BarCla Hill Private Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BarCla Hill Private Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	12% 5% 3 6% 6% 4 5% 5% 6% 8% 40%	74860
	Night	11% 5% 2 5% 5% 3 4 5% 6% 8% 46%	74839
Transparency	Day	39% 8% 12% 18% 17% 7%	74606
	Night	35% 7% 13% 19% 18% 8%	74614
Seeing	Day	13% 9% 21% 25% 21% 10%	13291
	Night	13% 6% 20% 29% 24% 7%	23105

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	16% 7% 2 4 5% 3 3 4 5% 6% 44%	1896
	11th to 20th	Day	16% 6% 3 5% 5% 2 3 3 4 7% 47%	1826
	21st to end	Day	20% 5% 3 5% 5% 2 4 4 4 4 44%	1980
February	1st to 10th	Day	19% 6% 3 5% 6% 3 4 3 5% 5% 41%	1800
	11th to 20th	Day	18% 5% 3 5% 4 3 4 3 4 7% 44%	1748
	21st to end	Day	18% 7% 3 7% 5% 4 5% 4 6% 7% 36%	1480
March	1st to 10th	Day	14% 5% 3 5% 6% 3 4 4 6% 7% 44%	1800
	11th to 20th	Day	15% 6% 4 6% 6% 3 5% 5% 4 8% 40%	1966
	21st to end	Day	12% 5% 2 5% 5% 3 5% 5% 6% 7% 46%	2335
April	1st to 10th	Day	11% 5% 3 5% 6% 4 5% 6% 6% 8% 41%	2160
	11th to 20th	Day	15% 6% 3 5% 5% 3 4 5% 7% 7% 40%	2134
	21st to end	Day	10% 4 2 4 5% 3 4 5% 6% 9% 48%	2160
May	1st to 10th	Day	11% 4 3 4 4 2 4 5% 6% 8% 48%	2160
	11th to 20th	Day	10% 5% 3 6% 6% 4 5% 6% 6% 7% 42%	2124
	21st to end	Day	8% 4 3 6% 6% 4 7% 6% 7% 11% 37%	2439
June	1st to 10th	Day	10% 4 3 7% 8% 5% 8% 7% 8% 10% 30%	2340
	11th to 20th	Day	5% 4 2 6% 8% 5% 8% 7% 8% 13% 34%	2340
	21st to end	Day	8% 6% 3 7% 9% 5% 8% 8% 8% 11% 26%	2363
July	1st to 10th	Day	8% 5% 4 9% 9% 6% 8% 9% 7% 11% 23%	2261
	11th to 20th	Day	10% 6% 3 8% 8% 6% 9% 8% 8% 10% 25%	2160
	21st to end	Day	8% 6% 3 8% 8% 5% 7% 9% 9% 11% 27%	2350
August	1st to 10th	Day	6% 4 3 8% 9% 5% 8% 9% 10% 11% 28%	2148
	11th to 20th	Day	11% 6% 4 7% 9% 5% 9% 7% 8% 8% 25%	2125
	21st to end	Day	10% 5% 4 8% 7% 5% 7% 8% 7% 9% 30%	2376
September	1st to 10th	Day	9% 6% 3 7% 8% 4 6% 6% 7% 8% 34%	2160
	11th to 20th	Day	10% 6% 2 6% 8% 4 6% 5% 6% 7% 38%	2054
	21st to end	Day	9% 4 2 5% 6% 3 5% 4 7% 7% 46%	1980
October	1st to 10th	Day	6% 4 2 4 5% 4 5% 5% 4 7% 55%	1980
	11th to 20th	Day	8% 4 2 4 5% 2 5% 4 5% 7% 55%	1823
	21st to end	Day	10% 4 2 4 4 3 4 3 5% 7% 55%	1980
November	1st to 10th	Day	9% 5% 2 4 3 2 4 4 4 6% 58%	1836
	11th to 20th	Day	11% 4 2 4 4 2 4 3 5% 6% 56%	1710
	21st to end	Day	12% 6% 2 5% 5% 3 4 4 5% 7% 46%	1710
December	1st to 10th	Day	14% 7% 3 5% 5% 2 4 3 5% 7% 45%	1710
	11th to 20th	Day	16% 8% 3 6% 5% 3 4 4 5% 6% 40%	2153
	21st to end	Day	18% 8% 2 5% 5% 4 5% 4 5% 7% 39%	3293
January	1st to 10th	Night	17% 6% 3 4 4 2 4 4 4 7% 46%	2269
	11th to 20th	Night	15% 7% 3 4 4 3 4 4 4 5% 48%	2196
	21st to end	Night	20% 7% 3 5% 4 2 3 5% 3 4 44%	2376
February	1st to 10th	Night	17% 6% 3 4 5% 3 4 4 5% 6% 44%	2160
	11th to 20th	Night	19% 6% 3 4 4 2 3 4 5% 7% 43%	2098
	21st to end	Night	19% 7% 3 7% 6% 3 3 5% 5% 6% 35%	1776
