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 2024-03-06.

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% 3 6% 6% 3 5% 5% 6% 8% 41%	79005
	Night	13% 6% 2 4 4 2 4 4 5% 7% 47%	80569
Transparency	Day	41% 7% 11% 18% 17% 7%	78730
	Night	36% 6% 12% 19% 18% 9%	80364
Seeing	Day	13% 8% 21% 26% 23% 8%	13920
	Night	16% 8% 24% 33% 17% 2	23964

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 5% 3 3 3 4 4 5% 45%	2847
	11th to 20th	Day	19% 6% 2 4 3 2 3 3 3 5% 51%	2850
	21st to end	Day	24% 8% 2 5% 3 2 3 3 5% 8% 36%	3135
February	1st to 10th	Day	23% 8% 4 6% 5% 2 4 4 3 5% 37%	1794
	11th to 20th	Day	22% 8% 3 7% 5% 2 3 3 3 6% 39%	1852
	21st to end	Day	20% 8% 3 6% 5% 3 3 3 3 5% 41%	1727
March	1st to 10th	Day	22% 8% 3 6% 5% 3 4 4 4 6% 35%	2035
	11th to 20th	Day	18% 8% 3 6% 5% 2 4 4 5% 6% 39%	1980
	21st to end	Day	16% 7% 3 5% 5% 4 4 4 4 7% 42%	2178
April	1st to 10th	Day	16% 9% 4 6% 6% 3 5% 4 5% 6% 38%	1980
	11th to 20th	Day	17% 7% 3 7% 5% 3 4 4 5% 7% 39%	2093
	21st to end	Day	11% 7% 3 6% 5% 3 5% 5% 6% 6% 42%	2160
May	1st to 10th	Day	11% 6% 3 6% 6% 4 7% 6% 6% 7% 37%	2229
	11th to 20th	Day	10% 6% 3 6% 6% 3 5% 5% 7% 8% 41%	2302
	21st to end	Day	10% 6% 3 6% 7% 4 7% 6% 7% 11% 31%	2531
June	1st to 10th	Day	6% 5% 2 6% 7% 4 6% 7% 8% 9% 41%	2340
	11th to 20th	Day	6% 3 2 4 6% 4 7% 7% 8% 11% 41%	2340
	21st to end	Day	7% 5% 3 8% 8% 5% 9% 7% 8% 10% 30%	2340
July	1st to 10th	Day	10% 5% 3 6% 7% 6% 7% 7% 8% 10% 32%	2340
	11th to 20th	Day	5% 4 3 6% 8% 4 7% 7% 8% 11% 37%	2340
	21st to end	Day	4 4 2 7% 8% 5% 8% 7% 8% 12% 35%	2546
August	1st to 10th	Day	3 3 2 4 6% 4 6% 7% 8% 12% 45%	2328
	11th to 20th	Day	5% 4 1 6% 7% 5% 6% 8% 8% 9% 42%	2230
	21st to end	Day	7% 4 2 6% 7% 5% 8% 7% 8% 10% 36%	2336
September	1st to 10th	Day	6% 5% 2 6% 7% 4 6% 7% 7% 9% 41%	1980
	11th to 20th	Day	12% 7% 3 7% 6% 5% 6% 5% 6% 8% 35%	1980
	21st to end	Day	7% 4 2 5% 5% 4 5% 6% 6% 8% 47%	1980
October	1st to 10th	Day	7% 3 2 4 4 3 5% 4 5% 7% 56%	1873
	11th to 20th	Day	10% 5% 3 5% 4 4 4 4 5% 6% 51%	1800
	21st to end	Day	13% 6% 2 4 3 3 3 3 4 5% 54%	1980
November	1st to 10th	Day	11% 4 2 5% 5% 3 5% 4 5% 8% 48%	1858
	11th to 20th	Day	11% 6% 3 5% 4 2 5% 4 5% 6% 49%	1900
	21st to end	Day	18% 6% 3 5% 5% 2 5% 4 4 5% 42%	1815
December	1st to 10th	Day	15% 7% 3 6% 6% 3 5% 4 4 5% 41%	1710
