Ballantyne Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ballantyne Observatory clear sky chart from 2005-11-06 to 2024-07-03.

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% 4 4 4 4 6% 7% 44%	89724
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	89438
Transparency	Day	19% 54% 5% 10% 10% 2	89498
	Night	19% 53% 5% 9% 10% 3	89268
Seeing	Day	16% 6% 22% 25% 21% 11%	14820
	Night	16% 5% 22% 32% 21% 3	24933

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	17% 5% 2 5% 3 3 3 2 4 6% 51%	2836
	11th to 20th	Day	13% 6% 2 5% 4 3 3 3 5% 5% 52%	2840
	21st to end	Day	21% 8% 2 5% 2 3 4 3 4 4 42%	3124
February	1st to 10th	Day	15% 7% 3 7% 3 4 5% 3 6% 5% 43%	1710
	11th to 20th	Day	20% 6% 2 5% 3 3 4 3 4 5% 46%	1813
	21st to end	Day	18% 8% 3 7% 5% 4 3 2 5% 6% 40%	1632
March	1st to 10th	Day	24% 7% 3 6% 3 3 3 3 5% 6% 38%	3435
	11th to 20th	Day	11% 5% 2 5% 3 4 4 3 5% 6% 53%	3480
	21st to end	Day	21% 7% 2 6% 3 3 3 3 5% 5% 43%	3815
April	1st to 10th	Day	10% 4 2 4 4 4 4 4 6% 7% 51%	2093
	11th to 20th	Day	12% 5% 2 5% 4 3 5% 4 6% 6% 48%	2254
	21st to end	Day	13% 5% 2 4 4 4 4 3 4 7% 50%	2403
May	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 5% 7% 10% 36%	4082
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 4 6% 8% 36%	4081
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 7% 9% 49%	4476
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 6% 7% 10% 39%	2470
	11th to 20th	Day	9% 6% 2 5% 5% 4 5% 4 7% 11% 42%	2470
	21st to end	Day	6% 4 2 6% 5% 5% 7% 6% 9% 11% 39%	2470
July	1st to 10th	Day	8% 5% 3 7% 7% 5% 6% 5% 8% 11% 34%	2366
	11th to 20th	Day	9% 5% 2 7% 5% 6% 6% 6% 9% 11% 33%	2340
	21st to end	Day	6% 6% 2 6% 6% 6% 7% 5% 9% 12% 35%	2547
August	1st to 10th	Day	11% 5% 3 7% 6% 5% 7% 5% 8% 10% 33%	2327
	11th to 20th	Day	13% 6% 3 7% 6% 6% 7% 4 8% 10% 31%	2303
	21st to end	Day	11% 6% 2 7% 5% 6% 6% 4 7% 9% 36%	2404
September	1st to 10th	Day	8% 5% 3 5% 5% 5% 5% 5% 6% 10% 44%	2020
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 42%	1980
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 7% 41%	1980
October	1st to 10th	Day	14% 6% 2 4 3 2 3 3 4 6% 53%	1862
	11th to 20th	Day	14% 4 2 4 4 3 3 2 4 5% 56%	1800
	21st to end	Day	13% 5% 2 5% 3 3 2 2 4 5% 56%	1980
November	1st to 10th	Day	14% 4 1 5% 3 3 2 2 4 5% 57%	1857
	11th to 20th	Day	13% 6% 2 3 3 3 3 3 5% 5% 53%	1777
	21st to end	Day	15% 5% 2 5% 3 4 3 3 4 6% 50%	1710
December	1st to 10th	Day	17% 8% 3 6% 3 4 3 3 6% 7% 39%	1710
	11th to 20th	Day	16% 5% 2 4 3 2 2 2 5% 6% 52%	2153
	21st to end	Day	17% 7% 3 5% 3 4 4 3 5% 5% 44%	3124
January	1st to 10th	Night	17% 6% 2 5% 3 3 3 2 3 4 50%	4109
	11th to 20th	Night	11% 6% 3 6% 4 4 4 4 5% 5% 48%	4120
	21st to end	Night	21% 9% 2 5% 3 3 3 2 4 4 44%	4532
February	1st to 10th	Night	16% 7% 3 6% 4 4 3 3 4 5% 45%	2470
	11th to 20th	Night	20% 7% 2 5% 4 3 3 3 5% 5% 43%	2252
