Barking Spider Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Barking Spider Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	7% 6% 2 5% 3 3 3 3 4 6% 59%	135879
	Night	9% 9% 4 7% 3 3 3 3 4 6% 49%	133284
Transparency	Day	25% 5% 8% 18% 24% 20%	130810
	Night	33% 5% 9% 17% 20% 15%	129339
Seeing	Day	10% 10% 25% 31% 18% 5%	16901
	Night	13% 4 13% 35% 29% 6%	26319

By Month

Percentage Cloud Cover SW (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	15% 6% 2 5% 4 3 4 3 6% 9% 45%	3936
	11th to 20th	Day	12% 6% 3 7% 4 3 3 2 3 4 52%	4155
	21st to end	Day	17% 8% 3 7% 4 4 3 3 4 6% 40%	4510
February	1st to 10th	Day	17% 8% 3 5% 4 3 3 3 5% 6% 44%	1800
	11th to 20th	Day	13% 9% 3 6% 4 3 4 3 6% 8% 41%	1849
	21st to end	Day	14% 7% 2 6% 5% 3 4 3 5% 6% 47%	1650
March	1st to 10th	Day	12% 10% 4 9% 6% 5% 5% 4 5% 6% 33%	4858
	11th to 20th	Day	13% 6% 2 5% 3 3 4 3 5% 8% 47%	5000
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 5% 8% 9% 35%	5572
April	1st to 10th	Day	13% 7% 2 5% 4 4 3 3 5% 7% 45%	2400
	11th to 20th	Day	9% 6% 1 5% 3 3 4 3 5% 6% 55%	2369
	21st to end	Day	6% 5% 2 5% 3 3 3 3 5% 9% 56%	2400
May	1st to 10th	Day	5% 3 1 2 1 2 2 2 3 5% 74%	5606
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 6% 72%	6003
	21st to end	Day	2 6% 2 4 2 2 2 2 3 6% 68%	6902
June	1st to 10th	Day	5% 6% 1 4 3 3 3 3 4 7% 60%	2800
	11th to 20th	Day	2 3 1 3 2 2 2 3 4 6% 72%	2800
	21st to end	Day	3 4 2 4 2 2 2 2 3 5% 71%	2800
July	1st to 10th	Day	2 2 3 2 1 2 2 2 4 79%	6319
	11th to 20th	Day	1 3 2 4 2 2 3 2 3 5% 74%	5934
	21st to end	Day	8% 2 4 2 3 4 3 4 7% 62%	6402
August	1st to 10th	Day	1 3 2 4 2 3 3 2 4 6% 68%	5777
	11th to 20th	Day	1 5% 2 4 2 2 2 2 3 5% 72%	5500
	21st to end	Day	1 3 2 5% 3 3 3 2 4 6% 69%	5984
September	1st to 10th	Day	2 3 2 4 2 2 2 2 3 5% 74%	2400
	11th to 20th	Day	3 7% 3 4 3 3 3 3 4 7% 61%	2400
	21st to end	Day	4 3 1 3 2 2 2 2 3 6% 73%	2125
October	1st to 10th	Day	2 3 1 3 2 2 3 2 4 6% 72%	3280
	11th to 20th	Day	4 5% 2 4 3 3 3 2 4 6% 64%	3261
	21st to end	Day	5% 6% 1 5% 3 3 3 3 5% 7% 59%	3558
November	1st to 10th	Day	8% 5% 2 4 2 3 4 3 6% 8% 55%	2012
	11th to 20th	Day	10% 7% 3 7% 4 3 3 3 5% 7% 47%	1890
	21st to end	Day	12% 6% 2 4 3 3 3 4 6% 6% 53%	1727
December	1st to 10th	Day	8% 5% 2 4 3 3 3 4 6% 9% 54%	2700
	11th to 20th	Day	22% 8% 3 7% 4 4 5% 4 6% 7% 30%	3108
	21st to end	Day	23% 12% 3 6% 4 4 4 3 5% 7% 28%	4092
January	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 5% 9% 48%	6221
	11th to 20th	Night	13% 7% 4 7% 4 4 4 3 4 5% 46%	5958
	21st to end	Night	16% 11% 5% 7% 3 3 3 3 4 4 41%	6468
February	1st to 10th	Night	19% 7% 2 4 3 3 3 3 5% 5% 47%	2600
	11th to 20th	Night	14% 7% 3 6% 4 4 4 3 5% 7% 43%	2438
	21st to end	Night	12% 7% 2 4 3 4 3 3 4 7% 51%	1980
March	1st to 10th	Night	16% 13% 5% 8% 5% 4 3 3 4 6% 34%	5031
