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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 2005-11-05 to 2023-05-20.

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	13% 5% 2 4 4 3 4 4 5% 7% 42%	69876
	Night	14% 5% 2 5% 4 2 4 4 5% 7% 43%	69382
Transparency	Day	39% 6% 11% 23% 16% 3	69579
	Night	38% 6% 11% 23% 17% 3	69187
Seeing	Day	18% 11% 26% 24% 13% 4	12947
	Night	17% 9% 29% 28% 12% 1	22498

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	14% 6% 2 4 5% 2 4 3 5% 7% 42%	1464
	11th to 20th	Day	16% 7% 1 5% 4 2 3 5% 5% 6% 41%	1616
	21st to end	Day	15% 6% 2 6% 5% 3 4 3 4 5% 42%	1741
February	1st to 10th	Day	15% 6% 2 4 5% 4 5% 4 5% 7% 37%	1600
	11th to 20th	Day	18% 6% 3 4 3 2 4 4 5% 6% 40%	1604
	21st to end	Day	18% 6% 2 6% 5% 3 3 4 4 6% 38%	1474
March	1st to 10th	Day	12% 6% 1 4 4 2 4 3 4 6% 49%	1938
	11th to 20th	Day	17% 5% 2 4 5% 3 5% 3 4 6% 41%	1947
	21st to end	Day	17% 5% 3 5% 6% 3 4 3 4 5% 38%	2203
April	1st to 10th	Day	12% 6% 2 4 4 3 4 4 5% 7% 44%	2128
	11th to 20th	Day	12% 5% 1 4 4 3 4 3 4 5% 48%	2100
	21st to end	Day	17% 5% 2 4 3 2 4 5% 5% 7% 41%	2152
May	1st to 10th	Day	13% 7% 2 5% 4 3 5% 5% 6% 8% 38%	2269
	11th to 20th	Day	16% 5% 2 4 5% 2 4 6% 5% 8% 37%	2345
	21st to end	Day	13% 4 2 4 5% 2 5% 5% 6% 8% 40%	2505
June	1st to 10th	Day	11% 3 2 4 5% 2 5% 5% 6% 10% 41%	2380
	11th to 20th	Day	11% 5% 1 5% 4 3 5% 6% 6% 9% 40%	2380
	21st to end	Day	7% 3 2 5% 5% 3 5% 6% 7% 9% 43%	2357
July	1st to 10th	Day	9% 4 2 5% 5% 3 5% 4 7% 8% 43%	2380
	11th to 20th	Day	5% 3 2 4 5% 3 6% 7% 7% 11% 43%	2273
	21st to end	Day	9% 5% 2 6% 5% 3 7% 6% 7% 10% 35%	2376
August	1st to 10th	Day	8% 5% 2 5% 5% 4 6% 6% 7% 8% 35%	2163
	11th to 20th	Day	11% 5% 1 4 6% 4 6% 6% 6% 9% 36%	2020
	21st to end	Day	9% 4 2 5% 5% 3 5% 6% 7% 9% 40%	2229
September	1st to 10th	Day	14% 4 1 5% 4 3 3 4 5% 7% 43%	2031
	11th to 20th	Day	10% 5% 2 3 4 2 4 3 6% 9% 46%	2036
	21st to end	Day	15% 7% 2 5% 3 2 4 5% 5% 6% 40%	1776
October	1st to 10th	Day	15% 5% 2 5% 5% 2 3 4 4 6% 44%	1694
	11th to 20th	Day	16% 4 2 4 3 2 3 3 5% 5% 49%	1679
	21st to end	Day	14% 6% 2 4 4 2 3 3 5% 6% 46%	1864
November	1st to 10th	Day	11% 4 1 3 3 3 4 4 4 6% 52%	1660
	11th to 20th	Day	14% 5% 1 3 3 2 3 3 4 7% 49%	1607
	21st to end	Day	14% 4 2 4 3 2 3 3 5% 6% 48%	1430
December	1st to 10th	Day	15% 5% 2 5% 4 2 4 4 6% 6% 43%	1433
	11th to 20th	Day	15% 6% 2 4 3 2 4 4 4 6% 44%	1440
	21st to end	Day	19% 6% 3 4 3 2 4 4 4 6% 41%	1582
January	1st to 10th	Night	15% 7% 2 4 3 2 3 4 4 6% 46%	2444
	11th to 20th	Night	16% 6% 2 5% 4 3 4 4 4 6% 40%	2332
	21st to end	Night	14% 7% 2 4 3 2 3 3 4 6% 46%	2536
February	1st to 10th	Night	15% 6% 2 4 5% 2 4 4 5% 6% 40%	2316
	11th to 20th	Night	18% 6% 2 5% 4 2 3 3 4 6% 43%	2159
	21st to end	Night	17% 7% 2 4 4 2 3 3 4 6% 42%	1772
March	1st to 10th	Night	14% 4 2 5% 4 2 3 4 4 6% 48%	2019