March	1st to 10th	Night	15% 6% 3 4 5% 3 4 4 5% 7% 44%	2160
	11th to 20th	Night	14% 7% 3 5% 5% 3 6% 5% 5% 8% 40%	2008
	21st to end	Night	13% 5% 2 4 4 2 3 4 5% 8% 51%	2021
April	1st to 10th	Night	15% 7% 2 5% 5% 2 4 3 5% 6% 46%	1800
	11th to 20th	Night	14% 5% 2 5% 5% 2 4 4 5% 7% 46%	1775
	21st to end	Night	7% 3 2 4 4 2 4 4 5% 8% 58%	1800
May	1st to 10th	Night	11% 3 2 3 3 2 4 4 5% 8% 55%	1800
	11th to 20th	Night	5% 4 3 5% 5% 3 6% 6% 7% 9% 47%	1769
	21st to end	Night	6% 2 2 5% 5% 3 5% 5% 8% 12% 47%	1831
June	1st to 10th	Night	8% 5% 2 5% 6% 3 5% 8% 7% 11% 40%	1620
	11th to 20th	Night	3 3 1 4 5% 3 5% 7% 8% 13% 48%	1620
	21st to end	Night	7% 5% 2 6% 4 3 6% 8% 8% 11% 40%	1566
July	1st to 10th	Night	6% 5% 2 5% 5% 3 7% 6% 8% 11% 41%	1678
	11th to 20th	Night	3 4 3 6% 6% 4 6% 5% 9% 13% 41%	1800
	21st to end	Night	5% 5% 3 5% 5% 4 5% 6% 9% 14% 40%	1968
August	1st to 10th	Night	2 3 2 4 5% 3 4 6% 8% 12% 50%	1790
	11th to 20th	Night	5% 4 2 5% 7% 4 6% 8% 11% 14% 34%	1776
	21st to end	Night	8% 4 2 5% 6% 4 6% 7% 8% 13% 38%	1980
September	1st to 10th	Night	7% 5% 3 5% 6% 4 5% 7% 7% 11% 40%	1800
	11th to 20th	Night	7% 6% 2 5% 4 4 4 5% 6% 9% 46%	1885
	21st to end	Night	7% 5% 3 4 6% 3 4 5% 5% 7% 51%	1980
October	1st to 10th	Night	6% 4 1 4 5% 2 4 4 4 7% 59%	1980
	11th to 20th	Night	7% 3 2 3 3 2 3 4 4 7% 62%	2132
	21st to end	Night	11% 5% 2 4 3 2 3 4 4 6% 56%	2376
November	1st to 10th	Night	11% 4 1 3 4 3 3 3 4 6% 57%	2239
	11th to 20th	Night	11% 5% 2 4 4 2 4 4 4 6% 55%	2470
	21st to end	Night	11% 6% 3 5% 5% 3 4 4 5% 6% 48%	2470
December	1st to 10th	Night	15% 6% 2 5% 4 3 3 3 4 7% 45%	2470
	11th to 20th	Night	15% 7% 2 5% 4 3 5% 5% 5% 6% 43%	3042
	21st to end	Night	18% 8% 3 6% 5% 3 4 4 4 6% 39%	4358

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% 16% 23% 10%	1897
	11th to 20th	Day	39% 4 7% 16% 25% 10%	1826
	21st to end	Day	44% 4 4 16% 21% 11%	1980
February	1st to 10th	Day	46% 4 8% 13% 19% 11%	1800
	11th to 20th	Day	41% 5% 8% 17% 19% 11%	1758
	21st to end	Day	47% 5% 9% 15% 16% 9%	1480
March	1st to 10th	Day	39% 5% 8% 20% 20% 8%	1800
	11th to 20th	Day	42% 7% 9% 14% 20% 8%	1966
	21st to end	Day	37% 6% 11% 19% 20% 7%	2335
April	1st to 10th	Day	36% 8% 11% 19% 17% 9%	2160
	11th to 20th	Day	40% 6% 8% 19% 19% 8%	2134
	21st to end	Day	31% 6% 10% 23% 23% 7%	2160
May	1st to 10th	Day	33% 6% 11% 23% 21% 7%	2160
	11th to 20th	Day	37% 8% 14% 21% 18% 2	2128
	21st to end	Day	36% 11% 13% 23% 15% 3	2439
June	1st to 10th	Day	43% 10% 15% 21% 9% 1	2340
	11th to 20th	Day	36% 12% 16% 25% 10% 2	2340
	21st to end	Day	44% 12% 19% 15% 9%	2363
July	1st to 10th	Day	48% 15% 19% 15% 4	2201
	11th to 20th	Day	47% 13% 21% 15% 3 1	2097
	21st to end	Day	43% 12% 22% 18% 4	2219
August	1st to 10th	Day	41% 14% 21% 17% 7%	2136
	11th to 20th	Day	50% 13% 18% 14% 5% 1	2125
	21st to end	Day	44% 14% 17% 16% 8% 2	2376
