Bolton
Clear Sky Chart
History

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

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	16% 8% 2 6% 4 4 4 4 5% 7% 39%	101252
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 40%	97825
Transparency	Day	43% 7% 12% 22% 14% 2	104803
	Night	43% 7% 12% 22% 15% 2	102363
Seeing	Day	23% 16% 32% 20% 8% 2	15024
	Night	22% 14% 33% 24% 7% 1	23929

By Month

Percentage Cloud Cover NE (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	14% 7% 3 7% 4 4 4 3 4 5% 45%	2517
	11th to 20th	Day	16% 7% 3 7% 5% 4 5% 4 4 5% 40%	2520
	21st to end	Day	21% 11% 3 6% 5% 3 4 3 4 5% 35%	2772
February	1st to 10th	Day	18% 7% 3 6% 5% 5% 4 4 6% 6% 36%	1767
	11th to 20th	Day	13% 8% 3 8% 4 4 5% 4 5% 7% 39%	1848
	21st to end	Day	18% 10% 3 6% 5% 4 4 3 3 6% 37%	1570
March	1st to 10th	Day	23% 13% 3 7% 4 3 4 3 4 5% 31%	3116
	11th to 20th	Day	13% 7% 2 5% 4 4 5% 5% 6% 8% 42%	3313
	21st to end	Day	21% 10% 2 6% 4 3 4 4 6% 7% 34%	4060
April	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 5% 6% 37%	2280
	11th to 20th	Day	17% 6% 2 6% 4 4 5% 4 6% 7% 39%	2254
	21st to end	Day	19% 7% 3 6% 5% 5% 4 4 4 6% 36%	2470
May	1st to 10th	Day	23% 11% 4 7% 4 5% 4 3 5% 6% 27%	4106
	11th to 20th	Day	22% 9% 2 8% 4 4 4 3 4 7% 33%	4194
	21st to end	Day	14% 5% 2 5% 4 4 4 4 6% 8% 44%	4837
June	1st to 10th	Day	18% 6% 3 5% 5% 5% 4 4 7% 8% 36%	2660
	11th to 20th	Day	16% 6% 2 5% 5% 5% 5% 5% 7% 8% 37%	2660
	21st to end	Day	18% 6% 2 6% 5% 5% 5% 4 6% 9% 34%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 6% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 6% 11% 40%	4440
	21st to end	Day	16% 8% 3 7% 5% 5% 4 4 6% 8% 35%	4814
August	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 4 7% 9% 34%	4180
	11th to 20th	Day	13% 8% 2 7% 4 5% 5% 4 6% 7% 38%	3959
	21st to end	Day	7% 4 2 6% 5% 5% 5% 5% 7% 9% 46%	4180
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 4 5% 7% 46%	2280
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 4 6% 50%	2099
	21st to end	Day	16% 7% 2 6% 4 4 4 3 4 6% 44%	2090
October	1st to 10th	Day	22% 6% 2 5% 3 3 4 4 4 6% 40%	2090
	11th to 20th	Day	13% 7% 2 5% 3 4 4 4 5% 7% 47%	1850
	21st to end	Day	20% 7% 2 6% 4 4 3 3 4 5% 42%	1881
November	1st to 10th	Day	15% 7% 2 5% 4 4 3 2 4 4 49%	1717
	11th to 20th	Day	19% 7% 1 4 3 3 4 4 4 5% 47%	1710