	11th to 20th	Day	16% 7% 3 5% 6% 3 3 4 4 6% 42%	2161
	21st to end	Day	17% 8% 2 5% 5% 2 3 4 4 5% 45%	3135
January	1st to 10th	Night	18% 7% 3 4 4 2 3 3 4 6% 47%	4108
	11th to 20th	Night	18% 7% 2 4 3 1 2 3 3 4 53%	4120
	21st to end	Night	23% 9% 3 4 4 2 3 3 4 6% 38%	4532
February	1st to 10th	Night	20% 9% 2 6% 5% 2 3 4 4 5% 40%	2402
	11th to 20th	Night	22% 8% 2 5% 4 2 3 3 3 6% 43%	2214
	21st to end	Night	21% 7% 3 6% 5% 2 4 4 3 6% 40%	1727
March	1st to 10th	Night	20% 8% 3 5% 5% 2 3 4 5% 6% 39%	2041
	11th to 20th	Night	17% 8% 3 5% 4 2 4 4 5% 7% 41%	1980
	21st to end	Night	15% 6% 3 4 4 3 4 3 4 6% 48%	2178
April	1st to 10th	Night	14% 7% 3 6% 5% 3 5% 4 6% 6% 42%	1980
	11th to 20th	Night	15% 7% 3 5% 4 2 3 3 5% 8% 45%	1814
	21st to end	Night	13% 6% 2 6% 5% 2 4 4 5% 6% 47%	1800
May	1st to 10th	Night	12% 6% 3 6% 6% 4 4 4 6% 9% 40%	1726
	11th to 20th	Night	12% 6% 3 4 5% 3 3 5% 5% 9% 46%	1593
	21st to end	Night	7% 4 3 4 6% 3 4 5% 6% 10% 47%	1745
June	1st to 10th	Night	6% 3 1 4 4 3 4 5% 7% 11% 53%	1620
	11th to 20th	Night	4 2 1 3 3 3 3 6% 7% 12% 56%	1620
	21st to end	Night	5% 4 2 5% 5% 3 5% 6% 8% 12% 45%	1620
July	1st to 10th	Night	6% 4 3 4 5% 4 5% 6% 8% 11% 45%	1620
	11th to 20th	Night	2 3 2 3 3 2 5% 5% 6% 13% 56%	1620
	21st to end	Night	3 2 2 3 4 2 6% 6% 8% 13% 51%	1772
August	1st to 10th	Night	2 1 1 2 3 2 3 4 7% 13% 63%	1611
	11th to 20th	Night	4 3 1 3 3 3 4 5% 8% 13% 52%	1670
	21st to end	Night	5% 2 2 4 5% 4 4 7% 8% 12% 47%	2015
September	1st to 10th	Night	4 5% 1 5% 6% 2 5% 5% 7% 10% 50%	1980
	11th to 20th	Night	11% 6% 2 6% 5% 3 5% 5% 6% 8% 43%	1980
	21st to end	Night	8% 4 2 4 4 2 3 4 6% 9% 54%	1980
October	1st to 10th	Night	5% 3 2 3 4 2 5% 4 4 9% 59%	2067
	11th to 20th	Night	11% 4 2 3 3 2 3 4 4 6% 59%	2160
	21st to end	Night	13% 6% 2 4 3 2 3 3 3 4 58%	2376
November	1st to 10th	Night	10% 5% 2 4 4 2 4 4 4 6% 54%	2220
	11th to 20th	Night	12% 5% 3 4 5% 3 5% 3 5% 6% 50%	2280
	21st to end	Night	17% 6% 3 5% 4 3 4 4 5% 6% 44%	2360
December	1st to 10th	Night	18% 7% 3 5% 4 3 4 4 3 6% 42%	2470
	11th to 20th	Night	16% 9% 3 5% 5% 3 4 3 4 5% 42%	3036
	21st to end	Night	17% 7% 2 5% 4 2 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	50% 4 9% 12% 17% 7%	2035
	11th to 20th	Day	47% 4 8% 12% 19% 10%	1980
	21st to end	Day	44% 5% 8% 14% 22% 7%	2178
April	1st to 10th	Day	49% 5% 6% 17% 15% 8%	1980