September	1st to 10th	Day	41% 12% 14% 18% 11% 5%	2160
	11th to 20th	Day	40% 11% 13% 15% 15% 7%	2054
	21st to end	Day	34% 8% 11% 22% 17% 9%	1980
October	1st to 10th	Day	27% 6% 11% 20% 21% 14%	1980
	11th to 20th	Day	28% 6% 8% 18% 27% 14%	1823
	21st to end	Day	30% 4 6% 16% 27% 17%	1980
November	1st to 10th	Day	28% 4 8% 20% 27% 12%	1836
	11th to 20th	Day	29% 5% 7% 18% 29% 12%	1710
	21st to end	Day	37% 4 8% 18% 20% 12%	1710
December	1st to 10th	Day	39% 4 9% 19% 20% 7%	1710
	11th to 20th	Day	43% 5% 7% 14% 21% 9%	2150
	21st to end	Day	45% 5% 8% 17% 21% 5%	3293
January	1st to 10th	Night	38% 4 8% 16% 25% 9%	2269
	11th to 20th	Night	39% 4 6% 17% 24% 11%	2196
	21st to end	Night	43% 4 5% 12% 25% 10%	2376
February	1st to 10th	Night	42% 4 8% 17% 19% 10%	2160
	11th to 20th	Night	43% 4 5% 16% 20% 12%	2099
	21st to end	Night	46% 7% 9% 14% 12% 12%	1776
March	1st to 10th	Night	39% 5% 8% 15% 23% 9%	2160
	11th to 20th	Night	40% 7% 13% 15% 18% 7%	2008
	21st to end	Night	33% 5% 12% 19% 23% 8%	2021
April	1st to 10th	Night	39% 5% 11% 17% 17% 11%	1800
	11th to 20th	Night	37% 5% 10% 22% 18% 8%	1775
	21st to end	Night	26% 5% 11% 25% 25% 9%	1800
May	1st to 10th	Night	29% 4 11% 27% 23% 6%	1800
	11th to 20th	Night	31% 9% 16% 22% 18% 3	1770
	21st to end	Night	29% 8% 18% 27% 16% 3	1832
June	1st to 10th	Night	34% 11% 20% 25% 10% 1	1620
	11th to 20th	Night	24% 12% 25% 27% 11% 1	1620
	21st to end	Night	34% 11% 25% 20% 9% 1	1566
July	1st to 10th	Night	34% 13% 28% 20% 4	1630
	11th to 20th	Night	30% 15% 32% 19% 3 1	1740
	21st to end	Night	31% 13% 29% 23% 4	1858
August	1st to 10th	Night	23% 12% 35% 23% 7%	1778
	11th to 20th	Night	33% 17% 27% 17% 5% 1	1776
	21st to end	Night	36% 14% 24% 17% 6% 3	1980
September	1st to 10th	Night	35% 11% 18% 17% 13% 6%	1800
	11th to 20th	Night	32% 10% 19% 17% 14% 8%	1885
	21st to end	Night	31% 6% 13% 23% 17% 9%	1980
October	1st to 10th	Night	25% 6% 11% 21% 22% 16%	1980
	11th to 20th	Night	23% 5% 10% 22% 26% 14%	2132
	21st to end	Night	30% 4 6% 16% 27% 17%	2376
November	1st to 10th	Night	30% 3 8% 18% 26% 15%	2239
	11th to 20th	Night	30% 4 7% 17% 28% 14%	2470
	21st to end	Night	36% 4 6% 21% 20% 13%	2470
December	1st to 10th	Night	39% 4 9% 20% 21% 7%	2470
	11th to 20th	Night	40% 6% 8% 14% 20% 13%	3044
	21st to end	Night	46% 5% 7% 18% 18% 6%	4358

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% 14% 39% 17% 6% 1	270
	11th to 20th	Day	22% 17% 31% 23% 5% 2	248
	21st to end	Day	21% 25% 37% 14% 3	264
February	1st to 10th	Day	28% 21% 35% 12% 5%	240
	11th to 20th	Day	30% 20% 28% 15% 6%	240
	21st to end	Day	16% 30% 40% 12% 2	198
March	1st to 10th	Day	14% 24% 41% 18% 3	240
	11th to 20th	Day	24% 22% 33% 17% 4	240
	21st to end	Day	19% 17% 31% 22% 10% 1	421
April	1st to 10th	Day	16% 15% 34% 24% 10% 1	420
	11th to 20th	Day	18% 17% 31% 19% 12% 3	412
	21st to end	Day	11% 12% 29% 30% 16% 2	420
