	40% 6% 10% 17% 23% 3	4086
	21st to end	Day	40% 9% 13% 27% 10% 1	4489
June	1st to 10th	Day	36% 9% 16% 22% 16% 1	2470
	11th to 20th	Day	33% 9% 17% 23% 15% 3	2470
	21st to end	Day	44% 11% 15% 19% 10%	2470
July	1st to 10th	Day	37% 8% 28% 23% 4	4056
	11th to 20th	Day	43% 8% 18% 21% 9% 1	4051
	21st to end	Day	50% 8% 17% 19% 4	4325
August	1st to 10th	Day	17% 7% 16% 37% 23%	4090
	11th to 20th	Day	26% 8% 30% 28% 6% 1	3953
	21st to end	Day	38% 11% 17% 20% 13% 2	4097
September	1st to 10th	Day	38% 10% 13% 18% 14% 6%	2090
	11th to 20th	Day	44% 7% 13% 17% 15% 4	2090
	21st to end	Day	33% 8% 12% 18% 17% 13%	2090
October	1st to 10th	Day	26% 6% 9% 22% 21% 16%	1977
	11th to 20th	Day	33% 6% 6% 17% 22% 16%	1900
	21st to end	Day	34% 5% 5% 14% 26% 16%	2090
November	1st to 10th	Day	36% 7% 10% 17% 21% 10%	1868
	11th to 20th	Day	36% 5% 10% 14% 22% 12%	1900
	21st to end	Day	44% 5% 6% 15% 18% 11%	1815
December	1st to 10th	Day	45% 4 10% 16% 18% 7%	1710
	11th to 20th	Day	43% 5% 7% 14% 21% 10%	2159
	21st to end	Day	42% 4 6% 14% 24% 11%	3135
January	1st to 10th	Night	38% 5% 7% 19% 19% 12%	4108
	11th to 20th	Night	36% 4 6% 17% 27% 10%	4120
	21st to end	Night	48% 4 4 16% 19% 9%	4532
February	1st to 10th	Night	48% 4 5% 13% 16% 14%	2402
	11th to 20th	Night	44% 4 7% 15% 18% 12%	2214
	21st to end	Night	47% 5% 7% 13% 15% 14%	1727
March	1st to 10th	Night	53% 6% 8% 13% 15% 5%	3419
	11th to 20th	Night	53% 7% 10% 13% 13% 5%	3480
	21st to end	Night	43% 5% 9% 14% 22% 7%	3817
April	1st to 10th	Night	42% 6% 10% 16% 16% 10%	2090
	11th to 20th	Night	39% 5% 11% 17% 16% 12%	1916
	21st to end	Night	39% 6% 9% 19% 21% 6%	1900
May	1st to 10th	Night	52% 7% 11% 16% 10% 4	3021
	11th to 20th	Night	40% 6% 11% 18% 20% 4	2824
	21st to end	Night	39% 9% 17% 26% 8% 1	3099
June	1st to 10th	Night	24% 8% 19% 31% 18%	1710
	11th to 20th	Night	21% 8% 20% 29% 18% 4	1710
	21st to end	Night	29% 11% 20% 27% 12% 1	1710
July	1st to 10th	Night	31% 8% 33% 25% 4	2805
	11th to 20th	Night	30% 9% 24% 28% 10%	2796
	21st to end	Night	41% 10% 21% 23% 4	2999
August	1st to 10th	Night	11% 6% 18% 43% 22% 1	2826
	11th to 20th	Night	16% 7% 35% 34% 8% 1	2947
	21st to end	Night	29% 12% 21% 26% 10% 2	3539
September	1st to 10th	Night	31% 9% 22% 20% 12% 6%	2090
	11th to 20th	Night	36% 9% 15% 19% 15% 6%	2090
	21st to end	Night	26% 6% 15% 21% 19% 12%	2090
October	1st to 10th	Night	22% 5% 11% 26% 18% 17%	2182
	11th to 20th	Night	26% 5% 7% 21% 25% 16%	2280
	21st to end	Night	31% 3 7% 15% 25% 19%	2508
November	1st to 10th	Night	32% 5% 11% 20% 21% 11%	2233
	11th to 20th	Night	36% 4 10% 18% 21% 12%	2280
	21st to end	Night	41% 5% 8% 16% 19% 11%	2360
December	1st to 10th	Night	44% 4 8% 19% 15% 9%	2470
	11th to 20th	Night	45% 4 6% 10% 20% 14%	3037
	21st to end	Night	40% 5% 7% 13% 28% 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	26% 14% 37% 19% 3 1	270
	11th to 20th	Day	30% 12% 30% 22% 5% 1	270
	21st to end	Day	26% 16% 37% 17% 5%	297
February	1st to 10th	Day	32% 18% 29% 16% 5%	270
	11th to 20th	Day	29% 20% 32% 17% 3	270
	21st to end	Day	28% 24% 38% 8% 1	225
