Bolingbroke
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bolingbroke 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	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	127216
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	124472
Transparency	Day	37% 7% 12% 19% 18% 7%	130991
	Night	36% 6% 11% 19% 20% 8%	128766
Seeing	Day	15% 10% 23% 24% 19% 9%	16551
	Night	14% 9% 21% 31% 21% 4	26610

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	15% 5% 1 5% 3 3 3 3 4 5% 52%	4146
	11th to 20th	Day	11% 6% 2 4 3 2 2 3 5% 7% 55%	4114
	21st to end	Day	19% 7% 3 6% 4 3 3 3 4 6% 42%	4650
February	1st to 10th	Day	16% 6% 3 7% 5% 4 5% 4 6% 6% 40%	2000
	11th to 20th	Day	20% 7% 2 5% 4 3 4 3 6% 6% 42%	1948
	21st to end	Day	16% 7% 2 7% 4 4 4 3 5% 6% 41%	1650
March	1st to 10th	Day	19% 8% 3 6% 4 4 4 4 5% 6% 37%	4705
	11th to 20th	Day	8% 5% 2 5% 3 4 4 4 5% 7% 54%	4980
	21st to end	Day	16% 6% 3 6% 4 4 4 3 4 5% 46%	5465
April	1st to 10th	Day	11% 6% 2 6% 5% 4 4 4 5% 7% 48%	2200
	11th to 20th	Day	11% 5% 2 4 4 4 4 3 5% 7% 51%	2355
	21st to end	Day	7% 5% 2 5% 5% 4 5% 3 5% 7% 52%	2570
May	1st to 10th	Day	10% 6% 3 7% 4 5% 5% 4 6% 9% 41%	5862
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 5% 7% 9% 32%	5861
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	6433
June	1st to 10th	Day	9% 7% 2 7% 6% 6% 8% 5% 8% 10% 32%	2600
	11th to 20th	Day	5% 4 2 6% 5% 5% 6% 6% 9% 12% 40%	2600
	21st to end	Day	5% 5% 2 7% 6% 7% 6% 5% 9% 10% 38%	2600
July	1st to 10th	Day	10% 6% 3 8% 6% 7% 7% 6% 9% 12% 26%	5900
	11th to 20th	Day	4 4 2 7% 6% 7% 7% 6% 10% 13% 35%	5900
	21st to end	Day	6% 7% 3 9% 7% 7% 8% 7% 10% 12% 23%	6424
August	1st to 10th	Day	12% 6% 2 6% 5% 6% 7% 6% 9% 11% 29%	4234
	11th to 20th	Day	6% 4 2 6% 4 5% 6% 5% 6% 9% 47%	3921
	21st to end	Day	8% 4 2 6% 4 5% 5% 5% 6% 10% 46%	4250
September	1st to 10th	Day	11% 7% 3 6% 5% 5% 5% 5% 7% 10% 38%	2200
	11th to 20th	Day	14% 6% 2 6% 4 4 4 5% 6% 8% 41%	2200
	21st to end	Day	14% 5% 2 6% 5% 5% 5% 4 6% 6% 44%	2200
October	1st to 10th	Day	13% 5% 2 4 3 4 4 3 4 7% 51%	2200
	11th to 20th	Day	11% 3 2 4 3 3 3 3 5% 6% 59%	2073
	21st to end	Day	12% 4 1 5% 3 3 4 3 4 4 57%	2200
November	1st to 10th	Day	13% 5% 2 5% 3 3 3 4 4 5% 53%	1947
	11th to 20th	Day	13% 5% 2 4 3 3 2 3 4 6% 56%	1890
	21st to end	Day	12% 6% 2 5% 4 4 4 4 5% 6% 48%	1890
December	1st to 10th	Day	15% 7% 2 6% 3 3 3 3 4 6% 48%	3020
	11th to 20th	Day	17% 7% 2 6% 3 3 3 3 4 5% 48%	3463
	21st to end	Day	21% 7% 2 5% 3 3 3 3 4 6% 44%	4565
January	1st to 10th	Night	14% 5% 2 5% 3 4 3 3 5% 6% 51%	6019
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 3 5% 6% 47%	5979
	21st to end	Night	18% 8% 2 5% 4 3 3 3 5% 6% 42%	6288
February	1st to 10th	Night	15% 6% 3 6% 4 3 4 3 5% 6% 45%	2400
	11th to 20th	Night	20% 7% 2 5% 4 3 4 2 4 5% 44%	2338
	21st to end	Night	14% 7% 2 7% 4 4 3 3 5% 6% 44%	1980