May	1st to 10th	Day	13% 11% 27% 27% 17% 5%	423
	11th to 20th	Day	13% 5% 22% 31% 23% 7%	447
	21st to end	Day	7% 3 18% 36% 26% 10%	485
June	1st to 10th	Day	12% 4 12% 33% 22% 18%	450
	11th to 20th	Day	8% 3 13% 31% 29% 16%	450
	21st to end	Day	10% 3 12% 29% 27% 18%	528
July	1st to 10th	Day	9% 1 6% 29% 32% 23%	546
	11th to 20th	Day	10% 2 4 18% 39% 27%	444
	21st to end	Day	8% 2 5% 25% 38% 22%	488
August	1st to 10th	Day	5% 2 6% 21% 37% 29%	446
	11th to 20th	Day	10% 2 4 19% 37% 28%	439
	21st to end	Day	10% 3 9% 20% 34% 23%	495
September	1st to 10th	Day	8% 3 5% 27% 38% 19%	450
	11th to 20th	Day	12% 3 11% 26% 35% 13%	450
	21st to end	Day	8% 4 11% 34% 31% 12%	450
October	1st to 10th	Day	6% 5% 23% 35% 24% 7%	450
	11th to 20th	Day	8% 7% 23% 35% 23% 6%	293
	21st to end	Day	18% 11% 22% 35% 11% 4	297
November	1st to 10th	Day	14% 8% 25% 35% 17% 1	270
	11th to 20th	Day	17% 11% 31% 26% 13% 2	270
	21st to end	Day	15% 15% 36% 23% 8% 3	270
December	1st to 10th	Day	18% 12% 34% 25% 10% 1	270
	11th to 20th	Day	21% 17% 36% 21% 4	270
	21st to end	Day	27% 16% 29% 18% 9% 1	297
January	1st to 10th	Night	21% 11% 32% 29% 6%	760
	11th to 20th	Night	17% 11% 29% 35% 8%	732
	21st to end	Night	22% 12% 32% 28% 5%	792
February	1st to 10th	Night	19% 13% 34% 29% 5%	720
	11th to 20th	Night	23% 13% 28% 28% 7%	703
	21st to end	Night	20% 16% 34% 26% 4	592
March	1st to 10th	Night	17% 13% 33% 31% 7%	720
	11th to 20th	Night	15% 9% 29% 31% 14% 1	568
	21st to end	Night	15% 9% 30% 32% 13% 1	594
April	1st to 10th	Night	18% 10% 28% 29% 15% 1	540
	11th to 20th	Night	15% 8% 29% 29% 17% 1	533
	21st to end	Night	9% 5% 25% 40% 20% 1	540
May	1st to 10th	Night	11% 4 21% 40% 22% 2	540
	11th to 20th	Night	7% 2 17% 40% 30% 4	531
	21st to end	Night	6% 2 11% 34% 39% 8%	584
June	1st to 10th	Night	10% 2 7% 30% 40% 10%	540
	11th to 20th	Night	4 1 5% 30% 44% 15%	540
	21st to end	Night	8% 2 5% 24% 43% 18%	540
July	1st to 10th	Night	8% 2 4 17% 47% 23%	525
	11th to 20th	Night	3 1 3 12% 49% 32%	522
	21st to end	Night	5% 1 5% 18% 44% 27%	591
August	1st to 10th	Night	3 2 14% 49% 31%	537
	11th to 20th	Night	6% 1 2 10% 52% 29%	534
	21st to end	Night	9% 2 5% 16% 46% 23%	594
September	1st to 10th	Night	9% 2 4 21% 44% 21%	540
	11th to 20th	Night	9% 3 8% 27% 42% 11%	625
	21st to end	Night	9% 1 9% 34% 40% 7%	720
October	1st to 10th	Night	8% 1 16% 37% 33% 5%	720
	11th to 20th	Night	10% 3 19% 35% 27% 6%	720
	21st to end	Night	14% 5% 20% 35% 23% 2	792
November	1st to 10th	Night	13% 6% 16% 41% 22% 3	740
	11th to 20th	Night	14% 7% 27% 34% 16% 2	760
	21st to end	Night	14% 8% 28% 34% 15% 1	760
December	1st to 10th	Night	18% 9% 28% 31% 14% 1	760
	11th to 20th	Night	20% 8% 29% 32% 11% 1	760
	21st to end	Night	26% 10% 30% 26% 7%	836

Page generated at 2024-01-10 18:35:25. Version ac07

Copyright 2024 Attilla Danko