	21st to end	Night	16% 7% 2 5% 4 3 3 3 6% 6% 44%	1822
March	1st to 10th	Night	23% 9% 3 7% 4 3 3 3 4 6% 36%	3418
	11th to 20th	Night	12% 5% 2 5% 3 3 4 4 5% 7% 51%	3480
	21st to end	Night	19% 4 2 5% 4 4 4 3 5% 6% 44%	3817
April	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 6% 7% 48%	2085
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 5% 6% 51%	1875
	21st to end	Night	11% 5% 2 6% 4 3 3 4 5% 6% 51%	1792
May	1st to 10th	Night	14% 7% 2 6% 4 3 5% 3 5% 8% 42%	2813
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 3 5% 7% 38%	2812
	21st to end	Night	8% 4 2 6% 4 5% 5% 5% 8% 11% 43%	3079
June	1st to 10th	Night	9% 7% 2 8% 6% 6% 5% 6% 6% 10% 35%	1710
	11th to 20th	Night	11% 5% 2 6% 6% 5% 5% 5% 8% 12% 35%	1710
	21st to end	Night	7% 6% 2 5% 6% 6% 6% 6% 8% 11% 37%	1710
July	1st to 10th	Night	8% 6% 2 8% 7% 6% 6% 5% 9% 11% 32%	1638
	11th to 20th	Night	7% 6% 2 6% 5% 5% 6% 6% 8% 13% 35%	1620
	21st to end	Night	5% 7% 2 8% 6% 6% 6% 6% 9% 12% 33%	1771
August	1st to 10th	Night	10% 6% 3 7% 4 6% 5% 5% 9% 12% 33%	1611
	11th to 20th	Night	9% 8% 3 10% 7% 5% 5% 5% 7% 9% 33%	1598
	21st to end	Night	9% 6% 2 8% 6% 6% 5% 5% 9% 10% 34%	1934
September	1st to 10th	Night	9% 5% 2 6% 4 5% 6% 4 5% 10% 44%	1935
	11th to 20th	Night	12% 7% 2 7% 4 4 5% 4 6% 8% 41%	1980
	21st to end	Night	18% 5% 2 6% 4 5% 5% 4 5% 6% 39%	1980
October	1st to 10th	Night	14% 5% 2 4 3 3 4 3 3 6% 52%	2096
	11th to 20th	Night	14% 5% 3 4 3 3 3 3 4 6% 53%	2160
	21st to end	Night	12% 6% 2 5% 3 3 3 2 4 5% 56%	2376
November	1st to 10th	Night	14% 5% 2 4 3 3 2 3 4 6% 54%	2221
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 4 6% 52%	2398
	21st to end	Night	14% 5% 2 4 4 4 4 3 5% 7% 49%	2470
December	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 4 5% 41%	2470
	11th to 20th	Night	17% 7% 2 4 3 3 3 2 3 5% 51%	3042
	21st to end	Night	19% 5% 2 5% 4 4 4 4 5% 6% 43%	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	23% 36% 2 18% 16% 5%	2837
	11th to 20th	Day	21% 37% 3 10% 24% 4	2840
	21st to end	Day	29% 40% 3 9% 17% 3	3124
February	1st to 10th	Day	15% 65% 2 9% 7% 2	1710
	11th to 20th	Day	17% 64% 3 6% 9% 2	1823
	21st to end	Day	18% 65% 3 4 8% 2	1632
March	1st to 10th	Day	35% 42% 5% 7% 5% 6%	3435
	11th to 20th	Day	15% 40% 4 9% 24% 9%	3480
	21st to end	Day	27% 40% 2 13% 16% 2	3815
April	1st to 10th	Day	13% 65% 3 7% 9% 2	2093
	11th to 20th	Day	16% 66% 3 6% 7% 2	2254
	21st to end	Day	12% 65% 4 10% 8% 1	2403
May	1st to 10th	Day	27% 44% 9% 12% 7% 1	4120
	11th to 20th	Day	29% 41% 5% 14% 10%	4085
	21st to end	Day	16% 42% 11% 12% 15% 3	4489
June	1st to 10th	Day	14% 67% 6% 9% 4 1	2470
	11th to 20th	Day	10% 66% 7% 10% 6%	2470
	21st to end	Day	14% 65% 6% 9% 6%	2470
July	1st to 10th	Day	15% 65% 9% 8% 3	2301
	11th to 20th	Day	13% 65% 9% 10% 2	2271
	21st to end	Day	14% 63% 6% 11% 4 1	2405
