This page made possible by the sponsorship of:

Friends of Beacon Field Airport

.

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 2025-09-19.

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 5% 4 6% 8% 42%	126196
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	122852
Transparency	Day	25% 39% 7% 15% 11% 3	129789
	Night	25% 39% 7% 15% 12% 3	127329
Seeing	Day	18% 12% 27% 25% 13% 4	16143
	Night	17% 10% 30% 29% 12% 1	25627

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% 4 1 4 4 3 4 3 5% 6% 51%	3712
	11th to 20th	Day	15% 8% 2 6% 4 3 3 3 4 5% 47%	4060
	21st to end	Day	15% 7% 2 7% 5% 4 4 3 4 6% 42%	4466
February	1st to 10th	Day	15% 7% 2 6% 5% 5% 5% 4 5% 7% 39%	1800
	11th to 20th	Day	19% 7% 3 5% 3 3 3 4 6% 6% 40%	1820
	21st to end	Day	18% 8% 2 6% 5% 4 4 3 4 7% 40%	1650
March	1st to 10th	Day	18% 6% 1 5% 3 4 5% 3 5% 7% 42%	4840
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 4 6% 51%	4980
	21st to end	Day	17% 6% 2 6% 5% 4 4 4 5% 7% 41%	5571
April	1st to 10th	Day	13% 7% 2 6% 4 5% 5% 4 6% 7% 43%	2400
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 6% 48%	2374
	21st to end	Day	17% 6% 2 5% 3 4 5% 4 6% 7% 42%	2400
May	1st to 10th	Day	19% 8% 2 7% 5% 4 5% 4 7% 9% 31%	5721
	11th to 20th	Day	20% 7% 3 6% 4 4 5% 5% 6% 10% 31%	6152
	21st to end	Day	15% 5% 2 6% 5% 5% 5% 4 6% 9% 39%	6934
June	1st to 10th	Day	11% 4 2 6% 5% 4 5% 4 7% 10% 43%	2800
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 5% 7% 9% 42%	2800
	21st to end	Day	8% 4 2 6% 4 4 5% 5% 8% 10% 43%	2800
July	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 5% 8% 11% 44%	6360
	11th to 20th	Day	9% 6% 3 7% 5% 5% 7% 6% 10% 12% 29%	6143
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 39%	6424
August	1st to 10th	Day	15% 6% 2 6% 5% 5% 6% 4 8% 10% 33%	4234
	11th to 20th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 9% 38%	3978
	21st to end	Day	9% 4 2 5% 4 4 5% 4 7% 9% 47%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 4 3 6% 7% 46%	2400
	11th to 20th	Day	11% 6% 3 4 4 3 4 3 6% 9% 47%	2376
	21st to end	Day	19% 8% 2 6% 3 4 4 4 6% 6% 37%	2001
October	1st to 10th	Day	15% 5% 2 5% 4 3 4 3 5% 6% 46%	1900
	11th to 20th	Day	16% 4 2 4 3 3 3 3 5% 6% 51%	1900
	21st to end	Day	13% 6% 2 5% 3 3 3 3 5% 7% 49%	2090
November	1st to 10th	Day	11% 5% 1 4 4 4 4 3 4 7% 52%	1852
	11th to 20th	Day	13% 6% 1 4 3 3 3 3 5% 8% 49%	1796
