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Beacon Field Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beacon Field Observatory clear sky chart from 2005-11-06 to 2024-05-13.

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	14% 6% 2 6% 4 4 4 4 6% 8% 42%	83640
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	85863
Transparency	Day	39% 6% 11% 24% 16% 3	83350
	Night	39% 6% 10% 24% 17% 3	85672
Seeing	Day	18% 12% 27% 25% 13% 5%	14321
	Night	17% 10% 30% 29% 12% 1	23978

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	17% 5% 2 4 3 3 4 3 4 7% 48%	2590
	11th to 20th	Day	16% 10% 2 7% 4 4 4 3 4 6% 39%	2840
	21st to end	Day	18% 9% 3 7% 5% 4 4 3 4 5% 37%	3124
February	1st to 10th	Day	15% 7% 2 6% 5% 5% 5% 4 5% 7% 39%	1710
	11th to 20th	Day	18% 7% 2 4 3 3 4 4 6% 6% 41%	1726
	21st to end	Day	18% 8% 2 6% 5% 4 4 3 4 7% 39%	1570
March	1st to 10th	Day	22% 7% 2 5% 4 4 4 3 5% 7% 36%	3368
	11th to 20th	Day	10% 4 2 5% 4 5% 4 4 5% 7% 51%	3480
	21st to end	Day	21% 6% 2 5% 4 4 3 3 5% 6% 40%	3893
April	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 6% 7% 43%	2280
	11th to 20th	Day	13% 6% 2 5% 5% 4 4 3 5% 6% 48%	2254
	21st to end	Day	17% 7% 2 5% 3 4 5% 4 6% 6% 41%	2280
May	1st to 10th	Day	14% 8% 2 7% 4 4 5% 4 7% 8% 37%	2408
	11th to 20th	Day	17% 6% 2 5% 5% 4 5% 5% 6% 8% 36%	2438
	21st to end	Day	14% 6% 2 6% 5% 4 5% 4 6% 8% 40%	2725
June	1st to 10th	Day	11% 4 2 5% 5% 4 5% 4 7% 10% 43%	2520
	11th to 20th	Day	11% 5% 2 6% 4 4 6% 6% 7% 9% 40%	2520
	21st to end	Day	9% 4 2 6% 5% 5% 5% 5% 8% 10% 42%	2520
July	1st to 10th	Day	9% 5% 2 7% 5% 6% 4 5% 8% 8% 41%	2520
	11th to 20th	Day	6% 4 2 5% 5% 4 6% 6% 8% 11% 43%	2443
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 6% 8% 10% 36%	2547
August	1st to 10th	Day	9% 6% 3 7% 5% 6% 6% 5% 8% 9% 36%	2327
	11th to 20th	Day	11% 5% 2 6% 5% 5% 7% 5% 7% 9% 38%	2197
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 40%	2376
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 3 6% 7% 45%	2160
	11th to 20th	Day	10% 6% 3 4 4 3 4 3 6% 9% 47%	2160
	21st to end	Day	17% 8% 2 6% 3 4 4 4 6% 6% 38%	1897
October	1st to 10th	Day	15% 6% 2 5% 4 3 4 3 5% 7% 46%	1800
	11th to 20th	Day	17% 5% 2 4 3 3 3 3 5% 6% 49%	1800
	21st to end	Day	14% 6% 2 6% 3 3 3 3 5% 7% 47%	1980
November	1st to 10th	Day	12% 5% 1 4 4 4 4 3 4 7% 52%	1758
	11th to 20th	Day	14% 6% 1 4 3 3 3 3 5% 8% 49%	1707
	21st to end	Day	14% 6% 2 5% 4 3 3 4 5% 6% 48%	1520
December	1st to 10th	Day	15% 5% 3 6% 4 4 4 3 6% 7% 42%	1520
	11th to 20th	Day	15% 7% 2 5% 3 4 4 3 4 7% 47%	1910
	21st to end	Day	17% 7% 3 6% 5% 4 5% 4 6% 7% 36%	2772
January	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 4 6% 46%	4351
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 4 5% 46%	4120
	21st to end	Night	19% 9% 3 6% 4 3 3 3 3 5% 42%	4532
February	1st to 10th	Night	15% 7% 3 6% 5% 4 4 3 6% 6% 42%	2470