August	1st to 10th	Day	19% 65% 7% 7% 2	2314
	11th to 20th	Day	16% 66% 6% 7% 4 1	2303
	21st to end	Day	13% 65% 8% 9% 4 2	2404
September	1st to 10th	Day	13% 65% 5% 9% 7% 1	2020
	11th to 20th	Day	14% 64% 5% 7% 8% 1	1980
	21st to end	Day	19% 64% 3 8% 5% 1	1980
October	1st to 10th	Day	13% 63% 5% 9% 9% 1	1862
	11th to 20th	Day	11% 63% 4 11% 8% 3	1800
	21st to end	Day	11% 61% 2 8% 12% 5%	1980
November	1st to 10th	Day	17% 59% 2 8% 11% 4	1857
	11th to 20th	Day	14% 59% 3 9% 12% 3	1777
	21st to end	Day	14% 60% 5% 9% 10% 3	1710
December	1st to 10th	Day	21% 60% 3 8% 5% 2	1710
	11th to 20th	Day	15% 47% 2 11% 20% 6%	2150
	21st to end	Day	28% 38% 4 15% 13% 2	3124
January	1st to 10th	Night	25% 36% 3 11% 19% 5%	4109
	11th to 20th	Night	23% 37% 4 9% 21% 5%	4120
	21st to end	Night	29% 39% 2 9% 17% 4	4532
February	1st to 10th	Night	14% 65% 4 8% 8% 2	2470
	11th to 20th	Night	19% 63% 2 6% 7% 2	2253
	21st to end	Night	14% 65% 3 7% 8% 3	1822
March	1st to 10th	Night	37% 42% 6% 7% 5% 3	3418
	11th to 20th	Night	17% 40% 3 9% 18% 13%	3480
	21st to end	Night	25% 40% 3 12% 14% 6%	3817
April	1st to 10th	Night	14% 65% 3 7% 9% 3	2085
	11th to 20th	Night	14% 67% 3 8% 6% 3	1875
	21st to end	Night	11% 65% 5% 11% 6% 2	1792
May	1st to 10th	Night	25% 43% 8% 15% 8% 1	2840
	11th to 20th	Night	27% 42% 7% 15% 10%	2813
	21st to end	Night	16% 43% 10% 19% 10% 2	3087
June	1st to 10th	Night	15% 67% 5% 9% 3 1	1710
	11th to 20th	Night	12% 67% 7% 8% 6%	1710
	21st to end	Night	14% 66% 7% 7% 5% 1	1710
July	1st to 10th	Night	15% 65% 11% 7% 2	1593
	11th to 20th	Night	13% 66% 9% 9% 3	1566
	21st to end	Night	13% 64% 7% 10% 4 1	1672
August	1st to 10th	Night	18% 66% 8% 6% 2	1600
	11th to 20th	Night	15% 67% 9% 6% 4 1	1598
	21st to end	Night	12% 66% 7% 11% 4 2	1934
September	1st to 10th	Night	11% 65% 7% 8% 7% 1	1935
	11th to 20th	Night	15% 65% 6% 6% 7% 1	1980
	21st to end	Night	19% 65% 4 7% 4	1980
October	1st to 10th	Night	13% 64% 4 8% 9% 2	2096
	11th to 20th	Night	10% 63% 5% 11% 7% 4	2160
	21st to end	Night	10% 62% 2 8% 13% 5%	2376
November	1st to 10th	Night	18% 58% 2 7% 11% 4	2221
	11th to 20th	Night	15% 59% 2 6% 11% 6%	2398
	21st to end	Night	14% 60% 2 10% 11% 2	2470
December	1st to 10th	Night	23% 60% 2 7% 7% 2	2470
	11th to 20th	Night	18% 48% 2 8% 17% 7%	3044
	21st to end	Night	26% 38% 5% 13% 16% 1	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	23% 10% 41% 20% 4	270
	11th to 20th	Day	21% 18% 31% 23% 6% 1	270
	21st to end	Day	20% 17% 38% 18% 6% 1	297
February	1st to 10th	Day	19% 15% 38% 18% 8% 1	270
	11th to 20th	Day	35% 10% 40% 13% 3	270
	21st to end	Day	25% 15% 36% 19% 5%	287
March	1st to 10th	Day	22% 8% 36% 24% 9% 2	460
	11th to 20th	Day	20% 8% 42% 22% 7% 1	460
	21st to end	Day	21% 10% 35% 25% 7% 1	506
April	1st to 10th	Day	18% 13% 32% 22% 12% 3	460
	11th to 20th	Day	15% 10% 33% 24% 15% 4	452
	21st to end	Day	16% 7% 25% 30% 17% 5%	460