	21st to end	Day	17% 7% 2 6% 4 3 4 3 6% 5% 43%	1710
December	1st to 10th	Day	17% 9% 2 6% 5% 4 4 3 5% 6% 38%	1530
	11th to 20th	Day	21% 7% 2 4 3 3 2 3 4 5% 45%	1906
	21st to end	Day	21% 10% 3 7% 4 4 3 3 5% 6% 34%	2772
January	1st to 10th	Night	18% 7% 2 4 3 3 3 3 4 6% 47%	4429
	11th to 20th	Night	14% 8% 3 10% 5% 4 4 3 4 6% 39%	4440
	21st to end	Night	22% 13% 4 7% 5% 4 4 3 4 5% 31%	4884
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 6% 6% 39%	2410
	11th to 20th	Night	13% 9% 2 7% 4 4 4 3 6% 6% 40%	2218
	21st to end	Night	17% 9% 2 7% 4 4 4 3 4 6% 40%	1884
March	1st to 10th	Night	27% 11% 3 5% 3 3 4 3 4 5% 33%	3724
	11th to 20th	Night	11% 10% 4 7% 4 5% 5% 3 5% 6% 40%	3645
	21st to end	Night	23% 8% 3 5% 4 4 4 4 6% 6% 34%	3568
April	1st to 10th	Night	17% 8% 3 7% 5% 4 3 3 6% 6% 37%	1900
	11th to 20th	Night	18% 7% 2 6% 5% 4 3 4 5% 6% 39%	1874
	21st to end	Night	20% 7% 2 7% 4 3 3 2 5% 6% 40%	1710
May	1st to 10th	Night	25% 10% 3 7% 5% 3 3 4 5% 6% 28%	2834
	11th to 20th	Night	21% 10% 3 7% 5% 5% 4 4 6% 7% 28%	2727
	21st to end	Night	15% 6% 2 7% 4 3 4 3 6% 8% 42%	2738
June	1st to 10th	Night	17% 9% 3 6% 4 4 3 3 6% 7% 38%	1520
	11th to 20th	Night	19% 7% 2 6% 5% 4 4 4 5% 7% 38%	1520
	21st to end	Night	14% 6% 2 6% 4 4 5% 4 7% 8% 40%	1520
July	1st to 10th	Night	11% 7% 2 6% 5% 6% 5% 5% 7% 10% 36%	2520
	11th to 20th	Night	11% 7% 3 6% 6% 4 4 5% 5% 9% 41%	2520
	21st to end	Night	15% 8% 3 7% 5% 4 4 4 5% 8% 38%	2739
August	1st to 10th	Night	19% 6% 3 7% 5% 5% 6% 4 6% 7% 33%	2717
	11th to 20th	Night	11% 7% 3 8% 5% 5% 5% 5% 6% 8% 37%	2865
	21st to end	Night	9% 4 2 4 3 3 4 3 5% 7% 57%	3476
September	1st to 10th	Night	12% 6% 2 5% 5% 3 3 3 5% 7% 48%	1900
	11th to 20th	Night	14% 5% 2 5% 3 3 4 3 5% 6% 53%	2080
	21st to end	Night	17% 6% 2 6% 3 3 4 3 5% 6% 44%	2090
October	1st to 10th	Night	20% 6% 2 6% 4 3 3 3 5% 5% 43%	2090
	11th to 20th	Night	16% 5% 2 5% 3 4 4 3 6% 6% 48%	2326
	21st to end	Night	22% 7% 2 6% 3 4 4 3 4 6% 39%	2717
November	1st to 10th	Night	15% 5% 2 5% 4 4 4 3 4 5% 49%	2483
	11th to 20th	Night	18% 7% 2 5% 3 3 4 3 5% 5% 46%	2470
	21st to end	Night	16% 7% 2 5% 4 4 4 3 5% 6% 45%	2470
December	1st to 10th	Night	18% 9% 3 6% 5% 4 4 3 5% 6% 39%	2645
	11th to 20th	Night	19% 7% 2 5% 3 4 4 3 5% 6% 42%	3288
	21st to end	Night	20% 9% 3 7% 4 4 4 3 5% 6% 35%	4884