	11th to 20th	Night	17% 8% 4 6% 3 3 3 2 4 6% 45%	5000
	21st to end	Night	17% 12% 3 6% 4 4 3 3 4 7% 37%	5402
April	1st to 10th	Night	10% 10% 2 6% 4 3 3 4 5% 7% 46%	2000
	11th to 20th	Night	11% 7% 3 5% 3 3 3 3 4 6% 52%	1979
	21st to end	Night	6% 6% 1 4 3 4 4 4 5% 8% 55%	2000
May	1st to 10th	Night	5% 6% 2 4 2 2 2 2 3 4 68%	4381
	11th to 20th	Night	3 9% 4 10% 4 3 3 3 3 5% 53%	3900
	21st to end	Night	3 16% 5% 5% 2 3 2 2 2 4 55%	3972
June	1st to 10th	Night	6% 8% 3 7% 3 3 3 4 5% 7% 52%	1600
	11th to 20th	Night	2 4 3 4 3 2 3 3 4 6% 66%	1600
	21st to end	Night	2 8% 4 6% 2 2 2 3 3 5% 63%	1600
July	1st to 10th	Night	4 5% 10% 3 2 2 2 3 4 66%	3640
	11th to 20th	Night	1 5% 10% 15% 4 2 2 3 3 5% 50%	4040
	21st to end	Night	2 30% 11% 7% 2 2 3 2 4 5% 34%	4472
August	1st to 10th	Night	2 10% 8% 18% 4 3 3 3 3 5% 42%	4035
	11th to 20th	Night	13% 7% 9% 3 2 3 2 3 4 53%	4361
	21st to end	Night	2 9% 6% 14% 3 3 3 2 3 5% 51%	5015
September	1st to 10th	Night	2 8% 4 5% 3 2 4 3 3 6% 61%	2000
	11th to 20th	Night	5% 10% 5% 9% 3 3 4 2 4 7% 50%	2000
	21st to end	Night	3 5% 3 5% 2 2 2 2 4 5% 65%	2272
October	1st to 10th	Night	3 3 2 4 2 2 2 3 4 5% 69%	3920
	11th to 20th	Night	5% 13% 6% 7% 3 2 2 2 3 4 53%	3897
	21st to end	Night	7% 5% 2 5% 3 3 4 3 5% 5% 57%	4253
November	1st to 10th	Night	8% 6% 2 4 3 4 3 3 5% 7% 53%	2506
	11th to 20th	Night	11% 8% 2 5% 3 4 3 3 5% 7% 49%	2730
	21st to end	Night	10% 5% 1 5% 3 3 3 3 5% 7% 54%	2891
December	1st to 10th	Night	8% 4 2 5% 3 3 3 3 4 6% 59%	4700
	11th to 20th	Night	23% 10% 3 6% 4 4 4 4 7% 7% 29%	5316
	21st to end	Night	23% 9% 3 7% 5% 4 5% 4 4 6% 31%	7106

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	35% 7% 18% 21% 14% 5%	3936
	11th to 20th	Day	36% 5% 8% 12% 23% 15%	4155
	21st to end	Day	45% 6% 7% 11% 15% 16%	4510
February	1st to 10th	Day	40% 5% 9% 18% 20% 8%	1800
	11th to 20th	Day	40% 7% 11% 17% 20% 6%	1858
	21st to end	Day	37% 5% 9% 24% 18% 6%	1650
March	1st to 10th	Day	47% 8% 8% 15% 19% 2	4858
	11th to 20th	Day	34% 6% 15% 27% 11% 8%	5000
	21st to end	Day	38% 11% 17% 22% 10% 2	5572
April	1st to 10th	Day	37% 6% 14% 20% 19% 4	2400
	11th to 20th	Day	29% 6% 15% 23% 22% 6%	2372
	21st to end	Day	24% 6% 14% 28% 24% 4	2400
May	1st to 10th	Day	14% 3 8% 28% 30% 18%	5606
	11th to 20th	Day	12% 4 7% 32% 37% 9%	6006
	21st to end	Day	14% 6% 8% 29% 40% 4	6904
June	1st to 10th	Day	22% 5% 11% 26% 27% 9%	2800
	11th to 20th	Day	11% 4 8% 21% 37% 19%	2800
	21st to end	Day	13% 3 4 13% 32% 36%	2800
July	1st to 10th	Day	8% 1 3 6% 21% 60%	6251
	11th to 20th	Day	11% 2 3 6% 10% 68%	5863
	21st to end	Day	17% 2 4 15% 26% 37%	6217
August	1st to 10th	Day	16% 2 4 10% 27% 41%	4206
	11th to 20th	Day	11% 2 4 9% 40% 34%	3982
	21st to end	Day	14% 3 4 11% 33% 35%	4311
September	1st to 10th	Day	12% 2 4 10% 31% 41%	2400
	11th to 20th	Day	20% 4 7% 21% 31% 17%	2400