	21st to end	Day	14% 6% 2 5% 4 3 3 4 5% 6% 48%	1600
December	1st to 10th	Day	11% 5% 2 7% 4 3 4 3 6% 7% 48%	2600
	11th to 20th	Day	18% 8% 2 5% 3 3 3 3 4 6% 45%	2990
	21st to end	Day	16% 8% 3 7% 4 4 4 4 6% 7% 38%	3960
January	1st to 10th	Night	12% 7% 2 5% 4 3 4 3 4 5% 50%	6229
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 5% 53%	5900
	21st to end	Night	14% 8% 3 6% 4 3 3 2 4 6% 47%	6490
February	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 6% 6% 41%	2600
	11th to 20th	Night	20% 7% 2 6% 3 3 3 3 4 6% 43%	2464
	21st to end	Night	17% 8% 2 5% 3 4 3 3 5% 7% 43%	1980
March	1st to 10th	Night	16% 6% 2 6% 4 3 3 3 4 5% 47%	5010
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 8% 50%	4980
	21st to end	Night	13% 7% 3 6% 4 4 4 3 5% 6% 44%	5360
April	1st to 10th	Night	15% 7% 2 6% 5% 5% 4 4 5% 6% 41%	2000
	11th to 20th	Night	14% 5% 2 6% 3 3 4 4 5% 7% 46%	1975
	21st to end	Night	16% 5% 2 5% 3 4 3 4 7% 7% 43%	2000
May	1st to 10th	Night	18% 10% 3 7% 5% 5% 5% 4 6% 8% 29%	4215
	11th to 20th	Night	22% 8% 3 6% 4 4 4 4 6% 9% 31%	3726
	21st to end	Night	17% 6% 3 7% 4 4 5% 4 7% 9% 35%	3920
June	1st to 10th	Night	10% 5% 2 6% 4 5% 6% 4 8% 8% 44%	1600
	11th to 20th	Night	13% 5% 1 6% 4 5% 5% 5% 6% 10% 40%	1600
	21st to end	Night	9% 5% 2 6% 5% 5% 4 5% 8% 10% 42%	1600
July	1st to 10th	Night	8% 6% 3 7% 5% 5% 6% 5% 7% 10% 40%	3598
	11th to 20th	Night	9% 8% 3 9% 6% 5% 7% 5% 8% 11% 29%	3796
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 8% 10% 39%	4427
August	1st to 10th	Night	16% 6% 2 8% 5% 5% 5% 4 7% 9% 33%	2915
	11th to 20th	Night	11% 7% 3 8% 6% 5% 5% 5% 7% 8% 35%	3035
	21st to end	Night	9% 5% 2 5% 4 4 3 3 6% 8% 51%	3586
September	1st to 10th	Night	13% 5% 3 7% 4 5% 4 3 5% 7% 45%	2000
	11th to 20th	Night	10% 7% 2 5% 4 3 4 3 5% 8% 48%	1981
	21st to end	Night	18% 8% 2 7% 4 4 4 3 6% 7% 37%	2173
October	1st to 10th	Night	17% 6% 3 5% 3 3 4 3 4 6% 46%	2280
	11th to 20th	Night	15% 5% 2 5% 3 4 3 2 4 6% 51%	2280
	21st to end	Night	14% 5% 2 5% 3 3 4 4 4 6% 50%	2508
November	1st to 10th	Night	12% 5% 2 5% 4 3 4 3 5% 5% 54%	2443
	11th to 20th	Night	14% 7% 2 4 4 3 3 3 4 7% 49%	2600
	21st to end	Night	13% 5% 2 4 5% 3 4 4 6% 7% 49%	2800
December	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 4 6% 53%	4580
	11th to 20th	Night	21% 6% 2 5% 4 4 4 3 5% 7% 40%	5205
	21st to end	Night	17% 7% 3 6% 4 4 5% 4 5% 7% 38%	6996

