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 2024-11-12.

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	11% 6% 2 7% 5% 5% 5% 5% 7% 8% 39%	100627
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 45%	98472
Transparency	Day	38% 7% 12% 18% 17% 7%	104437
	Night	35% 7% 13% 18% 18% 9%	102802
Seeing	Day	14% 9% 21% 25% 21% 10%	14414
	Night	13% 6% 20% 29% 24% 7%	24130

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% 6% 2 6% 4 3 4 4 5% 7% 44%	3156
	11th to 20th	Day	12% 5% 2 5% 3 3 2 3 4 6% 55%	3160
	21st to end	Day	26% 7% 2 5% 4 3 4 3 4 5% 38%	3476
February	1st to 10th	Day	18% 7% 3 6% 5% 4 4 3 5% 5% 41%	1900
	11th to 20th	Day	18% 6% 2 5% 3 4 3 3 4 7% 44%	1848
	21st to end	Day	17% 7% 2 8% 4 5% 4 3 6% 7% 37%	1570
March	1st to 10th	Day	22% 9% 3 7% 5% 4 4 3 5% 6% 31%	3120
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 4 5% 9% 36%	3466
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 6% 6% 42%	4096
April	1st to 10th	Day	12% 6% 2 5% 5% 5% 5% 5% 6% 8% 41%	2280
	11th to 20th	Day	15% 6% 3 6% 4 3 4 5% 7% 7% 39%	2254
	21st to end	Day	10% 5% 1 5% 5% 4 5% 4 6% 8% 48%	2280
May	1st to 10th	Day	10% 5% 3 7% 5% 5% 6% 5% 7% 9% 38%	3765
	11th to 20th	Day	14% 6% 3 6% 5% 4 3 4 6% 7% 41%	3764
	21st to end	Day	6% 4 2 5% 5% 5% 6% 4 7% 11% 45%	4314
June	1st to 10th	Day	10% 5% 3 8% 6% 6% 8% 6% 8% 10% 30%	2470
	11th to 20th	Day	5% 5% 1 7% 7% 7% 7% 6% 8% 12% 34%	2470
	21st to end	Day	8% 7% 3 8% 8% 7% 7% 7% 8% 11% 26%	2494
July	1st to 10th	Day	6% 6% 3 10% 8% 8% 9% 7% 9% 12% 22%	3971
	11th to 20th	Day	6% 5% 2 8% 8% 9% 8% 6% 10% 11% 27%	3800
	21st to end	Day	6% 6% 3 10% 8% 8% 8% 8% 10% 13% 20%	4118
August	1st to 10th	Day	4 3 2 6% 4 5% 6% 6% 8% 10% 47%	3785
	11th to 20th	Day	6% 4 2 6% 6% 7% 7% 6% 9% 11% 35%	3729
	21st to end	Day	7% 6% 4 11% 7% 7% 7% 6% 7% 8% 31%	4180
September	1st to 10th	Day	11% 7% 3 8% 7% 5% 6% 5% 7% 8% 33%	2280
	11th to 20th	Day	10% 7% 2 7% 6% 6% 6% 4 6% 7% 38%	2168
	21st to end	Day	8% 4 2 6% 4 5% 5% 3 7% 7% 48%	2090
October	1st to 10th	Day	7% 4 2 5% 4 5% 4 4 5% 6% 55%	2090
	11th to 20th	Day	7% 4 1 5% 4 4 5% 3 5% 7% 56%	1924
	21st to end	Day	9% 4 2 5% 4 3 3 2 5% 7% 57%	2090
November	1st to 10th	Day	10% 5% 2 5% 2 3 4 3 4 7% 55%	1934
	11th to 20th	Day	11% 4 1 4 4 2 4 3 4 6% 56%	1719
	21st to end	Day	12% 7% 2 6% 4 4 4 4 5% 7% 46%	1710
December	1st to 10th	Day	14% 7% 2 6% 4 4 4 2 5% 6% 45%	1710
	11th to 20th	Day	16% 9% 3 6% 4 4 4 4 5% 6% 40%	2153
	21st to end	Day	18% 8% 2 6% 4 5% 4 3 5% 7% 39%	3293
January	1st to 10th	Night	17% 6% 2 4 4 3 4 3 4 6% 47%	3789
	11th to 20th	Night	16% 7% 2 4 3 3 2 3 4 5% 53%	3800
	21st to end	Night	26% 7% 2 5% 3 2 3 3 3 5% 41%	4180