March	1st to 10th	Night	20% 7% 3 6% 4 3 4 3 4 6% 38%	5146
	11th to 20th	Night	10% 4 1 4 3 4 4 3 6% 8% 52%	4980
	21st to end	Night	14% 5% 2 6% 4 4 4 3 5% 6% 46%	5467
April	1st to 10th	Night	10% 5% 2 4 4 4 4 5% 6% 8% 48%	2200
	11th to 20th	Night	12% 4 1 4 3 3 4 3 6% 7% 52%	2009
	21st to end	Night	7% 4 2 5% 5% 4 3 3 6% 9% 52%	1830
May	1st to 10th	Night	8% 6% 2 7% 5% 5% 5% 4 8% 12% 38%	4033
	11th to 20th	Night	16% 5% 2 6% 4 4 5% 5% 7% 9% 35%	4032
	21st to end	Night	9% 5% 2 5% 4 4 4 4 7% 11% 47%	4421
June	1st to 10th	Night	8% 5% 3 6% 5% 6% 6% 6% 8% 11% 37%	1800
	11th to 20th	Night	5% 4 3 5% 4 5% 5% 4 8% 13% 44%	1800
	21st to end	Night	5% 5% 2 5% 6% 5% 7% 5% 9% 13% 39%	1800
July	1st to 10th	Night	10% 8% 3 10% 6% 7% 7% 6% 8% 10% 26%	4058
	11th to 20th	Night	3 4 2 7% 6% 6% 8% 6% 10% 14% 33%	4057
	21st to end	Night	8% 8% 4 8% 6% 7% 7% 6% 7% 12% 27%	4427
August	1st to 10th	Night	11% 6% 3 9% 6% 7% 7% 5% 9% 11% 28%	2915
	11th to 20th	Night	6% 5% 2 6% 4 5% 5% 4 7% 10% 46%	3123
	21st to end	Night	7% 5% 1 6% 4 4 4 4 6% 9% 50%	3614
September	1st to 10th	Night	8% 6% 3 8% 6% 6% 6% 5% 7% 9% 36%	2200
	11th to 20th	Night	11% 6% 2 6% 5% 5% 5% 4 5% 7% 43%	2200
	21st to end	Night	12% 5% 2 7% 4 5% 4 4 6% 7% 44%	2200
October	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 4 7% 52%	2200
	11th to 20th	Night	11% 4 2 4 3 3 3 2 4 5% 60%	2325
	21st to end	Night	11% 5% 1 5% 3 4 3 3 4 6% 56%	2640
November	1st to 10th	Night	12% 5% 2 5% 3 4 3 2 5% 6% 53%	2566
	11th to 20th	Night	13% 5% 2 3 3 3 3 3 4 5% 55%	2730
	21st to end	Night	13% 5% 2 6% 4 4 3 3 4 6% 50%	2730
December	1st to 10th	Night	14% 6% 2 4 3 3 3 3 4 6% 53%	4380
	11th to 20th	Night	16% 5% 2 5% 4 3 4 3 4 6% 49%	4952
	21st to end	Night	20% 7% 2 6% 3 4 4 3 4 5% 42%	6633

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	34% 4 6% 18% 31% 8%	4147
	11th to 20th	Day	30% 3 4 18% 32% 12%	4114
	21st to end	Day	44% 4 6% 15% 22% 10%	4650
February	1st to 10th	Day	43% 4 8% 18% 19% 8%	2000
	11th to 20th	Day	43% 3 5% 18% 23% 7%	1958
	21st to end	Day	42% 6% 7% 16% 20% 9%	1650
March	1st to 10th	Day	46% 4 8% 12% 23% 7%	4705
	11th to 20th	Day	30% 5% 8% 14% 21% 22%	4980
	21st to end	Day	41% 4 6% 20% 18% 11%	5465
April	1st to 10th	Day	36% 6% 10% 21% 18% 10%	2200
	11th to 20th	Day	32% 5% 8% 20% 23% 12%	2355
	21st to end	Day	30% 6% 12% 23% 25% 5%	2570
May	1st to 10th	Day	38% 8% 15% 21% 16% 2	5897
	11th to 20th	Day	43% 9% 18% 19% 10% 1	5865
	21st to end	Day	35% 8% 14% 20% 21% 2	6447
June	1st to 10th	Day	43% 10% 14% 19% 12% 2	2600
	11th to 20th	Day	32% 10% 18% 23% 15% 2	2600
	21st to end	Day	36% 11% 18% 20% 12% 3	2600
July	1st to 10th	Day	44% 14% 19% 18% 4 1	5835
	11th to 20th	Day	34% 14% 28% 21% 3 1	5831
	21st to end	Day	45% 14% 20% 18% 3	6240
August	1st to 10th	Day	42% 10% 18% 26% 3	4221
	11th to 20th	Day	30% 9% 15% 32% 13% 1	3959
	21st to end	Day	31% 8% 15% 30% 14% 2	4250