	11th to 20th	Night	19% 7% 2 6% 4 3 3 3 4 6% 43%	2338
	21st to end	Night	18% 8% 2 6% 4 4 3 3 5% 6% 43%	1884
March	1st to 10th	Night	21% 7% 3 6% 4 3 3 3 4 6% 38%	3482
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 5% 8% 50%	3480
	21st to end	Night	15% 8% 3 6% 4 3 3 3 4 5% 46%	3738
April	1st to 10th	Night	15% 7% 2 6% 5% 5% 4 4 5% 6% 42%	1900
	11th to 20th	Night	13% 5% 2 6% 3 3 3 4 5% 7% 48%	1875
	21st to end	Night	17% 6% 2 5% 3 4 3 4 6% 8% 42%	1900
May	1st to 10th	Night	15% 7% 3 5% 4 4 4 4 7% 8% 38%	1787
	11th to 20th	Night	16% 7% 3 6% 5% 4 4 4 6% 9% 37%	1509
	21st to end	Night	12% 6% 2 6% 4 3 5% 5% 7% 10% 39%	1550
June	1st to 10th	Night	10% 5% 2 5% 3 4 5% 4 8% 9% 44%	1440
	11th to 20th	Night	12% 5% 1 6% 4 5% 5% 5% 6% 10% 40%	1440
	21st to end	Night	9% 5% 2 6% 5% 4 4 5% 8% 10% 42%	1440
July	1st to 10th	Night	8% 5% 3 7% 5% 5% 6% 4 8% 10% 40%	1440
	11th to 20th	Night	6% 5% 2 6% 4 4 6% 4 7% 11% 46%	1513
	21st to end	Night	7% 5% 1 6% 5% 5% 5% 5% 10% 11% 40%	1771
August	1st to 10th	Night	8% 4 2 7% 4 6% 7% 5% 7% 9% 40%	1611
	11th to 20th	Night	11% 6% 3 7% 5% 5% 5% 5% 8% 7% 38%	1683
	21st to end	Night	9% 6% 3 6% 4 5% 5% 3 6% 9% 43%	1980
September	1st to 10th	Night	13% 6% 3 7% 3 5% 4 3 6% 8% 43%	1800
	11th to 20th	Night	9% 7% 2 5% 5% 3 4 3 5% 8% 50%	1800
	21st to end	Night	16% 8% 2 7% 4 4 4 4 6% 7% 39%	2057
October	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 4 6% 46%	2160
	11th to 20th	Night	15% 5% 2 5% 3 4 3 2 4 6% 50%	2160
	21st to end	Night	15% 5% 2 5% 3 3 4 4 4 6% 49%	2376
November	1st to 10th	Night	12% 5% 2 4 4 3 4 3 4 5% 54%	2317
	11th to 20th	Night	14% 8% 2 4 4 3 3 3 4 7% 50%	2470
	21st to end	Night	13% 5% 2 4 5% 3 4 5% 6% 7% 48%	2660
December	1st to 10th	Night	16% 8% 3 6% 3 3 4 3 4 6% 42%	2660
	11th to 20th	Night	17% 6% 2 5% 4 4 4 4 5% 8% 43%	3285
	21st to end	Night	16% 7% 3 6% 4 5% 5% 4 6% 7% 36%	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	36% 4 8% 31% 16% 4	2591
	11th to 20th	Day	45% 5% 9% 22% 15% 5%	2840
	21st to end	Day	48% 5% 10% 22% 11% 2	3124
February	1st to 10th	Day	44% 5% 12% 24% 13% 2	1710
	11th to 20th	Day	42% 4 8% 25% 18% 3	1735
	21st to end	Day	46% 5% 11% 18% 16% 3	1570
March	1st to 10th	Day	47% 6% 9% 23% 12% 4	3368
	11th to 20th	Day	31% 7% 7% 28% 23% 5%	3480
	21st to end	Day	45% 5% 10% 21% 15% 4	3893
April	1st to 10th	Day	39% 5% 11% 21% 19% 5%	2280
	11th to 20th	Day	36% 6% 9% 22% 21% 6%	2254
	21st to end	Day	41% 6% 10% 22% 17% 4	2280
May	1st to 10th	Day	42% 7% 12% 21% 15% 2	2408
	11th to 20th	Day	44% 7% 12% 21% 13% 2	2442
	21st to end	Day	40% 8% 13% 26% 12% 2	2725
June	1st to 10th	Day	35% 7% 14% 26% 15% 2	2520
	11th to 20th	Day	36% 10% 13% 22% 16% 2	2520
	21st to end	Day	33% 9% 15% 24% 17% 2	2520
July	1st to 10th	Day	37% 10% 12% 22% 16% 3	2450
	11th to 20th	Day	31% 9% 16% 26% 16% 3	2368
	21st to end	Day	38% 9% 14% 20% 18% 1	2405
August	1st to 10th	Day	40% 10% 15% 23% 12% 1	2314