	11th to 20th	Night	17% 6% 2 5% 4 2 3 3 4 7% 42%	1959
	21st to end	Night	15% 6% 3 5% 5% 2 4 4 4 6% 41%	2131
April	1st to 10th	Night	14% 6% 2 5% 4 3 4 4 5% 6% 41%	1781
	11th to 20th	Night	13% 4 2 4 3 2 3 4 5% 7% 48%	1747
	21st to end	Night	17% 5% 1 5% 3 2 3 4 6% 7% 43%	1788
May	1st to 10th	Night	15% 6% 3 5% 4 2 4 5% 6% 7% 39%	1685
	11th to 20th	Night	15% 5% 3 5% 4 2 4 4 5% 8% 38%	1456
	21st to end	Night	12% 5% 1 4 4 2 4 6% 7% 10% 40%	1424
June	1st to 10th	Night	10% 4 2 4 3 3 5% 5% 7% 9% 43%	1360
	11th to 20th	Night	12% 5% 1 5% 4 3 5% 6% 5% 9% 39%	1360
	21st to end	Night	7% 4 2 5% 5% 3 4 5% 7% 9% 43%	1348
July	1st to 10th	Night	7% 5% 2 5% 5% 3 5% 5% 7% 10% 40%	1359
	11th to 20th	Night	5% 3 2 5% 4 3 5% 6% 6% 10% 45%	1409
	21st to end	Night	8% 3 1 5% 4 3 6% 5% 9% 11% 40%	1640
August	1st to 10th	Night	8% 3 2 6% 5% 4 6% 6% 7% 9% 41%	1510
	11th to 20th	Night	11% 6% 2 6% 6% 3 5% 6% 7% 7% 37%	1564
	21st to end	Night	9% 5% 2 5% 4 3 5% 4 6% 8% 44%	1860
September	1st to 10th	Night	13% 5% 2 6% 3 3 4 3 5% 7% 42%	1697
	11th to 20th	Night	8% 6% 2 4 4 2 3 4 5% 8% 49%	1694
	21st to end	Night	14% 7% 2 6% 4 3 4 4 5% 6% 40%	1927
October	1st to 10th	Night	18% 5% 2 4 4 2 3 3 4 5% 44%	2035
	11th to 20th	Night	15% 4 2 4 4 3 3 2 3 6% 50%	2024
	21st to end	Night	15% 5% 1 4 4 2 3 4 4 6% 48%	2237
November	1st to 10th	Night	13% 4 2 4 4 2 3 3 3 4 53%	2185
	11th to 20th	Night	14% 6% 2 4 3 2 3 3 3 6% 48%	2327
	21st to end	Night	13% 4 1 3 4 2 3 5% 5% 7% 48%	2506
December	1st to 10th	Night	16% 7% 2 5% 3 2 4 4 4 5% 42%	2507
	11th to 20th	Night	15% 5% 2 5% 4 3 4 4 5% 7% 40%	2520
	21st to end	Night	16% 6% 2 4 5% 3 4 4 4 7% 40%	2764

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% 4 11% 23% 14% 4	1467
	11th to 20th	Day	42% 4 12% 22% 14% 2	1618
	21st to end	Day	44% 3 8% 23% 15% 4	1741
February	1st to 10th	Day	45% 5% 11% 23% 12% 1	1600
	11th to 20th	Day	43% 4 8% 24% 17% 2	1607
	21st to end	Day	46% 5% 10% 18% 15% 3	1473
March	1st to 10th	Day	35% 5% 10% 24% 20% 3	1938
	11th to 20th	Day	42% 4 9% 19% 17% 6%	1969
	21st to end	Day	46% 5% 8% 18% 17% 4	2194
April	1st to 10th	Day	38% 4 10% 20% 19% 5%	2130
	11th to 20th	Day	36% 6% 8% 21% 21% 6%	2100
	21st to end	Day	41% 5% 10% 21% 16% 4	2152
May	1st to 10th	Day	41% 6% 12% 20% 16% 2	2268
	11th to 20th	Day	42% 7% 11% 21% 13% 2	2352
	21st to end	Day	39% 8% 13% 26% 11% 1	2505
June	1st to 10th	Day	36% 7% 14% 25% 14% 1	2374
	11th to 20th	Day	36% 10% 12% 21% 15% 2	2379
	21st to end	Day	32% 8% 14% 23% 17% 2	2362
July	1st to 10th	Day	35% 8% 12% 23% 16% 3	2287
	11th to 20th	Day	31% 8% 15% 25% 15% 2	2180
	21st to end	Day	39% 8% 13% 19% 17% 1	2231
August	1st to 10th	Day	40% 9% 14% 22% 11%	2155
	11th to 20th	Day	40% 9% 13% 21% 13% 1	2022
	21st to end	Day	35% 7% 14% 23% 14% 3	2231