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	25% 27% 3 20% 19% 7%	3713
	11th to 20th	Day	29% 27% 4 17% 15% 7%	4060
	21st to end	Day	31% 30% 6% 21% 10% 2	4466
February	1st to 10th	Day	19% 63% 5% 9% 5% 1	1800
	11th to 20th	Day	18% 61% 3 9% 7% 2	1829
	21st to end	Day	18% 62% 4 8% 7% 1	1650
March	1st to 10th	Day	33% 30% 5% 14% 11% 7%	4840
	11th to 20th	Day	23% 30% 6% 20% 17% 4	4980
	21st to end	Day	30% 30% 7% 14% 13% 6%	5571
April	1st to 10th	Day	18% 63% 3 8% 7% 1	2400
	11th to 20th	Day	15% 63% 4 9% 8% 2	2374
	21st to end	Day	17% 62% 3 10% 7% 1	2400
May	1st to 10th	Day	37% 32% 10% 14% 6% 1	5754
	11th to 20th	Day	35% 32% 8% 19% 5%	6156
	21st to end	Day	30% 32% 9% 15% 12% 2	6949
June	1st to 10th	Day	15% 63% 5% 10% 6%	2800
	11th to 20th	Day	14% 64% 4 9% 8% 1	2800
	21st to end	Day	12% 62% 7% 11% 8% 1	2800
July	1st to 10th	Day	24% 31% 17% 14% 10% 4	6290
	11th to 20th	Day	35% 31% 14% 15% 4	6068
	21st to end	Day	28% 28% 8% 18% 18%	6240
August	1st to 10th	Day	30% 38% 11% 17% 4	4221
	11th to 20th	Day	24% 39% 9% 19% 8%	4017
	21st to end	Day	19% 38% 8% 20% 14% 1	4312
September	1st to 10th	Day	16% 59% 7% 9% 7% 2	2400
	11th to 20th	Day	16% 58% 4 11% 8% 2	2376
	21st to end	Day	22% 60% 4 10% 4 1	2001
October	1st to 10th	Day	24% 37% 3 9% 22% 4	3160
	11th to 20th	Day	11% 37% 4 20% 20% 9%	3140
	21st to end	Day	8% 36% 6% 21% 19% 9%	3428
November	1st to 10th	Day	17% 56% 6% 10% 8% 3	1852
	11th to 20th	Day	14% 57% 4 11% 13% 2	1796
	21st to end	Day	16% 57% 3 15% 8% 1	1600
December	1st to 10th	Day	23% 36% 7% 17% 13% 3	2600
	11th to 20th	Day	28% 31% 10% 21% 8% 2	2986
	21st to end	Day	33% 29% 9% 16% 12% 1	3960
January	1st to 10th	Night	27% 26% 4 18% 20% 4	6229
	11th to 20th	Night	24% 26% 4 20% 19% 7%	5900
	21st to end	Night	30% 28% 4 21% 14% 2	6490
February	1st to 10th	Night	17% 63% 6% 10% 4 1	2600
	11th to 20th	Night	18% 60% 3 8% 9% 2	2466
	21st to end	Night	16% 61% 4 9% 6% 3	1980
March	1st to 10th	Night	30% 30% 4 17% 11% 8%	5010
	11th to 20th	Night	21% 30% 7% 19% 17% 6%	4980
	21st to end	Night	29% 30% 5% 16% 16% 4	5360
April	1st to 10th	Night	18% 62% 3 7% 9% 1	2000
	11th to 20th	Night	14% 63% 5% 10% 7% 1	1975
	21st to end	Night	16% 63% 4 9% 7% 1	2000
May	1st to 10th	Night	41% 32% 9% 12% 5% 2	4245
	11th to 20th	Night	36% 32% 8% 16% 7%	3727
	21st to end	Night	34% 32% 9% 16% 8% 2	3927
June	1st to 10th	Night	15% 63% 4 10% 7% 1	1600
	11th to 20th	Night	14% 64% 6% 11% 5%	1600
	21st to end	Night	13% 62% 5% 10% 8% 1	1600
July	1st to 10th	Night	30% 31% 14% 13% 11% 1	3560
	11th to 20th	Night	37% 32% 15% 12% 4	3751
	21st to end	Night	29% 29% 10% 17% 14%	4297
August	1st to 10th	Night	34% 39% 10% 13% 4	2904
	11th to 20th	Night	28% 39% 8% 17% 7%	3062
	21st to end	Night	18% 36% 6% 23% 17%	3586
September	1st to 10th	Night	16% 58% 6% 12% 6% 2	2000
	11th to 20th	Night	16% 58% 4 11% 9% 2	1981
	21st to end	Night	22% 61% 4 9% 5%	2173
October	1st to 10th	Night	26% 37% 6% 13% 12% 5%	3800
	11th to 20th	Night	11% 37% 7% 13% 25% 8%	3779
	21st to end	Night	9% 37% 6% 23% 18% 7%	4120
November	1st to 10th	Night	16% 57% 5% 11% 8% 3	2443
	11th to 20th	Night	15% 56% 4 9% 12% 4	2600
	21st to end	Night	13% 57% 6% 13% 10% 1	2800
December	1st to 10th	Night	19% 36% 9% 19% 16% 2	4580
	11th to 20th	Night	32% 32% 8% 13% 10% 4	5208
	21st to end	Night	33% 29% 10% 16% 12%	6996