	11th to 20th	Day	39% 10% 14% 22% 15% 1	2197
	21st to end	Day	36% 8% 15% 23% 14% 4	2376
September	1st to 10th	Day	37% 7% 14% 19% 19% 4	2160
	11th to 20th	Day	33% 6% 12% 25% 21% 4	2160
	21st to end	Day	44% 6% 10% 20% 18% 2	1897
October	1st to 10th	Day	38% 5% 10% 25% 19% 3	1800
	11th to 20th	Day	36% 5% 9% 25% 22% 4	1800
	21st to end	Day	37% 3 8% 26% 23% 3	1980
November	1st to 10th	Day	32% 4 11% 27% 21% 4	1758
	11th to 20th	Day	33% 4 11% 25% 21% 5%	1707
	21st to end	Day	37% 4 9% 27% 19% 3	1520
December	1st to 10th	Day	42% 5% 13% 26% 12% 3	1520
	11th to 20th	Day	38% 5% 8% 32% 13% 3	1906
	21st to end	Day	44% 7% 11% 25% 12% 1	2772
January	1st to 10th	Night	39% 4 8% 27% 18% 4	4351
	11th to 20th	Night	40% 4 9% 24% 19% 4	4120
	21st to end	Night	45% 4 7% 26% 17% 1	4532
February	1st to 10th	Night	42% 5% 11% 24% 16% 2	2470
	11th to 20th	Night	44% 3 8% 22% 18% 5%	2340
	21st to end	Night	42% 4 10% 22% 16% 5%	1884
March	1st to 10th	Night	47% 5% 9% 24% 13% 2	3482
	11th to 20th	Night	31% 7% 9% 27% 22% 4	3480
	21st to end	Night	40% 5% 7% 22% 19% 6%	3738
April	1st to 10th	Night	42% 5% 9% 19% 21% 4	1900
	11th to 20th	Night	36% 6% 11% 21% 20% 6%	1875
	21st to end	Night	39% 6% 10% 25% 15% 5%	1900
May	1st to 10th	Night	42% 7% 12% 22% 13% 4	1787
	11th to 20th	Night	43% 7% 11% 19% 16% 3	1510
	21st to end	Night	37% 9% 17% 22% 13% 2	1551
June	1st to 10th	Night	34% 9% 12% 26% 17% 2	1440
	11th to 20th	Night	37% 9% 13% 24% 13% 3	1440
	21st to end	Night	34% 8% 16% 20% 19% 3	1440
July	1st to 10th	Night	38% 9% 16% 20% 13% 4	1400
	11th to 20th	Night	31% 10% 15% 26% 16% 2	1465
	21st to end	Night	31% 10% 16% 26% 15% 1	1672
August	1st to 10th	Night	35% 11% 17% 22% 15% 1	1600
	11th to 20th	Night	41% 10% 15% 21% 13% 2	1683
	21st to end	Night	37% 8% 14% 23% 14% 3	1980
September	1st to 10th	Night	38% 7% 10% 22% 17% 5%	1800
	11th to 20th	Night	32% 7% 10% 26% 22% 4	1800
	21st to end	Night	44% 7% 9% 19% 17% 4	2057
October	1st to 10th	Night	40% 5% 10% 23% 18% 4	2160
	11th to 20th	Night	36% 5% 8% 26% 22% 3	2160
	21st to end	Night	36% 5% 9% 24% 22% 4	2376
November	1st to 10th	Night	33% 5% 9% 26% 21% 6%	2317
	11th to 20th	Night	36% 4 9% 22% 22% 6%	2470
	21st to end	Night	34% 5% 11% 26% 22% 4	2660
December	1st to 10th	Night	43% 5% 10% 24% 15% 3	2660
	11th to 20th	Night	40% 4 10% 24% 18% 4	3288
	21st to end	Night	44% 7% 13% 22% 11% 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	28% 18% 33% 16% 5%	202
	11th to 20th	Day	29% 22% 31% 15% 3	270
	21st to end	Day	22% 23% 35% 15% 5%	297
February	1st to 10th	Day	22% 23% 38% 13% 4	270
	11th to 20th	Day	33% 21% 34% 11% 1	333
	21st to end	Day	29% 21% 30% 18% 2	382
March	1st to 10th	Day	22% 22% 31% 21% 3	460
	11th to 20th	Day	27% 20% 31% 17% 5% 1	460
	21st to end	Day	23% 16% 33% 23% 4 2	506
April	1st to 10th	Day	20% 23% 32% 19% 6% 1	460
	11th to 20th	Day	16% 18% 31% 21% 10% 3	452