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	40% 5% 10% 32% 11% 2	2518
	11th to 20th	Day	46% 6% 10% 25% 12% 2	2520
	21st to end	Day	50% 7% 11% 21% 10% 2	2772
February	1st to 10th	Day	46% 6% 14% 19% 12% 2	1767
	11th to 20th	Day	44% 7% 11% 20% 15% 3	1857
	21st to end	Day	49% 5% 10% 20% 13% 3	1570
March	1st to 10th	Day	56% 5% 11% 14% 11% 3	3119
	11th to 20th	Day	34% 9% 18% 24% 13% 3	3313
	21st to end	Day	48% 5% 8% 16% 17% 6%	4060
April	1st to 10th	Day	47% 6% 10% 18% 16% 3	2280
	11th to 20th	Day	41% 7% 12% 19% 17% 3	2254
	21st to end	Day	47% 7% 9% 17% 16% 4	2470
May	1st to 10th	Day	54% 9% 12% 14% 9% 1	4120
	11th to 20th	Day	50% 8% 15% 16% 10% 2	4198
	21st to end	Day	35% 9% 13% 24% 18% 2	4837
June	1st to 10th	Day	44% 8% 14% 23% 10% 1	2660
	11th to 20th	Day	41% 9% 14% 19% 15% 2	2660
	21st to end	Day	45% 9% 13% 20% 13% 1	2660
July	1st to 10th	Day	43% 8% 12% 21% 15% 1	4370
	11th to 20th	Day	38% 8% 16% 24% 12% 1	4365
	21st to end	Day	46% 7% 12% 20% 13% 2	4661
August	1st to 10th	Day	46% 9% 16% 21% 8% 1	4166
	11th to 20th	Day	43% 7% 15% 26% 9% 1	3998
	21st to end	Day	32% 7% 13% 30% 17% 1	4180
September	1st to 10th	Day	36% 7% 12% 24% 19% 2	2280
	11th to 20th	Day	35% 5% 9% 25% 22% 3	2099
	21st to end	Day	41% 5% 10% 20% 21% 2	2090
October	1st to 10th	Day	41% 6% 9% 22% 20% 3	3480
	11th to 20th	Day	31% 4 8% 27% 26% 4	3053
	21st to end	Day	32% 5% 12% 30% 18% 3	3081
November	1st to 10th	Day	40% 4 12% 25% 17% 2	1717
	11th to 20th	Day	39% 5% 11% 23% 20% 2	1710
	21st to end	Day	41% 6% 14% 24% 12% 2	1710
December	1st to 10th	Day	46% 6% 15% 16% 17% 1	1530
	11th to 20th	Day	42% 5% 14% 18% 17% 4	1906
	21st to end	Day	50% 8% 12% 19% 11% 1	2772
January	1st to 10th	Night	39% 4 13% 28% 12% 3	4429
	11th to 20th	Night	45% 6% 13% 22% 12% 3	4440
	21st to end	Night	55% 6% 10% 16% 11% 2	4884
February	1st to 10th	Night	45% 6% 15% 19% 13% 2	2410
	11th to 20th	Night	45% 5% 10% 20% 16% 4	2220
	21st to end	Night	45% 5% 8% 24% 14% 4	1884
March	1st to 10th	Night	53% 5% 10% 20% 10% 3	3734
	11th to 20th	Night	40% 9% 15% 18% 15% 2	3646
	21st to end	Night	49% 5% 7% 13% 18% 7%	3568
April	1st to 10th	Night	47% 6% 11% 19% 15% 3	1900
	11th to 20th	Night	45% 6% 9% 19% 18% 2	1874
	21st to end	Night	45% 7% 10% 19% 15% 4	1710
May	1st to 10th	Night	54% 9% 12% 15% 8% 2	2840
	11th to 20th	Night	52% 11% 14% 13% 8% 2	2728
	21st to end	Night	39% 9% 15% 22% 14% 1	2739
June	1st to 10th	Night	45% 8% 12% 22% 12% 1	1520
	11th to 20th	Night	45% 8% 13% 21% 13% 1	1520
	21st to end	Night	37% 11% 16% 22% 13% 1	1520
July	1st to 10th	Night	42% 8% 14% 21% 14% 1	2480
	11th to 20th	Night	40% 8% 17% 22% 14% 1	2472
	21st to end	Night	46% 8% 12% 18% 15% 1	2651
August	1st to 10th	Night	50% 9% 12% 18% 10% 1	2707
	11th to 20th	Night	42% 10% 15% 23% 9%	2892
	21st to end	Night	26% 7% 16% 30% 21% 1	3476
September	1st to 10th	Night	37% 6% 13% 24% 19% 1	1900
	11th to 20th	Night	33% 6% 11% 22% 26% 2	2080
	21st to end	Night	40% 7% 9% 23% 19% 2	2090
October	1st to 10th	Night	38% 6% 16% 23% 15% 2	3480
	11th to 20th	Night	26% 5% 10% 27% 28% 4	3862
	21st to end	Night	34% 4 12% 31% 17% 2	4467
November	1st to 10th	Night	38% 7% 10% 23% 19% 3	2483
	11th to 20th	Night	40% 4 12% 22% 19% 3	2470
	21st to end	Night	40% 5% 14% 26% 13% 2	2470
December	1st to 10th	Night	46% 5% 13% 22% 13% 1	2645
	11th to 20th	Night	42% 7% 15% 19% 16% 2	3288
	21st to end	Night	48% 8% 10% 24% 10% 1	4884