February	1st to 10th	Night	17% 7% 2 6% 4 3 4 3 5% 6% 44%	2280
	11th to 20th	Night	20% 7% 3 4 4 3 3 3 4 7% 42%	2218
	21st to end	Night	18% 8% 3 8% 5% 3 4 4 5% 6% 37%	1884
March	1st to 10th	Night	24% 12% 3 7% 4 4 4 3 4 6% 30%	3733
	11th to 20th	Night	15% 8% 2 6% 4 5% 5% 4 5% 8% 39%	3522
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 6% 44%	3535
April	1st to 10th	Night	15% 8% 2 5% 5% 3 3 3 5% 6% 44%	1900
	11th to 20th	Night	14% 6% 2 5% 5% 3 5% 3 5% 8% 45%	1875
	21st to end	Night	7% 4 1 5% 4 3 4 3 5% 8% 57%	1900
May	1st to 10th	Night	14% 6% 2 7% 4 4 4 3 5% 7% 44%	3130
	11th to 20th	Night	13% 6% 3 6% 5% 4 5% 3 6% 8% 42%	3129
	21st to end	Night	6% 3 2 5% 4 4 5% 4 8% 14% 46%	3236
June	1st to 10th	Night	8% 5% 2 6% 5% 4 6% 6% 7% 11% 40%	1710
	11th to 20th	Night	3 3 1 5% 5% 4 6% 6% 8% 12% 47%	1710
	21st to end	Night	7% 5% 1 6% 4 5% 6% 6% 8% 11% 40%	1653
July	1st to 10th	Night	4 5% 2 6% 6% 6% 7% 6% 9% 14% 36%	2960
	11th to 20th	Night	2 4 2 6% 5% 6% 5% 4 9% 13% 45%	3160
	21st to end	Night	4 5% 3 7% 6% 6% 7% 6% 11% 16% 30%	3435
August	1st to 10th	Night	1 2 1 3 3 4 4 5% 7% 12% 58%	3144
	11th to 20th	Night	3 3 2 5% 5% 5% 5% 5% 10% 13% 43%	3100
	21st to end	Night	5% 4 2 7% 5% 6% 8% 6% 9% 11% 39%	3476
September	1st to 10th	Night	8% 6% 3 7% 5% 5% 5% 5% 8% 10% 38%	1900
	11th to 20th	Night	8% 6% 2 6% 4 5% 4 5% 6% 9% 45%	1990
	21st to end	Night	7% 5% 2 5% 5% 4 4 4 5% 7% 52%	2090
October	1st to 10th	Night	7% 4 1 5% 4 3 4 3 4 7% 58%	2090
	11th to 20th	Night	6% 4 2 4 3 2 3 3 4 7% 63%	2251
	21st to end	Night	10% 4 2 4 3 3 3 3 4 6% 58%	2508
November	1st to 10th	Night	11% 4 1 5% 4 4 3 2 5% 5% 56%	2360
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 4 6% 55%	2484
	21st to end	Night	11% 6% 2 6% 4 4 4 3 5% 6% 48%	2470
December	1st to 10th	Night	15% 7% 2 6% 4 4 3 3 5% 7% 45%	2470
	11th to 20th	Night	15% 7% 2 5% 4 4 4 4 5% 6% 42%	3042
	21st to end	Night	18% 9% 2 7% 4 4 4 3 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	39% 4 6% 16% 22% 13%	3157
	11th to 20th	Day	30% 4 7% 17% 30% 11%	3160
	21st to end	Day	48% 5% 4 15% 19% 9%	3476
February	1st to 10th	Day	46% 4 8% 13% 19% 11%	1900
	11th to 20th	Day	41% 5% 8% 16% 19% 11%	1858
	21st to end	Day	46% 5% 9% 15% 16% 9%	1570
March	1st to 10th	Day	52% 5% 9% 17% 12% 5%	3120
	11th to 20th	Day	43% 7% 9% 17% 19% 5%	3466
	21st to end	Day	38% 7% 12% 16% 18% 9%	4096
April	1st to 10th	Day	37% 8% 11% 18% 16% 10%	2280
	11th to 20th	Day	40% 6% 8% 19% 18% 8%	2254
	21st to end	Day	31% 6% 10% 22% 23% 8%	2280
May	1st to 10th	Day	36% 10% 16% 21% 13% 4	3800
	11th to 20th	Day	40% 6% 13% 19% 20% 2	3768
	21st to end	Day	28% 9% 16% 34% 11% 2	4327