	21st to end	Day	13% 3 7% 20% 33% 24%	2125
October	1st to 10th	Day	15% 3 5% 11% 27% 39%	3280
	11th to 20th	Day	20% 4 7% 22% 28% 19%	3261
	21st to end	Day	24% 3 7% 20% 31% 15%	3558
November	1st to 10th	Day	27% 6% 11% 24% 22% 11%	2012
	11th to 20th	Day	35% 6% 11% 21% 22% 5%	1890
	21st to end	Day	30% 4 11% 19% 26% 9%	1727
December	1st to 10th	Day	26% 5% 7% 26% 30% 6%	2700
	11th to 20th	Day	50% 6% 9% 16% 14% 5%	3108
	21st to end	Day	53% 8% 11% 16% 10% 2	4092
January	1st to 10th	Night	32% 9% 20% 21% 14% 4	6221
	11th to 20th	Night	40% 7% 9% 11% 21% 12%	5958
	21st to end	Night	46% 5% 7% 10% 17% 15%	6468
February	1st to 10th	Night	39% 5% 10% 18% 18% 11%	2600
	11th to 20th	Night	39% 6% 11% 17% 19% 7%	2440
	21st to end	Night	34% 5% 13% 26% 17% 5%	1980
March	1st to 10th	Night	49% 8% 9% 16% 15% 3	5031
	11th to 20th	Night	37% 7% 13% 22% 13% 8%	5000
	21st to end	Night	43% 12% 14% 18% 10% 2	5402
April	1st to 10th	Night	34% 7% 15% 22% 17% 5%	2000
	11th to 20th	Night	31% 7% 12% 24% 18% 8%	1979
	21st to end	Night	24% 6% 13% 29% 22% 5%	2000
May	1st to 10th	Night	19% 5% 9% 26% 26% 16%	4378
	11th to 20th	Night	21% 8% 9% 28% 26% 9%	3901
	21st to end	Night	23% 7% 9% 24% 33% 3	3972
June	1st to 10th	Night	25% 6% 11% 25% 24% 10%	1600
	11th to 20th	Night	15% 4 8% 19% 32% 22%	1600
	21st to end	Night	15% 3 7% 15% 29% 32%	1600
July	1st to 10th	Night	17% 1 4 8% 18% 53%	3600
	11th to 20th	Night	31% 2 3 9% 11% 45%	3988
	21st to end	Night	47% 1 5% 9% 17% 21%	4345
August	1st to 10th	Night	40% 2 5% 12% 20% 22%	2929
	11th to 20th	Night	23% 2 4 10% 33% 27%	3148
	21st to end	Night	28% 2 6% 9% 27% 28%	3608
September	1st to 10th	Night	20% 4 4 9% 22% 41%	2000
	11th to 20th	Night	28% 4 8% 19% 24% 17%	2000
	21st to end	Night	16% 4 6% 19% 29% 25%	2272
October	1st to 10th	Night	15% 3 6% 11% 21% 43%	3920
	11th to 20th	Night	32% 4 6% 17% 19% 21%	3897
	21st to end	Night	26% 4 6% 20% 24% 20%	4253
November	1st to 10th	Night	28% 6% 11% 23% 18% 13%	2506
	11th to 20th	Night	34% 6% 11% 23% 19% 7%	2730
	21st to end	Night	29% 6% 10% 22% 22% 11%	2891
December	1st to 10th	Night	26% 5% 7% 24% 26% 11%	4700
	11th to 20th	Night	52% 5% 9% 14% 16% 4	5316
	21st to end	Night	53% 8% 14% 13% 9% 3	7106

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	24% 12% 26% 22% 13% 3	320
	11th to 20th	Day	17% 8% 22% 29% 21% 4	419
	21st to end	Day	16% 6% 25% 30% 19% 4	440
February	1st to 10th	Day	21% 11% 22% 24% 20% 3	400
	11th to 20th	Day	19% 14% 28% 25% 13% 2	442
	21st to end	Day	12% 14% 27% 33% 12% 2	414
March	1st to 10th	Day	20% 16% 29% 22% 10% 3	500
	11th to 20th	Day	20% 17% 23% 23% 13% 4	500
	21st to end	Day	17% 15% 34% 21% 11% 2	550
April	1st to 10th	Day	17% 14% 31% 24% 10% 4	500
	11th to 20th	Day	14% 16% 32% 24% 10% 4	492
	21st to end	Day	9% 18% 30% 27% 10% 6%	500
May	1st to 10th	Day	10% 14% 32% 30% 12% 2	503