May	1st to 10th	Day	11% 9% 33% 25% 17% 5%	463
	11th to 20th	Day	17% 4 17% 29% 22% 12%	487
	21st to end	Day	12% 2 14% 25% 28% 18%	529
June	1st to 10th	Day	11% 3 11% 32% 30% 13%	490
	11th to 20th	Day	12% 3 14% 24% 27% 20%	490
	21st to end	Day	9% 1 9% 32% 31% 18%	490
July	1st to 10th	Day	9% 2 7% 20% 36% 27%	453
	11th to 20th	Day	10% 1 6% 23% 34% 25%	444
	21st to end	Day	7% 2 5% 24% 39% 23%	488
August	1st to 10th	Day	14% 2 8% 24% 28% 25%	446
	11th to 20th	Day	13% 3 6% 21% 32% 26%	439
	21st to end	Day	14% 2 7% 24% 29% 25%	495
September	1st to 10th	Day	11% 2 8% 23% 35% 21%	450
	11th to 20th	Day	15% 4 10% 20% 32% 19%	450
	21st to end	Day	18% 4 15% 27% 27% 10%	450
October	1st to 10th	Day	18% 3 16% 25% 24% 14%	450
	11th to 20th	Day	13% 5% 21% 27% 24% 10%	450
	21st to end	Day	15% 3 23% 31% 19% 8%	495
November	1st to 10th	Day	18% 4 24% 29% 19% 6%	455
	11th to 20th	Day	17% 7% 34% 28% 11% 3	337
	21st to end	Day	14% 8% 32% 30% 13% 3	270
December	1st to 10th	Day	25% 10% 35% 21% 9%	270
	11th to 20th	Day	20% 7% 32% 29% 9% 3	270
	21st to end	Day	24% 12% 33% 21% 8% 2	297
January	1st to 10th	Night	21% 9% 35% 28% 7%	760
	11th to 20th	Night	20% 9% 33% 32% 6%	760
	21st to end	Night	20% 7% 38% 32% 4	836
February	1st to 10th	Night	19% 7% 36% 33% 4	760
	11th to 20th	Night	25% 8% 39% 26% 2	743
	21st to end	Night	20% 10% 39% 26% 5%	628
March	1st to 10th	Night	18% 8% 33% 36% 5%	760
	11th to 20th	Night	18% 9% 36% 27% 9% 1	760
	21st to end	Night	20% 8% 31% 33% 7%	836
April	1st to 10th	Night	14% 12% 34% 30% 10%	760
	11th to 20th	Night	14% 9% 27% 33% 15% 1	751
	21st to end	Night	13% 4 27% 39% 16%	652
May	1st to 10th	Night	12% 6% 26% 39% 16%	570
	11th to 20th	Night	15% 4 20% 35% 25% 1	561
	21st to end	Night	13% 2 9% 37% 35% 3	617
June	1st to 10th	Night	13% 2 11% 40% 28% 5%	570
	11th to 20th	Night	13% 2 12% 28% 38% 7%	570
	21st to end	Night	8% 2 11% 36% 38% 6%	570
July	1st to 10th	Night	10% 2 6% 31% 42% 9%	531
	11th to 20th	Night	10% 2 4 27% 48% 9%	522
	21st to end	Night	6% 2 7% 30% 47% 8%	591
August	1st to 10th	Night	12% 2 5% 28% 43% 9%	537
	11th to 20th	Night	11% 3 4 28% 46% 7%	534
	21st to end	Night	10% 2 5% 26% 48% 8%	746
September	1st to 10th	Night	11% 2 6% 28% 47% 7%	720
	11th to 20th	Night	15% 3 8% 26% 41% 7%	720
	21st to end	Night	20% 3 12% 33% 29% 4	720
October	1st to 10th	Night	16% 3 16% 29% 29% 7%	720
	11th to 20th	Night	17% 4 21% 32% 23% 3	720
	21st to end	Night	14% 5% 23% 34% 21% 3	792
November	1st to 10th	Night	17% 4 21% 35% 20% 3	740
	11th to 20th	Night	15% 6% 30% 36% 13% 1	760
	21st to end	Night	15% 5% 26% 39% 14% 1	760
December	1st to 10th	Night	21% 6% 29% 36% 7%	760
	11th to 20th	Night	20% 5% 25% 38% 12%	760
	21st to end	Night	25% 7% 25% 34% 9%	836

Page generated at 2024-06-29 22:08:51. Version ac07

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