June	1st to 10th	Day	42% 10% 16% 21% 9% 1	2470
	11th to 20th	Day	36% 11% 15% 25% 10% 2	2470
	21st to end	Day	44% 12% 19% 16% 9%	2494
July	1st to 10th	Day	49% 10% 24% 15% 2	3911
	11th to 20th	Day	46% 9% 34% 9% 2 1	3737
	21st to end	Day	49% 12% 22% 13% 3	3987
August	1st to 10th	Day	29% 8% 14% 25% 23% 1	3773
	11th to 20th	Day	39% 7% 18% 23% 12% 1	3765
	21st to end	Day	47% 11% 13% 15% 13% 2	4179
September	1st to 10th	Day	43% 11% 14% 17% 10% 4	2280
	11th to 20th	Day	40% 10% 13% 15% 15% 7%	2168
	21st to end	Day	32% 7% 11% 22% 18% 10%	2090
October	1st to 10th	Day	28% 3 6% 12% 20% 30%	3480
	11th to 20th	Day	17% 3 5% 18% 27% 30%	3177
	21st to end	Day	20% 3 5% 13% 37% 22%	3428
November	1st to 10th	Day	29% 4 9% 20% 26% 12%	1934
	11th to 20th	Day	29% 4 7% 18% 29% 12%	1719
	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% 5% 7% 14% 26% 11%	3789
	11th to 20th	Night	35% 3 5% 18% 29% 11%	3800
	21st to end	Night	46% 4 5% 14% 22% 8%	4180
February	1st to 10th	Night	41% 4 8% 17% 20% 10%	2280
	11th to 20th	Night	43% 4 5% 15% 20% 13%	2219
	21st to end	Night	45% 7% 9% 14% 13% 12%	1884
March	1st to 10th	Night	55% 6% 8% 13% 14% 5%	3733
	11th to 20th	Night	42% 7% 11% 16% 17% 7%	3522
	21st to end	Night	38% 5% 11% 19% 18% 8%	3535
April	1st to 10th	Night	39% 6% 10% 16% 17% 11%	1900
	11th to 20th	Night	38% 5% 10% 21% 18% 9%	1875
	21st to end	Night	26% 5% 10% 25% 25% 9%	1900
May	1st to 10th	Night	37% 7% 14% 21% 18% 4	3160
	11th to 20th	Night	39% 7% 13% 23% 16% 2	3130
	21st to end	Night	25% 9% 24% 28% 13% 2	3244
June	1st to 10th	Night	34% 11% 19% 25% 10% 1	1710
	11th to 20th	Night	26% 11% 24% 27% 11% 1	1710
	21st to end	Night	34% 11% 25% 20% 10% 1	1653
July	1st to 10th	Night	35% 10% 36% 16% 3	2912
	11th to 20th	Night	28% 12% 46% 11% 2	3100
	21st to end	Night	38% 19% 22% 18% 3	3325
August	1st to 10th	Night	18% 7% 22% 30% 22% 1	3132
	11th to 20th	Night	28% 10% 26% 27% 8%	3130
	21st to end	Night	37% 13% 19% 19% 9% 3	3476
September	1st to 10th	Night	37% 11% 18% 16% 12% 5%	1900
	11th to 20th	Night	33% 10% 18% 16% 15% 8%	1990
	21st to end	Night	30% 6% 12% 24% 17% 10%	2090
October	1st to 10th	Night	31% 3 7% 13% 23% 23%	3480
	11th to 20th	Night	15% 3 5% 20% 27% 30%	3737
	21st to end	Night	20% 2 5% 11% 38% 24%	4120
November	1st to 10th	Night	31% 3 8% 18% 25% 14%	2360
	11th to 20th	Night	31% 4 7% 17% 28% 14%	2484
	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	23% 18% 31% 21% 5% 1	270
	21st to end	Day	23% 25% 36% 13% 3	297
February	1st to 10th	Day	27% 22% 33% 12% 4 1	270
	11th to 20th	Day	31% 19% 30% 14% 6%	270
	21st to end	Day	16% 33% 38% 11% 1	225
March	1st to 10th	Day	17% 25% 39% 17% 3	270
	11th to 20th	Day	24% 22% 32% 17% 4	270