	11th to 20th	Day	46% 5% 9% 14% 17% 10%	2093
	21st to end	Day	40% 6% 9% 19% 20% 6%	2160
May	1st to 10th	Day	44% 8% 10% 15% 16% 7%	2229
	11th to 20th	Day	40% 7% 11% 21% 18% 3	2306
	21st to end	Day	44% 9% 13% 21% 11% 1	2531
June	1st to 10th	Day	36% 8% 16% 22% 15% 2	2340
	11th to 20th	Day	34% 9% 18% 23% 14% 3	2340
	21st to end	Day	46% 11% 15% 18% 9%	2340
July	1st to 10th	Day	43% 11% 18% 21% 6%	2276
	11th to 20th	Day	37% 10% 21% 21% 10%	2271
	21st to end	Day	36% 11% 21% 24% 7% 1	2405
August	1st to 10th	Day	28% 11% 23% 27% 11% 1	2314
	11th to 20th	Day	34% 11% 21% 23% 10% 2	2230
	21st to end	Day	39% 12% 18% 21% 8% 3	2336
September	1st to 10th	Day	37% 10% 14% 19% 14% 6%	1980
	11th to 20th	Day	45% 8% 13% 17% 13% 4	1980
	21st to end	Day	34% 8% 12% 18% 17% 11%	1980
October	1st to 10th	Day	28% 6% 9% 23% 21% 13%	1873
	11th to 20th	Day	34% 6% 7% 17% 20% 16%	1800
	21st to end	Day	34% 5% 6% 13% 25% 17%	1980
November	1st to 10th	Day	35% 7% 10% 17% 21% 10%	1858
	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	45% 5% 8% 16% 17% 9%	2041
	11th to 20th	Night	43% 6% 11% 12% 19% 9%	1980
	21st to end	Night	38% 5% 11% 15% 21% 9%	2178
April	1st to 10th	Night	42% 6% 10% 17% 16% 9%	1980
	11th to 20th	Night	39% 5% 11% 17% 16% 12%	1814
	21st to end	Night	39% 6% 8% 20% 21% 6%	1800
May	1st to 10th	Night	41% 5% 12% 18% 17% 8%	1726
	11th to 20th	Night	36% 6% 13% 24% 18% 4	1594
	21st to end	Night	32% 8% 17% 29% 12% 2	1746
June	1st to 10th	Night	24% 8% 19% 31% 18%	1620
	11th to 20th	Night	20% 8% 21% 30% 18% 3	1620
	21st to end	Night	30% 11% 19% 27% 12% 1	1620
July	1st to 10th	Night	29% 11% 27% 26% 7%	1575
	11th to 20th	Night	19% 11% 29% 30% 10%	1566
	21st to end	Night	19% 14% 30% 30% 7%	1673
August	1st to 10th	Night	13% 8% 30% 36% 12% 1	1601
	11th to 20th	Night	21% 10% 29% 29% 9% 1	1670
	21st to end	Night	28% 13% 24% 25% 8% 3	2015
September	1st to 10th	Night	29% 9% 23% 21% 12% 6%	1980
	11th to 20th	Night	37% 9% 16% 19% 14% 5%	1980
	21st to end	Night	27% 6% 16% 21% 19% 11%	1980
October	1st to 10th	Night	23% 5% 11% 28% 18% 14%	2067
	11th to 20th	Night	27% 5% 8% 20% 24% 16%	2160
	21st to end	Night	32% 3 7% 15% 23% 20%	2376
November	1st to 10th	Night	31% 5% 11% 20% 21% 11%	2220
	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% 21% 32% 16% 5%	255
	11th to 20th	Day	19% 23% 37% 17% 5%	240