September	1st to 10th	Day	38% 6% 13% 18% 19% 3	2033
	11th to 20th	Day	33% 5% 12% 24% 20% 3	2035
	21st to end	Day	42% 5% 9% 20% 19% 2	1776
October	1st to 10th	Day	39% 5% 10% 24% 17% 2	1694
	11th to 20th	Day	35% 4 8% 25% 22% 3	1681
	21st to end	Day	38% 3 7% 25% 21% 2	1864
November	1st to 10th	Day	33% 4 11% 26% 21% 4	1660
	11th to 20th	Day	34% 3 10% 24% 20% 5%	1609
	21st to end	Day	37% 3 9% 27% 19% 3	1432
December	1st to 10th	Day	40% 4 12% 26% 12% 2	1438
	11th to 20th	Day	40% 5% 10% 28% 11% 3	1440
	21st to end	Day	43% 4 10% 23% 15% 1	1582
January	1st to 10th	Night	38% 4 8% 22% 19% 5%	2444
	11th to 20th	Night	44% 5% 10% 22% 15% 1	2332
	21st to end	Night	38% 4 7% 25% 21% 2	2536
February	1st to 10th	Night	42% 5% 11% 23% 15% 2	2316
	11th to 20th	Night	43% 3 8% 21% 17% 5%	2167
	21st to end	Night	42% 4 9% 22% 16% 5%	1772
March	1st to 10th	Night	36% 5% 9% 25% 19% 3	2018
	11th to 20th	Night	40% 5% 10% 21% 17% 4	1969
	21st to end	Night	41% 5% 9% 20% 16% 6%	2134
April	1st to 10th	Night	41% 5% 8% 19% 20% 4	1778
	11th to 20th	Night	35% 5% 10% 20% 20% 6%	1747
	21st to end	Night	39% 5% 10% 24% 14% 5%	1788
May	1st to 10th	Night	41% 7% 11% 21% 13% 4	1688
	11th to 20th	Night	42% 6% 11% 19% 16% 2	1459
	21st to end	Night	36% 9% 17% 21% 13% 1	1425
June	1st to 10th	Night	34% 9% 12% 26% 15% 1	1355
	11th to 20th	Night	38% 9% 13% 22% 12% 2	1360
	21st to end	Night	33% 7% 15% 20% 20% 2	1348
July	1st to 10th	Night	36% 9% 15% 20% 14% 4	1312
	11th to 20th	Night	31% 9% 15% 25% 15% 2	1353
	21st to end	Night	32% 9% 15% 26% 15%	1542
August	1st to 10th	Night	35% 10% 17% 21% 15%	1499
	11th to 20th	Night	42% 8% 14% 20% 12% 1	1564
	21st to end	Night	36% 7% 13% 24% 14% 3	1859
September	1st to 10th	Night	39% 7% 9% 20% 17% 4	1696
	11th to 20th	Night	31% 6% 9% 26% 21% 3	1693
	21st to end	Night	42% 6% 8% 19% 18% 4	1927
October	1st to 10th	Night	41% 5% 10% 21% 17% 3	2036
	11th to 20th	Night	36% 4 8% 25% 22% 3	2024
	21st to end	Night	36% 5% 8% 24% 20% 4	2235
November	1st to 10th	Night	34% 4 8% 25% 20% 6%	2185
	11th to 20th	Night	37% 3 9% 21% 20% 6%	2328
	21st to end	Night	33% 4 10% 25% 21% 3	2507
December	1st to 10th	Night	43% 5% 10% 23% 15% 2	2512
	11th to 20th	Night	42% 4 12% 24% 15% 1	2520
	21st to end	Night	43% 5% 11% 24% 13% 2	2759

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	26% 18% 33% 14% 5%	180
	11th to 20th	Day	26% 22% 32% 15% 3	240
	21st to end	Day	23% 24% 34% 13% 3	261
February	1st to 10th	Day	23% 25% 35% 10% 3	240
	11th to 20th	Day	33% 20% 35% 11%	299
	21st to end	Day	29% 21% 31% 16% 1	346
March	1st to 10th	Day	20% 23% 31% 22% 2	420
	11th to 20th	Day	27% 19% 30% 17% 5%	418
	21st to end	Day	22% 16% 32% 22% 4 1	462
April	1st to 10th	Day	20% 21% 30% 20% 6%	415
	11th to 20th	Day	16% 17% 30% 21% 10% 3	404
	21st to end	Day	25% 12% 31% 22% 6% 1	417