	21st to end	Day	19% 19% 31% 21% 9% 1	463
April	1st to 10th	Day	18% 16% 33% 23% 10% 1	460
	11th to 20th	Day	18% 18% 31% 19% 11% 2	452
	21st to end	Day	10% 13% 29% 28% 17% 3	460
May	1st to 10th	Day	12% 12% 29% 26% 16% 4	463
	11th to 20th	Day	13% 6% 23% 30% 21% 7%	487
	21st to end	Day	7% 3 20% 37% 24% 9%	529
June	1st to 10th	Day	11% 4 13% 33% 22% 17%	490
	11th to 20th	Day	8% 3 14% 31% 28% 15%	490
	21st to end	Day	10% 3 13% 30% 27% 17%	573
July	1st to 10th	Day	9% 1 7% 29% 31% 22%	591
	11th to 20th	Day	9% 2 4 18% 38% 28%	484
	21st to end	Day	8% 2 5% 26% 38% 22%	532
August	1st to 10th	Day	5% 2 6% 24% 36% 27%	486
	11th to 20th	Day	9% 2 5% 20% 36% 28%	479
	21st to end	Day	10% 3 10% 22% 34% 21%	539
September	1st to 10th	Day	12% 3 6% 26% 36% 18%	490
	11th to 20th	Day	12% 3 12% 26% 34% 13%	490
	21st to end	Day	8% 6% 11% 34% 30% 11%	490
October	1st to 10th	Day	7% 5% 24% 35% 22% 7%	490
	11th to 20th	Day	7% 7% 27% 33% 21% 5%	324
	21st to end	Day	16% 10% 23% 36% 12% 4	330
November	1st to 10th	Day	15% 7% 27% 34% 15% 1	300
	11th to 20th	Day	16% 11% 32% 26% 12% 2	273
	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% 34% 8%	760
	21st to end	Night	23% 13% 33% 27% 5%	836
February	1st to 10th	Night	18% 13% 35% 29% 5%	760
	11th to 20th	Night	24% 13% 28% 28% 7%	743
	21st to end	Night	19% 17% 34% 26% 4	628
March	1st to 10th	Night	18% 13% 32% 31% 7%	760
	11th to 20th	Night	15% 9% 31% 31% 14% 1	599
	21st to end	Night	15% 9% 30% 32% 13%	627
April	1st to 10th	Night	18% 12% 28% 28% 14% 1	570
	11th to 20th	Night	15% 8% 29% 29% 17% 1	563
	21st to end	Night	9% 6% 25% 39% 19% 1	570
May	1st to 10th	Night	11% 4 21% 40% 22% 2	570
	11th to 20th	Night	8% 3 17% 40% 29% 4	561
	21st to end	Night	6% 2 12% 35% 37% 8%	617
June	1st to 10th	Night	10% 2 8% 31% 39% 10%	570
	11th to 20th	Night	4 2 6% 30% 43% 15%	570
	21st to end	Night	8% 2 6% 24% 43% 18%	570
July	1st to 10th	Night	8% 2 3 17% 48% 23%	555
	11th to 20th	Night	3 1 3 12% 50% 32%	552
	21st to end	Night	5% 1 4 18% 45% 26%	624
August	1st to 10th	Night	3 2 15% 50% 29%	567
	11th to 20th	Night	5% 1 3 10% 51% 29%	564
	21st to end	Night	9% 2 5% 17% 46% 22%	627
September	1st to 10th	Night	10% 2 5% 20% 42% 20%	570
	11th to 20th	Night	10% 3 8% 28% 41% 10%	660
	21st to end	Night	9% 2 9% 34% 39% 7%	760
October	1st to 10th	Night	9% 1 17% 37% 31% 4	760
	11th to 20th	Night	9% 4 19% 36% 26% 5%	760
	21st to end	Night	13% 5% 20% 36% 23% 2	836
November	1st to 10th	Night	13% 6% 17% 40% 21% 3	780
	11th to 20th	Night	14% 7% 27% 34% 16% 2	765
	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 2024-11-08 21:45:36. Version ac07

Copyright © 2024 Attilla Danko.