	11th to 20th	Day	12% 12% 30% 30% 14% 2	528
	21st to end	Day	12% 11% 29% 31% 13% 5%	573
June	1st to 10th	Day	6% 10% 31% 33% 16% 4	530
	11th to 20th	Day	3 10% 32% 38% 14% 3	530
	21st to end	Day	4 7% 27% 38% 18% 5%	530
July	1st to 10th	Day	4 5% 23% 45% 19% 5%	526
	11th to 20th	Day	1 2 22% 44% 28% 4	524
	21st to end	Day	5% 2 22% 42% 22% 7%	575
August	1st to 10th	Day	5% 5% 24% 39% 20% 7%	527
	11th to 20th	Day	5% 3 23% 42% 20% 7%	517
	21st to end	Day	4 3 20% 39% 26% 8%	583
September	1st to 10th	Day	4 5% 19% 40% 24% 8%	530
	11th to 20th	Day	7% 10% 25% 32% 19% 7%	530
	21st to end	Day	5% 8% 23% 32% 26% 7%	530
October	1st to 10th	Day	4 8% 26% 31% 22% 9%	530
	11th to 20th	Day	8% 9% 19% 31% 26% 8%	530
	21st to end	Day	8% 8% 25% 30% 21% 8%	583
November	1st to 10th	Day	8% 10% 22% 26% 26% 9%	488
	11th to 20th	Day	10% 11% 17% 32% 22% 8%	330
	21st to end	Day	12% 5% 23% 30% 27% 3	245
December	1st to 10th	Day	13% 10% 20% 25% 24% 8%	220
	11th to 20th	Day	17% 10% 17% 25% 25% 6%	220
	21st to end	Day	25% 11% 24% 21% 17% 2	242
January	1st to 10th	Night	19% 6% 13% 35% 21% 6%	840
	11th to 20th	Night	15% 4 12% 38% 26% 5%	824
	21st to end	Night	19% 4 12% 38% 22% 5%	880
February	1st to 10th	Night	20% 4 14% 36% 22% 4	800
	11th to 20th	Night	15% 5% 18% 36% 21% 4	784
	21st to end	Night	14% 8% 16% 42% 18% 3	660
March	1st to 10th	Night	20% 7% 18% 30% 21% 3	800
	11th to 20th	Night	21% 6% 14% 34% 22% 4	800
	21st to end	Night	18% 7% 18% 37% 19% 2	880
April	1st to 10th	Night	13% 6% 18% 39% 22% 2	800
	11th to 20th	Night	15% 6% 20% 34% 21% 4	791
	21st to end	Night	9% 5% 19% 39% 23% 5%	800
May	1st to 10th	Night	11% 4 16% 40% 25% 4	725
	11th to 20th	Night	12% 2 13% 39% 30% 5%	522
	21st to end	Night	15% 5% 14% 36% 26% 4	433
June	1st to 10th	Night	10% 2 13% 43% 30% 3	400
	11th to 20th	Night	5% 1 12% 51% 29% 2	400
	21st to end	Night	6% 4 10% 36% 41% 3	400
July	1st to 10th	Night	6% 2 6% 33% 49% 3	390
	11th to 20th	Night	6% 4 37% 42% 11%	550
	21st to end	Night	11% 2 8% 24% 45% 10%	657
August	1st to 10th	Night	14% 2 8% 29% 38% 9%	597
	11th to 20th	Night	9% 1 10% 34% 39% 7%	722
	21st to end	Night	7% 9% 35% 41% 9%	880
September	1st to 10th	Night	8% 1 9% 31% 41% 10%	800
	11th to 20th	Night	12% 2 13% 32% 34% 8%	800
	21st to end	Night	6% 2 10% 31% 40% 11%	800
October	1st to 10th	Night	9% 2 9% 37% 36% 8%	800
	11th to 20th	Night	10% 3 10% 31% 37% 9%	800
	21st to end	Night	10% 3 10% 34% 31% 11%	880
November	1st to 10th	Night	10% 4 12% 32% 33% 9%	820
	11th to 20th	Night	14% 3 13% 35% 28% 7%	840
	21st to end	Night	13% 2 14% 39% 26% 6%	840
December	1st to 10th	Night	15% 3 14% 37% 25% 5%	840
	11th to 20th	Night	24% 4 11% 35% 21% 4	840
	21st to end	Night	23% 5% 21% 32% 17% 2	924

Page generated at 2026-01-13 22:14:28. Version ac07

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