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	27% 25% 28% 15% 5%	180
	11th to 20th	Day	33% 23% 31% 8% 4	180
	21st to end	Day	25% 24% 35% 12% 4	198
February	1st to 10th	Day	31% 22% 31% 14% 2	358
	11th to 20th	Day	27% 29% 31% 11% 2	456
	21st to end	Day	31% 20% 32% 12% 4 1	382
March	1st to 10th	Day	30% 21% 33% 13% 3	460
	11th to 20th	Day	28% 25% 30% 14% 3 1	460
	21st to end	Day	32% 19% 32% 12% 5% 2	506
April	1st to 10th	Day	32% 21% 29% 12% 6% 1	460
	11th to 20th	Day	30% 21% 31% 11% 6%	452
	21st to end	Day	28% 20% 33% 15% 3 2	460
May	1st to 10th	Day	31% 20% 29% 14% 5% 1	463
	11th to 20th	Day	24% 14% 40% 16% 5% 1	487
	21st to end	Day	19% 14% 34% 23% 9% 2	529
June	1st to 10th	Day	17% 13% 38% 20% 10% 2	490
	11th to 20th	Day	18% 12% 38% 23% 7% 2	490
	21st to end	Day	19% 13% 36% 21% 8% 3	490
July	1st to 10th	Day	17% 10% 29% 27% 14% 2	485
	11th to 20th	Day	13% 7% 32% 32% 13% 3	484
	21st to end	Day	13% 8% 35% 32% 10% 2	532
August	1st to 10th	Day	10% 10% 32% 32% 14% 2	486
	11th to 20th	Day	17% 7% 30% 29% 13% 3	479
	21st to end	Day	12% 9% 32% 27% 14% 5%	539
September	1st to 10th	Day	18% 9% 30% 23% 14% 6%	490
	11th to 20th	Day	20% 8% 29% 21% 13% 10%	490
	21st to end	Day	20% 12% 30% 24% 9% 5%	490
October	1st to 10th	Day	27% 12% 26% 21% 11% 4	490
	11th to 20th	Day	18% 17% 30% 23% 10% 3	440
	21st to end	Day	28% 12% 31% 21% 7% 1	429
November	1st to 10th	Day	21% 16% 32% 20% 9% 2	381
	11th to 20th	Day	30% 21% 25% 19% 4 1	370
	21st to end	Day	28% 19% 31% 17% 6%	370
December	1st to 10th	Day	19% 30% 29% 17% 4	190
	11th to 20th	Day	31% 27% 32% 7% 3	180
	21st to end	Day	27% 22% 32% 14% 4 1	198
January	1st to 10th	Night	22% 19% 40% 17% 2	760
	11th to 20th	Night	27% 19% 36% 16% 2	760
	21st to end	Night	21% 20% 37% 19% 3	836
February	1st to 10th	Night	24% 18% 40% 18% 2	760
	11th to 20th	Night	22% 22% 40% 15% 1	743
	21st to end	Night	26% 20% 34% 17% 2	628
March	1st to 10th	Night	25% 18% 36% 17% 3	760
	11th to 20th	Night	21% 22% 38% 16% 3	760
	21st to end	Night	25% 20% 33% 18% 4	836
April	1st to 10th	Night	24% 21% 31% 20% 3	760
	11th to 20th	Night	23% 20% 33% 19% 6%	750
	21st to end	Night	22% 21% 35% 20% 3	570
May	1st to 10th	Night	29% 15% 30% 21% 3	570
	11th to 20th	Night	21% 17% 37% 21% 5%	515
	21st to end	Night	19% 9% 36% 30% 6%	411
June	1st to 10th	Night	20% 6% 37% 29% 8%	380
	11th to 20th	Night	21% 8% 33% 32% 5% 1	380
	21st to end	Night	16% 4 39% 35% 7%	380
July	1st to 10th	Night	15% 6% 29% 40% 10% 1	370
	11th to 20th	Night	13% 5% 29% 41% 11%	368
	21st to end	Night	13% 5% 29% 43% 9%	416
August	1st to 10th	Night	13% 4 30% 41% 12% 1	498
	11th to 20th	Night	13% 5% 30% 37% 14% 1	606
	21st to end	Night	15% 5% 25% 39% 15% 2	836
September	1st to 10th	Night	16% 6% 31% 33% 13% 1	760
	11th to 20th	Night	17% 8% 25% 29% 19% 2	760
	21st to end	Night	21% 8% 28% 29% 13% 2	760
October	1st to 10th	Night	24% 10% 28% 24% 11% 2	760
	11th to 20th	Night	20% 12% 31% 24% 11% 1	760
	21st to end	Night	27% 14% 32% 20% 6%	836
November	1st to 10th	Night	20% 13% 33% 26% 8% 1	764
	11th to 20th	Night	24% 18% 33% 18% 7% 1	760
	21st to end	Night	23% 19% 33% 19% 5% 1	760
December	1st to 10th	Night	26% 19% 34% 17% 4	760
	11th to 20th	Night	25% 18% 34% 21% 3	760
	21st to end	Night	27% 17% 37% 17% 3	836

Page generated at 2024-11-03 13:19:04. Version ac07

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