May	1st to 10th	Day	24% 15% 26% 20% 10% 2	422
	11th to 20th	Day	20% 11% 31% 23% 10% 2	443
	21st to end	Day	18% 5% 23% 25% 20% 6%	423
June	1st to 10th	Day	13% 9% 26% 24% 19% 6%	407
	11th to 20th	Day	14% 6% 25% 30% 17% 5%	408
	21st to end	Day	8% 5% 28% 34% 18% 4	405
July	1st to 10th	Day	12% 2 16% 33% 24% 11%	404
	11th to 20th	Day	4 1 14% 40% 28% 10%	399
	21st to end	Day	10% 2 19% 36% 23% 7%	440
August	1st to 10th	Day	9% 5% 17% 31% 27% 9%	398
	11th to 20th	Day	12% 2 13% 33% 26% 11%	389
	21st to end	Day	7% 2 18% 31% 26% 14%	450
September	1st to 10th	Day	17% 5% 21% 22% 18% 14%	410
	11th to 20th	Day	14% 3 17% 35% 17% 11%	409
	21st to end	Day	21% 11% 22% 26% 13% 4	406
October	1st to 10th	Day	22% 5% 22% 25% 18% 5%	409
	11th to 20th	Day	16% 13% 25% 25% 15% 3	408
	21st to end	Day	18% 11% 34% 23% 8% 3	451
November	1st to 10th	Day	16% 11% 29% 27% 11% 3	372
	11th to 20th	Day	18% 15% 32% 23% 8% 1	336
	21st to end	Day	21% 21% 26% 18% 10% 1	160
December	1st to 10th	Day	18% 21% 38% 13% 6% 1	160
	11th to 20th	Day	24% 19% 30% 19% 5%	160
	21st to end	Day	26% 15% 31% 20% 5%	176
January	1st to 10th	Night	20% 17% 39% 19% 3	712
	11th to 20th	Night	22% 12% 34% 25% 5%	718
	21st to end	Night	19% 16% 37% 23% 2	780
February	1st to 10th	Night	21% 15% 34% 25% 2	707
	11th to 20th	Night	24% 18% 38% 16% 1	688
	21st to end	Night	25% 17% 35% 20% 2	590
March	1st to 10th	Night	19% 13% 41% 23% 2	719
	11th to 20th	Night	22% 13% 38% 19% 5%	712
	21st to end	Night	18% 13% 41% 22% 3	790
April	1st to 10th	Night	17% 17% 38% 21% 4	712
	11th to 20th	Night	15% 13% 34% 29% 7%	700
	21st to end	Night	21% 8% 33% 27% 8%	715
May	1st to 10th	Night	18% 9% 31% 29% 10%	610
	11th to 20th	Night	17% 6% 31% 34% 9%	415
	21st to end	Night	15% 2 23% 36% 19% 1	359
June	1st to 10th	Night	10% 2 26% 35% 21% 1	337
	11th to 20th	Night	13% 5% 18% 40% 19% 1	338
	21st to end	Night	8% 2 24% 44% 18% 1	335
July	1st to 10th	Night	8% 1 19% 38% 29% 1	328
	11th to 20th	Night	6% 1 12% 41% 32% 4	393
	21st to end	Night	8% 1 18% 38% 30% 2	548
August	1st to 10th	Night	8% 2 11% 44% 30% 3	496
	11th to 20th	Night	13% 2 15% 39% 26% 2	575
	21st to end	Night	11% 1 16% 35% 29% 5%	744
September	1st to 10th	Night	16% 2 16% 33% 26% 4	679
	11th to 20th	Night	10% 2 15% 37% 28% 4	676
	21st to end	Night	18% 6% 23% 32% 18% 1	669
October	1st to 10th	Night	20% 5% 20% 30% 19% 4	679
	11th to 20th	Night	17% 9% 26% 28% 17% 1	674
	21st to end	Night	18% 10% 32% 25% 12%	745
November	1st to 10th	Night	14% 8% 33% 29% 12% 2	698
	11th to 20th	Night	19% 13% 28% 27% 9%	715
	21st to end	Night	17% 13% 31% 26% 10%	717
December	1st to 10th	Night	21% 13% 33% 23% 7%	717
	11th to 20th	Night	17% 11% 41% 24% 5%	720
	21st to end	Night	20% 12% 35% 28% 3	788

Page generated at 2023-05-22 06:21:18. Version ac06

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