	21st to end	Day	22% 16% 36% 20% 5%	264
April	1st to 10th	Day	17% 20% 39% 20% 5%	240
	11th to 20th	Day	25% 18% 24% 21% 11%	371
	21st to end	Day	15% 14% 38% 23% 9% 1	420
May	1st to 10th	Day	15% 13% 36% 24% 11% 1	492
	11th to 20th	Day	13% 7% 31% 31% 15% 3	625
	21st to end	Day	11% 5% 27% 35% 18% 4	679
June	1st to 10th	Day	6% 2 15% 37% 31% 10%	630
	11th to 20th	Day	6% 2 18% 38% 27% 9%	630
	21st to end	Day	9% 2 13% 31% 32% 13%	630
July	1st to 10th	Day	8% 2 10% 29% 35% 17%	621
	11th to 20th	Day	3 1 5% 31% 43% 17%	618
	21st to end	Day	4 1 5% 25% 49% 17%	684
August	1st to 10th	Day	3 1 4 26% 50% 17%	626
	11th to 20th	Day	5% 1 3 21% 49% 22%	544
	21st to end	Day	8% 2 7% 19% 34% 31%	455
September	1st to 10th	Day	6% 1 6% 25% 41% 21%	270
	11th to 20th	Day	10% 2 9% 29% 38% 12%	270
	21st to end	Day	10% 1 8% 31% 37% 11%	270
October	1st to 10th	Day	6% 3 14% 40% 31% 6%	270
	11th to 20th	Day	11% 7% 21% 34% 20% 6%	270
	21st to end	Day	22% 11% 25% 23% 16% 3	297
November	1st to 10th	Day	13% 7% 21% 37% 19% 1	270
	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	25% 12% 33% 26% 4	557
	11th to 20th	Night	21% 9% 36% 28% 6%	540
	21st to end	Night	18% 12% 39% 25% 6%	594
April	1st to 10th	Night	15% 11% 41% 28% 5%	540
	11th to 20th	Night	20% 10% 33% 28% 8%	533
	21st to end	Night	16% 11% 38% 25% 9%	540
May	1st to 10th	Night	16% 10% 34% 32% 6%	540
	11th to 20th	Night	15% 6% 30% 34% 13% 2	531
	21st to end	Night	9% 4 29% 37% 20% 1	584
June	1st to 10th	Night	7% 2 14% 46% 28% 3	540
	11th to 20th	Night	4 1 21% 48% 23% 3	540
	21st to end	Night	5% 3 12% 43% 32% 6%	540
July	1st to 10th	Night	4 2 10% 43% 34% 6%	525
	11th to 20th	Night	3 1 6% 46% 39% 6%	522
	21st to end	Night	3 1 7% 45% 39% 5%	591
August	1st to 10th	Night	2 5% 51% 38% 4	537
	11th to 20th	Night	5% 4 46% 38% 6%	534
	21st to end	Night	5% 2 6% 34% 47% 6%	594
September	1st to 10th	Night	6% 1 6% 33% 45% 9%	540
	11th to 20th	Night	12% 2 9% 31% 40% 6%	540
	21st to end	Night	9% 2 14% 33% 37% 6%	540
October	1st to 10th	Night	5% 3 14% 41% 32% 5%	627
	11th to 20th	Night	12% 4 23% 38% 21% 2	720
	21st to end	Night	15% 9% 27% 30% 18% 2	792
November	1st to 10th	Night	11% 5% 26% 36% 21% 1	740
	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 2024-03-03 05:29:00. Version ac07

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