September	1st to 10th	Day	40% 8% 16% 17% 16% 4	2200
	11th to 20th	Day	39% 7% 11% 21% 18% 4	2200
	21st to end	Day	39% 6% 9% 21% 19% 6%	2200
October	1st to 10th	Day	30% 4 7% 14% 32% 13%	3590
	11th to 20th	Day	17% 3 4 17% 28% 31%	3352
	21st to end	Day	23% 3 5% 18% 37% 15%	3538
November	1st to 10th	Day	34% 4 7% 13% 28% 14%	1947
	11th to 20th	Day	30% 4 6% 19% 27% 14%	1890
	21st to end	Day	37% 4 8% 17% 25% 9%	1890
December	1st to 10th	Day	38% 4 6% 17% 25% 10%	3020
	11th to 20th	Day	40% 2 8% 20% 22% 8%	3460
	21st to end	Day	42% 4 7% 21% 23% 3	4565
January	1st to 10th	Night	33% 5% 5% 19% 29% 9%	6019
	11th to 20th	Night	37% 5% 5% 19% 26% 9%	5979
	21st to end	Night	42% 4 5% 15% 27% 7%	6288
February	1st to 10th	Night	40% 4 7% 18% 22% 10%	2400
	11th to 20th	Night	43% 4 6% 16% 22% 10%	2339
	21st to end	Night	40% 5% 7% 15% 18% 14%	1980
March	1st to 10th	Night	46% 4 9% 14% 15% 11%	5146
	11th to 20th	Night	29% 5% 9% 13% 24% 20%	4980
	21st to end	Night	38% 5% 6% 18% 20% 13%	5467
April	1st to 10th	Night	33% 6% 11% 20% 19% 12%	2200
	11th to 20th	Night	30% 5% 7% 23% 24% 11%	2009
	21st to end	Night	28% 6% 12% 23% 23% 8%	1830
May	1st to 10th	Night	35% 9% 17% 22% 14% 3	4060
	11th to 20th	Night	42% 8% 17% 22% 10% 1	4033
	21st to end	Night	30% 8% 15% 25% 19% 3	4429
June	1st to 10th	Night	37% 12% 18% 19% 15% 1	1800
	11th to 20th	Night	29% 8% 19% 29% 12% 2	1800
	21st to end	Night	32% 12% 22% 17% 12% 4	1800
July	1st to 10th	Night	49% 14% 19% 14% 3 1	4015
	11th to 20th	Night	35% 14% 30% 17% 3	4006
	21st to end	Night	46% 14% 21% 15% 3 1	4297
August	1st to 10th	Night	46% 10% 19% 21% 3	2904
	11th to 20th	Night	32% 9% 18% 26% 14% 1	3151
	21st to end	Night	29% 8% 17% 29% 16% 2	3614
September	1st to 10th	Night	39% 11% 16% 16% 15% 4	2200
	11th to 20th	Night	38% 9% 12% 19% 18% 5%	2200
	21st to end	Night	38% 7% 10% 18% 20% 7%	2200
October	1st to 10th	Night	33% 5% 7% 13% 27% 14%	3590
	11th to 20th	Night	17% 2 4 13% 31% 32%	3785
	21st to end	Night	21% 3 4 19% 33% 20%	4252
November	1st to 10th	Night	32% 5% 7% 14% 27% 14%	2566
	11th to 20th	Night	32% 3 6% 17% 28% 14%	2730
	21st to end	Night	36% 4 7% 18% 24% 11%	2730
December	1st to 10th	Night	35% 3 6% 20% 29% 8%	4380
	11th to 20th	Night	37% 4 10% 18% 23% 8%	4954
	21st to end	Night	44% 4 5% 23% 22% 3	6633

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	18% 24% 43% 13% 2	330
	11th to 20th	Day	20% 24% 32% 16% 6% 1	318
	21st to end	Day	24% 25% 38% 11% 3 1	330
February	1st to 10th	Day	19% 21% 41% 14% 5%	300
	11th to 20th	Day	34% 20% 30% 14% 1	300
	21st to end	Day	23% 22% 39% 13% 2	249
March	1st to 10th	Day	20% 23% 29% 21% 6% 1	395
	11th to 20th	Day	20% 15% 35% 22% 8% 1	500
	21st to end	Day	20% 16% 35% 21% 7%	550
April	1st to 10th	Day	18% 17% 28% 25% 10% 1	500
	11th to 20th	Day	13% 15% 30% 25% 14% 3	492
	21st to end	Day	12% 9% 28% 28% 19% 4	500