March	1st to 10th	Day	25% 20% 33% 16% 5%	270
	11th to 20th	Day	19% 23% 38% 16% 4	270
	21st to end	Day	22% 16% 37% 20% 5%	297
April	1st to 10th	Day	17% 21% 38% 20% 4	270
	11th to 20th	Day	25% 18% 26% 21% 10%	409
	21st to end	Day	15% 14% 38% 23% 9% 1	460
May	1st to 10th	Day	15% 15% 36% 23% 10% 1	536
	11th to 20th	Day	14% 8% 31% 30% 15% 3	675
	21st to end	Day	11% 6% 29% 34% 17% 4	734
June	1st to 10th	Day	6% 3 16% 35% 30% 10%	680
	11th to 20th	Day	6% 2 18% 37% 28% 8%	680
	21st to end	Day	8% 2 13% 31% 33% 13%	680
July	1st to 10th	Day	8% 2 10% 28% 35% 17%	671
	11th to 20th	Day	4 1 4 32% 42% 17%	668
	21st to end	Day	6% 1 5% 26% 46% 16%	739
August	1st to 10th	Day	3 1 4 26% 49% 18%	676
	11th to 20th	Day	4 1 2 21% 50% 22%	590
	21st to end	Day	7% 3 8% 21% 33% 28%	496
September	1st to 10th	Day	8% 1 9% 26% 37% 19%	300
	11th to 20th	Day	10% 2 10% 29% 36% 13%	300
	21st to end	Day	9% 2 9% 32% 35% 12%	300
October	1st to 10th	Day	5% 3 16% 41% 30% 5%	300
	11th to 20th	Day	10% 6% 21% 38% 19% 6%	300
	21st to end	Day	21% 11% 24% 23% 18% 4	330
November	1st to 10th	Day	14% 7% 21% 38% 19% 1	273
	11th to 20th	Day	16% 10% 31% 31% 9% 2	270
	21st to end	Day	22% 20% 31% 17% 7% 3	270
December	1st to 10th	Day	18% 13% 33% 24% 8% 4	270
	11th to 20th	Day	23% 18% 33% 21% 5%	270
	21st to end	Day	25% 15% 33% 21% 6% 1	297
January	1st to 10th	Night	23% 13% 31% 27% 6%	950
	11th to 20th	Night	23% 14% 29% 27% 6%	950
	21st to end	Night	23% 13% 31% 27% 5%	1045
February	1st to 10th	Night	26% 14% 31% 25% 4	882
	11th to 20th	Night	28% 13% 30% 25% 4	740
	21st to end	Night	27% 16% 34% 20% 3	471
March	1st to 10th	Night	24% 13% 33% 26% 4	570
	11th to 20th	Night	21% 10% 36% 28% 5%	570
	21st to end	Night	18% 12% 40% 24% 6%	627
April	1st to 10th	Night	16% 11% 40% 28% 5%	570
	11th to 20th	Night	21% 11% 33% 28% 7%	563
	21st to end	Night	18% 12% 37% 25% 9%	570
May	1st to 10th	Night	17% 11% 34% 31% 6%	570
	11th to 20th	Night	14% 7% 30% 34% 13% 2	561
	21st to end	Night	9% 5% 30% 36% 19% 1	617
June	1st to 10th	Night	7% 2 14% 45% 28% 3	570
	11th to 20th	Night	4 1 20% 48% 24% 3	570
	21st to end	Night	5% 3 12% 43% 32% 5%	570
July	1st to 10th	Night	4 2 10% 42% 35% 6%	555
	11th to 20th	Night	4 1 5% 45% 39% 6%	552
	21st to end	Night	5% 1 7% 45% 38% 5%	624
August	1st to 10th	Night	2 1 4 50% 39% 5%	567
	11th to 20th	Night	5% 4 46% 39% 6%	564
	21st to end	Night	5% 2 6% 34% 47% 6%	627
September	1st to 10th	Night	7% 2 8% 33% 43% 8%	570
	11th to 20th	Night	12% 2 9% 32% 40% 6%	570
	21st to end	Night	9% 2 14% 35% 35% 6%	570
October	1st to 10th	Night	5% 3 13% 41% 33% 5%	662
	11th to 20th	Night	12% 4 23% 41% 20% 2	760
	21st to end	Night	14% 8% 27% 31% 18% 2	836
November	1st to 10th	Night	12% 5% 26% 36% 21% 1	745
	11th to 20th	Night	13% 11% 28% 33% 16%	760
	21st to end	Night	22% 9% 29% 26% 13% 1	840
December	1st to 10th	Night	22% 11% 27% 28% 11% 1	950
	11th to 20th	Night	26% 11% 29% 28% 6%	950
	21st to end	Night	23% 11% 29% 28% 7%	1045

Page generated at 2024-10-30 00:22:55. Version ac07

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