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	31% 18% 32% 14% 4	225
	11th to 20th	Day	29% 22% 32% 14% 3	300
	21st to end	Day	22% 23% 35% 15% 5%	330
February	1st to 10th	Day	24% 25% 36% 12% 3	300
	11th to 20th	Day	36% 21% 32% 10% 1	367
	21st to end	Day	28% 21% 31% 18% 2	414
March	1st to 10th	Day	23% 23% 31% 20% 3	500
	11th to 20th	Day	27% 19% 32% 16% 5% 1	500
	21st to end	Day	23% 17% 34% 21% 4 1	550
April	1st to 10th	Day	22% 23% 31% 18% 5% 1	500
	11th to 20th	Day	17% 19% 32% 20% 9% 3	492
	21st to end	Day	24% 12% 32% 23% 7% 1	500
May	1st to 10th	Day	25% 15% 28% 20% 10% 2	503
	11th to 20th	Day	22% 12% 30% 23% 11% 2	527
	21st to end	Day	18% 9% 24% 25% 19% 5%	573
June	1st to 10th	Day	12% 9% 29% 25% 19% 6%	530
	11th to 20th	Day	14% 8% 25% 33% 16% 4	530
	21st to end	Day	10% 5% 27% 35% 19% 5%	530
July	1st to 10th	Day	11% 3 17% 36% 22% 11%	525
	11th to 20th	Day	5% 2 16% 41% 26% 10%	524
	21st to end	Day	9% 3 19% 39% 23% 7%	576
August	1st to 10th	Day	11% 5% 22% 31% 23% 8%	526
	11th to 20th	Day	12% 4 18% 33% 24% 9%	519
	21st to end	Day	9% 4 21% 31% 23% 12%	583
September	1st to 10th	Day	15% 6% 23% 25% 18% 12%	530
	11th to 20th	Day	14% 4 20% 35% 17% 10%	522
	21st to end	Day	24% 12% 23% 24% 12% 4	490
October	1st to 10th	Day	21% 6% 23% 24% 18% 7%	490
	11th to 20th	Day	16% 14% 26% 27% 14% 3	490
	21st to end	Day	17% 11% 34% 27% 9% 4	539
November	1st to 10th	Day	16% 12% 31% 29% 10% 3	442
	11th to 20th	Day	18% 15% 35% 23% 9% 1	396
	21st to end	Day	23% 22% 28% 19% 9% 1	200
December	1st to 10th	Day	19% 19% 41% 15% 5% 2	200
	11th to 20th	Day	24% 20% 29% 21% 7% 1	200
	21st to end	Day	25% 17% 31% 21% 6%	220
January	1st to 10th	Night	21% 19% 38% 18% 4	800
	11th to 20th	Night	22% 14% 35% 24% 5%	800
	21st to end	Night	19% 17% 37% 24% 2	880
February	1st to 10th	Night	20% 15% 35% 26% 3	800
	11th to 20th	Night	26% 19% 37% 16% 1	783
	21st to end	Night	25% 17% 35% 21% 2	660
March	1st to 10th	Night	20% 15% 39% 23% 3	800
	11th to 20th	Night	22% 15% 38% 20% 6% 1	800
	21st to end	Night	19% 14% 41% 22% 3	880
April	1st to 10th	Night	20% 18% 39% 21% 4	800
	11th to 20th	Night	16% 14% 34% 28% 6%	791
	21st to end	Night	21% 9% 34% 28% 8%	800
May	1st to 10th	Night	19% 10% 31% 30% 10%	681
	11th to 20th	Night	18% 7% 30% 35% 10%	467
	21st to end	Night	15% 4 26% 36% 18% 1	433
June	1st to 10th	Night	10% 4 27% 38% 20% 2	400
	11th to 20th	Night	14% 5% 21% 42% 18% 1	400
	21st to end	Night	10% 3 24% 44% 18% 1	400
July	1st to 10th	Night	9% 2 22% 38% 28% 2	390
	11th to 20th	Night	7% 2 13% 44% 31% 4	470
	21st to end	Night	8% 2 19% 39% 29% 3	657
August	1st to 10th	Night	10% 2 13% 44% 28% 3	597
	11th to 20th	Night	13% 3 17% 39% 26% 2	689
	21st to end	Night	12% 2 17% 36% 28% 4	880
September	1st to 10th	Night	15% 3 19% 34% 26% 4	800
	11th to 20th	Night	13% 3 16% 38% 28% 4	793
	21st to end	Night	21% 7% 22% 32% 17% 1	760
October	1st to 10th	Night	19% 6% 20% 30% 19% 5%	760
	11th to 20th	Night	16% 10% 27% 30% 17% 1	760
	21st to end	Night	17% 10% 31% 28% 13% 1	836
November	1st to 10th	Night	13% 8% 34% 30% 12% 2	780
	11th to 20th	Night	19% 13% 30% 29% 9% 1	800
	21st to end	Night	17% 14% 33% 26% 10% 1	800
December	1st to 10th	Night	20% 13% 35% 23% 8% 1	800
	11th to 20th	Night	19% 11% 40% 26% 5%	800
	21st to end	Night	21% 12% 34% 30% 4	880

Page generated at 2025-09-16 01:49:15. Version ac07

Copyright © 2025 Attilla Danko.