May	1st to 10th	Day	11% 13% 28% 27% 15% 6%	503
	11th to 20th	Day	14% 5% 23% 28% 19% 11%	527
	21st to end	Day	12% 4 21% 29% 23% 12%	573
June	1st to 10th	Day	13% 5% 17% 26% 27% 12%	530
	11th to 20th	Day	7% 5% 17% 24% 27% 20%	530
	21st to end	Day	8% 3 13% 28% 29% 19%	530
July	1st to 10th	Day	9% 2 8% 19% 36% 26%	525
	11th to 20th	Day	5% 2 5% 23% 34% 31%	524
	21st to end	Day	5% 3 8% 24% 37% 23%	576
August	1st to 10th	Day	15% 4 10% 26% 26% 19%	526
	11th to 20th	Day	8% 3 7% 22% 38% 22%	519
	21st to end	Day	15% 3 7% 30% 29% 16%	583
September	1st to 10th	Day	12% 3 12% 27% 32% 14%	530
	11th to 20th	Day	15% 3 13% 29% 31% 10%	530
	21st to end	Day	16% 3 15% 32% 25% 9%	530
October	1st to 10th	Day	17% 5% 26% 26% 18% 8%	530
	11th to 20th	Day	12% 8% 20% 34% 20% 6%	530
	21st to end	Day	15% 7% 25% 30% 18% 4	583
November	1st to 10th	Day	21% 8% 25% 26% 16% 3	425
	11th to 20th	Day	14% 15% 40% 21% 10% 1	330
	21st to end	Day	14% 18% 34% 23% 11%	330
December	1st to 10th	Day	26% 17% 33% 18% 6% 1	330
	11th to 20th	Day	24% 17% 31% 18% 9% 1	330
	21st to end	Day	28% 15% 30% 21% 5% 1	363
January	1st to 10th	Night	20% 19% 30% 25% 6%	840
	11th to 20th	Night	20% 16% 29% 27% 8%	825
	21st to end	Night	20% 17% 34% 26% 3	880
February	1st to 10th	Night	18% 13% 31% 31% 7%	800
	11th to 20th	Night	23% 16% 30% 27% 3	783
	21st to end	Night	18% 15% 35% 29% 3	660
March	1st to 10th	Night	16% 14% 34% 31% 6%	800
	11th to 20th	Night	17% 14% 30% 28% 10%	800
	21st to end	Night	16% 14% 30% 31% 9% 1	880
April	1st to 10th	Night	13% 15% 29% 30% 12% 1	800
	11th to 20th	Night	14% 11% 26% 31% 16% 1	627
	21st to end	Night	9% 7% 24% 40% 20% 1	600
May	1st to 10th	Night	8% 7% 24% 39% 20% 1	600
	11th to 20th	Night	11% 4 20% 35% 24% 5%	591
	21st to end	Night	12% 2 14% 37% 29% 5%	650
June	1st to 10th	Night	10% 1 13% 37% 35% 4	600
	11th to 20th	Night	6% 2 12% 33% 35% 12%	600
	21st to end	Night	6% 2 7% 33% 44% 8%	600
July	1st to 10th	Night	8% 2 7% 25% 42% 15%	585
	11th to 20th	Night	8% 2 5% 22% 47% 16%	582
	21st to end	Night	6% 2 6% 26% 48% 12%	657
August	1st to 10th	Night	10% 2 6% 28% 42% 13%	597
	11th to 20th	Night	10% 2 7% 25% 45% 11%	594
	21st to end	Night	16% 2 7% 27% 38% 11%	675
September	1st to 10th	Night	10% 3 12% 26% 40% 10%	800
	11th to 20th	Night	14% 2 11% 29% 38% 5%	800
	21st to end	Night	15% 3 14% 30% 34% 4	800
October	1st to 10th	Night	14% 3 20% 33% 25% 5%	800
	11th to 20th	Night	12% 6% 21% 33% 25% 3	800
	21st to end	Night	13% 8% 21% 33% 22% 2	880
November	1st to 10th	Night	15% 7% 22% 35% 20% 1	820
	11th to 20th	Night	16% 11% 25% 33% 14% 1	840
	21st to end	Night	14% 12% 25% 34% 13% 1	840
December	1st to 10th	Night	18% 13% 29% 28% 11% 1	840
	11th to 20th	Night	20% 10% 27% 32% 10% 1	840
	21st to end	Night	26% 12% 24% 31% 7%	924

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

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