	21st to end	Day	25% 13% 31% 23% 7% 1	460
May	1st to 10th	Day	25% 15% 26% 21% 10% 3	463
	11th to 20th	Day	20% 12% 31% 24% 11% 2	456
	21st to end	Day	18% 6% 23% 27% 21% 5%	485
June	1st to 10th	Day	12% 9% 28% 26% 20% 6%	450
	11th to 20th	Day	14% 8% 26% 31% 16% 5%	450
	21st to end	Day	10% 6% 27% 35% 18% 4	450
July	1st to 10th	Day	12% 3 17% 33% 24% 12%	445
	11th to 20th	Day	5% 2 15% 41% 27% 10%	444
	21st to end	Day	9% 3 20% 38% 22% 7%	488
August	1st to 10th	Day	10% 5% 20% 31% 25% 9%	446
	11th to 20th	Day	11% 4 16% 32% 26% 11%	439
	21st to end	Day	9% 3 20% 31% 24% 13%	495
September	1st to 10th	Day	16% 5% 20% 24% 20% 14%	450
	11th to 20th	Day	14% 4 18% 36% 17% 11%	450
	21st to end	Day	22% 12% 24% 26% 13% 4	450
October	1st to 10th	Day	21% 6% 23% 25% 18% 7%	450
	11th to 20th	Day	16% 13% 27% 27% 14% 3	450
	21st to end	Day	18% 12% 34% 25% 8% 3	495
November	1st to 10th	Day	16% 12% 30% 28% 11% 3	408
	11th to 20th	Day	17% 15% 33% 24% 9% 1	367
	21st to end	Day	22% 20% 28% 20% 9% 1	180
December	1st to 10th	Day	18% 20% 38% 16% 6% 2	180
	11th to 20th	Day	23% 21% 28% 21% 7% 1	180
	21st to end	Day	25% 16% 32% 20% 7% 1	198
January	1st to 10th	Night	20% 18% 39% 19% 4	760
	11th to 20th	Night	22% 14% 35% 24% 5%	760
	21st to end	Night	19% 17% 37% 24% 2	836
February	1st to 10th	Night	20% 15% 35% 27% 3	760
	11th to 20th	Night	25% 19% 38% 16% 1	743
	21st to end	Night	25% 17% 34% 21% 2	628
March	1st to 10th	Night	20% 13% 40% 24% 3	760
	11th to 20th	Night	22% 15% 38% 19% 6% 1	760
	21st to end	Night	18% 14% 41% 23% 3	836
April	1st to 10th	Night	19% 18% 39% 21% 4	760
	11th to 20th	Night	16% 14% 35% 29% 7%	751
	21st to end	Night	21% 9% 33% 28% 9%	760
May	1st to 10th	Night	19% 9% 31% 30% 11%	647
	11th to 20th	Night	18% 6% 31% 35% 10%	430
	21st to end	Night	15% 3 24% 38% 19% 1	389
June	1st to 10th	Night	11% 3 27% 36% 21% 2	360
	11th to 20th	Night	14% 5% 20% 41% 19% 1	360
	21st to end	Night	10% 3 23% 46% 17% 1	360
July	1st to 10th	Night	9% 2 21% 38% 29% 2	350
	11th to 20th	Night	7% 2 12% 44% 31% 4	421
	21st to end	Night	8% 2 19% 39% 29% 3	591
August	1st to 10th	Night	8% 2 12% 45% 29% 3	537
	11th to 20th	Night	13% 3 16% 39% 26% 2	619
	21st to end	Night	12% 2 17% 35% 29% 5%	792
September	1st to 10th	Night	16% 3 17% 33% 27% 5%	720
	11th to 20th	Night	11% 3 16% 38% 29% 4	720
	21st to end	Night	19% 6% 23% 33% 18% 1	720
October	1st to 10th	Night	19% 6% 20% 31% 20% 5%	720
	11th to 20th	Night	17% 9% 27% 30% 17% 1	720
	21st to end	Night	18% 11% 32% 26% 13% 1	792
November	1st to 10th	Night	14% 8% 34% 30% 12% 2	740
	11th to 20th	Night	18% 13% 30% 29% 9% 1	760
	21st to end	Night	17% 14% 32% 27% 10% 1	760
December	1st to 10th	Night	20% 14% 34% 23% 8% 1	760
	11th to 20th	Night	18% 11% 41% 25% 5%	760
	21st to end	Night	21% 12% 35% 29% 3	836

Page generated at 2024-05-10 12:38:57. Version ac07

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